Intensive Care Medicine (ICM) Practice Exam

A patient shows arterial blood-gas results indicating an increase in CO2 retention. What condition does this suggest?

1. Respiratory alkalosis

2. Respiratory acidosis

3. Metabolic alkalosis

4. Metabolic acidosis

The correct answer is: Respiratory acidosis

An increase in CO2 retention in arterial blood gas results indicates a condition where there is an accumulation of carbon dioxide in the bloodstream, leading to respiratory acidosis. This occurs when the respiratory system is unable to remove sufficient CO2 due to various factors such as respiratory depression, airway obstruction, or lung disease. The retained CO2 combines with water to form carbonic acid, which decreases the pH of the blood, resulting in an acidotic state. In this scenario, the presence of elevated CO2 levels shows that the lungs are not effectively eliminating carbon dioxide, thus causing a shift toward acidosis. The other choices listed relate to different acid-base disturbances that do not involve CO2 retention. For instance, respiratory alkalosis arises from decreased CO2 due to hyperventilation, while metabolic acidosis and alkalosis are related to changes in bicarbonate levels rather than CO2 retention. Understanding the dynamics of carbon dioxide in relation to acid-base balance makes it clear why an increase in CO2 retention specifically indicates respiratory acidosis.