Which of the following is a common cause of metabolic alkalosis?

Excessive vomiting is a common cause of metabolic alkalosis because it leads to the loss of gastric acid, which contains hydrochloric acid (HCl). The loss of this acid causes a decrease in hydrogen ions in the bloodstream, leading to a relative increase in bicarbonate concentration and resulting in an alkaline state (metabolic alkalosis). When the stomach contents are expelled through vomiting, the body loses not only acid but also electrolytes, which can further contribute to the shifts in acid-base balance.

In contrast, carbon dioxide retention generally leads to respiratory acidosis due to the accumulation of CO2, which increases acidity in the blood. An increased respiratory rate typically results in respiratory alkalosis because it causes excessive loss of carbon dioxide, decreasing acidity. Decreased bicarbonate levels, on the other hand, would indicate a condition that leads to acidosis rather than alkalosis. Thus, excessive vomiting is the key factor that directly leads to metabolic alkalosis through the loss of stomach acid.