Arterial Blood Gas Analysis Guidelines

Primary Indications for ABG Testing

The British Thoracic Society recommends arterial blood gas analysis in all critically ill patients to assess oxygenation, ventilation, and acid-base status 1, 2
Initial blood gas measurement should be obtained from an arterial sample in patients with shock or hypotension (low blood pressure) 1
The American Heart Association suggests using the highest feasible inspired oxygen during cardiopulmonary resuscitation, then obtaining ABG once spontaneous circulation returns 3

The European Respiratory Society recommends ABG analysis in patients with unexpected or inappropriate fall in oxygen saturation below 94% in patients breathing air or oxygen 1, 2
Deteriorating oxygen saturation (fall of ≥3%) or increasing breathlessness in patients with previously stable chronic hypoxemia (e.g., severe COPD) requires ABG analysis 1, 2
Most previously stable patients who deteriorate clinically and require increased fraction of inspired oxygen (FiO2) to maintain constant oxygen saturation should undergo ABG analysis 1, 2

Patients with breathlessness who are thought to be at risk of metabolic conditions such as diabetic ketoacidosis or metabolic acidosis due to renal failure should undergo ABG analysis 1, 2

After oxygen titration, ABG analysis should be performed to determine whether adequate oxygenation has been achieved without precipitating respiratory acidosis and/or worsening hypercapnia 4, 5
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 6
After each titration of oxygen flow rate in patients with baseline hypercapnia, ABG analysis should be performed 4, 5

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, 6
A normal oxygen saturation does not negate the need for blood gas measurements, especially if the patient is on supplemental oxygen therapy 1
Pulse oximetry will be normal in patients with normal oxygen levels but abnormal acid-base status or ventilation, or with low blood oxygen content due to anemia 1

Local anesthesia should be used for all ABG specimens except in emergencies 1, 7
For most non-critical patients, either arterial blood gases or arterialized earlobe blood gases may be used to measure acid-base status and ventilation 1
Patients undergoing radial ABG should be assessed with an Allen's test first to ensure dual blood supply to the hand 4, 5

Failing to recognize that a normal oxygen saturation does not rule out significant acid-base disturbances or hypercapnia 1
Overlooking the need for ABG in patients with metabolic conditions that may cause acid-base disturbances 1, 2
Not repeating ABG measurements after changes in oxygen therapy, especially in patients at risk for CO2 retention 1, 6
Relying solely on pulse oximetry in situations where acid-base status and ventilation need to be assessed 1

Respiratory acidosis is characterized by an increase in PaCO2 and a decrease in pH, according to the Thorax journal 8
Respiratory alkalosis is characterized by a decrease in PaCO2 and an increase in pH, as stated in the Thorax journal 9

The British Thoracic Society recommends initiating oxygen therapy cautiously in patients with COPD or other risk factors for hypercapnic respiratory failure, starting with low flow oxygen (1 L/min) and titrating up in 1 L/min increments until SpO2 >90%, then confirming with repeat ABG 9
For patients with severe respiratory acidosis, the American Thoracic Society suggests considering non-invasive ventilation (NIV) or mechanical ventilation, and monitoring for worsening hypercapnia after each titration of oxygen flow rate in patients with baseline hypercapnia 9
The European Respiratory Society recommends starting with low flow oxygen (1 L/min) and titrating up in 1 L/min increments until SpO2 >90%, then confirming with repeat ABG, for patients with respiratory acidosis 8

Patients who develop respiratory acidosis (rise in PaCO2 >1 kPa or 7.5 mm Hg) during oxygen therapy may have clinically unstable disease and should undergo further medical optimization, as recommended by the Thorax journal 8
For patients with persistent respiratory acidosis despite optimization, the American College of Chest Physicians suggests considering nocturnal ventilatory support 8