Which ABG result would indicate respiratory alkalosis in a patient with aspirin overdose?

Which ABG result would indicate respiratory alkalosis in a patient with aspirin overdose?

• A. pH 7.54, PaCO2 41, PaO2 63, SaO2 91, HCO3 36
• B. pH 7.24, PaCO2 37, PaO2 83, SaO2 95, HCO3 18
• C. pH 7.49, PaCO2 30, PaO2 88, SaO2 92, HCO3 25
• D. pH 7.12, PaCO2 28, PaO2 72, SaO2 93, HCO3 10

Answer: (C)

Early respiratory alkalosis presents with an alkalemic pH and a reduced PaCO2 from hyperventilation; in aspirin overdose this happens because the respiratory center is stimulated, causing tachypnea and blowing off CO2. The bicarbonate may be near normal or slightly decreased depending on duration, since metabolic compensation hasn’t fully developed yet. The ABG that best fits this pattern is pH 7.49 with PaCO2 30 and HCO3 25: the pH is alkaline, the CO2 is low, and the bicarbonate is near normal, consistent with a primary respiratory process without significant metabolic compensation. The other results don’t fit as well: one shows alkalemia with normal CO2 and high bicarbonate, which points away from a primary respiratory cause; another shows acidemia with near-normal CO2, indicating metabolic acidosis; and the last shows severe acidemia despite low CO2, suggesting a mixed disorder or primary metabolic acidosis.

Early respiratory alkalosis presents with an alkalemic pH and a reduced PaCO2 from hyperventilation; in aspirin overdose this happens because the respiratory center is stimulated, causing tachypnea and blowing off CO2. The bicarbonate may be near normal or slightly decreased depending on duration, since metabolic compensation hasn’t fully developed yet.

The ABG that best fits this pattern is pH 7.49 with PaCO2 30 and HCO3 25: the pH is alkaline, the CO2 is low, and the bicarbonate is near normal, consistent with a primary respiratory process without significant metabolic compensation.

The other results don’t fit as well: one shows alkalemia with normal CO2 and high bicarbonate, which points away from a primary respiratory cause; another shows acidemia with near-normal CO2, indicating metabolic acidosis; and the last shows severe acidemia despite low CO2, suggesting a mixed disorder or primary metabolic acidosis.