In critical care, what is a key use of arterial blood gas data beyond initial diagnosis?

• A. Measure serum creatinine
• B. Assess liver function
• C. Screen for anemia
• D. Trend ABGs to gauge response to therapy

Answer: (D)

Serial arterial blood gas measurements are used to gauge response to therapy. ABGs provide pH, PaCO2, PaO2, and bicarbonate, which together reflect ventilation, oxygenation, and acid-base status. By tracking these values over time, you can see whether interventions are effective and when to adjust treatment. For example, in a patient on mechanical ventilation, a trend toward normalization of PaCO2 and pH indicates improving ventilation, while rising PaO2 or a lower FiO2 requirement signals better oxygenation. If acids persist or worsen, you may need to change ventilator settings, adjust oxygen delivery, or treat the underlying cause. ABGs reveal trajectory, not just a single snapshot, making them invaluable for monitoring response to therapy. In contrast, ABGs do not measure renal or liver function or screen for anemia, which rely on other laboratory tests.