Question

The metabolic derangement in congenital pyloric stenosis is:

• A. Hypochloremic alkalosis
• B. Hyperchloremic alkalosis
• C. Hyperchloremic acidosis
• D. Hypochloremic acidosis

Hint:

Vomiting stomach acid removes H+ and Cl-, so pyloric stenosis causes hypochloremic alkalosis.

Answer 1

The Correct Option is A

Step 1: Recall what pyloric stenosis does.
In congenital pyloric stenosis, the muscle around the stomach outlet (the pylorus) thickens and narrows, so food and stomach acid cannot pass into the small bowel. The baby responds with repeated, forceful vomiting of stomach contents.

Step 2: Track what is lost in the vomit.
Stomach fluid is rich in hydrochloric acid, so the vomit carries away large amounts of hydrogen ions and chloride ions. Losing acid from the body pushes the blood pH up, causing a metabolic alkalosis, and the chloride loss lowers the blood chloride level, so the alkalosis is called hypochloremic.

Step 3: Add the potassium and volume piece.
The vomiting also causes dehydration, which activates the kidney's renin-angiotensin-aldosterone system. Aldosterone makes the kidney hold on to sodium and water but throw away potassium and hydrogen ions in the urine, which deepens both the alkalosis and a low potassium level. This is why the full name for the picture is hypochloremic, hypokalemic metabolic alkalosis.

Step 4: Rule out the other options.
Hyperchloremic alkalosis and hyperchloremic acidosis would need chloride to be high or normal, which does not happen when chloride is being vomited out. Hypochloremic acidosis is wrong on the acid-base side, since the loss of stomach acid raises pH rather than lowering it.

Final Answer:
Repeated vomiting of acidic, chloride-rich stomach contents produces a hypochloremic metabolic alkalosis.
\[ \boxed{\text{Hypochloremic alkalosis}} \]