Which of the following conditions can lead to metabolic alkalosis in infants?

Pyloric stenosis is a condition that can indeed lead to metabolic alkalosis in infants. This condition involves a narrowing of the pylorus, the opening from the stomach into the duodenum. As a result of this narrowing, infants often experience projectile vomiting. The vomiting expels gastric contents, which are rich in hydrochloric acid (HCl), leading to a significant loss of hydrogen ions from the stomach. This loss creates a higher than normal concentration of bicarbonate in the body, resulting in metabolic alkalosis.

In essence, the vomiting associated with pyloric stenosis drives the body's pH balance towards alkalinity due to the depletion of acid, and this effect is particularly pronounced in infants who are more susceptible to changes in acid-base balance. Understanding this mechanism highlights why pyloric stenosis is a key condition to consider when evaluating cases of metabolic alkalosis in infants.