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What is hypertrophic pyloric stenosis?

- Narrowing of the pyloric opening due to progressive hypertrophy of pylorus (circumferential layer)


Risk factors for hypertrophic pyloric stenosis

- Male (85%)
- 1st born
- FHx, esp. maternal Hx


Peak age of incidence of hypertrophic pyloric stenosis

3-6 weeks


Findings on history of hypertrophic pyloric stenosis

• Progressive non-bilious vomiting
• Projectile - defined as past feet: stomach is so strong
• After every feed - cf malrotation who vomit less (so metabolic derangement not so severe)
• Blood stained in 10%
• Hungry infant (c.f. sepsis or malrotation) 
• Often hungry after vomiting
• Decreased stooling 
• Weight loss 


Examination findings of hypertrophic pyloric stenosis

• Visible gastric peristaltic waves
○ moving from left to right across epigastrium 
○ Esp after feed
• Dehydration 
• Growth
○ Weight and plot
• Pyloric mass - "palpable olive"
○ just to the right of the rectus muscle in a relaxed baby (in RUQ)
○ Feel when supine


What is the metabolic derangement found in hypertrophic pyloric stenosis? Why?

- Vomit contents: 
• HCl 
• NaCl 
• K 
- Therefore the metabolic derangement is a hypokalaemic, hypochloraemia (Cl <98) metabolic alkalosis.   
- No hyponatraemia unless extremely unwell - Body tries to preserve it!


What is the important finding in urine with hypertrophic pyloric stenosis? Why does it happen?

• Urine is paradoxically acidotic
○ kidneys are trying to hold on to sodium, and shunting out H+ (channel in kidneys)
○ Later sign


What is the best Ix to diagnose hypertrophic pyloric stenosis?

• USS (95% sensitive): look at length of channel >16mm, muscle thickness >4mm, total diameter >12mm


What is the medical management of hypertrophic pyloric stenosis?

Medical (not surgical) emergency:

• Resuscitate dehydrated infant
• Stop oral feeds
• Correct electrolyte anomaly
• Replace ongoing fluid loss
○ 150 ml/kg/day
○ 0.45 % NaCl with 5% dextrose
○ Add 20 mmol KCl/L after confirming K level


What fluid can you not use to replace fluid in hypertrophic pyloric stenosis, and why?

Plasmalyte is not used in the management of HPS as it contains bicarbonate precursors. Blood bicarbonate levels can be used to monitor response to fluid therapy in HPS.


Surgical Mx of hypertrophic pyloric stenosis

• Surgical division of hypertrophic muscle via pyloromyotomy - tear in the pyloric muscle, being careful not to tear the mucosa 


DDx of non-bilious vomiting in neonate

• Pyloric stenosis
• Sepsis
• Meningitis
• Reflux
• Overfeeding
• Metabolic diseases–rare
• Congenital adrenal hyperplasia-rare


Consequences of hypertrophic pyloric stenosis

Poorer neurodevelopmental outcomes