In pyloric stenosis, a 4-week-old infant presents with non-bilious projectile vomiting, visible peristalsis, and a palpable 'olive' in the right hypochondrium. Metabolic disturbance typically seen is:

• A Hyperchloraemic metabolic acidosis with hyperkalaemia
• B Normal metabolic parameters in the early stages
• C Respiratory alkalosis with mild hypokalaemia
• D Hypokalaemic, hypochloraemic metabolic alkalosis with paradoxical aciduria ✓

Explanation

Infantile hypertrophic pyloric stenosis causes loss of gastric HCl and K+ through persistent vomiting, producing a characteristic hypokalaemic, hypochloraemic metabolic alkalosis. Paradoxical aciduria occurs because the kidneys, attempting to conserve sodium in the face of volume depletion, exchange H+ (rather than K+, which is depleted) for Na+ in the distal tubule — excreting acid urine despite systemic alkalosis. Surgical repair (Ramstedt pyloromyotomy) is performed only after metabolic correction with IV normal saline and potassium supplementation.

Reference: Bailey & Love's Short Practice of Surgery, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.