CMS Practical Nursing (PN) Pediatrics Practice Test

When an infant with pyloric stenosis vomits repeatedly, they lose a lot of gastric fluid that is rich in hydrogen ions and chloride. Losing hydrogen ions raises the blood pH, producing a metabolic alkalosis, and losing chloride produces hypochloremia. The ongoing fluid loss also causes volume depletion, which activates mechanisms that retain bicarbonate and promote potassium loss in the kidneys, leading to hypokalemia. So the characteristic picture is low chloride with metabolic alkalosis and low potassium, fitting the described electrolyte disturbance.