In neonatal anaesthesia for pyloromyotomy, a 5-week-old infant has been vomiting for 3 weeks. Preoperative electrolytes show: Na+ 130, K+ 2.9, Cl- 84, HCO3 38 mEq/L. The primary metabolic disturbance and the recommended resuscitation fluid are:

• A Metabolic acidosis; normal saline 20 mL/kg bolus
• B Respiratory alkalosis; sodium bicarbonate infusion
• C Hypochloraemic hypokalaemic metabolic alkalosis; 0.9% saline + KCl to correct electrolytes BEFORE surgery ✓
• D Dilutional hyponatraemia; hypertonic saline 3%

Explanation

Hypertrophic pyloric stenosis causes projectile non-bilious vomiting with loss of HCl from gastric secretions, producing hypochloraemic hypokalaemic metabolic alkalosis. Surgery is NOT an emergency and must be postponed until the electrolyte and acid-base disturbance is corrected — typically with 0.45% or 0.9% saline + 20–40 mEq/L KCl over 24–48 hours until Cl- >100 mEq/L, K+ >3.5 mEq/L, and HCO3 <28 mEq/L. Uncorrected alkalosis causes postoperative apnoea because the elevated HCO3 blunts the CO2-mediated hypercapnic drive to breathe after anaesthesia.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.