Neonatal Nurse Practitioner Practice Exam

Which compensatory mechanism is typically observed in metabolic acidosis?

1. Increase in HCO3 and CO2

2. Decrease in HCO3 and CO2

3. Increase in CO2 and decrease in pH

4. Decrease in CO2 and increase in pH

The correct answer is: Decrease in HCO3 and CO2

In metabolic acidosis, the body employs various compensatory mechanisms to help restore acid-base balance. One primary response is increased ventilation, which leads to a decrease in carbon dioxide (CO2) levels in the blood. This respiratory compensation occurs because when the blood becomes more acidic (lower pH), the body attempts to reduce the acid load by expelling CO2, a component of carbonic acid (H2CO3) in the blood. While bicarbonate (HCO3) levels are typically decreased in metabolic acidosis due to the acidotic process itself, the body does not increase HCO3 in this scenario. Instead, the compensation mechanism aims at decreasing CO2 levels through hyperventilation, which ultimately may lead to an increase in pH as CO2 is a major determinant of acidity in the blood. Overall, the body's strategy in metabolic acidosis is to lower CO2 levels, which stabilizes the pH despite the underlying bicarbonate loss. This distinguishes it from other acid-base disorders and clarifies why the accurate answer reflects a decrease in both CO2 and HCO3 levels as part of the compensatory mechanism observed in metabolic acidosis.