A 2-week-old infant diagnosed with pyloric stenosis has been experiencing persistent projectile vomiting. Given the prolonged vomiting, which of the following electrolyte imbalances is the infant most likely to develop?

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AIIMS NORCET 8 Prelims Memory Based Paper 2025

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Answer 1

Correct Answer: Metabolic alkalosis

Rationale:

Pyloric stenosis is a condition where the pylorus (the opening between the stomach and the small intestine) becomes narrowed, obstructing the passage of food. It often presents in infants with symptoms such as projectile vomiting, leading to the loss of stomach contents, which are rich in hydrochloric acid (HCl).
The persistent vomiting in pyloric stenosis results in the loss of HCl, which is a crucial component of stomach acid. This leads to a decrease in hydrogen ion concentration (H+) in the blood, causing the pH to rise, and subsequently resulting in metabolic alkalosis.
Additionally, the vomiting leads to dehydration and a decrease in circulating blood volume. This triggers the renin-angiotensin-aldosterone system (RAAS), which promotes sodium reabsorption and potassium excretion in the kidneys. The loss of potassium further contributes to the alkalosis.

Additional Information:

Metabolic alkalosis is characterized by an elevated blood pH (>7.45) and an increase in serum bicarbonate levels. This condition is commonly associated with excessive vomiting, diuretic use, and overuse of antacids.
Clinical symptoms may include lethargy, irritability, muscle cramps, and, in severe cases, arrhythmias due to electrolyte imbalances.
Management of metabolic alkalosis typically involves addressing the underlying cause (e.g., correcting the pyloric stenosis via surgical intervention) and replenishing lost electrolytes, such as potassium and chloride.

Explanation of Other Options:

Respiratory acidosis

Rationale: Respiratory acidosis occurs when there is hypoventilation or impaired gas exchange in the lungs, leading to an accumulation of carbon dioxide (CO2). This condition is unrelated to vomiting or pyloric stenosis, as the primary issue is metabolic, not respiratory.

Respiratory alkalosis

Rationale: Respiratory alkalosis is caused by hyperventilation, which leads to excessive exhalation of CO2 and an increase in blood pH. This condition is unrelated to the loss of stomach acid due to vomiting, as the primary issue in pyloric stenosis is metabolic, not respiratory.

Metabolic acidosis

Rationale: Metabolic acidosis occurs due to an accumulation of acid or a loss of bicarbonate in the body (e.g., in diarrhea or kidney failure). In pyloric stenosis, however, the loss of acid through vomiting leads to alkalosis rather than acidosis.

Conclusion:

The prolonged vomiting associated with pyloric stenosis results in metabolic alkalosis due to the loss of hydrochloric acid and subsequent electrolyte imbalances. Understanding the pathophysiology of this condition is critical for proper diagnosis and treatment.