Category: Nursing Skills

The Definition, Classification and Pathophysiology of Shock

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In order to understand how to care for a patient in shock, we must first understand the pathophysiology of shock, as well as how to assess, diagnose, and manage it through appropriate nursing interventions. The most common types of shock are the Hypovolaemic Shock, Cardiogenic Shock, and Septic Shock. Throughout this blogpost we will be looking in detail at the definition, classification, and pathophysiology of shock.

What is Cardiac Output?

Cardiac Output (CO) is the volume of blood ejected from the heart over 1 minute. In adults, normal Cardiac Output is between 4-6L/min.

Cardiac Index (CI) is a haemodynamic parameter related to the cardiac output from the left ventricle in 1 minute to body surface area (BSA). In adults, normal Cardiac Index should be between 2.5-4L/min/m2.

Stroke volume (SV) is the volume of blood pumped out of the left ventricle during each systolic cardiac contraction.

Mean Arterial Pressure (MAP) is the average arterial pressure throughout one cardiac cycle, systole, and diastole.

Systemic Vascular Resistance (SVR) is the resistance in the circulatory system which affects the blood pressure and the flow of blood. SVR is also a component of cardiac function, eg. vasoconstriction leads to an increased SVR.

Formulas:

Cardiac Output (CO) = Heart Rate (HR) X Stroke Volume (SV)

Cardiac Index (CI) = Cardiac Output (CO) / Body Surface Area

Mean Arterial Pressure (MAP) = Cardiac Output X Systemic Vascular Resistance (SVR)

Cardiac Output Determinants

  • HEART RATE – influenced by both the sympathetic and parasympathetic system, as well as by intrinsic regulation
  • STROKE VOLUME – determined by cardiac preload (PL), afterload (AL), and cardiac contractility (CC).

Preload determinants

Preload (PL) is the stretching force exerted on the ventricle by the blood contained within at the end of diastole.

The Starling’s Law of the Heart indicates that increased volume returned to the heart causes an increase in Cardiac Output, however, following a certain increase in volume returned causes a decrease in Cardiac Output.

Retrieved from https://ecgwaves.com/topic/pressure-volume-curves-preload-afterload-stroke-volume-wall-stress-frank-starlings-law/ on 10th January 2023

Preload determinants include:

  • VOLUME OF BLOOD RETURNED TO LEFT VENTRICLE – influenced by venous return, total blood volume, and atrial kick
  • LEFT VENTRICLE COMPLIANCE (stretching ability) – influenced by the stiffness and thickness of the muscle wall

Examples: in Hypervolaemia, preload is too low, whilst in Congestive Heart Failure, preload is too much.

Afterload Determinants

Afterload (AL) is the resistance (a.k.a. Systemic Vascular Resistance SVR) that the heart must overcome to push blood into the systemic circulation.

An increase in Afterload causes an increase in the required effort and oxygen demand by the heart, eg. vasoconstriction increases Systemic Vascular Resistance, total blood volume and viscosity.

To reduce the heart’s workload we can provide therapeutic nursing management, including the administration of vasodilators.

pathophysiology of shock
Retrieved from https://www.studypk.com/articles/nursing-mnemonics-preload-vs-afterload/ on 10th January 2023

Cardiac Contractility Determinants

Cardiac Contractility (CC) is the force by which the heart contracts. CC is determined by:

  • VENOUS RETURN – Starling’s Mechanism
    • STIMULATION OF THE SYMPATHETIC NERVOUS SYSTEM
    • INCREASE IN INTRACELLULAR CALCIUM (Ca++) – such as after use of Digoxin
    • PHARMACOLOGICAL INTERVENTIONS – eg. administration of Inotropes
Retrieved from https://step1.medbullets.com/cardiovascular/108003/cardiac-output-and-variables on 11th January 2023

Shock Definition

Shock can be defined as an acute widespread process of impaired tissue perfusion resulting in cellular, metabolic and haemodynamic changes, causing an imbalance between cellular oxygen supply and demand. Shock leads to death if not controlled in time.

Normal tissue perfusion requires:

  • adequate blood volume
  • adequate cardiac pump
  • effective circulatory system

Impairment of any of the above, thus, impairment in normal tissue perfusion, may lead to SHOCK…

Impaired oxygen perfusion causes:

  1. inadequate blood flow reaching the tissues
  2. inadequate delivery of oxygen and nutrients to the cells
  3. cell starvation due to oxygen and nutrient deprivation
  4. cell death
  5. multiple organ failure
  6. death

Classification of Shock

Shock can be classified into 3 different types. Whilst the management of shock varies based on the type of shock it is, the resulting effect of all 3 types of shock is the same – decreased tissue perfusion.

Hypovolaemic Shock

Hypovolaemic shock is the most commonly occurring type of shock, which is also easily reversible if treated in a timely manner. Features of a hypovolaemic shock include:

  • loss of circulating or intravascular volume
  • impaired tissue perfusion
  • inadequate delivery of oxygen and nutrients
  • may be caused by relative and absolute hypovolaemia, or loss of blood or other fluids
Retrieved from https://twitter.com/misirg1/status/1382458804995035144 on 19th January 2023

Cardiogenic Shock

  • impaired ability of the heart to pump blood as it should (left or right ventricle dysfunction), causing systemic hypoperfusion and tissue hypoxia
  • may be caused by cardiac injury (eg. cardiac tamponade), cardiopulmonary arrest, following cardiac surgery, dysrhythmias (severe tachycardia or bradycardia), myocardial tissue necrosis following a Myocardial Infarction, or structural problems (eg. valvular damage or regurgitation, pulmonary embolus, acute myocarditis, papillary muscle rupture, intracardiac tumour, and congenital defects
  • compensatory mechanisms may worsen the situation…eg. reduced cardiac output due to myocardium death causes increased contractility which further increases the heart’s workload and oxygen demand; reduced blood pressure causes the release of catecholamines which leads to vasoconstriction, subsequently leading to a further increase in cardiac workload and oxygen demand
Retrieved from https://www.facebook.com/jamajournal/photos/a.10158814898548341/10158814906348341/?type=3&locale=zh_HK on 19th January 2023

Distributive Shock

  • impaired distribution of circulating blood volume
  • vasodilation
  • capillary leaks

Distributive Shock is further sub-classified into 3 other types of shock:

SEPTIC SHOCK:

While sepsis is defined as a life-threatening organ dysfunction caused by dysregulated host response to infection, a septic shock is defined as a subset of sepsis in which underlying circulatory, cellular and metabolic abnormalities and profound enough to substantially increase the risk of mortality.

  • microorganism entry into the patient’s body
  • dysregulated host response characterised by excessive peripheral vasodilation, causing maldistribution of blood volume, over-perfused peripheral areas and under-perfused central areas
  • is the major cause of admission in the critical care setting

Septic Shock may originate from the community (>80% of cases) or during a stay in a healthcare facility.

ANAPHYLACTIC SHOCK:

  • severe antigen-antibody reaction causing histamine release
  • signs & symptoms include vasodilation, hypotension, bradycardia, increased capillary permeability, bronchospasm, laryngeal oedema, and stridor

NEUROGENIC SHOCK:

  • disruption of sympathetic nerve activity below the level of a spinal cord injury or disease
  • signs & symptoms include vasodilation, hypotension, bradycardia, warm dry skin, and loss of thermoregulation

Obstructive Shock

  • obstructive shock is often classified with cardiogenic shock
  • obstructive shock is mechanical obstruction which impedes the heart from generating adequate cardiac output
  • examples of obstructive shock include Tension Pneumothorax, Pericardial Tamponade and Pulmonary Embolus
pathophysiology of shock
Retrieved from https://www.pinterest.com/pin/34762228362737082/ on 11th January 2023

The Pathophysiology of Shock

pathophysiology of shock
Retrieved from https://slideplayer.com/slide/17204705/ on 11th January 2023

Initial Stage

Within the initial phase of shock, effects are very subtle and at cellular level. An increase in serum lactate indicates metabolic acidosis due to cells switching from aerobic to anaerobic respiration.

  1. Decrease in Cardiac Output
  2. Decrease in tissue perfusion
  3. Cells switch from aerobic to anaerobic respiration
  4. Accumulation of Lactic Acid
  5. Lactic Acidaemia (Low pH)
  6. Cellular Damage

Compensatory Stage

During the compensatory stage of shock, the patient’s body attempts to improve tissue perfusion through neural, chemical, and hormonal compensation, mediated by the sympathetic nervous system.

NEURAL COMPENSATORY MECHANISMS

  • increased Heart Rate and Cardiac Contractility
  • arterial and venous vasoconstriction
  • circulation lessens within the peripheries and becomes more focused on vital organs perfusion

CHEMICAL COMPENSATORY MECHANISM

  • chemoreceptors detect acidosis and stimulate hyperventilation so more Carbon Dioxide is exhaled

HORMONAL COMPENSATORY MECHANISMS

Hormonal compensatory mechanisms aim to increase the blood pressure to cause an increase in tissue perfusion.

  • the anterior pituitary gland is stimulated, causing secretion of ACTH (Adrenocorticotropic Hormone), which then stimulates the adrenal cortex to produce glucocorticoids (glucagon), which causes an increase in blood glucose level
  • the adrenal medulla is also stimulated, causing the release of adrenaline and noradrenaline, which result in vasoconstriction, leading to an increased Blood Pressure and increased Heart Rate
  • renin response is activated, which facilitates the conversion of Angiotensinogen into Angiotensin II; this conversion causes vasoconstriction, release of aldosterone (which leads to sodium retension), and release of antidiuretic hormone (ADH) by the posterior pituitary gland (which leads to water retention)
pathophysiology of shock
Retrieved from https://en.wikipedia.org/wiki/Renin%E2%80%93angiotensin_system on 11th January 2023

SYMPTOMS EXPERIENCED DURING THE COMPENSATORY PHASE:

  • cold, clammy skin
  • drop in urine output
  • tachycardia
  • tachypnoea
  • hyperglycaemia

Progressive Stage

  • compensatory mechanisms start failing
  • shock cycle continues indefinitely
  • anaerobic respiration causes energy exertion within the cells
  • cells are unable to function, and irreversible damage occurs (Mitochondria become unable to use oxygen for the production of energy, and Lysosomes release digestive enzymes which then cause further cellular damage)
  • utilisation of the limited oxygen delivered into the cells becomes problematic

During the progressive stage, organ systems start to fail…

  • Myocardial Hypoperfusion causes decreased Cardiac Output leading to ventricular failure, enabling shock to progress further
  • Decreased Cerebral Blood Flow causes CNS dysfunction, causing failure of the sympathetic nervous system, failure of the thermoregulation mechanism, cardiac and respiratory depression, and altered mental status
  • Impaired Coagulation leading to microclot formation, which may cause Disseminated Intravascular Coagulation (DIC)
  • Renal Vasoconstriction & Hypoperfusion causes decreased urine output and increased creatinine, which may also lead to Acute Tubular Necrosis (ATN)
  • GastroIntestinal Tract Hypoperfusion causes decreased peristalsis (decreased bowel sounds), release of Gram-negative bacteria (which worsens shock), and liver hypoperfusion due to deranged LFTs
  • Pulmonary Vasoconstriction along with microemboli, parenchymal inflammation, and alveolar oedema all lead to respiratory failure (Acute respiratory distress syndrome ARDS)

SYMPTOMS EXPERIENCED DURING THE PROGRESSIVE PHASE:

  • electrolyte imbalance
  • metabolic acidosis
  • respiratory acidosis
  • peripheral oedema
  • tachycardia
  • arrhythmias
  • hypotension
  • pallor
  • cool clammy skin
  • altered level of consciousness
  • reduced bowel sounds

Refractory Stage

In the final stage of shock, the patient becomes unresponsive to treatment, experiences multiple organ failure, eventually leading to death.

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Preventing Secondary Brain Injury

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Primary brain injury can only be prevented through education and health promotion, and surviving the initial head injury is only a small part of the battle for the patient with a brain injury. Preventing secondary brain injury is even more important since it may have a greater influence on the final outcome than the primary brain injury itself. Throughout this blogpost we will go through ways of preventing secondary brain injury as much as possible.

Causes of Secondary Brain Injury

Causes of secondary brain injury include:

  • hypoxia
  • hypotension
  • hypercapnia
  • acidaemia
  • anaemia
  • intracranial mass
  • hyperglycaemia OR hypoglycaemia
  • hyperthermia OR hypothermia
  • Preventing secondary brain injury is possible by preventing ALL mentioned causes through early treatment
  • Most causes mentioned are related to raised ICP – Intracranial Pressure

The Monro-Kellie Hypothesis

The Monro-Kellie hypothesis states that the total volumes of brain (approximately 80%), CSF (approximately 10%) and intracerebral blood (approximately 10%) are constant. The cavity in which these three are housed a.k.a. the cranial cavity, is not able to expand, and so, an increase in one should cause a decrease in one or both of the remaining two. This ensures that the total volume of the three components remains fixed, and that no rise in ICP is caused.

ICP (Intracranial Pressure) is the pressure exerted by the intracranial contents against the skull. The brain normally is able to tolerate a significant increase in intracranial volume WITHOUT increasing much the ICP. If, however, this normal compensation mechanism becomes exhausted and the compliance limit is exceeded, an increase in ICP becomes imminent.

NOTE: an increase in ICP causes changes within the patient’s Vital Signs.

In normal circumstances, ICP is less than 10mmHg (in adults). If ICP increases to >20mmHg treatment is required!

preventing secondary brain injury
Retrieved from https://resources.wfsahq.org/atotw/cerebral-physiology-part-2-intracranial-pressure-anaesthesia-tutorial-of-the-week-71/ on 2nd January 2023
preventing secondary brain injury
Retrieved from https://www.cambridge.org/core/books/abs/managing-the-critically-ill-child/child-with-raised-intracranial-pressure/8950B2DE746C13B6DBBCB293BD42E5D3 on 2nd January 2023

Signs of Increased ICP

  • unexplained changes in vital signs
  • cushing’s triad – isolated systolic hypertension, bradycardia, and altered breathing patterns
  • headache
  • nausea & vomiting
  • sensory deficits
  • impaired motor function
  • pupillary changes – if ICP >18mmHg
  • altered level of consciousness
  • decreased level of consciousness
  • seizures

Cushing’s Triad

Monitoring Intracranial Pressure

Monitoring ICP can be done through the use of:

  • ventriculostomy – intraventricular catheter
  • subarachnoid bolt or screw
  • subdural OR epidural catheter or sensor
  • fibreoptic transducer-tipped intraparenchymal catheter
  • non-invasive methods such as an automated IR pupillometry
preventing secondary brain injury
Retrieved from https://www.pinterest.com/pin/57491332723434138/ on 2nd January 2023

Possible Causes of Increased ICP

Pathological CausesNon-Pathological Causes
traumatic brain injurycoughing / sneezing
temperaturelifting / bending / body positioning
intra-thoracic pressurestress / emotional responses
intra-abdominal pressurepain
acidosis / hypoxiablood pressure changes
lesions occupying space eg. bleeding, hydrocephalus, tumour, oedema, abscess, infectionvalsalva manoeuvre

Factors affecting ICP

  • MAP : Mean Arterial Pressure – both hypertension and hypotension may raise ICP
  • Brain Trauma – expanding lesions increase ICP and may cause herniation a.k.a. brain matter displacement
  • CMR Changes – Changes in Cerebral Metabolic Rate may happen due to hyperthermia and increase in blood flow to meet demands, which leads to an increase in ICP
  • Conditions Causing Acidosis – results in cerebral vascular dilation such as hypoxia, ischaemia, and hypercapnia
  • Increased Intra-Thoracic / Intra-Abdominal Pressure – may happen during coughing or suctioning and due to high PEEP
  • Conditions Affecting Venous Return – pressure on jugular veins or patient positioning

Cerebral Perfusion Pressure

Cerebral Perfusion Pressure CPP is the difference between the MAP (Mean Arterial Pressure) and the ICP.

CPP = MAP – ICP

Ideally, CPP should be between 50-70mmHg, as this ensures an adequate blood supply to the brain. On the other hand, ICP should be approximately 10mmHg.

A decrease in CPP or rise in ICP may cause ischaemia, neuronal hypoxia, and even death.

NOTE: if MAP = ICP, cerebral blood flow may cease.

Preventing Rise in Intracranial Pressure

1. Control of Vital Signs

  • HYPOTENSION reduces oxygen and nutrient perfusion; CPP = MAP – ICP; aim for MAP of >80mmHg to ensure CPP of >60mmHg with ICP of 20mmHg; to increase blood pressure administer fluids and vasopressors.
  • HYPERTENSION may result following interventions or due to decreased cerebral perfusion; sedatives may help avoid blood pressure from increasing during procedures; primary anti-hypertensives such as beta blockers can be administered, but only if ICP is monitored, OR SBP is >180mmHg, OR MAP is >110mmHg; AVOID vasodilators as these increase ICP.

2. Ventilation

  • HYPERCAPNIA causes vasodilation – a 30% increase in cerebral blood flow leads to a 10mmHg increase in PaCO2, which raises ICP.
  • HYPOCAPNIA causes vasoconstriction, which in return reduces cerebral blood volume and ICP, leading to ischaemia.
  • HYPOXIA causes cerebral vasodilation, leading to an increased intracranial blood volume and increased ICP (high levels of PaO2 have not shown evidence of any affect on CBF).
  • GOOD OXYGENATION should be maintained (ideal SPO2 of >95% and PaO2 of >80mmHg), if needed, through intubation and mechanical ventilation. IMPORTANT – avoid high tidal volume (as this may cause acute lung injury) and use a low level of PEEP (5-8mmHg) to maintain good oxygenation.
  • pH BALANCE should be maintained between 7.35 and 7.45
  • AIM FOR LOW NORMAL PaCO2 (approx. 35mmHg) – although hyperventilation may be required temporarily to reduce cerebral vasodilation and enhance venous return; AVOID LOW PaCO2 as excessive vasoconstriction leads to ischaemia, restricting oxygen supply to the injured area, leading to an increase in damage.
Relationship between CBF and PaC02 (1st image) & Relationship between CBF and PaO 2 showing almost no effect on CBF in the
normoxaemic range (2nd image); CBF increases if PaO 2 is less than 50mmHg. – Retrieved from https://www.frca.co.uk/Documents/170907%20Cerebral%20physiology%20I.pdf on 3rd January 2023

3. Patient Positioning

  • ELEVATE HEAD OF BED to about 30% – patient’s neck should be3 kept midline; gravity promotes CSF and venous drainage, resulting in a lowered ICP; NOTE: evidence as to whether or not bed elevation may lower CPP has been inconclusive in a recent systematic review (Alarcon et al., 2017).
  • VENOUS RETURN OBSTRUCTION causes an increased ICP due to factors such as head rotation to one side, extreme flexion of arms and hips, neck angulation and pressure on jugular veins (eg. from tight ETT tie or lateral positioning), trendelburg positioning, and prone positioning.

4. Procedures & Environmental Factors

  • SUCTIONING
  • RAPID POSITION CHANGES
  • PAIN & COUGHING
  • VENEPUNCTURE
  • REMOVING ADHESIVE TAPE
  • USE OF BEDPANS/ENEMA
  • AVOID ACTIVITY CLUSTERING and instead promote resting periods between procedures mentioned above. If needed, a short acting sedative may be administered as a bolus prior to the procedure.
  • AVOID UNNECESSARY INSTRUMENTAL TOUCH & PAINFUL PROCEDURES
  • REDUCE LIGHTING in the patient’s room
  • REDUCE UNNECESSARY ENVIRONMENTAL NOISE such as unneeded alarms – set appropriately and in relation to the patient’s norms
  • SUCTIONING increases intra-thoracic pressure, impedes venous return and increases ICP; hypoxia may lead to cerebral ischaemia. Reduce impact on the patient by providing hyperoxygenation before and/or after the procedure, hyperventilating, suctioning using a closed suction system, limiting the frequency and the duration of suctioning, administering a sedation bolus, or Lignocaine IV or via Tracheal Tube.

NOTE: Some studies have shown that the presence, touch, and voice of patient relatives may help decrease ICP. Other unrelated studies have also shown that oral hygiene, bed bathing, catheter care and chest percussion do not result in a significant rise in ICP.

Retrieved from http://www.learnpicu.com/neurology/ICP (left image) & http://pedsccm.org/FILE-CABINET/head_trauma/sld028.htm (right image) on 3rd January 2023

5. Sedation & Analgesia

  • SEDATIVES, MUSCLE RELAXANTS & ANALGESICS can help reduce the effects of unpleasant procedures; Sedatives administered are usually opioids or benzodiazepines; Muscle relaxants should be avoided if possible, and should they be administered, ensure that the patient is sedated first.
  • ADEQUATE VENTILATION may also be achieved through the effect of sedation and analgesia.
  • ATTENTION!! Sedation and Analgesia may affect the MAP, leading to an affect on the CPP (cerebral perfusion pressure), thus, ensure adequate fluid volume. Similarly, sedation and analgesia may also mask certain aspects related to the neuro assessment, thus, for a patient on such medication, rely more on pupillary reaction rather than the neuro assessment.

6. Fluid Management

  • In relation to OSMOTIC THERAPY, large molecules (eg. Mannitol) or Hyperosmolar solution (eg. hypertonic saline, which is considered to be superior and with less side effects) remain in circulation, increasing osmolarity. For osmosis to happen, an intact blood-brain-barrier is required, where fluid is drawn from diluted areas to more concentrated areas (from extracellular to intravascular space). This reduces cerebral oedema whilst improving blood flow.
  • When administering osmotic therapy, CAREFUL MONITORING is required – monitor electrolyte levels especially Potassium and Sodium; replace fluid as necessary to avoid hypovolaemia; serum osmolarity should not exceed 320mOsm/L…higher levels may induce pulmonary oedema or rebound cerebral oedema.
  • HYPERTHERMIA, unless infection is involved, may be induced by localised damage in the thermoregulatory centre within the hypothalamus. A 1°C rise in body temperature causes 6-10% increase in cerebral metabolic rate, increased oxygen demand, increased blood flow and volume due to vasodilation, and increased ICP. IMPORTANT: monitor the patient’s body temperature and help cooling by removing any extra blankets and administering antipyretics.
  • THERAPEUTIC HYPOTHERMIA may reduce ICP, however, evidence of improved survival is still inconclusive to date. Additionally, avoid rapid cooling as shivering raises ICP, thus, should be prevented.

7. Seizure Control

  • POST-TRAUMATIC SEIZURES happen in 5% of patients with head injuries.
  • Seizures increase CEREBRAL METABOLIC DEMANDS: increased blood flow causes an increase in ICP; if flow doesn’t meet the cerebral metabolic demands, the patient experiences ischaemia and neuronal destruction.
  • PHENYTOIN is considered to be an effective medication in the prevention of early seizures (always monitor serum levels when administering).

8. Nutrition & Elimination

  • PROTEIN is very much required by a hypermetabolic brain.
  • STRESS ULCER PROPHYLAXIS is commonly administered to patients with an increased risk of stress-related mucosal bleeding from the upper gastrointestinal tract. Apart from administering early enteral feeding, ideally through an orogastric tube, administer pharmacological prophylaxis such as H2-blockers, proton-pump inhibitors, or sucralfate.
  • Attempt to maintain NORMOGLYCAEMIA – hyperglycaemia is associated with increased ICP, while hypoglycaemia is associated with aggravated brain injury. It’s also important to mention that intensive insulin therapy does not improve outcome, and may actually worsen the patient’s condition and prognosis.
  • STOOL SOFTENERS may be required especially if the patient is constipated, since constipation increases intra-abdominal pressure and ICP.
  • GASTRIC DECOMPRESSION is intended for patientS with gastric distention receiving aggressive ventilatory resuscitative measures prior to intubation. A NG tube may be used to perform gastric decompression for the patient with known or suspected gastric distension. Check tube placement. Attach suction or a large syringe and evacuate the stomach.NOTE: for patients with facial trauma use an orogastric tube instead.

In Summary…

List of Interventions to Minimise ICP

1. AIRWAY & VENTILATION

  • monitor pH, pCO2 and pO2
  • if GCS <9 ensure early intubation and mechanical ventilation
  • avoid tight ETT or Tracheostomy ties
  • avoid high PEEP
  • suction only when necessary
  • keep head elevated and aligned
  • provide mouth care to eliminate oral secretions
  • perform gastric decompression

2. ICP & CPP

  • prevent rise in ICP
  • prevent drop in CPP
  • remember: CPP = MAP – ICP
  • mannitol or furosemide may be administrated to reduce intracellular volume
  • hypertonic saline reduces cerebral oedema whilst improving blood flow

3. NEUROLOGICAL & HAEMODYNAMIC MONITORING

  • avoid drops in the patient’s blood pressure
  • monitor the patient neurological status through the Glasgow Coma Scale and Pupil Reactivity

4. NUTRITION & FLUIDS

  • ensure adequate nutrition and fluid intake as indicated
  • fluid restriction may be indicated so as to prevent an increase in ICP
  • monitor the patient’s electrolytes
  • an adequate MAP can be achieved through administration of normal saline +/- inotropes
  • monitor for diabetes insipidus (a rare condition which causes increased urination (polyuria) and increased thirst (polydipsia); Diabetes Insipidus is not related to type 1 or type 2 diabetes)

5. PREVENTION

  • prevent hyperthermia
  • prevent hyperglycaemia
  • prevent hypoglycaemia
  • prevent seizures
  • prevent pain
  • prevent anxiety
  • prevent venous thromboembolism VTE

6. NEUROLOGICAL INTERVENTIONS

  • an expanding haematoma may require ventriculostomy for CSF drainage and ICP monitoring
  • craniectomy may also be indicated if an increase in space is required

7. PATIENT SAFETY

  • ensure patient safety at all times

8. PSYCHOSOCIAL CARE

  • promote congnitive function
  • provide support to the patient’s relatives
  • provide health literacy and rehabilitation advice to the patient and relatives

References

Alarcon, J. D., Rubiano, A. M., Okonkwo, D. O., Alarcón, J., Martinez-Zapata, M. J., Urrútia, G., & Bonfill Cosp, X. (2017). Elevation of the head during intensive care management in people with severe traumatic brain injury. The Cochrane database of systematic reviews, 12(12), CD009986. https://doi.org/10.1002/14651858.CD009986.pub2

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Performing a Neurological Assessment – GCS & Pupillary Reaction

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Performing a Neurological Assessment

When performing a neurological assessment, one would be assessing the nervous system for the purpose of identifying abnormalities affecting the activities of daily living. The Glasgow Coma Scale (GCS) is an assessment tool which can objectively describe the extent of consciousness impairment incurred by acute medical and trauma patients. Similarly, pupillary reaction is assessed as an attempt to trigger a normal physiological response to the size of the pupil via the optic and oculomotor cranial nerve.

The Glasgow Coma Scale GCS Neurological Assessment

Through the use of the Glasgow Coma Scale GCS the nurse assesses the patient’s level of consciousness in a way that determines the degree of stimulation required to elicit a response.

  • the GCS is based on 3 modes of behaviour, namely Eye Opening, Verbal Response, and Motor Response
  • the GCS’s overall score should not be used alone in determining clinical findings, and must be combined with Pupillary Reaction and Vital Signs
  • the patient can score from 3 to 15, with 15 being the best score possible, and 3 being the least score possible; a patient with a score of <9 is considered to be severe, requiring an ETT
  • repeated observations indicate static, improving, or worsening of the patient’s neurological condition
  • action must be taken even if minor changes are noted
Retrieved from https://www.firstaidforfree.com/glasgow-coma-scale-gcs-first-aiders/ on 29th December 2022
neurological assessment
Retrieved from https://standardofcare.com/abnormal-posturing/ on 29th December 2022
neurological assessment
Retrieved from https://www.researchgate.net/figure/moToR-ReSpoNSeS-IN-GlASGow-ComA-SCAle_fig1_267035268 no 29th December 2022

Structured GCS Assessment

#1 – CHECK

  • identify factors which may interfere with assessment such as pre-existing factors (eg. language barrier, intellectual deficits), effects of current treatment (eg. sedation or tracheostomy), and effects of pre-incurred injuries (eg. cranial fracture or spinal cord damage)
  • if any of the above factors are determined, NT (Not Testable) should be recorded, and no total score should be listed

#2 – OBSERVE

  • observe patient for evidence of spontaneous behaviour
  • if no spontaneous behaviour is noted, observe behaviour in response to stimulation

#3 – STIMULATE

  • try to illicit a response by increasing the stimulus intensity gradually
  • for auditory stimulus, speak, and if needed, shout, using the patient’s preferred name
  • for physical stimulus to illicit eye opening, use a peripheral method by pressing on the distal part of the patient’s fingernail, increasing the intensity for up to 10 seconds
  • for physical stimulus to illicit localisation, use central methods such as the trapezius pinch or the supra-orbital notch pressure
  • AVOID sternal rub since this method can cause bruising to the patient!

#4 – RATE

  • if during your initial ‘check’ you determine that certain domains are not testable, document as NT and do not list total score
  • determine if top criteria is met based on observation – if yes, document appropriately; if no, attempt to illicit a response through stimulus as mentioned above
  • in relation to motor response, different responses between the left and right side (arms or legs) of the patient, document the best response
  • different responses between the peripheral stimulus and central stimulus, document the response stimulated centrally

NOTE:

  • EYE OPENING aim is to assess brain stem function
  • VERBAL RESPONSE aim is to assess interpretative speech and language area in the temporal lobe within the brain
  • MOTOR RESPONSE aim is to ascertain whether the cerebral cortex can interpret sensory messages and translate them to a motor response
Retrieved from https://www.physio-pedia.com/Glasgow_Coma_Scale on 29th December 2022

For more information about the Glasgow Coma Scale please visit https://www.glasgowcomascale.org/

Pupillary Reaction

In the Critical Care setting, the eyes are considered to be a ‘window to the brain’.

  • pupillary reaction to light may be brisk, sluggish, or fixed
  • sluggish, suddenly dilating, or unequal pupils may indicate compression of oculomotor cranial nerve (3rd), and/or compressed brain stem due to oedema or haematoma worsening; urgent intervention may improve outcome
  • pinpoint pupils may indicate narcotic/opioid use

NOTE: certain eye drops such as Atropine may dilate pupils.

neurological assessment
Retrieved from https://pocketdentistry.com/8-neurologic-evaluation-and-management/ on 29th December 2022

Additional Signs & Symptoms

  • Autonomic Dysfunction a.k.a. Dysautonomia – happens when the autonomic nervous system, which controls functions responsible for wellbeing and maintaining balance, does not regulate properly; signs include hypertension and hyperpyrexia
  • Persistent Vegetative State – a state of ‘eyes-open unresponsiveness’ in patients in a coma for 30 days or more; it is considered to be a chronic disorder in which a patient with severe brain damage appears to be awake but shows no evidence of awareness of their surroundings
  • Prolonged Unconsciousness a.k.a. Coma – a prolonged state of unconsciousness during which a person is unresponsive to their surrounding environment; while the patient is alive and looks like they are sleeping, they cannot be awakened by any stimulation, including pain

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Head Injury Nursing Care of the Patient in ICU

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Head Injury is a phrase referring to a vast array of injuries occurring to the scalp, skull, brain, or the underlying tissue and blood vessels within the head. Based on the extent of the head trauma, a head injury is commonly referred to as brain injury or traumatic brain injury. Head injury nursing care varies according to the cause, damage and complications.

The Parietal and Temporal bones are more likely to fracture in a head injury. And since the brain is quite soft in texture, a cranium injury can easily be the cause of a brain injury.

Retrieved from https://twitter.com/medillustrates/status/1347603734508015617?lang=fr on 26th December 2022

The Meninges

The meninges consist of three membranous connective tissue which enclose the brain, namely the pia mater, arachnoid mater and dura mater.

PAD – the 3 layers of the brain = Pia Mater, Arachnoid Mater, and Dura Mater.

Retrieved from http://treattheathlete.com/head/meninges/ on 26th December 2022

Cerebral Blood Flow

The brain has high metabolic demands. It depends on ongoing energy/glucose which can be supplied through continuous blood flow, especially since it does not store any glucose itself. Blood is supplied to the brain through 4 arteries which are fused together, forming the Circle of Willis.

  • the brain amounts to not more than 2% of the total body weight
  • the brain requires between 15 to 20% of resting cardiac output (50ml/100g of brain tissue per minute which amounts to 700ml/min in an individual weighing 70kgs)
  • the brain requires 15% of the body’s total oxygen demand
  • the brain doesn’t store glucose, and doesn’t have any glycogen stores
  • the brain doesn’t tolerate hypoperfusion
Retrieved from https://www.vedantu.com/question-answer/the-amount-of-blood-supplied-to-the-brain-per-class-10-biology-cbse-5f4cbf7956e9d4741097efd0 on 26th December 2022

Traumatic Brain Injury

A traumatic brain injury refers to a blunt or penetrating head injury which disrupts the brain from functioning in its normal way, causing impaired thinking and memory, personality changes, and sometimes sensory and motor changes.

A traumatic brain injury can be classified as either Primary or Secondary, as listed below…

Primary Brain InjurySecondary Brain Injury
– damage incurred at the time of injury– complications following initial injury
– cerebral laceration– hypoxia / ischaemia
– concussion / contusion– brain oedema
– skull fractures– brain herniation
– intracranial bleeding– intracranial hypertension
– diffuse axonal injury– CSF leak and infection

A primary brain injury can only be prevented through education and health promotion, whilst a secondary brain injury can be prevented from a clinical point of view.

Primary Brain Injury

Focal Injuries:

  • affect specific brain locations as in cerebral contusion (scattered areas of bleeding on the brain’s surface, commonly located along the under-surface and poles of the frontal and temporal lobes), laceration, or intracranial haemorrhage (bleeding into the brain tissue – can be classified as Epidural Haematoma, Subdural Haematoma, Subarachnoid Haemorrhage, or Intracerebral Haemorrhage)

Diffuse Injuries (diffused/spread injuries):

  • concussion (caused by a bump, blow, or jolt to the head, or by a hit to the body which causes the head and brain to move rapidly back and forth)
  • moderate to severe Diffuse Axonal Injury (shearing of the brain’s long connecting nerve fibers a.k.a. axons, which happens when the brain is injured through shifting or rotating inside the skull; DAI commonly causes coma and injury to many different parts of the brain)
head injury nursing care
Retrieved from https://www.physio-pedia.com/Classification_of_Traumatic_Brain_Injury on 26th December 2022

Cerebral Contusion ~ Focal Injury

Cerebral Contusion refers to scattered areas of bleeding on the brain’s surface, commonly located along the under-surface and poles of the frontal and temporal lobes. This is typically caused by coup and/or contrecoup injuries, happening by:

  • blunt trauma to the brain tissue
  • bruising of the brain due to capillary bleeding into superficial brain tissue, typically in the frontal or temporal bone areas of the skull

Cerebral Contusion signs & symptoms may include:

  • confusion
  • neurological deficit (featuring changes related to personality or speech and vision)
head injury nursing care
Retrieved from https://quizlet.com/537126249/health-flash-cards/ on 26th December 2022

Cranial Fracture ~ Focal Injury

Types of cranial fractures include:

  • Linear Fracture – a thin-line break in a cranial bone, without any splintering, depression, or distortion of bone; in a linear fracture, the dura mater remains intact
  • Depressed Fracture – a break in the cranial bone or a crushed part on the skull with depression of the cranial bone toward the brain
  • Open Fracture – an injury in which the fractured bone or haematoma are exposed to the external environment due to a traumatic violation of the soft tissue and skin; the wound may lie at a site distant to the fracture, not directly over the fracture itself
  • Impaled Object – an injury in which an object remains impaled into the cranium eg. a bullet or knife; it is crucial that no one attempts to remove an impaled object unless in a healthcare facility where emergencies can be attended to
head injury nursing care
Retrieved from https://slideplayer.com/slide/12216357/ on 26th December 2022

Base of skull fracture a.k.a. basilar skull fracture ~ Focal Injury

Typical signs of a base of skull fracture include:

  • Raccoon Eyes – unilateral and/or bilateral periorbital ecchymosis
  • Battle’s Sign – unilateral retro-auricular / mastoid ecchymosis
  • Haematotympanum – blood behind the ear drum
  • Halo’s Sign – a fracture located at the base of the skull may lead to blood or CSF leakage, or both, from the nose (rhinorrhoea) and/or the ear (otorhoea); CSF is a straw-coloured fluid which typically produces the ‘halo sign’

Retrieved from https://www.semanticscholar.org/paper/Periorbital-Ecchymosis-%28Raccoon-Eye%29-and-Orbital-Nasiri-Zamani/0337e88c6d4e2ff8d234edc189bee96dc2bdaca3, https://25hournews.com/news/the-battle-sign-that-appears-behind-the-ears-3000 & https://onlinelibrary.wiley.com/doi/pdf/10.1197/j.aem.2003.09.004 on 26th December 2022

Basilar Skull Fracture Head Injury Nursing Care

  • DO NOT perform nasal suctioning
  • DO NOT attempt to insert a NGT
  • If a gastric tube is indicated, it is better to insert an orogastric tube instead. The risk is higher with NGT insertion than with an orogastric tube because the roof of the nasal cavity is practically shared with the base of the skull
  • DO NOT plug bleeding site – instead wipe drainage with a sterile swab
  • Instruct patient to perform NO STRAINING and NO VALSALVA (breathing method that may slow the heart during tachycardia)
  • QUERY SURGERY – if indicated, surgery may be attempted to seal CSF leak, repair damaged vessel/s or relieve ICP

Complications:

  • brain injury
  • cranial nerve palsy
  • blood vessel injury
  • CSF leak (may lead to infection: meningitis)

Intracranial Bleed ~ Focal Injury

Risk factors for intracranial bleeds include:

  • basilar skull fracture
  • older age
  • previous neurosurgery
  • use of anticoagulants
  • blood clotting disorders
  • history of loss of consciousness
  • retrograde amnesia (amnesia where one cannot recall memories formed before the event which caused the amnesia)
  • anterograde amnesia (memory loss which occurs when one cannot form new memories, permanently losing the ability to learn or retain new information)

Epidural Haematoma ~ Focal Injury

FACTS:

  • bleeding is located between the skull and the dura mater
  • commonly results from a temporal bone fracture
  • commonly involves arterial bleeding, usually from the middle meningeal artery
  • typically features a ‘lucid interval’, which is a temporary improvement in the patient’s condition after a traumatic brain injury, following which fast deterioration occurs
  • if left undrained may displace brain into foramen magnum
  • requires immediate surgery

CT SCAN FEATURES:

  • edges are sharply defined
  • convex or lens-shaped appearance
  • the dura strips from the cranium’s under-surface, causing the haematoma to assume its shape
  • the ventricular system’s midline shifts to the side opposite the haematoma
head injury nursing care
Retrieved from https://healthjade.com/epidural-hematoma/ on 27th December 2022
head injury nursing care
Retrieved from https://www.beyondachondroplasia.org/en/library/medicine/160-foramen-magnum-growth-in-achondroplasia on 27th December 2022
Retrieved from https://radiopaedia.org/cases/epidural-haematoma-4 on 27th December 2022

Subdural Haematoma ~ Focal Injury

FACTS:

  • venous bleed occurs between the dura mater and the arachnoid mater, within the meninges
  • bleed may be acute, sub-acute, or chronic
  • neurological deterioration progresses slowly
  • risk factors include trauma, hypertension, anticoagulant use, and alcohol abuse
    • excessive blood is usually drained by an extravascular catheter

CT SCAN FEATURES:

  • an acute subdural haematoma presents in a crescent shape, covering the entire brain surface
  • prognosis for an acute subdural haematoma is worse than that of an epidural haematoma, with underlying brain damage typically being more severe
  • rapid surgical evacuation is required especially in the case of >5mm midline shift and raised intracranial pressure
head injury nursing care
Retrieved from https://twitter.com/jclinicalmedres/status/1407923308134207491?lang=da on 27th December 2022
Acute-on-Chronic Subdural Haematoma – Retrieved from https://radiopaedia.org/cases/acute-on-chronic-subdural-haematoma-1 on 27th December 2022

Subarachnoid Haemorrhage ~ Focal Injury

FACTS:

  • blood pooling is located in the subarachnoid space, between the arachnoid membrane and the pia mater
  • bleeding happens spontaneously through ruptured aneurism, trauma, or hypertension
  • a common sign of a subarachnoid haemorrhage is a ‘thunderclap headache’ – a headache that strikes suddenly like a clap of thunder as the name implies

CT SCAN FEATURES:

  • in a CT scan, a subarachnoid haemorrhage appears as a high-attenuating, amorphous substance that fills the normally dark, CSF-filled subarachnoid spaces around the brain

ATTENTION!!

  • avoid an increase in intracranial pressure
  • explore possibility of surgery for haematoma drainage
  • explore possibility of surgery for aneurism clipping
head injury nursing care
Retrieved from https://www.firstaidforfree.com/what-is-a-subarachnoid-hemorrhage-sah/ on 27th December 2022
Retrieved from https://en.wikipedia.org/wiki/Subarachnoid_hemorrhage on 27th December 2022

Intracerebral Haemorrhage A.k.a. intraparenchymal cerebral haemorrhage ~ Focal Injury

FACTS:

  • blood pooling caused by rupture of a blood vessel within the brain tissue – the cerebrum
  • may be a spontaneous rupture as in a CVA
  • may be caused by a traumatic event as in a penetrating injury, depressed skull fracture, contusion, or laceration
  • signs and symptoms are similar to that of a stroke
  • prognosis depends on the size and location of the intracerebral haemorrhage, however, this type of haemorrhage carries a high mortality rate

CT SCAN FEATURES:

  • a CT scan of an Intracerebral Haemorrhage features a hyper-dense collection of blood, commonly surrounded by hypo-dense oedema
  • complications such as extension of the haemorrhage into other intracranial compartments may also be present
head injury nursing care
Retrieved from https://healthjade.net/intracerebral-hemorrhage/ on 27th December 2022

Concussion ~ Diffuse Injury

FACTS:

  • the brain remains structurally intact when a concussion is incurred
  • transient loss of consciousness may take from a couple of seconds to hours
  • concussion prognosis is commonly a complete recovery without treatment

SIGNS & SYMPTOMS:

  • mild headache
  • dizziness
  • lethargy
  • irritability
  • poor concentration
  • confusion / disorientation
  • post-traumatic amnesia

Severe Diffuse Axonal Injury

FACTS:

  • shearing and tearing of axons in the cerebral hemispheres and brainstem usually result from rapid deceleration
  • damage is on a microscopic scale, thus is usually invisible in tests
  • symptoms include coma, persistent vegetative state, and abnormal posture
  • severe diffuse axonal injury carries a high mortality rate
head injury nursing care
Retrieved from https://propelphysiotherapy.com/neurological/diffuse-axonal-brain-injury/ on 28th December 2022

Secondary Brain Injury

As previously mentioned, a primary brain injury can only be prevented through education and health promotion, whilst a secondary brain injury can be prevented from a clinical point of view.

For this reason, another blogpost focusing on secondary brain injury prevention will be published in the upcoming days. Subscribe below to receive notification of newly published blogposts in your inbox 😉

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Pulmonary Oedema Nursing Care of the Critically Ill Patient

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Pulmonary Oedema refers to an accumulation of fluid in the interstitial spaces of the lungs that diffuses into the alveoli. This accumulation causes severe hypoxia. Thus, in pulmonary oedema nursing care, the patient’s oxygenation needs are prioritised.

Pulmonary Circulation VS Systemic Circulation

Pulmonary Oedema Pathophysiology

  1. excess vascular water fills the interstitium
  2. interstitial lymphatics situated within the pulmonary system are unable to drain excess water
  3. alveolar spaces flood and become unable to perform gas exchange due to ventilation/perfusion (V/Q) mismatch

RIGHT SIDE Heart Failure = Peripheral Oedema

LEFT SIDE Heart Failure = Pulmonary Oedema

Retrieved from https://www.otsuka.co.jp/en/health-and-illness/heart-failure/symptoms/ on 19th December 2022

Cardiogenic Pulmonary Oedema VS Non-Cardiogenic Pulmonary Oedema

Pulmonary oedema can be Cardiogenic Pulmonary Oedema a.k.a. Hydrostatic (pressure-related), Non-Cardiogenic Pulmonary Oedema (increased permeability), or a combination of both.

Cardiogenic Pulmonary Oedema a.k.a. Hydrostatic Oedema happens due to increased left ventricular filling pressure.

Non-Cardiogenic Pulmonary Oedema happens in the absence of elevated left ventricular pressure.

Pulmonary Oedema Signs & Symptoms + Radiographic Features

Pulmonary Oedema signs and symptoms onset is usually sudden, requiring immediate medical attention, usually due to intense dyspnoea resulting from the sudden V/Q Mismatch (happens when part of the lung receives oxygen without blood flow or blood flow without oxygen – respiratory reserve can help continue/preserve perfusion in V/Q mismatch, but only for a limited time), which leads to the patient becoming anxious and scared. Noisy respirations are also present due to secretions within the larynx and trachea. The patient’s skin becomes moist, cold and clammy – signs of shock.

Cyanosis develops rapidly in the late stage of respiratory failure. The patient develops a cough with copious frothy blood-stained sputum. Crepitations are heard throughout the chest on auscultation. A chest x-ray typically features a bat-like picture of the lungs. Note that a chest x-ray featuring pneumonia is very similar to one featuring pulmonary oedema, thus, in critical care it is important to distinguish between the two.

Full list of signs & symptoms of pulmonary oedema includes:

  • restlessness
  • anxiety
  • breathlessness
  • sense of suffocation
  • cyanotic nail beds
  • greyish skin tone
  • cold and moist hands
  • weak and rapid pulse
  • jugular vein distension
  • coughing
  • increasing foamy sputum
  • confusion and stuporous (as pulmonary oedema progresses)
  • rapid noisy moist-sounding breathing
  • significant decrease in oxygen saturation level
  • assessment includes crackles on auscultation
Retrieved from https://twitter.com/onsquares/status/1346344297214447616 on 18th December 2022

Cardiogenic Pulmonary Oedema Causes

  • Congestive Heart Failure (CHF) – the heart muscle doesn’t pump enough blood as it should, causing blood to back up, leading to fluid build-up in the lungs
  • Mitral Stenosis – narrowing of the valve between the two left heart chambers which reduces or blocks the blood flow into the heart’s left ventricle, leading to left-sided heart failure
  • Cor Pulmonale – a condition that causes the right side of the heart to fail
  • Myocardial Infarction a.k.a. heart attack – when blood flow to the heart muscle is blocked

Non-Cardiogenic Pulmonary Oedema Causes

  • Acute Respiratory Distress Syndrome – ARDS occurs when fluid builds up in the alveoli, keeping the lungs from filling with enough air; less oxygen reaches the bloodstream, depriving the organs of much needed oxygen to function adequately
  • Smoke Inhalation Burns

Pulmonary Oedema Nursing Care

  • record and monitor vital signs
  • administer high oxygen concentration to relieve cyanosis
  • position patient in an upright position or with legs and feet down or ideally dangling over the side of bed to promote better circulation – correct positioning increases the vital capacity of the patient’s lungs
  • reassure patient to reduce anxiety – do not leave patient alone
  • morphine can be administered to help further with the reduction of anxiety, as well as dilating peripheral circulation leading to a reduction in left ventricular pressure during diastole; IMPORTANT – morphine can depress the respiratory system, so never leave patient unattended
  • administer diuretics – monitor for medication effects including patient’s fluid and electrolyte levels; diuretics, especially if loop diuretics are administered, waste potassium and sodium; potassium administration may be required
  • bronchodilators can be used to relieve bronchospasm and facilitate bronchial toilet a.k.a. toilet bronchoscopy – a potentially therapeutic intervention to aspirate retained secretions within the endotracheal tube and airways and revert atelectasis; aspiration of airway secretions is the most common indication to perform a therapeutic bronchoscopy in the intensive care unit (ICU)
  • patients with pulmonary oedema are at times electively ventilated so that through PEEP,t further water leakage into the alveoli may be prevented
  • identify and treat primary cause eg. need for mitral valve prosthesis, opening blocked arteries etc.

NOTE: intubation and mechanical ventilation may be required if the patient’s condition worsens; haemodynamic monitoring (BP and PAWP) and ABGs act as guidance in artificial ventilation management.

NOTE: PAWP refers to Pulmonary Artery Wedge Pressure which is the pressure within the pulmonary arterial system that occurs when catheter tip ‘wedges’ in the tapering branch of one of the pulmonary arteries.

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Cross Sectional Study Critical Appraisal

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A cross sectional study is observational in nature. It involves collection of information about a population at a particular point in time.

  • A descriptive cross sectional study would assess distribution and frequency eg. measuring the prevalence of cancer amongst a defined population
  • An analytical cross sectional study would examine the association between variables to identify determining factors related to health eg. examining the association between living a sedentary lifestyle and having hypertension

Hierarchy of evidence

Retrieved from https://www.sketchbubble.com/en/presentation-hierarchy-of-evidence.html on 18th February 2023

Advantages

  • affordable – a cross sectional study requires no follow-ups since only one set of data is analysed, making this a low-cost research method
  • efficient – a cross sectional study is ideal for studying exposures or conditions that are reasonably common, and which require only one-time assessment
  • no risks – this type of study requires no long-term considerations.
  • potential completeness – due to easily accessed key data points

Disadvantages

  • collecting data at one point in time leads to limited causation testing especially where exposure and/or outcome are expected to change over time
  • needs to be an adequate representation of the population being studied
  • requires a larger sample size for accuracy basis
  • bias may affect results if for example incomplete responders are related to a specific group
  • may result in an association, however such association may not be the reason for the association
  • unable to measure incidence

Critically Appraising a Cross Sectional Study

When critically appraising a cross sectional study you need to focus on the following:

  • Sampling
  • Non-response
  • Methods used for measuring variables of interest
  • Controlling for confounders in the analysis

Sampling

  • note sampling bias – population needs to be clearly identified since final results will be inferred onto the target population
  • consider choice of sampling frame – how was the sample selected from the actual population? Remember that when it comes to measuring prevalence, the actual population is of utmost importance. Thus, consider sampling procedure used eg. random vs convenience sampling, using inclusion or exclusion criteria etc
  • consider the procedure used for the selection of participants – was inclusion/exclusion criteria used? And was the sample taken at random or was it convenience sampling?
  • consider sampling size – ideally, previous studies performed within the same area should be sought so that the occurrence frequency within the sample reflects the occurrence within the target population
  • consider expected precision of results – rare occurrence and precise results require a bigger sample

Non-Response

  • respondents may differ from non-respondents – respondents are more likely to be interested in the subject being studied, which may lead to more adherence to suggestions/requirements. Thus, replacing non-respondents to increase the sample size may still not bypass the sampling bias resulting from no response
  • researchers are required to report the response rate as well as to compare the characteristics of both the respondents and non-respondents

Controlling Confounders

A confounding factor is a third variable in a study which examines a possible cause-and-effect connection. It is related to both the supposed cause and supposed effect of the study. At times it is difficult to separate the true effect of the independent variable from the effect of the confounding variable.

Whilst performing a research study, it is important that potential confounding variables are identified and a plan is drawn so that their impact is reduced.

Example of a Cross Sectional Study

Breast feeding and obesity: cross sectional study (full reference in the references section): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC28161/

Appraisal Tool for Cross Sectional Studies (AXIS)

Cross Sectional Study Appraisal Checklist

Retrieved from https://bmjopen.bmj.com/content/bmjopen/6/12/e011458/DC2/embed/inline-supplementary-material-2.pdf?download=true on 17th December 2022

NOTE: To view blogpost featuring Cochrane videos on all types of studies please click here.

References

BMJ Open (2016). Appraisal Tool for Cross-Sectional Studies (AXIS). Retrieved from https://bmjopen.bmj.com/content/bmjopen/6/12/e011458/DC2/embed/inline-supplementary-material-2.pdf?download=true on 17th December 2022

von Kries, R., Koletzko, B., Sauerwald, T., von Mutius, E., Barnert, D., Grunert, V., & von Voss, H. (1999). Breast feeding and obesity: cross sectional study. BMJ (Clinical research ed.), 319(7203), 147–150. https://doi.org/10.1136/bmj.319.7203.147

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Ventilated Patient Nursing Care in the ICU

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Ventilated patient nursing care requires a lot of observation, preparation and monitoring. This is not just specific to monitor readings…the patient needs to be evaluated as a whole in conjunction to the readings being provided.

Safety Checks

When working in a critical care setting, at the beginning of each shift:

  1. check that the manual ventilation bag is connected to oxygen supply
  2. check that the suctioning equipment is in good working order
  3. check for availability of equipment and drugs required for re-intubation and resuscitation
  4. check that the ventilator settings are the same as documented and mentioned in handover

Whenever you move or turn your patient:

  1. check that the endotracheal tube or the tracheostomy tube are secure
  2. check that any other catheters/lines are in place and still secure

Constant safety checks:

  1. monitor the patient’s haemodynamic stability
  2. monitor the patient’s respiratory stability
  3. ensure that alarms are set sensibly
  4. DO NOT IGNORE ALARMS!
Ventilated Patient Nursing Care
Retrieved from https://slideplayer.com/slide/2746191/ on 12th December 2022

Airway Management of the Ventilated Patient

Ventilated patient nursing care includes:

  • care of the endotracheal tube or tracheostomy
  • humidification
  • suctioning
  • cuff pressure management
  • patient communication
  • patient swallowing ability
  • weaning from mechanical ventilation

Ventilated Patient Monitoring

Ventilated patient monitoring is crucial, especially since deterioration can happen fast. Monitoring requirements include monitoring the patient’s:

  • haemodynamic stability
  • pulse oxymetry
  • capnography
  • level of consciousness
  • pain and agitation

Sedation and Analgesia

A ventilated patient can benefit from sedation and/or analgesia since these:

  • provide the patient with comfort and tube tolerance
  • reduce oxygen consumption by promoting patient-ventilator synchronisation whilst reducing dyspnoea and anxiety
  • reduce the risk of complications such as self-extubation and laryngeal damage
  • reduce the need of muscle relaxants

NOTE: Muscle relaxants may still be necessary in patients with head injuries and/or with excessive airway pressure; when administering muscle relaxants ensure that the patient is fully sedated.

sedation disadvantages

  • vasodilation – patient may need IV fluids and inotropes eg. norepinephrine, epinephrine, and vasopressin
  • sedative accumulation – sedatives with long half-life are not ideal for patients with hepatic or renal failure
  • over-sedation – prolongs ventilation period and lengthens the patient’s stay in the critical care setting

NOTE: sedation breaks may lead to shorter duration of mechanical ventilation and shorter stay in the critical care setting.

NOTE: sedation scores such as the Ramsay Sedation Scale, the Richmond Agitation-Sedation Scale (RASS), and the Nursing Instrument for the Communication of Sedation (NICS) can help prevent over-sedation.

Ventilated Patient Nursing Care
Ramsay Sedation Scale – Retrieved from https://www.researchgate.net/figure/Ramsay-Sedation-Scale_tbl1_228361277 on 12th December 2022
Ventilated Patient Nursing Care
Retrieved from https://www.researchgate.net/figure/Richmond-Agitation-Sedation-Scale-RASS_fig1_51078510 on 12th December 2022
Retrieved from https://ebrary.net/40984/health/sedation_assessment_with_subjective_methods on 12th December 2022

Analgosedation

Retrieved from https://healthmanagement.org/c/icu/issuearticle/sedation-and-analgesia on 12th December 2022

Patient Comfort Guidance

E-CASH – early comfort with the use of analgesia, minimum sedation and maximum care.

ABCDEF BUNDLE:

  • A = ASSESS, prevent, and manage pain
  • B = BOTH Spontaneous Awakening Trials (SAT) and Spontaneous Breathing Trials (SBT)
  • C = CHOICE of analgesia and sedation
  • D = DELIRIUM – assess, prevent and manage
  • E = EARLY mobility and exercise
  • F = FAMILY engagement and empowerment

Ventilated Patient Personal Care

Mouth Care

  • clean patient’s teeth using a small soft toothbrush and toothpaste twice daily
  • use antiseptic liquid or gel between brushing for oral cleansing and moisturising; this helps prevent plaque formation whilst reducing oral colonisation of Gram-negative bacteria and resulting respiratory infections
  • provide frequent oropharyngeal suctioning for the hypersalivating patient due to endotracheal tube use; this reduces the risk of central line contamination and risk of micro-aspiration

Eye Care

  • provide artificial eye lubricant (methyl cellulose) – a patient on sedation loses the blink reflex, making the eyes exposed to corneal drying, infection, abrasion and dust
  • apply eye pads and/or tape if required
  • assess regularly for infection and conjunctival oedema

Nutritional Care

While the patient is Nil-By-Mouth, a nasogastric tube is usually used so that abdominal distension is prevented, since it hinders ventilation.

  • ensure that the patient is started on enteral nutrition early since this promotes gut integrity whilst reducing GI complications; it also helps provide the patient with caloric and protein required for mechanical ventilation, prevents muscle atrophy, as well as helps during the weaning process
  • prop the patient up in a semi-raised position to prevent aspiration; aspirate the patient’s stomach regularly to assess absorption
  • assess for need of a PEG or TPN
  • stress ulcer prophylaxis may be prescribed

Elimination & Related Care

  • document patient intake and output on proper charting sheets to ensure patient fluid and electrolyte balance; document any abnormal stools
  • constipation may result from use of drugs, diet changes and immobility, which may cause abdominal distension; to avoid problems with diaphragmatic and ventilatory capacity consider using glycerin suppositories and enemas
  • diarrhoea may result from antibiotic resistance and enteral feed intolerance; take stool specimens for culture and sensitivity testing and Cl. difficile, apply barrier cream to prevent moisture lesion formation, and ensure fluid and electrolyte balance are maintained

Psychosocial Care

  • assist patient to use alternate means of communication since this is a common trigger for patient frustration
  • provide constant orientation and reassurance
  • provide health literacy to the patient’s family in simple terms free from medical jargon
  • involve relatives in patient care – encourage touch and patient reassurance, communication and orientation, and lip care

Patient positioning

  • ensure that no lines, wires and catheters are left under the patient
  • provide regular position changes for pressure relief and movement of secretions; this also helps provide a conscious patient with a different perspective of surroundings
  • splints, passive and active ROM (range of motion) exercises
  • ensure patient is seen by physiotherapist and that chest physio in the form of percussion, vibration, and postural drainage is provided (unless contraindicated as with neurological patients)
  • whenever possible help the patient into prone position since this optimises alveolar recruitment by expanding the dorsal aspect of the lungs, and improves oxygenation and survival in ARDS (acute respiratory distress syndrome) patients

NOTE: with prone positioning, caution needs to be exerted: ensure an adequate amount of personnel are available to reposition patient, ensure that the patient’s airway is protected at all times, ensure that the ETT, IV lines and tubes are all secure, ensure adequate pressure area care, and provision of mouth and eye care as well as suctioning as required.

Ventilated Patient Nursing Care
Retrieved from https://turnmedical.com/helpful-links/ on 12th December 2022
Ventilated Patient Nursing Care
Retrieved from https://www.grepmed.com/images/2314/pronepositioning-criticalcare-cornishpasty-instructions-management on 12th December 2022

The HOTSPUD Ventilator Care Bundle

  1. Head of bed elevated 30-45 degrees
  2. Oral care performed frequently
  3. Turn patient from side to back to side every 2 hours
  4. Sedation vacation – adjust sedation so as to wake patient up once every 24 hours
  5. Peptic Ulcer prophylaxis to be administered to high risk patients
  6. Deep vein thrombosis prophylaxis in the form of drugs or leg compression

Other Ventilation Strategies

ECMO – Extra-Corporeal membrane oxygenation

  • blood oxygenation outside of the body
  • allows lung rest without exposure to high pressure oxygen levels

Permissive Hypercapnia

  • tolerate higher carbon dioxide levels to provide protection to the lung from barotrauma

High Frequency Ventilation HFV

  • very high frequency ventilation of 60-2000breaths/min
  • very low tidal volume of 1-5ml/kg

Preventing Ventilator-Associated Pneumonia (VAP)

  • avoid intubation unless absolutely necessary
  • extubate as soon as possible
  • perform meticulous hand washing and gloving
  • ensure correct endotracheal tube cuff pressure is maintained
  • use HME (heat and moisture exchanger filters)
  • remove any condensation formation from ventilator circuits
  • avoid unplanned extubation
  • perform endotracheal and supraglottic suctioning

High Flow Nasal Cannula

High Flow Nasal Cannula is a light cannula with soft pliable prongs, warmed and humidified, with a Flow of up to 60L/min and FiO2 up to 100%. The HFNC:

  • improves oxygenation
  • reduces breathing work
  • provides a continuous flow of fresh gas at high flow rates, replacing the patient’s pharyngeal dead space
  • washes out the patient’s re-breathes of carbon dioxide and replaces it with oxygen
Retrieved from https://www.researchgate.net/figure/Basic-components-of-a-high-flow-nasal-cannula-HFNC-system_fig1_333448617 on 12th December 2022

Respiratory Support Progression

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Mechanical Ventilation of Critically Ill Patients

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Ventilation is the movement of air into and out of the lungs. Ventilation carries oxygen to provide tissue perfusion and removes carbon dioxide which accumulates from aerobic metabolism. Sometimes, especially within the critical care setting self-ventilating becomes difficult or impossible for the patient. This is where mechanical ventilation is introduced – to provide artificial control or support during each breathing cycle through the use of a machine, namely a ventilator.

A ventilator typically has the following colour-coded pipes:

  • white pipe – oxygen at 100%
    • white and black pipe – compressed air at 21%
  • yellow pipe – suction

These pipes have the following features:

  • uncrushable – cannot be crushed if stepped over etc
  • pin indexed – one pipe cannot be inserted by mistake into a different socket by mistake
  • tug test – may tug oxygen hose after the probe is plugged into wall or cylinder socket to ensure it is firmly attached
  • internal battery
  • electricity supply

Mechanical Ventilation Indications

Before mechanical ventilation takes place, clinical judgement has to ascertain that such an intervention would be providing improved quality of life whilst lowering the mortality risk of the patient. Thus, mechanical ventilation should be opted for…

  • when the patient’s own ventilation mechanism is unable to sustain life
  • when the critically ill patient needs ventilation control
  • when there is the risk of impending collapse of physiological functions, in which case mechanical ventilation is opted for as a prophylactic measure

(Byrd et al., 2006)

Mechanical Ventilation helps the critically ill patient by:

  • improving alveolar ventilation and oxygenation
  • decreasing the required breathing effort and oxygen consumption
  • reversing hypoxaemia (low level of partial pressure oxygen in the blood)
  • reversing acute respiratory acidosis (too much carbon dioxide leading to an acidic base)
  • enabling sedation and muscle relaxation eg. prior to surgery

Specific indications for mechanical ventilation include:

  • apnoea
  • impending respiratory arrest
  • heart failure
  • pulmonary oedema
  • pneumonia
  • sepsis
  • chest trauma
  • surgery complications
  • ARDS (Acute Respiratory Distress Syndrome – a life-threatening condition with which the lungs are unable to provide the body’s vital organs with enough oxygen)
  • COAD acute exacerbation (Chronic Obstructive Airway Disease – a long term lung disease a.k.a. chronic bronchitis or emphysema, or the latest term COPD)
  • neuromuscular disorder
  • acute brain injury – mechanical ventilation almost always required since it controls the level of air that is exchange; the more carbon dioxide, the more vasodilation and the more blood pooling in the brain
  • coma

Mechanical Ventilation aims to prolong life, not prolong death…

Negative Pressure Ventilation

Air moves from one area to the other due to the difference in pressure a.k.a. pressure gradient. Spontaneous breathing happens through the generation of negative pressure. Negative pressure ventilation increases the normal physiological breathing pattern by producing a negative pressure outside the chest wall, which then causes the air to be automatically inhaled when the patient opens the airway.

Retrieved from https://understanding-vertebrates.weebly.com/respiratory-system.html on 9th December 2022

The Iron Lung vs Today’s Negative Pressure Ventilation Equipment

The Iron Lung, which was used extensively for patients up to the mid 1950’s, was a large airtight metal cylinder which enclosed patients fully, exposing only their head and neck. It worked through an electric pump which generated negative pressure, causing the patient’s chest to rise.

The Iron Lung – Retrieved from https://www.rochester.edu/newscenter/brief-history-of-ventilators-424312/ on 9th December 2022

Modern Negative Pressure Ventilation equipment comprises of airtight jackets or flexible canopies a.k.a. cuirass, which cover the chest area only. They are available in oscillatory mode so as to assist with secretion clearing.

Patients who benefit from such equipment include patients receiving home care who suffer from respiratory muscle group weakness, skeletal problems which restrict thoracic function, and patients with central hypoventilation syndrome.

mechanical ventilation
Modern Negative Pressure Ventilation Equipment – Retrieved from https://link.springer.com/article/10.1007/s42600-021-00149-0 on 9th December 2022

Negative Pressure Ventilation Limitations

Within the critical care setting, it is difficult to achieve accurate pressure, volume and gas flow due to abnormal lung compliance and impaired airway control. Additionally, the seal required around the patient’s chest wall may lead to pressure sores. With regards to nursing care, invasive procedures and chest examinations become difficult to perform. And while a Negative Pressure Ventilator provides ventilation, it does not provide oxygenation.

(Ashurst, 1997)

Positive Pressure Ventilation

Through positive pressure ventilation, the normal pressure gradient is reversed as oxygenated air is forced into the patient’s lung by the ventilator, and as airway pressure drops, recoil of the chest causes passive exhalation by pushing out the tidal volume.

mechanical ventilation
Retrieved from https://journals.rcni.com/nursing-standard/an-overview-of-mechanical-ventilation-in-the-intensive-care-unit-aop-ns.2018.e10710 on 10th December 2022

Routes for Positive Pressure Ventilation Delivery

INVASIVE ROUTES:

NON-INVASIVE ROUTE:

This is achieved through the use of a NIV – non-invasive ventilator. Whilst this type of ventilation does not require sedation and it reduces the risk of nosocomial pneumonia, a NIV requires that the patient is conscious, breathing spontaneously and is compliant. It also requires the use of a tight-fitting face mask, nasal cannula or helmet.

mechanical ventilation
Retrieved from https://www.sciencedirect.com/science/article/pii/S2452247317302765 on 10th December 2022

NON-INVASIVE VENTILATION with CONTINUOUS POSITIVE AIRWAY PRESSURE (CPAP):

  • PEEP – positive pressure is maintained throughout inspiration and expiration
  • reduces breathing effort requirement
  • improves oxygenation
  • improves compliance

NON-INVASIVE VENTILATION with BI-LEVEL POSITIVE AIRWAY PRESSURE (BiPAP):

  • 2 positive pressure settings include IPAP – inspiratory positive airway pressure, and EPAP – expiratory positive airway pressure
  • increases tidal volume
  • reduces PaCO2
  • improves oxygenation
  • reduces breathing effort requirement
mechanical ventilation
Retrieved from https://www.cpap.com/blog/difference-bipap-cpap/ on 10th December 2022

Mechanical Ventilation Ventilator Variables

CONTROL: ventilator controls the pressure and the volume

TRIGGER: what starts off inspiration, where the flow, pressure or volume are generated by the patient, whist the time is triggered by the ventilator itself if the inspiration is not initiated by the patient (in other words, either the patient triggers inspiration, or the ventilator)

CYCLING: time, flow and volume trigger expiration

mechanical ventilation
Retrieved from https://rc.rcjournal.com/content/56/1/39 on 10th December 2022

Volume Controlled Ventilation

In Volume Controlled Ventilation, a preset gas volume is forced into the lungs, whilst pressure is dependable on lung compliance.

Volume Controlled Ventilation ensures delivery of a constant tidal and minute volume, and is set based on the patient’s ideal body weight, height and sex.

However…

When a patient’s lung compliance decreases, an increased amount of pressure is required. Volume Controlled Ventilation will deliver the preset tidal volume with no regards to a patient’s airway condition change, which may lead to VILI (Ventilator-Induced Lung Injury)

Pressure Controlled Ventilation

In Pressure Controlled Ventilation, the lungs are inflated up to a preset pressure. The tidal volume is variable, depending on both lung compliance and resistance in breath delivery.

Pressure Controlled Ventilation helps prevent excessive airway pressure whilst reducing the risk of VILI (Ventilator-Induced Lung Injury).

However…

It does not guarantee minute volume, and this may lead to the patient experiencing hypoventilation leading to hypoxia.

To prevent this from happening, Volume Guaranteed Pressure Control Ventilation ensures that with each mandatory breath, a set tidal volume (VT) is applied with minimum pressure. Additionally, pressure adapts gradually to resistance and/or compliance changes so the set tidal volume is administered.

Mechanical Ventilation Ventilator Settings

FiO2 – FRACTION OF INSPIRED OXYGEN

FiO2 is the fraction of oxygen in each delivered breath. FiO2 should be set somewhere between 21% (0.21) and 100% (1.0). FiO2 is used to maintain oxygenation along with PEEP.

Oxygen toxicity risk increases when the patient’s dependency and duration on FiO2 are high. Additionally, oxygen metabolites may lead to tracheobronchitis (inflammation of the trachea and bronchi), absorptive atelectasis (loss of lung volume caused by the resorption of air within the alveoli), hypercarbia (increase in carbon dioxide in the bloodstream), lung fibrosis (lung tissue damage and scarring), and diffuse alveolar pulmonary membrane damage (changes which occur to the structure of the lungs).

PEEP – POSITIVE END-EXPIRATORY PRESSURE

Positive pressure is maintained throughout inspiration and expiration, thus, pressure is not allowed to drop to zero at the end of expiration. This prevents the alveoli from collapsing, improves oxygenation without increasing the FiO2, helps prevent oxygen toxicity, whilst increasing the availability of alveolar surface area for gaseous exchange.

However, PEEP should be used with caution in patients with either a head injury and/or poor cardiac output. This is because PEEP increases the intra-thoracic pressure and hence reduces venous return, therefore cardiac output is reduced, and intracranial pressure is increased.

Similarly, patients with COPD and/or asthmatic patients who are not able to completely exhale tidal volume should also receive PEEP with caution.

Mechanical Ventilation Modes

CMV – COntinuous Mandatory Ventilation

CMV delivers a preset number of breaths with a preset tidal volume or pressure. In CMV the patient’s inspiratory efforts make no difference since all settings are preset. Settings involved include TV, Inspiration Pressure, FiO2, PEEP and RR.

All breaths controlled by ventilator, no triggered breaths – Retrieved from https://ddxof.com/tag/ards/ on 11th December 2022

a/c – Assist / control Ventilation

In A/C ventilation, the patient can trigger the ventilator to deliver the breath. This type of setting has the ability to sense the natural negative pressure generated by the patient, delivering a breath with a set volume or pressure. However, if the patient does not trigger any breaths, a set number of breaths is still delivered.

Every patient-triggered breath is fully supported, a backup rate is set; in the absence of patient-triggered breaths, AC acts like CMV – Retrieved from https://ddxof.com/tag/ards/ on 11th December 2022

simv – Synchronised Intermittent Mandatory Ventilation

In SIMV, a preset number of ventilator breaths per minute are delivered. Spontaneous breaths may be initiated by the patient at any point between ventilator breaths.

To augment the tidal volume of spontaneous breaths, pressure support is often used. Settings involved include a set rate, tidal volume, FiO2, with optional pressure support and PEEP.

NOTE: monitor total breathing rate, minute volume, and airway pressure.

Preset minimum mandatory breaths are synchronised to the patient’s efforts, with the patient able to breathe spontaneously between supported breaths – Retrieved from https://ddxof.com/tag/ards/ on 11th December 2022

PS/ spn-cpap: Pressure support ventilation

SPN refers to spontaneous mode of ventilation in which respirations are started and ended by the patient. SPN requires no preset rate and TV since both are determined by the patient, thus, need to be monitored well.

SPN may be combined with pressure support, where spontaneous breaths are aided by an extra push from the ventilator. Thus, if apnoea is detected, the ventilator starts providing backup mandatory ventilation.

With Pressure Support, all breaths are triggered by the patient, each of which is supported by preset pressure – Retrieved from https://ddxof.com/tag/ards/ on 11th December 2022
CPAP promotes spontaneous breathing at an elevated baseline pressure – Retrieved from https://ddxof.com/tag/ards/ on 11th December 2022

BiPAP – Bi-Phasic Positive Airway Pressure

In BiPAP, the ventilator alternates between IPAP (Inspiratory Pressure) and PEEP. BiPAP provides mandatory breaths synchronised with the patient’s breathing attempts for both inspiration and expiration. With this setting in place, the patient can breathe spontaneously at any time, supported by pressure support. This helps reduce the need for patient sedation whilst improving oxygenation.

Complications of Mechanical Ventilation

Carbery, 2008. Retrieved from https://journals.sagepub.com/doi/10.1177/175045890801800303 on 11th December 2022

Weaning Patient from Mechanical Ventilation

A patient on mechanical ventilation can be weaned off of the ventilator if he/she:

  • is conscious and cooperative
  • has an FiO2 of <50%
  • has adequate minute ventilation
  • is able to cough
  • has minimal or clear secretions
  • has no evidence of septic shock
  • has an adequate fluid status
  • has no significant acid-base or electrolyte imbalance
  • has minimal vasopressor requirement
  • is showing evidence of resolution of the primary reason which required mechanical ventilation

If the patient meets the criteria mentioned above, ventilatory support is decreased (mandatory breaths, FiO2 and Pressure Support), and replaced with spontaneous ventilation. Spontaneous breathing trials can be performed with the use of T-piece humidifier and flow inflated ventilation bags.

Whilst attempting to wean patient off of mechanical ventilation, it is very important to monitor for signs of respiratory distress!

Signs of respiratory distress include:

  • tachypnoea
  • tachycardia
  • hypoventilation
  • bradycardia
  • hypertension
  • hypotension
  • hypoxaemia – SPO2 <90%
  • agitation
  • altered level of consciousness
  • labored breathing
  • use of accessory muscles of breathing

References

Ashurst, S. (1997). Nursing care of the mechanically ventilated patients in ITU: Part 1 and 2. British Journal of Nursing 6(8, 9): 447-454, 475-485.

Byrd, R.P., Eggleston, K.L., Hnatyuk, O.W. (2006). Mechanical Ventilation.

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Introduction to Medical Statistics

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Statistics VS Medical Statistics

Statistics are quantities or sets of quantities which one can calculate from observed data. Thus, unless they are ratios, statistics should be reported in units. Medical statistics is a subdiscipline of statistics. Medical statistics can assist researchers in answering healthcare-related challenging questions.

“It is the science of summarizing, collecting, presenting and interpreting data in medical practice, and using them to estimate the magnitude of associations and test hypotheses. It has a central role in medical investigations. It not only provides a way of organizing information on a wider and more formal basis than relying on the exchange of anecdotes and personal experience, but also takes into account the intrinsic variation inherent in most biological processes.”

Kirkwood, 2003.

Population VS Sample

In relation to statistics, the term population refers to a well defined group of subjects that a researcher chooses to investigate about a particular issue. The size of such a population may be known or unknown, but when the study population is too big to be investigated fully, sampling becomes needed.

A sample is a feasible number of subjects chosen to represent a population, thus, the sample involved in the study needs to be as representative as possible to the target population. This can be achieved by:

  • selecting an adequate sampling population
  • using randomly selected participants rather than convenience sampling

Simple Random Sampling

Simple random sampling is a sampling method in which all members of a population have an equal chance of being chosen to participate in the study sample.

Retrieved from https://www.shsu.edu/~mgt_ves/mgt481/lesson9/sld014.htm on 20th November 2022

Stratified Random Sampling

In stratified random sampling, the population is stratified into defining blocks eg. gender and age.

medical statistics
Retrieved from https://analyticssteps.com/blogs/stratified-random-sampling-everything-you-need-know on 20th November 2022

Weighted Sampling

In weighted random sampling the subjects are weighted and the probability of each item to be selected is determined by its relative weight. This allows the sample to be more representative of the population.

Retrieved from https://www.geopoll.com/blog/weighting-survey-data-raking-cell-weighting/ on 20th November 2022

Cluster Sampling

In cluster sampling, random groups of individuals are recruited for the study sample.

medical statistics
Retrieved from https://www.simplypsychology.org/cluster-sampling.html on 20th November 2022

Convenience Sampling a.k.a. Opportunity Sampling

In this type of sampling, no consideration is taken with regards to representation. Thus, all members of a population that a researcher can access have the opportunity to be recruited.

medical statistics
Retrieved from https://sites.google.com/site/glossary2019/c/convenience-sampling on 20th November 2022

Snowball Sampling

When recruiting members into a sample population becomes difficult, researchers revert to snowball sampling, where recruits are asked to suggest friends who may be willing to participate in the study.

medical statistics
Retrieved from https://www.simplypsychology.org/snowball-sampling.html on 20th November 2022

Sampling Used in Qualitative Studies

Sampling used in qualitative studies is usually either purposeful sampling or theoretical sampling:

  • PURPOSEFUL SAMPLING – the researcher seeks individuals who can provide the required data
  • THEORETICAL SAMPLING – the researcher uses a sampling method which, although similar to purposeful sampling, also includes changing and/or adapting the participants’ selection throughout the study based on results obtained from previous participants

NOTE: sample size does not matter in qualitative studies, since the aim is to acquire in-depth understanding of a phenomena.

Data Collection Variables in Medical Statistics

Variables are characteristics, numbers, or quantities which can be measured or counted. Some examples of variables include age, sex, blood pressure results, oxygen saturation levels etc.

Categorical Variables a.k.a. Qualitative Variables

Data collection in qualitative studies typically takes place during in-depth interviews such as one-to-one interviews or focus group interviews, and in some cases, non-structured observation may also be involved.

Categorical variables give qualitative information about the subject being investigated. Thus, possible responses in this variable are not numerical in nature, but instead are different categories related to the subject.

Categorical variables can also be divided into two:

  • Nominal Variable – a variable with a number of categories eg. occupation
  • Binary Variable – a variable with only two possible responses eg. yes or no

Continuous variables a.k.a. Quantitative Variables

Continuous variables give quantitative information about the subject in question. Thus, continuous variable responses can be any quantities within a set interval of values. Some examples would be age and BMI.

Data collection in quantitative studies may include:

  • readily available data such as data related to hospital activity, registers, prevalence and determinants
  • self-administered questionnaires which may include numerical scales
  • structured interviews through phone, electronic media, or face to face interviews, all of which allow an element of explanation and feedback between the researcher and the participant
  • structured observation which typically happen during observation schedules within a particular setting

Ordinal Variables a.k.a. Discrete Variables

Ordinal variables give limited quantitative information because responses achieved are numerically related to each other, yet have to be one within a limited number of values.

medical statistics
Retrieved from https://prinsli.com/categorical-variables/ on 20th November 2022

Data Analysis

Descriptive Statistics

Descriptive statistics feature a summary of data in a clear, concise and easy-to-understand way, usually through a numerical approach.

Inferential Statistics

Inferential statistics are statistics which, after being calculated from a sample, inferences are made on the original population using the same statistics.

medical statistics
Retrieved from https://www.z-table.com/z-score-table-blog/the-differences-between-descriptive-and-inferential-statistics on 20th November 2022

Reference

Kirkwood, Betty R. (2003). essential medical statistics. Blackwell Science, Inc., 350 Main Street, Malden, Massachusetts 02148–5020, USA: Blackwell. ISBN978-0-86542-871-3.

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Literature Searching Strategies For Dissertation Writing

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When searching through literature searching strategies for the purpose of writing your dissertation, you need to seek a good strategy which is both comprehensive and systematic. A systematic collection of observations from research subjects (such as demographic characteristics, physical characteristics, biological markers, behaviours, or feelings, emotions or views) aiming to create information about these subjects is otherwise referred to as research. This can be performed in the following order:

  1. Reflect on potential research areas or questions which are of interest to you
  2. Carry out simple searches, both on Google and in textbooks so as to obtain general knowledge on the subject of your interest
  3. Attempt to develop your research question; you may find the need to refine your question at a later stage or even restart your search from scratch to change your chosen subject
  4. Seek assistance by experts in the field of your interest and discuss related information sources
  5. Carry out advanced electronic research
  6. As part of the selection process, search manually through resulting key studies so as to confirm their relevance to your PICO question
  7. At this stage you should now have a clear idea of which relevant studies you can use for your own review
  8. Seek once again your chosen expert in the same field of study to confirm whether your refined idea is appropriate and relevant to the local scenario and clarify any related questions

Study Approaches and Designs

Every research study aims to answer a research question, which in itself determines the best approach and design to be used.

CHOOSING THE BEST DESIGN:

  • EXPERIMENTAL DESIGN – Randomised Control Trial (RCT)
  • OBSERVATIONAL DESIGN – Cross Sectional, Cohort, and Case Control Study

CHOOSING THE BEST APPROACH:

  • QUANTITATIVE APPROACH – emphasises on objective quantifiable measurements of attributes, aiming to generalise to a wider population; this approach involves theory testing and numerical data collection which can be analysed using statistical techniques
  • QUALITATIVE APPROACH – emphasises on subjective measures which may be varied or may change over time; this approach, which usually relies heavily on data interpretation, involves theory development, commonly including data in words and narratives such as perceptions and experiences aiming to understand or explain a typical behaviour.

NOTE: in qualitative research, rigor influences the validity of the produced results, which in turn determines how useful the evidence produced is, in terms of evidence based practice.

Literature Searching Strategies

Carrying out an Electronic Search

To carry out an electronic search you should search for articles within electronic databases which provide access to various electronic journals eg. International Journal of Nursing Studies and Journal of Nursing Education. Such journals include a number of publications a.k.a. articles.

The efficacy of an electronic search depends on how well your research question has been designed, how extensive was your search in relation to words and phrases used, the use of search tools such as Truncations and Boolean Operators, the use of good databases, and your review of literature search strategies until you are happy with your end results.

Choosing Search words and/or Phrases

A well designed research question should feature PICO elements…

Retrieved from https://libguides.cdu.edu.au/c.php?g=167917&p=3738712 on 19th November 2022

Search terms used can be in the form of single words or phrases. Phrases should be put in inverted commas. Always keep in mind that search engines provide you ONLY with articles containing the words you use in your searches.

Finding synonyms for each of the PICO components may be facilitated by:

  • brainstorming
  • thesaurus
  • MeSH browser
  • taking ideas from previously written related articles
  • using all word options including words containing hyphenations, alternative spelling and abbreviations

Additional Search Tools

Boolean Logic Operators

Use of Boolean Logic Operators AND, Or, and NOT:

  • AND combines words/phrases together so that both appear within one article found by a search.

Example: a search for ‘needles AND fear’ will find only those articles that contain both the words needles and fear.

  • OR enables a selection of any one of a number of specified words in a list.

Example: behavioural OR behavioral

  • NOT excludes specific words so articles containing them will not be identified.

Example: ‘fear of needles NOT fear of hospitals’

Truncation

  • Truncation helps search all the variations of a word without writing them.

Example: Child* picks up child, children, childhood etc

Wildcard

  • Wildcard helps you identify alternative spellings of the same word easily.

Example 1: An?emia would pick up anaemia and anemia

Example 2: H?emoglobin would pick up haemoglobin and hemoglobin

Phrase Searching

  • Phrase searching through the use of inverted commas helps you pick up articles containing your chosen phrase only.

Example: “pressure sores” picks up the phrase as written and not where both words are used separately

Searching within a Database

When conducting an electronic search, you can use databases that facilitate your work. Universities tend to subscribe to a substantial number of databases which include a wide variety of articles across different fields of study. For students following a course at the University of Malta there are a good number of databases that students can use for their literature searching strategies.

After finding a database to search in:

  1. use limiters – eg. ticking peer reviewed articles increases the likelihood of finding articles which are of good quality
  2. choose date/s – ideally limit your search to the last 3 years; if no interesting articles come up, widen your search to the last 5 years or more if need be
  3. do not use ‘Full text’ as a limiter
  4. do not use unnecessary limiters
  5. combine keywords in your searches using Boolean Operators
  6. use other search tools as mentioned further above to help define your searches
  7. stop searching only when you have exhausted all possible literature searching strategies for relevant content

NOTE: Keep a record of ALL searches you apply, including implemented changes, as well as the results obtained with each of your searches!

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