American Board of Internal Medicine (ABIM) Certification Practice Exam

What complicating condition arises if HCO3 fails to increase in respiratory acidosis?

1. Metabolic alkalosis

2. Respiratory alkalosis

3. Metabolic acidosis

4. Respiratory failure

The correct answer is: Metabolic acidosis

In the context of respiratory acidosis, when there is an increase in carbon dioxide (CO2) levels in the blood due to inadequate ventilation, the body typically seeks to compensate for this by increasing bicarbonate (HCO3-) levels through metabolic processes. This increase in bicarbonate helps to neutralize the excess acid created by the elevated CO2, thereby helping to restore a better acid-base balance. If the bicarbonate level fails to increase despite the ongoing respiratory acidosis, it indicates that the compensatory mechanism is inadequate or overwhelmed. This failure can lead to a predominance of acid in the system, pushing the body into a state of metabolic acidosis. In such a scenario, the body is unable to effectively buffer the acidotic state, which can result in a significant drop in pH and an overall worsening of the acid-base disturbance. This condition is distinct from other options, as the failure of bicarbonate to increase does not lead to the formation of metabolic alkalosis or respiratory alkalosis. Instead, it establishes a baseline of metabolic acidosis, as the body is unable to properly compensate for the elevated CO2 levels adequately. It also does not directly indicate respiratory failure, although chronic respiratory acidosis can indeed lead to respiratory failure as a separate