Pyloric Stenosis

OVERVIEW

Pyloric Stenosis is a medial emergency that requires urgent fluid resuscitation and resolution of biochemical abnormalities. Definitive surgical treatment can then be undertaken to restore enteral nutrition.

CLINICAL FEATURES

• commoner in first born males
• 80% males
• 10% are premature
• projectile vomiting in neonate (not billous)
• 2-8 weeks
• dehydration
• weight loss
• hyperaldosteronism with paradoxical aciduria
• visible peristalsis and olive sized mass in epigastrium
• confirmed on US
• associated pathology: cleft palate, GORD

PATHOPHYSIOLOGY AND BIOCHEMISTRY

Develops:

1. hypochloraemia
2. metabolic alkalosis
3. hyponatraemia
4. hypokalaemia
5. initially, alkaline urine -> later, acidic urine
6. dehydration

• hypochloraemia
  – loss of chloride in vomitus
• metabolic alkalosis
  – loss of H+ in vomitus
  – decreased secretion of pancreatic HCO3-
  – increased HCO3- presented to distal tubule and eliminated producing an alkaline urine
• hyponatraemia
  – loss of Na+ in vomitus
  – decreased absorption of Na+
  – loss of Na+ in urine until kidney adjusts to increased HCO3- load
  – activation of renin-AG-ALD system to off set this and restore Na+ and H2O
• hypokalaemia
  – K+ loss in vomitus
  – activation of rennin-AG-ALD system with produces loss of K+ in urine
  – with extreme K+ loss in urine -> it gets reabsorbed in distal tubule with loss of H+ worsening metabolic alkalosis and producing and acidic urine
• initially, alkaline urine -> later, paradoxical aciduria
  – in order to prevent hypokalaemia
• dehydration
  – inability to absorb enteral fluid and vomiting
  – activation of rennin-AG-ALD system + ADH

MANAGEMENT

Fluid resuscitation — determined by weight and degree of dehydration assessed clinically (tissue turgor, pulse, fontanelle, CR centrally, peripheral perfusion, respiratory rate)

• IV boluses of normal saline or colloid (4% albumin) – 10-20mL/kg to restore circulating volume
• maintenance @ 4mL/kg/hr with 5% dextrose with 0.45% normal saline and 20mmoL KCl
• fluid therapy should be titrated to clinical variable including urine output (2mL/kg/hr)
• need a lot of K+ once they pee

Laboratory criteria by which patient is sufficiently resuscitated for surgery — ideally biochemical abnormalities would be normal before surgery however, variable associated with adequate resuscitation and resolution of metabolic alkalosis include:

• serum Cl- of at least 105mmol/L
• serum HCO3- (normal)
• urinary Cl- of >20mmol/L
• urinary K+
• urinary Na+

Intraoperative

• operation = splitting of the pylorus muscle longitudinally down to the mucosa (myomectomy)
• risk of pulmonary aspiration from gastric outflow obstruction
• aspirate N/G and don’t remove as will help to decompress stomach from vigorous ventilation
• RSI or use of NDNMBD
• fentanyl 1mcg/kg
• paracetamol suppository 30-40mg/kg
• bupivacaine infiltration
• extubate awake and in left lateral position

Postoperative

• remove N/G
• feed within 6 hours
• give maintenance IVF until feeding established
• use apnoea alarm overnight