Hypertrophic Pyloric Stenosis

Quick Answer: Hypertrophic Pyloric Stenosis (HPS) is progressive hypertrophy of the pyloric smooth muscle causing gastric outlet obstruction in infants aged 2-12 weeks (peak 3-6 weeks). Classic triad: projectile non-bilious vomiting, visible gastric peristalsis, palpable 'olive' mass (only 10-30% cases). Diagnosis by ultrasound (pyloric muscle thickness greater than 3 mm, length greater than 15 mm, diameter greater than 12 mm). Biochemical hallmark: hypochloraemic hypokalaemic metabolic alkalosis. Management: IV fluid resuscitation, correct electrolytes and acid-base BEFORE surgery, definitive treatment is Ramstedt pyloromyotomy (open or laparoscopic). Mortality below 0.5% with appropriate resuscitation and timely surgery. NOT a surgical emergency – correct dehydration first.

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ACEM Exam Focus

Fellowship Written SAQ Expectations

Must know:

• Pathophysiology of hypochloraemic hypokalaemic metabolic alkalosis
• Ultrasound diagnostic criteria (3-12-15 rule: greater than 3 mm muscle thickness, greater than 12 mm diameter, greater than 15 mm length)
• Pre-operative resuscitation targets (urine output greater than 1 mL/kg/h, chloride greater than 100 mmol/L, K+ normalised, pH below 7.45)
• Complications: incomplete pyloromyotomy, perforation/mucosal breach, wound infection, post-operative apnoea
• Differentials: gastro-oesophageal reflux, malrotation with volvulus, milk protein intolerance, sepsis

Common SAQ themes:

• Management of dehydrated infant with projectile vomiting
• Interpretation of blood gas showing metabolic alkalosis
• Fluid resuscitation calculation and electrolyte correction
• Discussion of imaging modality choice
• Disposition planning in remote/rural setting

Fellowship OSCE Stations

Likely scenarios:

1. History from parent of 5-week-old with vomiting
2. Examination demonstrating 'olive' mass and gastric peristaltic waves
3. Counselling parent regarding diagnosis, surgery, prognosis
4. Breaking news of surgical intervention requirement
5. Discussion of imaging findings with radiology/paediatric surgery

Viva Pearls

• Examiners expect knowledge that pyloric stenosis is NOT a surgical emergency – adequate resuscitation takes priority
• Classic error: rushing to theatre without correcting electrolytes → post-operative apnoea from persistent alkalosis
• Always consider malrotation/volvulus if bilious vomiting present (surgical emergency)
• Palpable 'olive' mass diagnostic specificity ~99%, but only present in 10-30% of cases
• Post-operative vomiting in 50-80% (usually self-limiting, resolves by day 5)

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Key Points

1. Epidemiology: Incidence 2-5 per 1,000 live births; male predominance 4-5:1; firstborn male infants at highest risk; Caucasians > Asians/Africans
2. Presentation: Progressive projectile non-bilious vomiting starting at 2-12 weeks (peak 3-6 weeks), infant hungry after vomiting, weight loss, dehydration, constipation
3. Biochemistry: Hypochloraemic hypokalaemic metabolic alkalosis (Cl⁻ below 85 mmol/L, K⁺ below 3.5 mmol/L, pH greater than 7.45, HCO₃⁻ greater than 30 mmol/L); paradoxical aciduria
4. Diagnosis: Point-of-care ultrasound (sensitivity 97-100%, specificity 99-100%): pyloric muscle thickness greater than 3 mm, pyloric channel length greater than 15 mm, transverse diameter greater than 12 mm
5. Management: IV fluid resuscitation (0.9% sodium chloride ± potassium chloride 20 mmol/L), correct electrolytes BEFORE surgery, Ramstedt pyloromyotomy (open vs laparoscopic – similar outcomes)
6. Prognosis: Excellent with mortality below 0.5%; 50-80% post-operative vomiting (resolves within 5 days); incomplete pyloromyotomy rate 1-3%
7. Remote/Rural: Early ultrasound, telehealth consultation with paediatric surgery, RFDS/retrieval coordination, IV fluid resuscitation during transport

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Epidemiology

Incidence and Demographics

Incidence: 2-5 per 1,000 live births in Caucasian populations (range 1-4 per 1,000 across different ethnicities) [PMID: 9373863]. Lower rates in Asian (0.6-1.1 per 1,000) and African populations (0.7-1.5 per 1,000).

Gender: Male predominance 4-5:1 male-to-female ratio [PMID: 34599053].

Age: Typically presents between 2-12 weeks of age with peak incidence at 3-6 weeks. Mean age at diagnosis 4-5.5 weeks (historically 5.9 weeks, now earlier due to increased awareness and ultrasound availability). Premature infants may present later (corrected gestational age typically used) [PMID: 30677197].

Risk Factors:

• Family history: 20% of male offspring and 10% of female offspring of affected mothers develop HPS; sibling recurrence risk 4-8% [PMID: 16249217]
• Firstborn male infant at highest risk
• Race: Caucasians > Hispanics > Asians/Africans
• Erythromycin exposure: 8-fold increased risk if administered in first 2 weeks of life (motilin agonist effect) [PMID: 10408742]
• Maternal smoking, bottle feeding (vs breastfeeding), younger maternal age
• Blood group: Higher in B and O blood types

Australian/NZ Context:

• Australian incidence approximately 3 per 1,000 live births [PMID: 30677197]
• Aboriginal and Torres Strait Islander infants: Limited specific data, but likely similar to non-Indigenous populations (no significant disparity identified in paediatric surgical conditions) [PMID: 27765019]
• Māori infants: Similar incidence to NZ European populations

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Pathophysiology

Pyloric Muscle Hypertrophy

Primary defect: Progressive hypertrophy and hyperplasia of the circular smooth muscle layer of the pylorus (pyloric sphincter). The pyloric muscle can increase to 3-4 times normal thickness (normal below 2 mm, HPS greater than 3 mm).

Mechanism: Exact aetiology unclear – likely multifactorial:

• Genetic factors: Familial clustering, twin concordance studies suggest genetic predisposition (polygenic inheritance pattern)
• Neurohormonal abnormalities:
  • Decreased nitric oxide synthase (NOS) activity in pyloric muscle → impaired smooth muscle relaxation
  • Reduced interstitial cells of Cajal (pacemaker cells)
  • Imbalance between excitatory (acetylcholine) and inhibitory (nitric oxide, vasoactive intestinal peptide) neurotransmitters
• Environmental factors: Erythromycin (motilin agonist), prostaglandin E2 administration
• Acquired condition: Not present at birth – develops over first 2-8 weeks of life

Result: Gastric outlet obstruction → impaired gastric emptying → progressive vomiting → dehydration and electrolyte derangement.

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Metabolic Derangement: The Classic Alkalosis

Hypochloraemic Hypokalaemic Metabolic Alkalosis – pathognomonic biochemical picture [PMID: 2686579]:

Mechanism

1. Vomiting → Loss of gastric HCl

   • Stomach secretes H⁺ and Cl⁻ (as HCl)
   • Vomiting removes HCl → net loss of H⁺ and Cl⁻ from body
   • Result: Hypochloraemia (Cl⁻ below 85 mmol/L) and metabolic alkalosis (pH greater than 7.45, HCO₃⁻ greater than 30 mmol/L)

2. Contraction alkalosis

   • Dehydration → decreased circulating volume
   • Renal sodium and water reabsorption increases
   • Preferential reabsorption of HCO₃⁻ (to maintain electroneutrality) → worsening alkalosis

3. Hypokalaemia

   • Initial loss of K⁺ in gastric fluid (though gastric K⁺ content relatively low – 10 mmol/L)
   • Renal K⁺ wasting (major mechanism):
     • Volume depletion → aldosterone secretion → distal tubule K⁺ secretion
     • Hypochloraemia → less Cl⁻ available for reabsorption → distal delivery of Na⁺ → increased distal Na⁺ reabsorption coupled with K⁺ secretion
     • Alkalosis → intracellular shift of H⁺ (in exchange for K⁺) → serum hypokalaemia

4. Paradoxical aciduria

   • Despite systemic alkalosis, urine may be acidic (pH below 6.0)
   • Mechanism: Severe hypokalaemia → distal tubule H⁺ secretion (in exchange for K⁺ reabsorption) → acidic urine
   • Once K⁺ and Cl⁻ repleted, urine becomes alkaline (as HCO₃⁻ excreted)

Typical Blood Gas (severe cases):

• pH 7.50-7.60 (metabolic alkalosis)
• HCO₃⁻ 32-45 mmol/L
• PaCO₂ 45-55 mmHg (respiratory compensation)
• Base excess +8 to +15
• Cl⁻ 75-90 mmol/L (hypochloraemia)
• K⁺ 2.5-3.5 mmol/L (hypokalaemia)
• Na⁺ usually normal or mildly elevated (hypernatraemia from free water loss)

Clinical relevance: Metabolic alkalosis must be corrected BEFORE surgery – residual alkalosis increases risk of post-operative apnoea (alkalosis → leftward shift of oxyhaemoglobin dissociation curve → decreased O₂ delivery; also central respiratory depression) [PMID: 35427043].

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Clinical Presentation

History

Classic Triad (variable presence):

1. Projectile non-bilious vomiting (most consistent feature – present in 97% of cases)
2. Visible gastric peristaltic waves (left-to-right across upper abdomen)
3. Palpable 'olive' mass (only 10-30% of cases in modern series – reduced palpation skill with widespread ultrasound use) [PMID: 8461768]

Vomiting Characteristics:

• Non-bilious (green vomit suggests malrotation/volvulus – surgical emergency)
• Projectile – forceful expulsion up to several feet
• Progressive – starts as occasional possets, progresses to after every feed
• Timing: Begins 2-12 weeks after birth (peak 3-6 weeks), typically 5-7 days of symptoms before presentation
• Relationship to feeds: Usually occurs 30 minutes to 1 hour after feeds
• Hungry infant: Baby eager to feed again immediately after vomiting (distinguishes from other causes like sepsis where infant lethargic)

Associated Features:

• Weight loss or failure to regain birth weight
• Decreased urine output (oliguria – marker of dehydration severity)
• Constipation (reduced stool frequency and volume – "starvation stools")
• Jaundice (10-15% of cases – unconjugated hyperbilirubinaemia from decreased glucuronyl transferase activity in starvation)

Important Negatives:

• No bile in vomitus (if present, consider malrotation)
• No fever (if febrile, consider sepsis, gastroenteritis)
• No diarrhoea (if present, suggests gastroenteritis)
• No blood in vomit (haematemesis suggests oesophagitis, though Mallory-Weiss tears can occur)

Examination

General Inspection:

• Dehydration signs: Sunken eyes, dry mucous membranes, delayed capillary refill (greater than 2 seconds), decreased skin turgor, sunken fontanelle
• Weight loss: Often 5-10% below birth weight
• Jaundice: Mild unconjugated hyperbilirubinaemia in 10-15% cases

Abdominal Examination:

1. Inspection

• Visible gastric peristaltic waves: Observe abdomen for 2-3 minutes (patient should be calm and relaxed)
  • Left-to-right peristaltic waves across upper abdomen (gastric peristalsis attempting to overcome pyloric obstruction)
  • Best seen after feed
  • Present in 40-60% of cases

2. Palpation for 'Olive' Mass

Technique (maximal yield):

• Infant relaxed (give pacifier/dummy or small feed)
• Stand on infant's right side
• Use left hand to palpate
• Location: Deep palpation in right upper quadrant, lateral to rectus abdominis, midway between costal margin and umbilicus
• Texture: Firm, mobile, olive-shaped mass (1.5-2 cm), moves with respiration
• Timing: Best palpated immediately after vomiting or during feed (pylorus relaxes briefly)

Sensitivity: Only 10-30% in modern series (historically 60-80% before widespread ultrasound availability) [PMID: 8461768]. Palpation skills declining due to early ultrasound diagnosis.

Specificity: ~99% when present (virtually diagnostic).

3. Test Feed (Historical – rarely performed now)

• Give small feed (30-60 mL formula or expressed breast milk)
• Observe for visible gastric peristalsis (left-to-right waves)
• Palpate during feed for 'olive' mass
• Often followed by projectile vomiting
• Rarely performed in modern practice – ultrasound preferred

Red Flags (Suggesting Alternative Diagnosis)

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Differential Diagnosis

Structured Approach to Vomiting in Young Infant

Surgical causes (require urgent/emergency intervention):

1. Malrotation with volvulus – bilious vomiting, abdominal distension, peritonism, shock (SURGICAL EMERGENCY)
2. Intussusception – usually greater than 3 months, colicky pain, blood per rectum ("redcurrant jelly"), sausage-shaped mass
3. Incarcerated inguinal hernia – tender groin mass, bowel obstruction
4. Hirschsprung disease – delayed meconium passage, abdominal distension, chronic constipation

Non-surgical causes:

1. Gastro-oesophageal reflux disease (GORD) – most common differential; non-projectile, effortless regurgitation; infant thriving (unless severe); responds to positional therapy ± proton pump inhibitors
2. Overfeeding – excessive volume, normal examination, thriving infant
3. Milk protein allergy – vomiting + diarrhoea ± blood in stool, eczema, family history of atopy
4. Sepsis/UTI – fever, lethargy, irritability, abnormal vital signs
5. Gastroenteritis – vomiting + diarrhoea, fever, contact history
6. Metabolic disorders – rare; consider if persistent vomiting, lethargy, hypoglycaemia (e.g., congenital adrenal hyperplasia, urea cycle defects, organic acidaemias)
7. Raised intracranial pressure – bulging fontanelle, altered conscious state, apnoea, bradycardia
8. Medication effect – erythromycin, azithromycin

Distinguishing HPS from GORD (most common clinical dilemma):

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Investigations

Bedside

Point-of-Care Ultrasound (POCUS):

• Emergency physician-performed pyloric ultrasound – high sensitivity and specificity when performed by trained operators (100% sensitivity, 100% specificity in prospective ACEP study) [PMID: 28459155]
• Availability of POCUS in ED expedites diagnosis (median time to diagnosis 30 minutes vs 4 hours with radiology ultrasound) [PMID: 28984152]
• If POCUS unavailable or inconclusive, formal radiology ultrasound required

Vital Signs:

• Tachycardia (dehydration)
• Delayed capillary refill greater than 2 seconds (moderate-severe dehydration)
• Weight (compare to birth weight and previous weights)

Laboratory

Essential tests:

1. Venous Blood Gas (VBG) or arterial blood gas (ABG):

   • pH greater than 7.45 (metabolic alkalosis) – may be 7.50-7.60 in severe cases
   • HCO₃⁻ greater than 30 mmol/L (often 32-45 mmol/L)
   • Base excess +5 to +15
   • Cl⁻ below 85 mmol/L (hypochloraemia) – often 70-85 mmol/L
   • K⁺ below 3.5 mmol/L (hypokalaemia) – may be 2.5-3.5 mmol/L
   • Note: Only ~50% of infants with HPS present with classic alkalosis at time of ED presentation (earlier diagnosis with improved awareness) [PMID: 2686579]

2. Urea and Electrolytes (U&E):

   • Elevated urea (pre-renal from dehydration)
   • Sodium usually normal or elevated (hypernatraemia from free water loss)
   • Creatinine may be elevated (pre-renal)

3. Glucose (bedside glucometer + laboratory confirmation):

   • Hypoglycaemia possible (decreased glycogen stores from poor feeding)

4. Urinalysis:

   • Paradoxical aciduria (urine pH below 6.0 despite systemic alkalosis – due to hypokalaemia)
   • Becomes alkaline once K⁺ repleted

Additional tests (if diagnostic uncertainty):

• Unconjugated bilirubin: Elevated in 10-15% (decreased glucuronyl transferase activity)
• Full blood count: Usually normal; haemoconcentration if severely dehydrated
• Blood culture: If sepsis considered in differential

Imaging

Ultrasound (Gold Standard)

Modality of choice: Sensitivity 97-100%, specificity 99-100% [PMID: 17297428].

Technique:

• Patient preparation: Ideally 2-3 hours fasted (or immediately after vomiting) – reduces gastric contents for optimal visualisation
• Position: Supine or right lateral decubitus
• Probe: High-frequency linear probe (7.5-12 MHz)
• Approach:
  1. Identify liver and gallbladder
  2. Scan transversely just caudal to gallbladder
  3. Identify fluid-filled pyloric channel (target sign in transverse)
  4. Rotate probe to obtain longitudinal view
  5. Measure pyloric muscle thickness, channel length, and transverse diameter

Diagnostic Criteria ("3-12-15 Rule"):

Modified criteria (from recent meta-analysis) [PMID: 34608732]:

• Some centres use greater than 3 mm muscle thickness alone as sufficient
• Piotto et al. (2022) suggest greater than 2.5 mm muscle thickness with greater than 14 mm channel length may improve sensitivity without compromising specificity [DOI: 10.1002/ajum.12305]

Ultrasound Signs:

1. Target sign (transverse): Hypoechoic thickened pyloric muscle surrounding echogenic mucosa (concentric rings)
2. Cervix sign (longitudinal): Elongated pyloric channel protruding into gastric antrum
3. Antral nipple sign: Redundant pyloric mucosa protruding into gastric antrum
4. Failure of pyloric opening: Real-time observation – no or minimal passage of gastric contents through pylorus during 10-15 minute scan

False negatives: below 3% with experienced sonographer. Causes: inadequate gastric distension, inexperienced operator, early/mild HPS (muscle thickness 2.5-3 mm).

False positives: Rare (below 1%). Causes: Pylorospasm (self-limiting muscular contraction – resolves during scan; pylorus opens and closes on real-time imaging).

Upper Gastrointestinal Contrast Study (Historical)

Rarely performed in modern practice (replaced by ultrasound).

Indications: If ultrasound inconclusive and high clinical suspicion persists.

Findings:

• String sign: Narrow elongated pyloric channel
• Shoulder sign: Bulging pyloric muscle into gastric antrum
• Double track sign: Parallel lines of barium in narrowed pyloric channel
• Delayed gastric emptying (greater than 4 hours)

Disadvantages: Radiation exposure, aspiration risk, time-consuming, lower sensitivity than ultrasound.

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Management

ED Resuscitation and Stabilisation

Key Principle: Hypertrophic pyloric stenosis is NOT a surgical emergency. Adequate resuscitation and correction of electrolyte/acid-base abnormalities takes priority BEFORE surgery. Rushing to theatre with uncorrected alkalosis risks post-operative apnoea.

1. Fluid Resuscitation

Goals:

• Restore circulating volume
• Correct hypochloraemia (Cl⁻ greater than 100 mmol/L)
• Correct hypokalaemia (K⁺ greater than 3.5 mmol/L)
• Normalise pH (below 7.45)
• Establish urine output greater than 1 mL/kg/h

Initial Resuscitation (if moderate-severe dehydration):

• 0.9% Sodium Chloride bolus: 10-20 mL/kg IV over 30-60 minutes
• Reassess after each bolus
• Repeat if signs of shock/severe dehydration persist

Maintenance Fluids + Deficit Correction:

Fluid Choice: 0.9% Sodium Chloride with Potassium Chloride 20 mmol/L (once urine output established)

Why NaCl 0.9%? – High chloride content (154 mmol/L) corrects hypochloraemia rapidly. Avoid hypotonic fluids (e.g., 0.45% NaCl) which delay chloride correction.

Potassium Replacement:

• DO NOT give potassium until urine output established (risk of hyperkalaemia if anuric)
• Add KCl 20 mmol/L to maintenance fluids (max concentration 40 mmol/L in peripheral IV)
• If severe hypokalaemia (K⁺ below 2.5 mmol/L), consider higher concentrations via central line or slower infusion

Rate:

• Maintenance rate (Holliday-Segar):
  • 0-10 kg: 4 mL/kg/h
  • 10-20 kg: 40 mL/h + 2 mL/kg/h for each kg greater than 10 kg
  • "Example: 4 kg infant = 4 × 4 = 16 mL/h"
• Add deficit replacement: Estimate percentage dehydration (typically 5-10%), replace over 24-48 hours
• Example: 4 kg infant, 10% dehydrated = 400 mL deficit. Give 200 mL over 12 hours (16 mL/h) + 16 mL/h maintenance = 32 mL/h for first 12 hours

Monitoring:

• Urine output: Goal greater than 1 mL/kg/h (insert urinary catheter if severe dehydration or difficult to monitor)
• Repeat VBG/U&E: Every 4-6 hours until normalised
• Weight: Daily (best marker of hydration status)

2. Electrolyte Correction Targets (Pre-Operative)

Safe for surgery when ALL criteria met:

• Chloride greater than 100 mmol/L (ideally greater than 105 mmol/L)
• Potassium greater than 3.5 mmol/L (ideally greater than 4.0 mmol/L)
• pH below 7.45 (ideally 7.35-7.42)
• Urine output greater than 1 mL/kg/h for at least 4-6 hours

Time to normalisation: Typically 12-24 hours (may take up to 48 hours in severe cases). Do NOT proceed to surgery until targets met.

3. Nasogastric Tube (NGT)

Indications:

• Persistent vomiting
• Gastric distension
• Aspiration risk

Management:

• Insert NGT (size 8 Fr for infant)
• Leave on free drainage
• Aspirate hourly and discard (replace with additional IV fluid if large volumes)
• Do NOT replace aspirates with IV fluid mL-for-mL – overestimates losses (normal gastric secretion ~1-2 mL/kg/h)

4. Analgesia

Usually not required pre-operatively (HPS not a painful condition). Post-operatively: paracetamol ± opiates.

5. NBM (Nil By Mouth)

• NBM from time of diagnosis until after surgery
• IV fluids for hydration
• Pacifier/dummy for non-nutritive sucking comfort

Definitive Management: Pyloromyotomy

Gold Standard: Ramstedt pyloromyotomy – longitudinal incision through hypertrophied pyloric muscle down to submucosa WITHOUT breaching mucosa.

Surgical Approaches

1. Open Pyloromyotomy (Traditional)

Incision options:

• Transverse right upper quadrant (most common) – 2-3 cm incision
• Periumbilical (circumumbilical incision, better cosmetic result)

Technique:

• Deliver pylorus through incision
• Longitudinal incision through serosa and muscle on anterior surface (avoidance of gastroduodenal artery branches)
• Blunt dissection to spread muscle fibres (using pyloric spreader or mosquito forceps)
• Ensure complete division – muscle fibres should splay apart, exposing submucosa
• Check for mucosal breach (insufflate air via NGT or inject saline via NGT into stomach – look for bubbles)

Duration: 20-30 minutes

Advantages: Faster, less equipment required, suitable for remote centres without laparoscopic equipment

Disadvantages: Larger scar, slightly higher wound infection rate

2. Laparoscopic Pyloromyotomy

Technique:

• Three ports (umbilical 5 mm, two 3 mm working ports in upper abdomen)
• Grasp pylorus with atraumatic grasper
• Perform pyloromyotomy with laparoscopic knife/electrocautery
• Spread muscle with blunt dissection

Duration: 30-40 minutes (longer than open initially, decreases with experience)

Advantages:

• Better cosmesis
• Slightly shorter hospital stay (mean difference 0.3 days) [PMID: 19198609]
• Less post-operative pain (questionable – both approaches have low pain)

Disadvantages:

• Longer operative time
• Requires laparoscopic equipment and expertise
• Slightly higher incomplete pyloromyotomy rate (1.8% vs 0.8% open) [PMID: 22538694]
• Risk of omental herniation through port sites (case reports)

Comparison: Cochrane Review and Meta-Analyses:

• No significant difference in major complications (mucosal perforation ~1-3% both approaches, incomplete pyloromyotomy 1-3%)
• Laparoscopic associated with slightly shorter hospital stay (0.3 days, 95% CI 0.1-0.5 days) [PMID: 33606222]
• Time to full feeds similar (both approaches)
• Post-operative vomiting similar (50-80% in both)
• Choice depends on surgeon preference and institutional resources

Complications

Intra-operative:

1. Mucosal Perforation (1-3% of cases):

   • Recognition: Air/saline leak test positive (bubbles from pyloromyotomy site when air insufflated via NGT)
   • Management: Primary repair with 4-0 or 5-0 absorbable suture, omental patch, repeat leak test
   • If unrecognised: Peritonitis post-operatively (fever, abdominal distension, irritability, tachycardia) – requires re-operation

2. Incomplete Pyloromyotomy (1-3%):

   • Recognition: Persistent projectile vomiting greater than 5 days post-op, ultrasound shows residual muscle hypertrophy
   • Management: Re-operation

Post-operative:

1. Post-operative Vomiting (50-80% of cases):

   • Usually self-limiting, resolves by day 3-5 [PMID: 30677197]
   • Causes: Pylorospasm, gastric atony (from prolonged obstruction), gastro-oesophageal reflux, oedema at pyloromyotomy site
   • Management: Continue gradual feed advancement; NGT if persistent large-volume vomiting; antiemetics rarely required
   • Distinguish from incomplete pyloromyotomy: Post-op vomiting improves over 3-5 days; incomplete pyloromyotomy shows persistent/worsening projectile vomiting

2. Wound Infection (1-5%):

   • More common with open approach
   • Management: Antibiotics (flucloxacillin), wound care; abscess drainage if required

3. Post-operative Apnoea (below 5%, higher in ex-premature infants):

   • Risk factors: Prematurity (below 37 weeks), uncorrected metabolic alkalosis, post-conceptual age below 44-45 weeks
   • Mechanism: Residual alkalosis → respiratory depression + leftward shift of oxyhaemoglobin dissociation curve [PMID: 35427043]
   • Prevention: Correct alkalosis pre-operatively (pH below 7.45, chloride greater than 100 mmol/L)
   • Management: Apnoea monitoring for 24 hours post-op (especially if ex-premature or residual alkalosis)

4. Incisional Hernia (rare, below 1%):

   • More common at umbilical incision sites

Post-Operative Feeding

Feeding Regimens (vary by institution):

Traditional "Graded Feeding":

• Start with small frequent feeds 4-6 hours post-op
• Example: 15 mL every 2 hours × 2 feeds, then 30 mL every 3 hours × 2, then 45 mL every 3 hours × 2, then on-demand feeds
• Advance as tolerated

Ad Libitum Feeding (increasingly popular):

• Some centres start on-demand feeds 4-6 hours post-op (no graded advancement)
• Evidence: RCTs show no difference in time to full feeds, length of stay, or vomiting compared to graded feeding [PMID: 19109437]

Both approaches acceptable – institutional preference.

Management of Post-Op Vomiting:

• Expected in 50-80% (usually small volume, non-projectile)
• Continue feed advancement if vomiting not large volume or persistent
• If persistent: Slow advancement, consider anti-reflux measures (head-up positioning, thickened feeds), ensure adequate analgesia

Disposition

Admission: All cases – paediatric surgery ward (or general paediatric ward with paediatric surgery follow-up)

Typical Length of Stay:

• Open pyloromyotomy: 1-3 days (median 2 days)
• Laparoscopic pyloromyotomy: 1-2 days (median 1.5 days)

Discharge Criteria:

• Tolerating full feeds (on-demand or goal volume for age/weight)
• No significant vomiting (small possets acceptable)
• Adequate urine output
• No complications (wound infection, fever)
• Parent/caregiver education provided

Follow-Up:

• Paediatric surgery outpatient clinic in 4-6 weeks
• GP review in 1-2 weeks (weight check, wound inspection)
• Parent education: Expect some vomiting in first week (usually resolves); seek review if persistent projectile vomiting, fever, wound redness/discharge, decreased feeding

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Remote and Rural Considerations

Challenges in Rural/Remote Australia and NZ

Epidemiology: Aboriginal and Torres Strait Islander children have similar rates of pyloric stenosis to non-Indigenous children (no significant disparity identified in large-scale studies) [PMID: 27765019]. However, access to paediatric surgery is concentrated in metropolitan centres, requiring aeromedical retrieval.

Distance and Retrieval:

• Most paediatric surgery performed at tertiary centres (Perth, Adelaide, Melbourne, Sydney, Brisbane, Darwin, Auckland, Wellington, Christchurch)
• Rural/remote infants require RFDS or state-based retrieval services (e.g., NSW Newborn and Paediatric Emergency Transport Service – NETS)
• Mean retrieval distance for paediatric surgical conditions in outback Australia: 800-1,200 km [PMID: 31461413]

ED Management in Rural/Remote Settings

1. Early Diagnosis

POCUS: Emergency physician-performed pyloric ultrasound highly accurate (100% sensitivity/specificity with training) [PMID: 28459155]

• If POCUS available: Perform ED ultrasound
• If POCUS unavailable: Radiology ultrasound (may need teleradiology with image transmission to tertiary centre for interpretation if local radiology unavailable)

Telehealth: Many rural hospitals have telehealth links to tertiary paediatric centres

• Video consultation with paediatrician/paediatric surgeon
• Transmit ultrasound images for remote interpretation

2. Resuscitation Before Retrieval

Critical: DO NOT delay resuscitation waiting for retrieval – start IV fluids immediately.

Protocol:

1. Obtain IV access (if difficult, consider intraosseous in severely shocked infant)
2. Bolus resuscitation if moderate-severe dehydration: 0.9% NaCl 10-20 mL/kg IV over 30-60 minutes
3. Maintenance fluids: 0.9% NaCl + KCl 20 mmol/L (once urine output established) at maintenance rate + deficit replacement
4. NGT: Insert if persistent vomiting or gastric distension
5. VBG/U&E: Check electrolytes and acid-base status; repeat every 4-6 hours
6. Glucose: Check BSL; correct hypoglycaemia if present

Target: Aim for Cl⁻ greater than 100 mmol/L, K⁺ greater than 3.5 mmol/L, pH below 7.45 BEFORE or DURING retrieval. Resuscitation may take 12-24 hours – retrieval team will continue IV fluids en route.

3. Retrieval Coordination

RFDS (Royal Flying Doctor Service):

• Contact: RFDS retrieval coordination centre (varies by state – NSW, QLD, SA, WA, NT, TAS all have dedicated RFDS services)
• Example (NSW): RFDS NSW – 1800 625 800 (24/7)
• NETS (NSW Newborn and Paediatric Emergency Transport Service): 1300 36 2500

State-Based Services:

• Victoria: PIPER (Paediatric Infant Perinatal Emergency Retrieval) – 1300 137 650
• Queensland: Queensland Paediatric Retrieval Service – 1300 799 127
• South Australia: MedSTAR – 1300 763 887
• Western Australia: Neonatal/Paediatric Retrieval Service – 1800 222 003
• New Zealand: National Ambulance Sector Office coordinates retrieval between DHBs

Retrieval Process:

1. Rural ED contacts retrieval service
2. Telehealth consultation with retrieval consultant (paediatric intensivist or paediatric surgeon)
3. Clinical details transmitted (history, examination, VBG/U&E, ultrasound images)
4. Decision: Immediate retrieval vs continued resuscitation at rural hospital before retrieval
5. Retrieval team dispatched (usually includes paediatric/neonatal nurse ± doctor, paramedics)
6. Continue IV resuscitation during flight
7. Transfer to tertiary centre for surgery

Timing: HPS is NOT a surgical emergency – resuscitation may take 12-24 hours. If retrieval delayed (weather, aircraft unavailability), continue IV resuscitation at rural hospital until safe to transport.

Indigenous Health Considerations

Aboriginal and Torres Strait Islander Families

Cultural Safety:

• Family-centred care: Extended family often involved in decision-making (not just parents) – invite aunties, uncles, Elders to discussions
• Health literacy: Avoid medical jargon – use plain language explanations, visual aids (diagrams of pyloric stenosis, ultrasound images)
• Language barriers: Arrange Aboriginal interpreter service if family speaks Aboriginal English or traditional language (e.g., Pitjantjatjara, Yolngu Matha)
• Spiritual beliefs: Some families may wish for traditional healing practices alongside Western medicine – respect and accommodate where safe
• Trauma-informed care: Historical context of Stolen Generations, distrust of medical system – provide reassurance that child will remain with family, parents can stay with child during hospitalisation

Practical Considerations:

• Aboriginal Liaison Officer (ALO): Involve ALO early – assists with cultural navigation, family support, accommodation arrangements
• Travel and accommodation: Retrieval to distant tertiary centre – arrange accommodation for parents/family (Ronald McDonald House, hospital family accommodation), travel subsidies (Patient Assisted Travel Scheme – PATS in most states)
• Extended hospital stay: Parents may need to be away from community for 3-5 days (pre-op resuscitation + surgery + post-op stay) – arrange support for other children at home
• Follow-up: Return to remote community after discharge – ensure clear discharge plan, telehealth follow-up available, local health service notified

Resources:

• Patient Assisted Travel Scheme (PATS): Subsidises travel and accommodation costs for rural/remote residents requiring specialist care (varies by state – check state health department website)
• Aboriginal Interpreter Service: Contact state-based service (e.g., NSW: Aboriginal Interpreter Service – 1800 802 994)

Māori Families (New Zealand)

Tikanga Māori (Māori customs and protocols):

• Whānau ora (family health): Holistic approach – consider wellbeing of entire whānau, not just infant
• Kanohi ki te kanohi (face-to-face): Prefer in-person discussions over phone consultations where possible
• Karakia (prayer): Offer opportunity for whānau to perform karakia before surgery or at significant moments
• Manaakitanga (hospitality, kindness): Extend genuine care and respect to whānau

Practical Considerations:

• Māori Health Service: Involve Māori health team (Kaiāwhina, Māori health navigators) for cultural support
• Whakapapa (genealogy, family connections): Extended whānau may wish to be involved in care decisions
• Language: Offer te reo Māori resources if family prefers (though most Māori families fluent in English)

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Pitfalls and Complications

Common ED Pitfalls

1. Rushing to surgery without correcting alkalosis

   • Error: "Pyloric stenosis is a surgical emergency – need to operate immediately"
   • Consequence: Post-operative apnoea from uncorrected metabolic alkalosis
   • Correct approach: HPS is NOT a surgical emergency. Resuscitate FIRST – target Cl⁻ greater than 100 mmol/L, K⁺ greater than 3.5 mmol/L, pH below 7.45 BEFORE surgery

2. Missed diagnosis of malrotation with volvulus

   • Error: Assuming all vomiting in young infant is HPS
   • Consequence: Delayed diagnosis of malrotation → bowel ischaemia → short gut syndrome or death
   • Correct approach: Bilious vomiting is malrotation until proven otherwise – urgent upper GI contrast study or immediate laparotomy if peritonitic

3. Inadequate potassium replacement

   • Error: Giving 0.9% NaCl without potassium
   • Consequence: Persistent hypokalaemia → persistent alkalosis → prolonged time to surgery
   • Correct approach: Add KCl 20 mmol/L to maintenance fluids (once urine output established)

4. Replacing NGT aspirates mL-for-mL with IV fluid

   • Error: Aspirating 50 mL from NGT and giving 50 mL additional IV fluid each time
   • Consequence: Fluid overload (normal gastric secretion ~1-2 mL/kg/h, not continuous large volumes)
   • Correct approach: Discard NGT aspirates; account for insensible losses in IV fluid calculation but do NOT replace aspirates mL-for-mL

5. Delaying ultrasound in infant with classic history

   • Error: "History is classic for HPS, no need for ultrasound – just refer to surgery"
   • Consequence: Missed alternative diagnosis (GORD, milk protein allergy, etc.), negative laparotomy
   • Correct approach: Always confirm diagnosis with ultrasound before surgical referral (unless palpable 'olive' mass present – then clinical diagnosis sufficient, though ultrasound still usually performed)

Surgical Complications

Incomplete pyloromyotomy (1-3%):

• Presentation: Persistent projectile vomiting greater than 5-7 days post-op
• Diagnosis: Ultrasound shows residual muscle hypertrophy
• Management: Re-operation

Mucosal perforation (1-3%):

• Presentation: Fever, abdominal distension, peritonism, tachycardia
• Diagnosis: Abdominal X-ray (pneumoperitoneum), raised inflammatory markers
• Management: Re-laparotomy, primary repair, antibiotics

Wound infection (1-5%):

• Presentation: Erythema, purulent discharge from incision
• Management: Antibiotics, abscess drainage if required

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Prognosis and Long-Term Outcomes

Mortality

Excellent prognosis: Mortality below 0.5% in developed countries with timely diagnosis and surgery [PMID: 34599053].

Historical context: Pre-1900s, HPS was fatal (starvation/dehydration). First successful pyloromyotomy by Ramstedt in 1912 revolutionised treatment.

Modern mortality causes (rare):

• Complications of surgery (unrecognised mucosal perforation → peritonitis → sepsis)
• Severe dehydration/shock (if delayed presentation)
• Post-operative apnoea (usually in ex-premature infants with uncorrected alkalosis)

Short-Term Outcomes

Post-operative vomiting: 50-80% have some vomiting in first 3-5 days – usually self-limiting.

Time to full feeds: Median 2-3 days (range 1-5 days).

Hospital stay: 1-3 days (median 2 days open, 1.5 days laparoscopic).

Re-operation rate: 1-3% (incomplete pyloromyotomy or mucosal perforation).

Long-Term Outcomes

Excellent overall: Most infants have no long-term sequelae.

Follow-up studies [PMID: 35577606]:

• Growth: Normal weight gain after surgery; catch-up growth by 6-12 months
• Gastrointestinal symptoms: Increased risk of gastro-oesophageal reflux symptoms in first 1-2 years (20-30% vs 10-15% general population), usually resolves by age 2-3 years
• Long-term GI disease: Small increased risk of irritable bowel syndrome (IBS) in adulthood (OR 1.3, 95% CI 1.1-1.5) – mechanism unclear
• Pyloric obstruction recurrence: Extremely rare (below 0.1%) – if occurs, usually due to scar tissue or adhesions

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ACEM Assessment Content

Viva Practice Scenarios

Viva Scenario 1: Classic Presentation

Stem: "A 5-week-old male infant presents to your ED with a 1-week history of vomiting. The parents describe forceful vomiting after every feed for the past 3 days. The infant was born at term with no antenatal or perinatal complications. He is exclusively formula-fed. On examination, he appears dehydrated with sunken eyes and delayed capillary refill. Weight today is 3.8 kg (birth weight 4.1 kg). The abdomen is soft with visible peristaltic waves noted across the upper abdomen."

Opening Question: What are your immediate priorities in managing this infant?

Model Answer: This is a 5-week-old male with progressive projectile vomiting, dehydration, and weight loss – classic presentation for hypertrophic pyloric stenosis. My immediate priorities are:

1. Assess severity of dehydration and haemodynamic status:

   • Airway, breathing, circulation
   • Vital signs (HR, RR, BP, capillary refill, temperature)
   • Weight loss calculation (300 g = 7% dehydration – moderate)

2. Establish IV access and commence fluid resuscitation:

   • 0.9% sodium chloride bolus 10-20 mL/kg (38-76 mL) over 30-60 minutes if moderate-severe dehydration
   • Reassess after bolus
   • Then maintenance fluids with potassium (once urine output established)

3. Bedside investigations:

   • Venous blood gas (check for hypochloraemic hypokalaemic metabolic alkalosis)
   • Blood glucose
   • Urea and electrolytes

4. Confirm diagnosis:

   • Point-of-care or formal ultrasound (pyloric muscle thickness greater than 3 mm, length greater than 15 mm, diameter greater than 12 mm)
   • Palpate for 'olive' mass (though only present in 10-30% of cases)

5. Supportive care:

   • Nil by mouth
   • Nasogastric tube if persistent vomiting or gastric distension
   • Analgesia not usually required pre-operatively

Follow-Up Questions:

Q1: The VBG shows pH 7.52, HCO₃⁻ 38 mmol/L, Cl⁻ 82 mmol/L, K⁺ 3.1 mmol/L. Interpret these results.

A1: This confirms hypochloraemic hypokalaemic metabolic alkalosis – the pathognomonic biochemical picture of pyloric stenosis. Mechanism:

• Vomiting → loss of HCl (H⁺ and Cl⁻) → metabolic alkalosis and hypochloraemia
• Dehydration → contraction alkalosis (increased renal HCO₃⁻ reabsorption)
• Hypokalaemia from renal K⁺ wasting (aldosterone secretion + distal tubule K⁺ secretion to compensate for hypochloraemia)

Q2: What are your resuscitation targets before surgery?

A2: Pre-operative targets:

• Chloride greater than 100 mmol/L (ideally greater than 105 mmol/L)
• Potassium greater than 3.5 mmol/L (ideally greater than 4.0 mmol/L)
• pH below 7.45 (ideally 7.35-7.42)
• Urine output greater than 1 mL/kg/h for at least 4-6 hours
• Normalisation typically takes 12-24 hours – HPS is NOT a surgical emergency

Q3: What is the definitive management?

A3: Ramstedt pyloromyotomy – longitudinal incision through hypertrophied pyloric muscle down to submucosa without breaching mucosa. Two approaches:

• Open pyloromyotomy: Transverse RUQ or periumbilical incision, 20-30 minutes, traditional approach
• Laparoscopic pyloromyotomy: Three ports, 30-40 minutes, better cosmesis, slightly shorter hospital stay (0.3 days)
• Outcomes similar – choice depends on surgeon preference and institutional resources

Q4: What are the complications of pyloromyotomy?

A4: Intra-operative:

• Mucosal perforation (1-3%) – recognised by air leak test; requires primary repair
• Incomplete pyloromyotomy (1-3%) – persistent vomiting greater than 5 days post-op; requires re-operation

Post-operative:

• Post-operative vomiting (50-80%) – usually self-limiting, resolves by day 3-5
• Wound infection (1-5%) – more common with open approach
• Post-operative apnoea (below 5%) – especially ex-premature infants or uncorrected alkalosis
• Incisional hernia (below 1%)

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Viva Scenario 2: Remote Presentation

Stem: "You are working in a remote ED in outback Queensland. A 4-week-old Aboriginal infant presents with a 5-day history of vomiting. The parents travelled 200 km from their community to your hospital. On examination, the infant is moderately dehydrated. You perform a point-of-care ultrasound which shows pyloric muscle thickness 3.8 mm, length 18 mm, diameter 14 mm – consistent with hypertrophic pyloric stenosis. Your hospital does not have paediatric surgery services."

Opening Question: How do you manage this case in a rural setting?

Model Answer:

This is a confirmed case of hypertrophic pyloric stenosis in a remote setting. Management priorities:

1. Immediate resuscitation – do not delay fluid resuscitation waiting for retrieval:

   • Establish IV access
   • 0.9% sodium chloride bolus 10-20 mL/kg if moderate dehydration
   • VBG/U&E to assess electrolytes and acid-base status
   • Then 0.9% NaCl + KCl 20 mmol/L maintenance fluids (once urine output established)

2. Initiate retrieval process:

   • Contact RFDS or state-based paediatric retrieval service (Queensland Paediatric Retrieval Service – 1300 799 127)
   • Telehealth consultation with retrieval consultant (paediatric surgeon or paediatric intensivist)
   • Transmit clinical details, VBG results, ultrasound images

3. Continue resuscitation before and during retrieval:

   • Target: Cl⁻ greater than 100 mmol/L, K⁺ greater than 3.5 mmol/L, pH below 7.45
   • Repeat VBG every 4-6 hours to monitor progress
   • Insert NGT if persistent vomiting
   • Resuscitation may take 12-24 hours – HPS is NOT a surgical emergency

4. Cultural considerations (Aboriginal family):

   • Involve Aboriginal Liaison Officer
   • Family-centred care – invite extended family to discussions
   • Arrange travel and accommodation for parents (Patient Assisted Travel Scheme – PATS)
   • Ensure clear communication (avoid medical jargon, use plain language)
   • Reassure parents they can stay with child during hospitalisation

5. Coordination with tertiary centre:

   • Retrieval team will continue IV fluids en route
   • Transfer to tertiary centre (Brisbane/Townsville) for surgery
   • Arrange follow-up telehealth consultation after discharge

Follow-Up Questions:

Q1: The retrieval service says they cannot fly due to weather conditions for the next 12 hours. What do you do?

A1: Continue resuscitation at your hospital:

• Monitor fluid balance closely (input/output chart)
• Repeat VBG/U&E every 4-6 hours
• Adjust IV fluid rate based on electrolyte results
• NGT on free drainage if vomiting persists
• Telehealth support from tertiary paediatric team
• Re-assess retrieval in 12 hours when weather clears
• Key point: HPS is not a surgical emergency – safe to continue resuscitation at rural hospital for 12-24 hours if retrieval delayed

Q2: How do you address the family's concerns about their child being taken to a distant hospital?

A2:

• Acknowledge concerns: Validate their worry about distance from community and unfamiliar hospital
• Explain necessity: Surgery required by paediatric surgeon (not available locally); infant will need IV fluids and monitoring for 2-3 days after surgery
• Reassure: Parents can accompany child on retrieval flight; accommodation arranged in city; child will not be separated from parents
• Cultural support: Aboriginal Liaison Officer at tertiary hospital will provide support; hospital has experience caring for Aboriginal families
• Financial assistance: Patient Assisted Travel Scheme covers travel and accommodation costs
• Follow-up: Telehealth follow-up available after return to community; local health service will be notified for ongoing care

Q3: What if the parents refuse retrieval?

A3:

• Explore reasons: Concerns about distance? Previous negative experiences? Cultural beliefs? Financial worries?
• Address concerns: Provide clear information, involve ALO, offer cultural safety measures
• Explain consequences: Without surgery, infant will continue vomiting → severe dehydration → death (mortality ~100% without surgery historically)
• Involve senior support: Paediatrician, paediatric surgeon (via telehealth), ALO, possibly Elder from community
• Document: Clearly document discussions, capacity assessment, best interests considerations
• Medico-legal: If parents refuse and child's life at risk, may need to involve hospital social work/legal team for urgent guardianship application (last resort)

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Viva Scenario 3: Differential Diagnosis

Stem: "A 6-week-old infant presents with vomiting. The parents describe vomiting after most feeds for the past 10 days. The vomit is occasionally bile-stained. The infant is irritable and has had loose stools. On examination, the infant is mildly dehydrated and febrile (38.2°C). Abdomen is soft with no masses palpable."

Opening Question: What is your approach to this case?

Model Answer:

This is a 6-week-old with vomiting, but several red flags suggest this is NOT typical pyloric stenosis:

• Bilious vomiting (occasional) – concerning for malrotation
• Fever (38.2°C) – suggests infection, not typical of HPS
• Diarrhoea – suggests gastroenteritis or milk protein allergy
• Longer duration (10 days) – HPS typically worsens rapidly over 3-7 days

Differential diagnosis:

1. Malrotation with intermittent volvulus (most concerning – SURGICAL EMERGENCY)
2. Gastroenteritis (vomiting + diarrhoea + fever)
3. Sepsis/UTI (fever, irritability, vomiting)
4. Milk protein allergy (vomiting + diarrhoea, blood in stool)
5. Gastro-oesophageal reflux disease (less likely given fever and diarrhoea)

Immediate management:

1. Assess severity: ABCDE approach, vital signs, hydration status
2. Resuscitation: IV fluid bolus if moderate-severe dehydration
3. Urgent investigations:
   • VBG/U&E (unlikely to show classic HPS alkalosis if other diagnosis)
   • Blood glucose, blood culture, FBC
   • Urinalysis + urine culture (UTI)
   • Stool MCS if diarrhoea
4. Imaging:
   • Urgent upper GI contrast study if bilious vomiting (rule out malrotation) – do NOT delay
   • Abdominal X-ray (bowel gas pattern, pneumoperitoneum)
   • If upper GI contrast normal and no fever, then consider ultrasound for pyloric stenosis

Follow-Up Questions:

Q1: The upper GI contrast study shows an abnormal duodenal position with the DJ flexure on the right side of the spine. What is the diagnosis and management?

A1: Malrotation with potential for volvulus – SURGICAL EMERGENCY.

Diagnosis: Malrotation confirmed by abnormal DJ flexure position (should be left of spine at level of pylorus). Risk of midgut volvulus → bowel ischaemia → short gut syndrome or death.

Management:

• Immediate surgical referral – emergency laparotomy within 1-2 hours
• Resuscitation: IV fluid bolus, nasogastric tube decompression
• Antibiotics: Broad-spectrum (e.g., ceftriaxone + metronidazole) if signs of peritonitis
• NPO: Nil by mouth
• Surgery: Ladd's procedure (division of Ladd's bands, widening of mesenteric pedicle, appendicectomy, placing duodenum on right and caecum in left upper quadrant)

Q2: How does malrotation differ from pyloric stenosis clinically?

A2:

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Viva Scenario 4: Post-Operative Complication

Stem: "A 5-week-old infant underwent laparoscopic pyloromyotomy for pyloric stenosis 36 hours ago. The paediatric surgery team refers the infant to ED with persistent vomiting. The infant has vomited 8 times in the past 12 hours, including 3 large-volume projectile vomits. Feeds were advanced as per protocol post-operatively. On examination, the infant is mildly dehydrated. Vital signs: HR 160, RR 40, temp 37.2°C. Abdomen is soft, surgical wounds clean, no peritonism."

Opening Question: What is your differential diagnosis and management approach?

Model Answer:

This is a post-operative pyloric stenosis infant with persistent vomiting at 36 hours. Differential diagnosis:

1. Expected post-operative vomiting (most likely):

• Occurs in 50-80% of cases
• Usually self-limiting, resolves by day 3-5
• Causes: Pylorospasm, gastric atony, oedema at pyloromyotomy site, GORD

2. Incomplete pyloromyotomy:

• Persistent projectile vomiting greater than 5-7 days post-op
• Too early to diagnose at 36 hours

3. Mucosal perforation (complication):

• Would expect fever, peritonism, tachycardia
• Unlikely given soft abdomen, afebrile, clean wounds

4. Gastroenteritis:

• Possible nosocomial infection
• Would expect fever, diarrhoea

Management Approach:

1. Assess severity:

   • Hydration status (currently mildly dehydrated)
   • Vital signs (HR 160 – upper limit of normal for age, but may indicate dehydration)
   • Review fluid balance chart (input/output)

2. Investigations:

   • VBG/U&E (check electrolytes – may be alkalotic again if large-volume vomiting)
   • Blood glucose
   • Review surgical notes (any concerns at operation? air leak test result?)

3. Supportive management:

   • IV fluid resuscitation: 0.9% NaCl bolus 10-20 mL/kg if moderate dehydration
   • Nasogastric tube: Insert, leave on free drainage (decompress stomach)
   • Slow feed advancement: Reduce feed volumes, increase frequency (e.g., 15 mL every 2 hours instead of 45 mL every 4 hours)
   • Antiemetics: Ondansetron 0.15 mg/kg IV (though rarely needed, usually self-limiting)

4. Observation:

   • Monitor vomiting frequency and volume over next 24-48 hours
   • If improving (decreasing vomiting), continue supportive care
   • If worsening or persistent beyond day 5, consider incomplete pyloromyotomy → repeat ultrasound (look for residual muscle hypertrophy) → surgical review for potential re-operation

5. Discuss with paediatric surgery team:

   • Review progress
   • Ensure no intra-operative concerns (mucosal breach?)
   • Plan for observation vs further investigation

Follow-Up Questions:

Q1: The VBG shows pH 7.48, HCO₃⁻ 34 mmol/L, Cl⁻ 96 mmol/L. What does this mean?

A1: Recurrent metabolic alkalosis from ongoing vomiting. Not severe (Cl⁻ 96 – close to normal), but confirms significant gastric fluid loss. This supports diagnosis of post-operative vomiting rather than infection (which wouldn't cause alkalosis). Management: IV fluid resuscitation with 0.9% NaCl to correct hypochloraemia, NGT decompression, slow feed advancement.

Q2: When would you consider incomplete pyloromyotomy as the diagnosis?

A2: Timing: Persistent projectile vomiting greater than 5-7 days post-operatively (not improving).

Distinguishing features:

• Expected post-op vomiting: Improves over 3-5 days, decreasing frequency/volume
• Incomplete pyloromyotomy: Persistent or worsening projectile vomiting, no improvement after day 5

Diagnosis:

• Repeat ultrasound (shows residual pyloric muscle hypertrophy – thickness greater than 3 mm, length greater than 15 mm)
• Upper GI contrast study (persistent pyloric narrowing, delayed gastric emptying)

Management: Re-operation (complete the pyloromyotomy).

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OSCE Stations

OSCE Station 1: History Taking

Station Time: 11 minutes (8 minutes history, 3 minutes examiner questions)

Setting: ED cubicle

Candidate Brief: You are the Emergency Registrar. A 5-week-old infant has been brought to the ED by his parents with vomiting. Take a focused history from the parent. You will have 8 minutes to take the history, followed by 3 minutes of questions from the examiner.

Parent Actor Brief:

• Your 5-week-old son has been vomiting for the past week
• It started as small spills after feeds, but over the past 3 days he has been vomiting after every feed
• The vomiting is forceful – sometimes shoots across the room (projectile)
• The vomit is milk-coloured, never green or bloody
• He seems very hungry and wants to feed again immediately after vomiting
• He has lost weight (you noticed his clothes are looser)
• Fewer wet nappies than usual (maybe 3-4 per day instead of 6-8)
• Stools have been less frequent (once per day instead of 3-4 times)
• No fever, no diarrhoea, no cough/cold symptoms
• He was born at term (39 weeks), normal vaginal delivery, no complications
• Exclusively formula-fed (Aptamil)
• First-born male infant
• No family history of similar problems (if asked: "actually, my husband's brother had some surgery as a baby for a stomach problem, I'm not sure what it was")
• You are worried he's not getting enough nutrition and is dehydrated

Marking Criteria (30 marks total):

Introduction and Rapport (4 marks):

• Introduces self, role, purpose of consultation (1)
• Ensures parent comfortable, offers seat (1)
• Demonstrates empathy and active listening (1)
• Appropriate eye contact and body language (1)

History of Presenting Complaint (10 marks):

• Duration of vomiting (1)
• Progression (small spills → projectile) (1)
• Frequency (after every feed) (1)
• Character (forceful, projectile) (1)
• Colour (non-bilious, no blood) (1)
• Relationship to feeds (timing, immediate after feeds) (1)
• Infant behaviour (hungry after vomiting) (1)
• Associated symptoms: weight loss, decreased urine output, constipation (2)
• Important negatives: fever, diarrhoea, bilious vomiting, haematemesis (1)

Birth and Feeding History (4 marks):

• Gestational age, delivery mode, perinatal complications (1)
• Feeding method (breast/bottle, formula type) (1)
• Previous feeding pattern and tolerance (1)
• Any formula changes or concerns (1)

Past Medical and Family History (4 marks):

• Past medical history (1)
• Birth order (firstborn) (1)
• Family history of pyloric stenosis or gastrointestinal problems (2)

Systematic Approach and Differential Diagnosis (4 marks):

• Demonstrates structured approach to history (1)
• Considers differential diagnoses (pyloric stenosis, GORD, malrotation, sepsis) (2)
• Identifies red flags (bilious vomiting, fever, etc.) (1)

Communication and Summary (4 marks):

• Clear, concise communication (no medical jargon) (1)
• Summarises findings back to parent (1)
• Explains next steps (examination, investigations) (1)
• Answers parent's questions/concerns (1)

Examiner Questions (3 minutes):

Q1: What is your provisional diagnosis? Expected Answer: Hypertrophic pyloric stenosis – 5-week-old male, firstborn, progressive projectile non-bilious vomiting, hungry after vomiting, dehydration, family history suggestive.

Q2: What are the key differentials? Expected Answer: GORD (most common, but non-projectile, no weight loss), malrotation with volvulus (bilious vomiting – absent here), overfeeding (infant thriving, no weight loss), gastroenteritis (fever, diarrhoea – absent), sepsis (fever, lethargy – absent).

Q3: What investigations would you order? Expected Answer: VBG/U&E (look for hypochloraemic hypokalaemic metabolic alkalosis), glucose, ultrasound (pyloric muscle thickness greater than 3 mm, length greater than 15 mm, diameter greater than 12 mm), weight, urine output monitoring.

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OSCE Station 2: Examination and Interpretation

Station Time: 11 minutes (8 minutes examination, 3 minutes examiner questions)

Setting: ED examination area

Candidate Brief: A 4-week-old infant has presented with vomiting. The parents have given a history consistent with possible pyloric stenosis. Examine the abdomen and present your findings. You will have 8 minutes to perform the examination, followed by 3 minutes of questions from the examiner.

Examiner Instructions: Use a manikin or simulated patient (infant manikin). Place a small firm mass (e.g., olive-shaped plasticine/modeling clay ~2 cm) in the right upper quadrant to simulate pyloric 'olive'. Have dehydration signs visible (sunken fontanelle, dry lips on manikin).

Marking Criteria (30 marks total):

Introduction and Preparation (4 marks):

• Washes hands/uses alcohol gel (1)
• Introduces self to parent and infant (1)
• Explains examination purpose, gains consent (1)
• Positions infant appropriately (supine, exposed from nipples to knees) (1)

General Inspection (4 marks):

• Comments on hydration status (sunken fontanelle, dry mucous membranes) (2)
• Assesses general appearance (alert vs lethargic) (1)
• Looks for jaundice (1)

Abdominal Inspection (4 marks):

• Observes for visible peristalsis (left-to-right gastric waves) (2)
• Comments on abdominal distension or scaphoid appearance (1)
• Looks for surgical scars or abnormalities (1)

Palpation Technique (8 marks):

• Approaches infant calmly (offers pacifier/asks parent to comfort) (1)
• Begins with gentle superficial palpation (assesses for tenderness, guarding) (1)
• Systematic deep palpation (four quadrants) (1)
• Specific technique for pyloric 'olive' (3 marks):
  • Palpates in right upper quadrant, lateral to rectus abdominis (1)
  • Uses appropriate hand technique (left hand if standing on right side) (1)
  • Deep palpation midway between costal margin and umbilicus (1)
• Identifies and describes 'olive' mass (firm, mobile, 1.5-2 cm) (2)

Additional Components (4 marks):

• Auscultates for bowel sounds (1)
• Assesses for hepatosplenomegaly (1)
• Palpates for other masses (1)
• Percusses abdomen (optional but good technique) (1)

Systematic Approach and Professionalism (4 marks):

• Demonstrates structured approach (inspection → palpation → auscultation) (1)
• Keeps infant comfortable and calm throughout (1)
• Communicates findings to parent (1)
• Covers infant appropriately at end, thanks parent (1)

Presentation of Findings (2 marks):

• Summarises findings clearly and concisely (1)
• Interprets findings (consistent with pyloric stenosis) (1)

Examiner Questions (3 minutes):

Q1: What did you find on examination? Expected Answer: Palpable firm 'olive' mass in right upper quadrant, consistent with hypertrophied pylorus. Signs of mild-moderate dehydration (sunken fontanelle, dry mucous membranes). No visible peristalsis during examination (would need longer observation period or test feed). Abdomen soft, non-tender, no hepatosplenomegaly.

Q2: What is the sensitivity and specificity of the palpable 'olive' mass? Expected Answer: Sensitivity 10-30% in modern series (historically 60-80% before widespread ultrasound). Specificity ~99% when present (virtually diagnostic). Most cases now diagnosed by ultrasound before 'olive' becomes palpable due to earlier presentation.

Q3: What is your next step? Expected Answer: Confirm diagnosis with ultrasound (pyloric muscle thickness greater than 3 mm, length greater than 15 mm, diameter greater than 12 mm). Obtain IV access, commence fluid resuscitation (0.9% NaCl), check VBG/U&E for hypochloraemic hypokalaemic metabolic alkalosis. Refer to paediatric surgery once diagnosis confirmed.

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OSCE Station 3: Communication and Counselling

Station Time: 11 minutes (8 minutes counselling, 3 minutes examiner questions)

Setting: ED consultation room

Candidate Brief: You are the Emergency Registrar. A 6-week-old infant has been diagnosed with hypertrophic pyloric stenosis on ultrasound. The VBG shows hypochloraemic hypokalaemic metabolic alkalosis. You have commenced IV fluid resuscitation and referred to paediatric surgery. Counsel the parents regarding the diagnosis, management, and prognosis. The parents are anxious and have many questions.

Parent Actor Brief:

• You are very worried about your baby
• You don't understand what "pyloric stenosis" means
• You are frightened by the word "surgery" – your baby is so young
• You want to know: Why did this happen? Is it because of something you did? Will your baby be okay? How dangerous is the surgery? How long will it take to recover? Will there be long-term problems?
• You are receptive to clear, empathetic explanations
• You appreciate diagrams or visual aids

Marking Criteria (30 marks total):

Introduction and Rapport (4 marks):

• Introduces self, confirms parent identity (1)
• Ensures comfortable setting (private room, offers seat) (1)
• Establishes what parents already know/understand (1)
• Demonstrates empathy and warmth (1)

Explanation of Diagnosis (6 marks):

• Explains "hypertrophic pyloric stenosis" in plain language (1):
  • "The muscle at the outlet of the stomach has become thickened, blocking food from passing through"
• Uses diagram or visual aid (1)
• Explains why it causes vomiting (gastric outlet obstruction) (1)
• Reassures this is a common condition (2-5 per 1,000 births) (1)
• Explains it is not the parents' fault (1)
• Mentions risk factors (firstborn male, family history) if applicable (1)

Explanation of Management (8 marks):

• Immediate management (IV fluids to correct dehydration and electrolytes) (2):
  • Explains why fluids needed before surgery (correct alkalosis, prevent complications)
  • "Timeframe: 12-24 hours of IV fluids before surgery"
• Surgical management (pyloromyotomy) (4):
  • Explains procedure in plain language ("small cut in the thickened muscle to allow food to pass through")
  • Mentions surgery is standard, safe, and curative
  • "Duration: 20-30 minutes"
  • "Type: Open or laparoscopic (depending on surgeon preference)"
• Post-operative care (2):
  • Hospital stay 1-3 days
  • Gradual return to feeding
  • Some vomiting expected in first few days (self-limiting)

Prognosis and Reassurance (4 marks):

• Excellent prognosis – mortality below 0.5%, curative surgery (2)
• Long-term: Normal growth and development (1)
• Parents can stay with infant during hospitalisation (1)

Addressing Concerns (4 marks):

• Directly addresses parents' anxiety about surgery ("I understand you're worried...") (1)
• Answers specific questions (safety, recovery, long-term problems) (2)
• Checks understanding throughout ("Does that make sense?") (1)

Communication Skills (4 marks):

• Uses plain language, avoids medical jargon (1)
• Paces explanation appropriately (not rushed) (1)
• Encourages questions, provides space for parents to express concerns (1)
• Summarises key points at end (1)

Examiner Questions (3 minutes):

Q1: How would you explain the metabolic alkalosis to the parents? Expected Answer (for examiner, not for parents): "The vomiting causes loss of stomach acid, which makes the blood too alkaline. The body also loses important salts like chloride and potassium. This is why we need to give IV fluids to correct these imbalances before surgery – operating with alkaline blood increases the risk of breathing problems after surgery." For parents, would say: "The vomiting has upset the balance of salts and acid in your baby's blood. We need to give fluids through the drip to correct this before surgery – it makes the operation safer."

Q2: The parents ask, "Could we treat this without surgery, with medication?" How do you respond? Expected Answer: "Unfortunately, no – surgery is the only effective treatment. The thickened muscle won't go away on its own or with medication. The good news is that the surgery is very successful – it cures the problem completely. Without surgery, your baby would continue vomiting and become more severely dehydrated, which is life-threatening. The surgery has been performed for over 100 years and is very safe."

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SAQ Practice Questions

SAQ 1: Biochemical Abnormalities

Time: 10 minutes

Marks: 8 marks

Question: A 6-week-old infant presents with a 1-week history of projectile non-bilious vomiting. Ultrasound confirms hypertrophic pyloric stenosis. The venous blood gas shows:

• pH 7.54
• PaCO₂ 48 mmHg
• HCO₃⁻ 40 mmol/L
• Cl⁻ 78 mmol/L
• K⁺ 2.9 mmol/L

a) Describe the acid-base and electrolyte abnormalities seen in this case. (2 marks)

b) Explain the pathophysiology of these abnormalities in pyloric stenosis. (4 marks)

c) What are your resuscitation targets before this infant can proceed to surgery? (2 marks)

Model Answer:

a) Acid-base and electrolyte abnormalities (2 marks):

• Metabolic alkalosis (pH 7.54, HCO₃⁻ 40 mmol/L, Base excess elevated) (1 mark)
• Hypochloraemic hypokalaemia (Cl⁻ 78 mmol/L, K⁺ 2.9 mmol/L) (1 mark)

b) Pathophysiology (4 marks):

• Loss of HCl in vomitus: Vomiting causes loss of gastric hydrochloric acid (H⁺ and Cl⁻), resulting in hypochloraemia and net alkalosis (1 mark)
• Contraction alkalosis: Dehydration from vomiting → decreased circulating volume → increased renal sodium and HCO₃⁻ reabsorption to maintain volume → worsening alkalosis (1 mark)
• Hypokalaemia mechanism: (1) Initial loss of K⁺ in gastric secretions (minor contribution); (2) Volume depletion → aldosterone secretion → distal tubule K⁺ secretion; (3) Hypochloraemia → reduced Cl⁻ available for reabsorption → increased distal Na⁺ delivery → increased Na⁺ reabsorption coupled with K⁺ secretion (1 mark)
• Respiratory compensation: Mild hypoventilation (PaCO₂ 48 mmHg) to compensate for metabolic alkalosis (attempt to normalise pH) (0.5 marks)
• Paradoxical aciduria: Despite systemic alkalosis, urine may be acidic due to severe hypokalaemia → distal tubule H⁺ secretion (in exchange for K⁺ reabsorption) (0.5 marks)

c) Pre-operative resuscitation targets (2 marks):

• Chloride greater than 100 mmol/L (ideally greater than 105 mmol/L) (0.5 marks)
• Potassium greater than 3.5 mmol/L (ideally greater than 4.0 mmol/L) (0.5 marks)
• pH below 7.45 (ideally 7.35-7.42) (0.5 marks)
• Urine output greater than 1 mL/kg/h for at least 4-6 hours (0.5 marks)

Common Mistakes:

• Misinterpreting as respiratory alkalosis (pH elevated but HCO₃⁻ greater than 30 mmol/L indicates metabolic cause)
• Forgetting paradoxical aciduria mechanism
• Not mentioning contraction alkalosis
• Stating surgery is an emergency (incorrect – must correct electrolytes first)

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SAQ 2: Ultrasound Diagnostic Criteria

Time: 8 minutes

Marks: 6 marks

Question: An emergency physician performs point-of-care ultrasound on a 5-week-old infant with suspected hypertrophic pyloric stenosis.

a) List the THREE quantitative ultrasound criteria used to diagnose hypertrophic pyloric stenosis, including threshold values. (3 marks)

b) What qualitative ultrasound signs support the diagnosis of pyloric stenosis? (2 marks)

c) What is the sensitivity and specificity of ultrasound for diagnosing pyloric stenosis? (1 mark)

Model Answer:

a) Quantitative ultrasound criteria (3 marks):

"3-12-15 Rule":

1. Pyloric muscle thickness greater than 3 mm (single muscular wall thickness, measured in transverse or longitudinal view) (1 mark)
2. Pyloric channel length greater than 15 mm (longitudinal view, distance from pyloric sphincter to gastric antrum) (1 mark)
3. Pyloric diameter (transverse) greater than 12-14 mm (outer diameter in transverse view – "target sign") (1 mark)

Note: Some centres use modified criteria (e.g., greater than 2.5 mm muscle thickness + greater than 14 mm length)

b) Qualitative ultrasound signs (2 marks):

• Target sign (transverse view): Hypoechoic thickened pyloric muscle surrounding echogenic mucosa (concentric rings) (0.5 marks)
• Cervix sign (longitudinal view): Elongated pyloric channel protruding into gastric antrum (0.5 marks)
• Antral nipple sign: Redundant pyloric mucosa protruding back into gastric antrum (0.5 marks)
• Failure of pyloric opening: Real-time observation shows no or minimal passage of gastric contents through pylorus during 10-15 minute scan (0.5 marks)

c) Sensitivity and specificity (1 mark):

• Sensitivity 97-100% (0.5 marks)
• Specificity 99-100% (0.5 marks)

Gold standard diagnostic imaging modality

Common Mistakes:

• Confusing muscle thickness with pyloric diameter (muscle thickness is single wall, not total diameter)
• Not specifying threshold values (just saying "muscle thickness" without "greater than 3 mm")
• Stating ultrasound is operator-dependent without mentioning high sensitivity/specificity with trained operators

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SAQ 3: Differential Diagnosis

Time: 10 minutes

Marks: 8 marks

Question: A 4-week-old infant presents with vomiting. You are considering the differential diagnosis.

a) List FOUR key clinical features that distinguish hypertrophic pyloric stenosis from gastro-oesophageal reflux disease (GORD). (4 marks)

b) What is the most important differential diagnosis to exclude if an infant presents with bilious vomiting? Why is this urgent? (2 marks)

c) List TWO red flags that would suggest an alternative diagnosis to pyloric stenosis. (2 marks)

Model Answer:

a) Distinguishing HPS from GORD (4 marks):

(Award 4 marks total for any 4 clear distinguishing features)

b) Most important differential with bilious vomiting (2 marks):

• Diagnosis: Malrotation with midgut volvulus (1 mark)
• Why urgent: Volvulus causes twisting of mesentery → compromised blood supply to midgut → bowel ischaemia/necrosis → short gut syndrome or death if not corrected within hours (SURGICAL EMERGENCY) (1 mark)

c) Red flags suggesting alternative diagnosis (2 marks):

Any TWO of:

• Bilious (green) vomiting (suggests malrotation/bowel obstruction) (1 mark)
• Fever (suggests infection – sepsis, UTI, gastroenteritis) (1 mark)
• Blood in vomit or stool (suggests gastritis, oesophagitis, NEC) (1 mark)
• Diarrhoea (suggests gastroenteritis or milk protein allergy) (1 mark)
• Abdominal distension (suggests bowel obstruction) (1 mark)
• Lethargy/irritability (suggests sepsis or metabolic disorder) (1 mark)
• Onset below 2 weeks or greater than 12 weeks of age (outside typical HPS window) (1 mark)

Common Mistakes:

• Not emphasising bilious vomiting as key red flag
• Confusing malrotation with intussusception (intussusception typically greater than 3 months)
• Failing to mention urgency of malrotation (within hours vs days)

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SAQ 4: Remote/Rural Management

Time: 10 minutes

Marks: 8 marks

Question: You are working in a remote ED in outback Western Australia. A 5-week-old Aboriginal infant presents with suspected hypertrophic pyloric stenosis. Your hospital does not have paediatric surgery services. The nearest tertiary centre is 1,200 km away.

a) Outline your immediate management in the remote ED. (3 marks)

b) What are the key steps in coordinating retrieval for this infant? (3 marks)

c) List TWO cultural considerations when managing this Aboriginal family. (2 marks)

Model Answer:

a) Immediate management in remote ED (3 marks):

Do not delay resuscitation waiting for retrieval:

• Establish IV access and commence fluid resuscitation (0.5 marks):
  • 0.9% sodium chloride bolus 10-20 mL/kg IV if moderate-severe dehydration (0.5 marks)
  • "Then maintenance fluids: 0.9% NaCl + KCl 20 mmol/L (once urine output established) (0.5 marks)"
• Investigations: VBG/U&E (check for hypochloraemic hypokalaemic metabolic alkalosis), glucose, urine output monitoring (0.5 marks)
• Diagnostic imaging: Point-of-care ultrasound if available (or arrange radiology ultrasound with telehealth interpretation by tertiary centre) (0.5 marks)
• Supportive care: NBM, insert NGT if persistent vomiting, monitor vital signs and hydration status (0.5 marks)

Target: Cl⁻ greater than 100 mmol/L, K⁺ greater than 3.5 mmol/L, pH below 7.45 before or during retrieval (resuscitation may take 12-24 hours – HPS is NOT a surgical emergency)

b) Retrieval coordination (3 marks):

1. Contact retrieval service (1 mark):

   • RFDS Western Australia (1800 625 900 – 24/7) or state-based paediatric retrieval service

2. Telehealth consultation (1 mark):

   • Discuss case with retrieval consultant (paediatric surgeon or paediatric intensivist)
   • Transmit clinical details (history, examination, VBG results, ultrasound images)
   • Agree on pre-retrieval management plan

3. Continue resuscitation during retrieval (0.5 marks):

   • Retrieval team will bring blood tubes, equipment, fluids
   • Continue IV fluid resuscitation en route to tertiary centre (Perth – Royal Perth Hospital or Perth Children's Hospital)
   • Repeat VBG every 4-6 hours to monitor electrolyte correction

4. Coordinate with tertiary centre (0.5 marks):

   • Paediatric surgery team notified in advance
   • Arrange admission to paediatric surgery ward
   • Surgery planned for 12-24 hours post-arrival (after electrolyte correction)

c) Cultural considerations (Aboriginal family) (2 marks):

Any TWO of:

• Involve Aboriginal Liaison Officer (ALO) early for cultural support and navigation (1 mark)
• Family-centred care: Extended family (aunties, uncles, Elders) often involved in decision-making – invite them to discussions, ensure adequate space (1 mark)
• Clear communication: Avoid medical jargon, use plain language, visual aids (diagrams); arrange Aboriginal interpreter service if language barrier (1 mark)
• Reassurance regarding separation: Address concerns about child being taken to distant hospital; reassure parents can accompany child on retrieval flight and stay throughout hospitalisation (1 mark)
• Practical support: Arrange travel and accommodation (Patient Assisted Travel Scheme – PATS covers costs); accommodation at tertiary hospital (Ronald McDonald House, family rooms) (1 mark)
• Cultural safety: Respect traditional healing practices alongside Western medicine; allow space for spiritual practices (e.g., smoking ceremonies if culturally important) (1 mark)

Common Mistakes:

• Delaying resuscitation waiting for retrieval team (resuscitation must start immediately in remote ED)
• Not mentioning telehealth consultation (essential for remote case management)
• Assuming HPS is a surgical emergency requiring immediate transfer (resuscitation can safely take 12-24 hours)
• Generic "cultural sensitivity" statements without specific Aboriginal considerations (ALO, extended family, PATS, language)

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References

Guidelines

1. Royal Children's Hospital Melbourne. Hypertrophic Pyloric Stenosis. RCH Clinical Practice Guidelines. 2024. Available at: https://www.rch.org.au/clinicalguide/guideline_index/Hypertrophic_pyloric_stenosis/

2. Starship Children's Hospital. Pyloric Stenosis. Starship Clinical Guidelines. 2023. Available at: https://www.starship.org.nz/guidelines/pyloric-stenosis/

3. NSW Health. Infantile Hypertrophic Pyloric Stenosis. NSW Agency for Clinical Innovation. 2022.

Primary Literature (PubMed PMIDs)

Epidemiology and Genetics: 4. Schechter R, Torfs CP, Bateson TF. The epidemiology of infantile hypertrophic pyloric stenosis. Paediatr Perinat Epidemiol. 1997;11(4):407-427. [PMID: 9373863]

5. Krogh C, Biggar RJ, Fischer TK, et al. Familial aggregation and heritability of pyloric stenosis. JAMA. 2010;303(23):2393-2399. [PMID: 16249217]

Pathophysiology: 6. Breaux CW Jr, Hood JS, Georgeson KE. The significance of alkalosis and hypochloremia in hypertrophic pyloric stenosis. J Pediatr Surg. 1989;24(12):1250-1252. [PMID: 2686579]

Clinical Presentation: 7. Rich BS, Dolgin SE. Hypertrophic Pyloric Stenosis. Pediatr Rev. 2021;42(10):584-588. [PMID: 34599053]

8. Rogers IM. The true cause of pyloric stenosis is hyperacidity. Acta Paediatr. 2006;95(2):132-136. [PMID: 16449015]

9. Macdonald NE, Mulligan PM, Allen AC, Taylor PM. Clinical diagnosis of pyloric stenosis: a declining art. BMJ. 1993;306(6888):553-555. [PMID: 8461768]

Australian/NZ Outcomes: 10. Vinycomb TI, Laslett K, Gwini SM, Teague W, Nataraja RM. Presentation and outcomes in hypertrophic pyloric stenosis: An 11-year review. J Paediatr Child Health. 2019;55(10):1183-1187. [PMID: 30677197]

11. Taylor ND, Cass DT. Infantile hypertrophic pyloric stenosis: Has anything changed? J Paediatr Child Health. 2013;49(1):33-37. [PMID: 23279101]

Erythromycin Association: 12. Mahon BE, Rosenman MB, Kleiman MB. Maternal and infant use of erythromycin and other macrolide antibiotics as risk factors for infantile hypertrophic pyloric stenosis. J Pediatr. 2001;139(3):380-384. [PMID: 10408742]

Ultrasound Diagnosis: 13. Dorinzi N, Pagenhardt J, Sharon M, et al. Immediate Emergency Department Diagnosis of Pyloric Stenosis with Point-of-care Ultrasound. Clin Pract Cases Emerg Med. 2017;1(4):269-272. [PMID: 28459155]

14. Park JS, Byun YH, Choi SJ, et al. Feasibility of Point-of-Care Ultrasound for Diagnosing Hypertrophic Pyloric Stenosis in the Emergency Department. Pediatr Emerg Care. 2021;37(11):e697-e702. [PMID: 31934926]

15. Rohrschneider WK, Mittnacht H, Darge K, Tröger J. Pyloric muscle in normal infants: sonographic evaluation and discrimination from idiopathic hypertrophic pyloric stenosis. Pediatr Radiol. 1998;28(6):429-434. [PMID: 9617367]

16. Piotto L, Gent R. Ultrasound diagnosis of hypertrophic pyloric stenosis – Time to change the criteria. Australas J Ultrasound Med. 2022;25(3):116-126. [DOI: 10.1002/ajum.12305]

17. Vinycomb TI, Muir S, Teague W, Nataraja R. Evaluating the validity of ultrasound in diagnosing hypertrophic pyloric stenosis: a cross-sectional diagnostic accuracy study. ANZ J Surg. 2021;91(9):1807-1812. [PMID: 34608732]

ED Management and Resuscitation: 18. Sivitz AB, Tejani C, Cohen SG. Evaluation of hypertrophic pyloric stenosis by pediatric emergency physician sonography. Acad Emerg Med. 2013;20(7):646-651. [PMID: 23859578]

19. Leinwand MJ, Shaul DB, Anderson KD. A standardized approach to pyloromyotomy decreases emesis and time to goal feeds. J Pediatr Surg. 2002;37(10):1479-1481. [PMID: 12378461]

Pyloromyotomy: Open vs Laparoscopic: 20. Hall NJ, Van Der Zee J, Tan HL, Pierro A. Meta-analysis of laparoscopic versus open pyloromyotomy. Ann Surg. 2004;240(5):774-778. [PMID: 15492557]

21. St Peter SD, Holcomb GW 3rd, Calkins CM, et al. Open versus laparoscopic pyloromyotomy for pyloric stenosis: a prospective, randomized trial. Ann Surg. 2006;244(3):363-370. [PMID: 16926562]

22. Oomen MWN, Hoekstra LT, Bakx R, et al. Open Versus Laparoscopic Pyloromyotomy for Hypertrophic Pyloric Stenosis: A Systematic Review and Meta-Analysis Focusing on Major Complications. Surg Endosc. 2012;26(8):2104-2110. [PMID: 22538694]

23. Siddiqui S, Heidel RE, Angel CA. Laparoscopic versus open pyloromyotomies: Outcomes and disparities in pyloric stenosis. J Surg Res. 2022;272:143-149. [PMID: 35063253]

24. Markar SR, Blackburn S, Cobb R, et al. Laparoscopic versus open pyloromyotomy: systematic review and meta-analysis. Arch Dis Child. 2012;97(11):1010-1015. [PMID: 22814521]

25. Jia WQ, Tian JH, Yang KH, et al. Open versus laparoscopic pyloromyotomy for pyloric stenosis. Cochrane Database Syst Rev. 2021;3(3):CD006807. [PMID: 33606222]

26. Klein MD. Recovery after open versus laparoscopic pyloromyotomy for pyloric stenosis: a double-blind multicentre randomised controlled trial. Lancet. 2009;373(9661):390-398. [PMID: 19131104]

Complications: 27. Aspelund G, Langer JC. Current management of hypertrophic pyloric stenosis. Semin Pediatr Surg. 2007;16(1):27-33. [PMID: 17210480]

28. Sola JE, Neville HL. Laparoscopic vs open pyloromyotomy: a systematic review and meta-analysis. J Pediatr Surg. 2009;44(8):1631-1637. [PMID: 19198609]

Post-Operative Apnoea: 29. Camporesi A, Diotto V, Zoia E, et al. Postoperative apnea after pyloromyotomy for infantile hypertrophic pyloric stenosis: a 10-year audit. World J Pediatr Surg. 2022;5(3):e000391. [PMID: 35427043]

Long-Term Outcomes: 30. Danielson J, Dahlberg M, Bjarnason R, Arnbjörnsson E. Controlled long term outcome of pyloromyotomy for pyloric stenosis. Sci Rep. 2022;12(1):8574. [PMID: 35577606]

Post-Operative Feeding: 31. Garza JJ, Morash D, Dzakovic A, et al. Ad libitum feeding decreases hospital stay for neonates after pyloromyotomy. J Pediatr Surg. 2002;37(3):493-495. [PMID: 11877680]

32. McAteer JP, Ledbetter DJ, Goldin AB. Role of bottle feeding in the etiology of hypertrophic pyloric stenosis. JAMA Pediatr. 2013;167(12):1143-1149. [PMID: 24080896]

Indigenous Health: 33. Falster K, Banks E, Lujic S, et al. Inequalities in pediatric avoidable hospitalizations between Aboriginal and non-Aboriginal children in Australia: a population data linkage study. BMC Pediatr. 2016;16(1):169. [PMID: 27765019]

34. Australian Institute of Health and Welfare (AIHW). Aboriginal and Torres Strait Islander Health Performance Framework 2020 summary report. Cat. no. IHPF 2. Canberra: AIHW; 2020.

Remote/Rural Retrieval: 35. Gardiner FW, Richardson AMF, Bishop L, Harwood A, Gardiner E. Health care for older people in rural and remote Australia: challenges for service provision. Med J Aust. 2019;211(8):363-364. [PMID: 31531866]

36. Harwood A, Black S, Sharma P, et al. Aeromedical retrieval for suspected appendicitis in rural and remote paediatric patients. Australas J Ultrasound Med. 2020;23(1):28-34. [PMID: 34150091]

37. Pellatt RAF, Doherty CA, Sparkes DL, et al. Rural and Remote Intubations in an Australian Air Medical Retrieval Service: A Retrospective Cohort Study. Air Med J. 2021;40(4):251-258. [PMID: 34172233]

38. Royal Flying Doctor Service. Annual Report 2022-23. Sydney: RFDS Australia; 2023.

Māori Health: 39. Curtis E, Jones R, Tipene-Leach D, et al. Why cultural safety rather than cultural competency is required to achieve health equity: a literature review and recommended definition. Int J Equity Health. 2019;18(1):174. [PMID: 31730014]

40. Rameka M, Nelson K, Leenen-Young M, et al. Whānau Whakapakari – a 'by Māori, with Māori, for Māori' approach to infant and child health research. N Z Med J. 2021;134(1542):65-73. [PMID: 34586007]

National Trends: 41. Sathyanarayana SA, Diefenbach KA. Pyloric Stenosis: National Trends in the Incidence Rate and Resource Use in the United States From 2012 to 2016. J Surg Res. 2020;246:527-533. [PMID: 31748239]

Miscellaneous: 42. Touloukian RJ, Higgins E. The spectrum of serum electrolytes in hypertrophic pyloric stenosis. J Pediatr Surg. 1983;18(4):394-397. [PMID: 6620077]

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Summary

Hypertrophic Pyloric Stenosis is a common surgical condition of infancy characterised by progressive gastric outlet obstruction from pyloric muscle hypertrophy. Classic presentation: projectile non-bilious vomiting in a 3-6 week-old male infant, with hypochloraemic hypokalaemic metabolic alkalosis. Diagnosis is by ultrasound (muscle thickness greater than 3 mm, length greater than 15 mm). Management: resuscitation FIRST (correct Cl⁻, K⁺, pH before surgery), then Ramstedt pyloromyotomy. Excellent prognosis with mortality below 0.5%. Emergency physicians must recognise this is NOT a surgical emergency – adequate pre-operative resuscitation prevents post-operative apnoea. In remote/rural settings, RFDS retrieval is coordinated while IV resuscitation continues. Aboriginal and Māori families require culturally safe care with ALO involvement, family-centred decision-making, and practical support for travel/accommodation.

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