In metabolic acidosis, which ABG finding would indicate respiratory compensation?

In metabolic acidosis, which ABG finding would indicate respiratory compensation?

• A. Decreased PaCO2
• B. Increased PaCO2
• C. Decreased pH
• D. Decreased PaO2

Answer: (A)

In metabolic acidosis, the body tries to balance the falling bicarbonate by blowing off carbon dioxide through faster, deeper breathing. This respiratory response lowers the partial pressure of CO2 in the blood (PaCO2). So the ABG finding that indicates this compensation is a decreased PaCO2, reflecting hyperventilation aimed at raising pH toward normal. Think of the equation pH = pKa + log(HCO3-/CO2). When HCO3- drops in metabolic acidosis, pH falls. The body offsets this by reducing CO2 (lower PaCO2) to push the pH back up toward normal. The other options don’t reflect compensation. Increased PaCO2 would worsen acidosis (not compensation). Decreased pH is a feature of metabolic acidosis itself, not a sign of the lungs compensating. Decreased PaO2 isn’t a compensatory mechanism and doesn’t indicate respiratory compensation.

In metabolic acidosis, the body tries to balance the falling bicarbonate by blowing off carbon dioxide through faster, deeper breathing. This respiratory response lowers the partial pressure of CO2 in the blood (PaCO2). So the ABG finding that indicates this compensation is a decreased PaCO2, reflecting hyperventilation aimed at raising pH toward normal.

Think of the equation pH = pKa + log(HCO3-/CO2). When HCO3- drops in metabolic acidosis, pH falls. The body offsets this by reducing CO2 (lower PaCO2) to push the pH back up toward normal.

The other options don’t reflect compensation. Increased PaCO2 would worsen acidosis (not compensation). Decreased pH is a feature of metabolic acidosis itself, not a sign of the lungs compensating. Decreased PaO2 isn’t a compensatory mechanism and doesn’t indicate respiratory compensation.