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 vigourous 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
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