In the critical care setting the nurse’s observatory role is crucial in maintaining optimum care of the critical patient, which is why, ideally, the nurse-patient ratio should be 1:1. Additionally, technology plays a very important role within the same setting. However, one must not forget the GI-GO paradigm, a.k.a. Garbage In, Garbage Out – whilst analytical technology can be very useful in critical care, produced data always depends on how well the data is collected.
Invasive Monitoring Equipment in Critical Care
Invasive monitoring equipment used within the critical care setting includes:
- invasive (arterial) catheter – a small cannula, usually containing an anti-reflux switch, which is inserted (sometimes with the help of a guidewire) into an artery to constantly monitor a patient’s blood pressure
- high pressure tubing – helps preserve pressure and prevent loss of pressure between the patient’s vein or artery and the transducer
- transducer – delivers numerical blood pressure readings and arterial pressure waveforms with every heartbeat to a bedside monitor by sensing blood-generated pressure passing past a catheter tip; readings and waveforms delivered are dynamic and change with every beat of the cardiac cycle; the transducer and line are attached to the arterial line via a connector, allowing the changing of the transducer set (ideally every 96 hours) without requiring re-insertion of the arterial line
- flush system – helps keep the line clear and avoid blood backflow through the catheter; saline bag is used under the pressure bag, usually with 2 units of heparin per cc, to help keep the artery open UNLESS the patient has a known allergy to heparin; NOTE: even a little bit of heparin can cause heparin-induced thrombocytopaenia (immune system causes platelets to clot in the presence of heparin, resulting in platelet levels dropping), so if the patient’s platelet count drops for no apparent reason, remove the heparinised saline bag and change to saline bag instead
- monitor – commonly displays ECG, heart rate, intermittent cuff blood pressure, arterial blood pressure, internal temperature, peripheral venous oxygen saturation, partial pressure of CO2
Arterial Catheter Indications
An arterial catheter is indicated in instances:
- when continuous blood pressure monitoring is required eg. during surgery, during use of vasoactive medications, or in the case of compromised cardiac output, fluid volume, and tissue perfusion
- when patients require frequent arterial blood gas sampling eg. if they are experiencing respiratory failure or are on mechanical ventilation
Arterial Line Placement Sites
- Radial Artery – easily accessible site which is also considered to be safe since collateral hand circulation is supplied by the ulnar artery – circulation within both these arteries can be checked via an allens test; this site is also preferred due to a decreased risk of complications when compared to other larger vessels
- Brachial Artery – located close to joint thus blood flow may be easily interrupted
- Femoral Artery – large vessel which, due to its location, is difficult to observe on a continuous basis
- Dorsalis Pedis Artery – needs to be avoided if the patient has severe peripheral vascular disease
Allens Test
Arterial Blood Pressure Reading
When using an arterial catheter, a constant second by second reading of the systolic (SBP), diastolic (DBP), and the mean arterial blood pressure (MAP) can be provided. The MAP is a more accurate indicator of the patient’s condition since it also reflects the perfusion rate of essential organs such as the kidneys.
The MAP is usually calculated automatically by most monitors. However, it can be calculated using the following formula:
Arterial Waveform
Respiratory Swing
The respiratory swing is more pronounced in the case of mechanical ventilation. It can help indicate dehydration.
Care of the Patient with an Arterial Line
- perform regular checks for loose connections, blood backflow, a deflated pressure bag, or lack of fluid in the flush bag
- ensure that the arterial catheter site is easily accessible and always visible
- DO NOT inject any medication in the arterial catheter!
A patient with an arterial line may eventually develop complications. Monitor the patient for:
- Infection – perform frequent patient checks, noting any redness, discharge, warmth to touch, or fever; preventative measures include using an aseptic non-touch technique during insertion of catheter, blood sampling, and line maintenance
- Haemorrhage – perform frequent checks at the arterial catheter insertion site especially if it was inserted into the femoral artery since this is a large vessel
- Thrombosis – perform frequent checks on patient’s legs, taking note of the colour, pulse, temperature and sensation; preventative measures include adequate flushing following blood sampling, and using the smallest catheter possible during the insertion procedure
Levelling and re-zeroing
The transducer system must be leveled and zeroed to provide accurate haemodynamic values, since this eliminates atmospheric pressure effects. The exact point where the 4th intercostal space crosses the mid-axillary line is referred to as the Phlebostatic Axis. The nurse should ensure that zeroing is done at the beginning of every shift, as well as after any major positional changes.
How To Remove Arterial Line
- perform hand hygiene
- don gloves
- gather necessary equipment
- remove any dressings and sutures if present
- whilst applying firm pressure to insertion site pull out the arterial line gently
- apply manual pressure and elevate limb
- apply small occlusive dressing which allows periodic observation for blood leakage
NOTE: an adequate blood pressure reading doesn’t automatically signify adequate perfusion…always take into consideration the whole clinical picture, biochemical values, along with haemodynamic parameters.
NOTE: additional monitoring equipment can also be used along with the arterial line to measure cardiac output.
Central Venous Catheters CVC
Central Venous Catheters are indwelling catheters within the superior vena cava, inferior vena cava, right atrium, or any large vein leading to these vessels. They are sought in the case of:
- administration of large amounts of fluid
- administration of vesicant drugs (drugs that can cause tissue necrosis or blister formation if accidentally infused into tissue surrounding vein)
- total parenteral nutrition
- repeated venous blood sampling
- measurement of pressure within the right atrium (Central Venous Pressure a.k.a. CVP) – this provides the measurement of the right atrium filling pressure, and indicates right ventricular function.
CVCs are inserted via the:
- internal jugular veins
- subclavian veins
- femoral veins
CVCs usually have 3 or 5 lumens. The distal port is used for monitoring of the CVP, however, it can also be used to administer blood products since it is the biggest port in a CVC. The other ports are used for fluid or drug administration. CVC line requires priming by approximately 1ml of fluid.
In a triple port lumen, the brown port opens up distally (at the tip), the blue port is the medial one, and the white port opens up proximally. If TPN is planned for the patient, it cannot be used intermittently with other infusions. Once TPN is stopped from being run through a particular port for any reason, and another infusion or medication is run instead, TPN cannot be re-administered again through that port.
NOTE: Always label CVC catheters and include insertion date! Note that central lines should be removed within a week from insertion.
Central Venous Catheter Insertion
- provide patient with information about the procedure and address any questions or concerns
- patient is positioned head down
- patient’s skin is prepared for insertion
- local anaesthetic is administered
- preferred vein is located by needle and syringe
- a guide wire is introduced through the needle, after which the needle is removed
- CVC is introduced over the guide wire, and is then attached to primed system
- CVC is sutured in place
- a chest x-ray is performed to confirm correct placement
Central Line Dressing Change
Possible CVC Insertion Complications
- pneumothorax – lung collapse following air leakage into the pleural space between the lung and chest wall
- right atrium perforation
- cardiac tamponade – when the pericardial space fills up with blood or other fluid, putting pressure on the heart, reducing blood pumping activity whilst causing a drop in blood pressure
- arterial puncture
- haemorrhage
- air embolus
NOTE: preventative measures pre-procedure include positioning the patient in the Trendelberg position for both insertion and removal, and performing a chest x-ray following CVC insertion.
Other Complications related to CVC
- CVC occlusion – may happen due to mechanical obstruction, precipitation of medications or parenteral nutrition, or due to thrombosis
- CVC displacement
- air entering the system (always check connections and taps)
- local infection
- systemic infection
NOTE: preventative measures for infection include adequate and correct hand hygiene, using an aseptic technique whilst handling the CVC, and replacing catheter when needed or required.
CVC Removal
CVCs pose a great risk of infection and are considered as major causes of morbidity and mortality. Additionally, they are also the main source of bacteraemia and septicaemia in hospitalised patients. Thus, CVCs should be removed as soon as possible.
- ensure that no medication or fluids are being administered to the patient and/or listed in the patient’s treatment chart
- use an aseptic non-touch technique
- remove dressing and cut sutures
- place patient head-down and lying flat
- using the valsava maneuver, ask patient to hold his breath while you slowly remove the catheter; if resistance is felt on removal seek further help
- apply pressure to the punctured site until bleeding stops
- use an air occlusive dressing for the first 24 hours
- if required send tip of CVC for culture and sensitivity
CVP Central Venous Pressure Measurement
Central Venous Pressure measurement, which is transduced electronically through the use of the CVC, should read between 0-8mmHg in normally breathing patients, and higher in mechanically ventilated patients. Attention should be given more to the measurement trend rather than individual readings.
The main limitation of the CVP measurement is that it does not initially reflect left ventricular dysfunction.
Whilst traditionally CVP monitoring was used to assess a patient’s fluid status on which hydration management was decided, studies have shown no correlation between CVP and preload (left ventricular end diastolic volume). Thus, CVP measurements should no longer be relied upon when making clinical decisions on patient fluid management (Marik et al., 2008).
Patient Monitoring – Non-Invasive & Minimally Invasive Techniques in Critical care
- minimally invasive using data from arterial or CPV lines, a special type of transducer or catheter
- calculations based on arterial waveform and patient demographic data such as weight, sex, age, and height
- calculates CO (cardiac output), CI (cardiac index), SV (stroke volume), SVI (stroke volume index) and SV Variation; if interfaced with CVP data, calculations of SVR (systemic vascular resistance) and SVRI (systemic vascular resistance index) are also produced (more info on listed terms here)
- may be calibrated (eg. PiCCO) or non-calibrated (eg. Vigileo)
Vigileo / flotrac (non-calibrated)
Vigileo uses a normal arterial catheter without the need for intermittent calibration. However, it is not recommended in the case of arterial wave artefacts, compromised arterial cannula, intense peripheral vasoconstriction, or arrhythmias. It also does not measure advanced volumetrics which can provide accurate CO measuring in a non-invasive way.
Key parameters provided by a Vigileo include:
- SV and SVI
- CO (CO = SV x HR)
- SVV – reflects preload and fluid responsiveness
Limitations can be imposed by spontaneous breaths, open chest, or arrhythmias.
Picco Monitoring (calibrated)
PiCCO, which stands for Pulse Contour Cardiac Output, combines pulse contour analysis with transpulmonary thermodilution using a Thermodilution Arterial Catheter, which is inserted preferably in the femoral artery, or else through the brachial, axillary, or radial artery (which requires a longer catheter).
Transpulmonary thermodilution is picked up by a temperature sensor located at the catheter tip, whilst the arterial blood pressure ABP is measured through the pressure extension line.
The artery pressure curve provides the following parameters:
- CCO (CCI) – Continuous Cardiac Output
- SV (SVI) – Stroke Volume
- SVR (SVRI) – Systemic Vascular Resistance
- CPO (CPI) – Cardiac Power Output
- SVV – Stroke Volume Variation
- PPV – Pulse Pressure Variation
- dPmx – Left Ventricular Contractility
- HR – Heart Rate
- pArt-M – Mean Arterial Blood Pressure
- pArt-S – Systolic Arterial Blood Pressure
- pArt-D – Diastolic Arterial Blood Pressure
- CVP – Central Venous Pressure
The Intermittent Transpulmonary Thermodilution provides the following parameters:
- Q – Cardiac Output / CI – Cardiac Index
- GEDV (GEDI) – Global End-Diastolic Volume
- EVLW (ELWI) 0 Extravascular Lung Water
- GEF – Global Ejection Fraction
- PVPI – Pulmonary Vascular Permeability Index
- CFI (Cardiac Function Index
- ITBV (ITBI) – Intrathoracic Blood Volume
GEDV and ITBV reflect PRELOAD – GEDV indicates end volume at rest in all 4 heart chambers and ITBV indicates the volume in heart and pulmonary vessels.
ELWI indicates the water content in the lungs, thus can clearly indicate pulmonary oedema, if present.
GEF indicates the ration of 4 stroke volumes divided by GEDV. It helps detect ventricular dysfunction, if present.
PICCO Setup & Monitor
PiCCO Advantages
Picco Disadvantages
- cannot be used with an intra-aortic balloon pump
- needs to be recalibrated whenever patient changes position, therapy or condition
- EVLW is underestimated when it comes to use on obese patients and post-pneumonectomy patients
- AAA (abdominal aortic aneurysm) raises GEDV and ITBB measurements
Haemodynamic and Volumetric Monitoring
Pulse Oximetry in Critical Care
Pulse Oximetry is a non-invasive method which monitors oxygen saturation (SaO2). It indiates the percentage of haemoglobin bound to oxygen.
In normal healthy adults, oxygen saturation should be >96%.
Accurate pulse oximeter readings depend on whether it is positioned well on a patient’s finger, ear, toe or nose, and how good the patient’s peripheral circulation is. Similarly, if a patient is shivering, the pulse oximeter may not be able to pick up a signal. Nail varnish may also affect reading outcome. Additionally, pulse oximetry cannot differentiate between normal and abnormal haemoglobin, thus may result in false high readings.
NOTE: always interpret pulse oximeter readings in conjunction with shown waveform.
Capnography in Critical Care
Capnography measures exhaled carbon dioxide gas, depicting a squarish waveform. Its measurement approximates PaCO2, usually being about 1-5mmHg lower than the actual PaCO2.
Capnography is non-invasive.
Capnography is very useful in cases where the patient is suffering from a head injury or from intracranial hypertension.
Very low ETCO2 values given through capnography can help indicate gastric intubation rather than an intended tracheal intubation.
With regards to CPR assessment, one should aim for a minimum of 10mmHg.
An increased disparity between PaCO2 and ETCO2 suggests poor pulmonary blood flow, poor cardiac output, or lung disease.
Reference
Marik, P. E., Baram, M., & Vahid, B. (2008). Does central venous pressure predict fluid responsiveness? A systematic review of the literature and the tale of seven mares. Chest, 134(1), 172–178. https://doi.org/10.1378/chest.07-2331
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Claire is keen about public education on health-related subjects as well as holistic patient-centered care. She is also passionate about spreading awareness on the negative effects that domestic abuse leaves on its victims’ mental, emotional, social and physical wellbeing.
Claire aspires to continue studying following completion of her Nursing Degree, because she truly believes in lifelong education.
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