## **Core Concept**
Congenital hypertrophic pyloric stenosis (CHPS) is a condition characterized by the thickening of the pyloric muscle in infants, leading to gastric outlet obstruction. The etiology is multifactorial, involving genetic, hormonal, and environmental factors. It typically presents with projectile vomiting in infants.

## **Why the Correct Answer is Right**
The correct answer, **D. Hypokalemic, hypochloremic metabolic alkalosis**, is associated with CHPS due to the persistent vomiting of gastric contents. This leads to the loss of hydrochloric acid (HCl) and potassium ions (K+), causing a decrease in chloride and potassium levels in the blood. The loss of hydrogen ions (H+) results in a rise in blood pH, leading to metabolic alkalosis. The kidneys compensate for the loss of chloride by retaining bicarbonate, further contributing to the alkalosis.

## **Why Each Wrong Option is Incorrect**
- **Option A: Hyperkalemic, hyperchloremic metabolic acidosis** - This is incorrect because CHPS leads to loss, not retention, of potassium and chloride ions.
- **Option B: Hypokalemic, hyperchloremic metabolic acidosis** - This is incorrect because while hypokalemia is correct, the condition leads to hypochloremia (low chloride levels), not hyperchloremia.
- **Option C: Hyperkalemic, hypochloremic metabolic alkalosis** - This is incorrect because CHPS results in hypokalemia (low potassium levels), not hyperkalemia.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that the diagnosis of CHPS can often be made clinically, supported by the classic presentation of projectile vomiting and a palpable "olive" mass in the epigastric region. Ultrasound confirmation is highly sensitive and specific. The condition requires prompt surgical intervention, usually pyloromyotomy, to relieve the obstruction.

## **Correct Answer:** D. Hypokalemic, hypochloremic metabolic alkalosis