Arterial Blood Gases provide a measurement of an individual’s pH (acidity) as well as the oxygen and carbon dioxide level in arterial blood: blood which is aspirated from an artery, namely from the radial, brachial or femoral artery. In other words, when interpreting arterial blood gases, one can determine the capability of gaseous exchange within the lungs (oxygen going into the blood and carbon dioxide going out of the blood).
Arterial Blood Gases Fundamentals
Human cells require oxygen. Breathing allows oxygen to be absorbed into the bloodstream through the alveoli in the lungs and expels carbon dioxide out from the lungs.
Haemoglobin molecules, which have 4 binding sites, act as carriers of oxygen to the tissues. Other molecules can also attach to the oxygen binding sites, and if this happens, hypoxia can happen (eg. if carbon dioxide attaches in the binding sites instead of oxygen).
Haemoglobin molecule + 4 O2 molecules = Oxyhaemoglobin
When Carbon Monoxide attaches to the Haemoglobin binding sites instead of Oxygen, blood will become cherry red in colour. This is called Carboxyhaemoglobin, and it can be measured in ABGs.
Haemoglobin molecule + 4 CO molecules = Carboxyhaemoglobin
Haemoglobin may also be affected by a genetic condition or when exposed to certain poisons. This produces Methaemoglobin, which shows up in a brownish shade, and which can also be measured in ABGs.
O2’s affinity to haemoglobin is much more than CO2’s affinity to haemoglobin, thus when both are available, O2 attaches to haemoglobin first. Oxygen binding however can be affected by the levels of O2, CO2 and blood pH.
Where there is lack of O2 within the tissues, haemoglobin carries CO2, forming Carbaminohaemoglobin due to low levels of O2, high levels of CO2 and decreased blood pH.
Carbon Dioxide Transportation
Carbonic Acid – Bicarbonate Buffer System (Reversible System)
ABG Components
Arterial Blood pH
Normal ABG Values
Indications for ABGs
- assessing acid-base status (measuring pH in the body to assess for respiratory alkalosis/acidosis)
- assessing ventilation (effective gaseous exchange in the body)
- assessing for electrolyte imbalances (through ABGs testing, electrolyte balance reading is available in just a few minutes)
- assessing for treatment response (eg. following asthma exacerbation treatment)
ABGs Contraindications
- bleeding disorders (eg. patients undergoing anticoagulation therapy)
- arteriovenous fistula (an abnormal connection between an artery and a vein)
- peripheral vascular disease (a pre-known problem with circulation)
- infection on site
ABGs Complications
- Haematoma – apply pressure on site for 2-3 minutes to avoid
- Thrombus formation within the artery due to the bleeding
- Infection on site – introduction of pathogens into the patient’s artery causes infection; use chlorhexidine swab to clean skin thoroughly and allow to dry prior to puncturing skin)
Equipment Needed
- a 23G (blue) needle
- 2ml syringe with heparin and a plastic bung (to avoid blood clotting in the needle and ABGs testing machine)
- sharps bin
- gloves
- gauze
- alcohol wipe
Below you can find a collection of videos that can help provide a more visual approach to Arterial Blood Gases Interpretation.
Arterial Blood Gases Balance Animation
Arterial Blood Gases Made Easy
Partially vs Fully Compensated & Uncompensated Arterial Blood Gases
Respiratory Acidosis
https://www.youtube.com/watch?v=X0VjnFKDNI0
Respiratory Alkalosis
Metabolic Acidosis
Metabolic Alkalosis
Special thanks to the creators of the featured videos on this post, specifically Youtube Channels Alila Medical Media and RegisteredNurseRN.
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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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