Hypertrophic Pyloric Stenosis

A 4-week-old first-born male presents with projectile non-bilious vomiting after feeds for 1 week. He remains hungry after vomiting but shows signs of dehydration and poor weight gain. On examination, an olive-sized mass is palpable in the epigastrium. Ultrasound confirms hypertrophic pyloric stenosis. Laboratory investigations reveal the electrolyte abnormality marked as **D** in the diagram. Which of the following is the MOST CRITICAL reason why this electrolyte derangement must be corrected BEFORE surgical intervention?

A 4-week-old previously healthy male infant, firstborn to a family with a history of pyloric stenosis, presents with projectile non-bilious vomiting after feeds and visible gastric peristaltic waves. On examination after nasogastric decompression, a firm, olive-shaped mass is palpated in the right upper quadrant. The structure marked **A** in the diagram represents the pathological finding. Which of the following is the MOST LIKELY etiology for the development of this lesion in this clinical context?

A 4-week-old male infant presents with progressive projectile vomiting after feeds for the past 10 days. He is eager to feed immediately after vomiting. On examination, a palpable olive-shaped mass is felt in the right upper quadrant. Abdominal ultrasound is performed. The structure marked **A** in the diagram (thickened pyloric muscle wall) measures 4.2 mm in thickness, with a pyloric channel length of 17 mm. Which of the following is the MOST appropriate next step in management?