In a COPD exacerbation, when should ABG be obtained?

• A. ABG to assess gas exchange should be considered in moderate to severe exacerbations.
• B. ABG to be done in all cases.
• C. ABG is never needed.
• D. ABG should replace pulse oximetry.

Answer: (A)

Assessing gas exchange with an arterial blood gas is crucial when a COPD patient experiences a moderate to severe exacerbation because these episodes can rapidly worsen ventilation and oxygenation. An ABG provides direct measurements of arterial O2 (PaO2), arterial CO2 (PaCO2), and acid-base status (pH, bicarbonate), which helps identify hypercapnic respiratory failure and whether the patient is acidemic. This information guides management: it shows whether oxygen therapy is achieving adequate oxygenation without depressing respiration, indicates the need for ventilatory support such as noninvasive ventilation, and helps detect worsening respiratory failure that may require more advanced support. In milder exacerbations, if oxygenation is adequate on pulse oximetry and the patient is clinically stable, ABG is often not necessary. Pulse oximetry remains the noninvasive monitoring mainstay and ABG should not replace it.