At what FEV1 percentage should arterial blood gas (AGB) be ordered?

Ordering arterial blood gas (ABG) analysis is typically indicated when a patient's forced expiratory volume in one second (FEV1) is significantly low, as this can suggest severe airway obstruction or respiratory failure. An FEV1 percentage of 35% represents a level of impairment that indicates a high risk of hypoxemia (low oxygen in the blood) and hypercapnia (elevated carbon dioxide). At this level of function, a patient is likely experiencing significant difficulties with gas exchange, which necessitates a more detailed evaluation of their respiratory status, including pH, partial pressures of oxygen and carbon dioxide, and bicarbonate levels provided by ABG analysis.

In contrast, an FEV1 of 65%, 85%, or 50% does not typically suggest the same immediacy for ABG testing. While these percentages are indicative of varying degrees of obstructive lung disease, they usually do not meet the threshold where immediate and critical assessment of blood gases is warranted unless the patient is exhibiting concerning clinical signs that might suggest otherwise. Therefore, the 35% FEV1 threshold stands out as it signals a need for further investigation into the patient's oxygenation and ventilation status.