Indications for Arterial Blood Gas Measurement

Critical Indications for ABG Testing

The British Thoracic Society recommends that all critically ill patients require ABG measurement, with samples obtained from arterial rather than venous sources 1, 2
Patients in peri-arrest situations or those requiring immediate medical intervention should have an ABG measurement 1
After return of spontaneous circulation following cardiopulmonary resuscitation, an ABG measurement should be taken to guide ongoing oxygen therapy 3
In critical illness including major trauma, sepsis, shock, and anaphylaxis, ABG measurement is recommended 3
Cases of carbon monoxide poisoning require ABG measurement, as pulse oximetry readings may be falsely normal 3

Unexpected or inappropriate fall in SpO2 below 94% in patients breathing air or oxygen requires an ABG measurement 2
Deteriorating oxygen saturation or increasing breathlessness in patients with previously stable chronic hypoxemia should prompt an ABG measurement 2
Previously stable patients who deteriorate clinically and require increased FiO2 to maintain constant oxygen saturation should have an ABG measurement 2
Any patient with risk factors for hypercapnic respiratory failure who develops acute breathlessness, deteriorating oxygen saturation, drowsiness or other features of carbon dioxide retention requires an ABG measurement 2
Major head injury cases require an ABG measurement prior to securing the airway 3
Acute asthma, pneumonia, and acute respiratory exacerbations requiring oxygen therapy should prompt an ABG measurement 3

Patients with breathlessness who may have metabolic conditions such as diabetic ketoacidosis or metabolic acidosis due to renal failure require an ABG measurement 2

After oxygen titration is complete, an ABG measurement should be taken to determine whether adequate oxygenation has been achieved without precipitating respiratory acidosis or worsening hypercapnia 4
Within 60 minutes of starting oxygen therapy in patients with COPD or other risk factors for hypercapnic respiratory failure, an ABG measurement should be taken 5
Within 60 minutes of any change in inspired oxygen concentration in at-risk patients, an ABG measurement should be taken 5
When there is an unexpected change in "track and trigger" systems such as a sudden rise in NEWS or an unexpected fall in oxygen saturation of 3% or more, an ABG measurement should be taken 2

For patients with baseline hypercapnia, ABG should be monitored after each titration of oxygen flow rate to detect respiratory acidosis 6
In patients with COPD aged 50 years or more, ABG should be checked before giving an FiO2 of more than 28% via Venturi mask or 2 L/min via nasal cannulae 5
For home oxygen assessment, patients should undergo two ABG measurements at least 3 weeks apart during a period of clinical stability 4, 6

Local anesthesia should be used for all ABG specimens except in emergencies 2
Patients undergoing radial ABG should have an Allen's test performed first to ensure dual blood supply to the hand 4
Informed consent should be obtained for the procedure with discussion of possible risks 4
For most non-critical patients requiring blood gas sampling, arterialised earlobe blood gases may be used as an alternative to obtain accurate pH and PCO2 measurements, though PO2 is less accurate in these samples 2

A normal SpO2 does not negate the need for blood gas measurements, especially if the patient is on supplemental oxygen therapy 2
Pulse oximetry will appear normal in patients with normal PO2 but abnormal pH or PCO2, or with low oxygen content due to anemia 2
In carbon monoxide poisoning, pulse oximetry readings may be falsely normal, necessitating ABG regardless of oximeter readings 3
When using earlobe blood gas samples, oximetry should be monitored carefully and a repeat arterial specimen taken if there are concerns about accuracy 2