## **Core Concept**
Congenital hypertrophic pyloric stenosis (CHPS) is a condition characterized by the thickening of the pylorus muscle in infants, leading to gastric outlet obstruction. The metabolic abnormality most commonly associated with this condition is hypochloremic, hypokalemic metabolic alkalosis.

## **Why the Correct Answer is Right**
The correct answer, **D. Hypochloremic, hypokalemic metabolic alkalosis**, is right because in CHPS, the persistent vomiting leads to the loss of gastric contents, which are rich in hydrochloric acid (HCl) and potassium (K+). The loss of HCl results in a decrease in chloride levels (hypochloremia) and a rise in blood pH (metabolic alkalosis) as bicarbonate is retained. The loss of potassium through vomiting and the subsequent renal compensation mechanisms lead to hypokalemia. The kidneys try to conserve sodium and water, leading to increased bicarbonate reabsorption, which further exacerbates the metabolic alkalosis.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because while metabolic acidosis can occur in various conditions, it is not the typical metabolic abnormality seen in CHPS.
- **Option B:** This option is incorrect as it mentions hyperchloremic metabolic acidosis, which is the opposite of what is typically observed in CHPS.
- **Option C:** This option is incorrect because, although hypokalemic metabolic alkalosis is part of the picture, specifying "metabolic alkalosis with normal chloride levels" does not accurately reflect the chloride loss that occurs.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that in cases of congenital hypertrophic pyloric stenosis, the diagnosis can often be made clinically, and the metabolic disturbance of hypochloremic, hypokalemic metabolic alkalosis is a critical consideration in the preoperative management. Correction of the electrolyte imbalance is essential before surgery.

## **Correct Answer:** D. Hypochloremic, hypokalemic metabolic alkalosis