What is idiopathic hypertrophic pyloric stenosis (IHPS)?

This is a congenital condition that presents in infants at around 6 weeks of age. There is hypertrophy of the circular muscle of the pylorus causing gastric outflow obstruction. It is a familial condition and seen especially in the first-born males. IHPS is considered a surgical emergency as the infant is unable to feed and loses large quantities of acidic gastric fluid leading to dehydration, alkalosis and electrolyte imbalances.

What is the biochemical abnormality in an infant with pyloric stenosis?

Hypochloraemic metabolic alkalosis. The serum potassium and sodium may also be decreased. There may even be a paradoxical acid urine as the kidneys excrete hydrogen ions in order to preserve potassium.

How is IHPS diagnosed?

Classically there is a history of non-bilious projectile vomiting, dehydration and failure to thrive. The child remains hungry after each vomiting. Clinically the thickened pylorus can be palpated in the epigastrium as an olive-sized mass. The diagnosis can be further supported with a test feed and confirmed on ultrasound scanning.

What is the management of an infant with pyloric stenosis?

• Fluid resuscitation using 0.45% normal saline with the addition of potassium chloride to each bag

• NGT insertion and regular aspiration of the gastric contents

• Surgery (Ramstedt's pyloromyotomy) after the alkalosis is corrected (typically after HCO3 is below 25 mmol/l)

Describe the steps taken in performing a Ramstedt's pyloromyotomy

Position The infant is placed supine with whole abdomen prepared and draped.

Incision Usually a right upper quadrant cutting or muscle splitting incision is used (upper midline, umbilical and laparoscopic approaches may also be used).