Arterial Blood Gas Analysis in Critical Care

Primary Indications for ABG Testing

The American College of Critical Care Medicine recommends ABG analysis in all critically ill patients to assess oxygenation, ventilation, and acid-base status 1
Initial blood gas measurement should be obtained from an arterial sample in patients with shock or hypotension 1
ABG analysis is indicated when patients have unexpected or inappropriate fall in oxygen saturation below 94% while breathing room air or supplemental oxygen 1
Patients with deteriorating oxygen saturation (fall of ≥3%) or increasing breathlessness with previously stable chronic hypoxemia require ABG analysis 1

ABG is essential for patients with suspected metabolic conditions such as diabetic ketoacidosis or metabolic acidosis due to renal failure 1
Base excess values from ABG analysis provide valuable information about the effectiveness of resuscitation efforts in critically ill patients, particularly in trauma, shock, and sepsis 2
For patients with COPD or other conditions causing fixed airflow obstruction, ABG should be checked when starting oxygen therapy, especially if the patient has known CO2 retention 1
ABG helps distinguish chronic respiratory acidosis from acute-on-chronic respiratory failure in patients with baseline hypercapnia 2

After oxygen titration, ABG analysis should be performed to determine whether adequate oxygenation has been achieved without precipitating respiratory acidosis 1
ABG analysis should be performed within 60 minutes of starting oxygen therapy and within 60 minutes of a change in inspired oxygen concentration in COPD patients 1
In patients with hepatopulmonary syndrome (HPS), ABG analysis should be carried out every six months to monitor for worsening hypoxemia, which can affect liver transplantation prioritization 3, 4

A systematic approach to ABG interpretation involves first evaluating pH to determine if acidemia or alkalemia is present, then examining PCO2 to identify respiratory component, and finally evaluating base excess to identify metabolic component 2
The degree of compensation can help determine if the acid-base disorder is acute, chronic, or mixed 2