Anaesthesia for Pyloric Stenosis

Quick Answer

Infantile hypertrophic pyloric stenosis (IHPS) is a medical emergency requiring correction of hypochloraemic hypokalaemic metabolic alkalosis BEFORE surgery - it is NOT a surgical emergency. Presentation is typically at 2-8 weeks of age with non-bilious projectile vomiting, palpable "olive" mass, and visible peristalsis. The metabolic derangement results from loss of gastric HCl, causing compensatory renal retention of H+ (exchanging for K+ and Na+), paradoxical aciduria, and potential life-threatening alkalosis. Preoperative targets: serum chloride >100 mmol/L, potassium >3.5 mmol/L, bicarbonate <30 mmol/L, urine output >1 mL/kg/hr. Resuscitation uses 0.9% NaCl or 0.45% NaCl with KCl (20-40 mmol/L) over 24-48 hours. Nasogastric tube aspiration is mandatory pre-induction (aspirate in all four quadrants, left lateral and supine positions). Anaesthetic management involves RSI or modified RSI debate - most institutions favour awake NG aspiration followed by preoxygenation and rapid sequence induction with cricoid pressure. Atropine (20 mcg/kg) is commonly given to prevent vagal bradycardia during laryngoscopy and pyloromyotomy. Rocuronium (1.2 mg/kg) or suxamethonium (2 mg/kg) are used. Postoperative care includes early feeding (often within 4-6 hours), multimodal analgesia (paracetamol, local infiltration), and apnoea monitoring for 12-24 hours in high-risk infants. [1-8]

---

Pathophysiology and Presentation

Definition and Epidemiology

Infantile hypertrophic pyloric stenosis (IHPS) is a condition characterised by progressive hypertrophy and hyperplasia of the pyloric muscle, causing gastric outlet obstruction. The circular muscle layer of the pylorus thickens, elongates, and becomes firm, creating a palpable "tumour" or "olive" on abdominal examination. [1,2]

Epidemiological Characteristics:

The condition is more common in Caucasian populations and demonstrates familial clustering, with a 10-20 fold increased risk in offspring of affected parents. Monozygotic twin concordance is approximately 25-40%, suggesting both genetic and environmental factors. [3,4]

Risk Factors

Established Risk Factors:

• Male sex (4-5 times higher risk)
• Firstborn status
• Family history (especially affected mother)
• Caucasian ethnicity
• Macrolide antibiotic exposure (erythromycin) in first 2 weeks of life
• Maternal macrolide use during breastfeeding
• Bottle feeding (protective effect of breastfeeding)

Association with Macrolides: The association between erythromycin exposure and pyloric stenosis is well-established, with a 7-10 fold increased risk when administered in the first two weeks of life. This is particularly relevant as erythromycin was historically used for pertussis prophylaxis. Azithromycin appears to carry lower risk but should still be used with caution. [5,6]

Clinical Presentation

Classic Triad:

1. Non-bilious projectile vomiting (may become blood-stained due to gastritis)
2. Visible gastric peristalsis (left to right across upper abdomen)
3. Palpable pyloric "olive" mass (right upper quadrant)

Typical History:

• Onset usually 2-4 weeks of age
• Initially intermittent vomiting, becoming progressively more frequent and forceful
• Vomiting occurs during or shortly after feeds
• Infant remains hungry after vomiting ("hungry vomiter")
• Progressive weight loss or failure to gain weight
• Decreasing wet nappies (dehydration)
• Constipation (reduced stool output)

Physical Examination Findings:

• Dehydration (sunken fontanelle, reduced skin turgor, dry mucous membranes)
• Weight loss from birth weight
• Visible peristaltic waves across upper abdomen (best seen with tangential lighting during feeding)
• Palpable pyloric "olive" in right upper quadrant or epigastrium (sensitivity 60-80%)
• Jaundice in 2-5% (unconjugated hyperbilirubinaemia due to hepatic glucuronyl transferase inhibition)

Clinical Pearl: The diagnosis of pyloric stenosis should be suspected in any infant aged 2-8 weeks presenting with non-bilious projectile vomiting. A palpable olive is pathognomonic but requires a relaxed, non-crying infant and experienced examiner. The classic teaching is to feed the infant during examination to observe peristalsis and palpate the relaxed abdomen. [7,8]

Metabolic Derangement

The hallmark metabolic abnormality is hypochloraemic hypokalaemic metabolic alkalosis, which develops secondary to loss of gastric secretions rich in hydrochloric acid.

Pathogenesis of Metabolic Alkalosis:

Stage 1 - Early Compensation:

• Gastric secretions contain H+, Cl-, K+, and Na+ (H+ and Cl- at 100-150 mmol/L)
• Vomiting causes loss of H+ and Cl- primarily
• Plasma bicarbonate rises as H+ is lost
• Kidneys initially excrete HCO3- with Na+ and K+ to maintain electroneutrality
• Urine is alkaline at this stage

Stage 2 - Volume Depletion:

• Continued vomiting causes ECF volume depletion
• Aldosterone secretion increases (renin-angiotensin-aldosterone system activation)
• Proximal tubule HCO3- reabsorption increases with Na+
• K+ secretion increases in exchange for Na+ reabsorption

Stage 3 - Paradoxical Aciduria:

• Severe hypochloraemia limits Cl- availability for renal exchange
• Profound hypokalaemia develops
• Kidneys must retain Na+ despite alkalosis (volume takes priority)
• H+ is secreted in exchange for Na+ in distal tubule
• Paradoxically acid urine despite systemic alkalosis
• This represents decompensation and severe derangement

Biochemical Abnormalities:

Clinical Pearl: Paradoxical aciduria (acid urine in the presence of systemic alkalosis) indicates severe derangement and is a sign of decompensation. The kidneys are prioritising sodium and water retention over acid-base correction due to severe volume depletion. This patient requires aggressive fluid resuscitation. [9-11]

Consequences of Metabolic Alkalosis for Anaesthesia

Respiratory Compensation:

• Hypoventilation as respiratory compensation for metabolic alkalosis
• Reduced minute ventilation and hypercapnia (PaCO2 may rise to 50-60 mmHg)
• Left shift of oxygen-haemoglobin dissociation curve (reduced tissue oxygen delivery)
• May present with respiratory distress if trying to maintain normal pH

Cardiovascular Effects:

• Hypokalaemia causes arrhythmia risk (U waves, prolonged QT, ventricular ectopy)
• Dehydration reduces circulating volume
• Reduced cardiac reserve in dehydrated infant

Neurological Concerns:

• Alkalosis reduces ionised calcium (increased protein binding)
• Risk of tetany, seizures in severe cases
• Apnoea risk if pH >7.55

Drug Effects:

• Reduced volume of distribution affects drug dosing
• Protein binding changes alter free drug fractions
• Reduced hepatic and renal clearance in dehydrated state [12-14]

---

Diagnosis

Ultrasound Criteria

Abdominal ultrasound is the diagnostic investigation of choice with sensitivity and specificity approaching 100% in experienced hands.

Diagnostic Criteria:

Ultrasound Technique:

• Real-time scanning with high-frequency linear probe (7.5-12 MHz)
• Transverse and longitudinal views of pylorus
• Best performed with small amount of oral fluid to distend antrum
• "Target sign" or "doughnut sign" on transverse view
• "Cervix sign" or "antral nipple sign" on longitudinal view

Differential Diagnosis

Clinical Pearl: Bilious vomiting is NEVER pyloric stenosis. Bilious vomiting in a neonate is malrotation with midgut volvulus until proven otherwise and requires emergency surgical consultation. [15,16]

---

Preoperative Preparation

Key Principle: Medical Emergency, Not Surgical Emergency

CRITICAL CONCEPT: Pyloric stenosis is a MEDICAL emergency requiring fluid and electrolyte correction BEFORE surgery. It is NOT a surgical emergency. Pyloromyotomy is a semi-elective procedure performed only after metabolic normalisation. Mortality in modern series is virtually zero with appropriate preoperative resuscitation, but historical mortality was 25-50% when surgery was performed emergently in dehydrated, alkalotic infants. [1,2,17]

Preoperative Targets

Electrolyte Correction Targets Before Surgery:

Fluid Resuscitation Protocol

Initial Assessment:

• Weigh infant accurately (compare to birth weight)
• Calculate fluid deficit based on clinical assessment and weight loss
• Assess degree of dehydration:
  • Mild (5%): Slightly dry mucous membranes
  • Moderate (5-10%): Sunken fontanelle, reduced skin turgor, reduced urine output
  • Severe (>10%): Marked dehydration signs, lethargy, tachycardia, hypotension

Fluid Resuscitation Protocol:

Phase 1 - Initial Resuscitation (if severely dehydrated):

• 0.9% sodium chloride 10-20 mL/kg bolus over 20-60 minutes
• Repeat if necessary based on clinical response
• Aim: restore circulating volume, urine output

Phase 2 - Deficit Replacement + Maintenance:

• Calculate deficit: % dehydration x body weight (kg) x 1000 = deficit in mL
• Add maintenance fluids (4 mL/kg/hr for first 10 kg)
• Replace deficit over 24-48 hours
• Fluid choice: 0.9% NaCl or 0.45% NaCl with 5% dextrose
• Add KCl 20-40 mmol/L once urine output established

Example Calculation: 3.5 kg infant, estimated 10% dehydrated:

• Deficit = 0.10 x 3.5 x 1000 = 350 mL
• Maintenance = 4 x 3.5 = 14 mL/hr
• Total for 24 hours = 350 + (14 x 24) = 350 + 336 = 686 mL over 24 hours
• Rate approximately 28-30 mL/hr

Monitoring During Resuscitation:

• Serum electrolytes every 6-12 hours initially
• Strict fluid balance (weigh nappies)
• Continuous ECG monitoring if K+ <3.0 mmol/L
• Blood glucose monitoring (risk of hypoglycaemia with fasting)

Timing of Surgery

Surgery should be delayed until:

1. Electrolyte targets achieved (Cl- >100, K+ >3.5, HCO3- <30)
2. Urine output adequate (>1-2 mL/kg/hr)
3. Clinical hydration status satisfactory
4. Typically requires 24-48 hours of resuscitation
5. Surgery can be performed on next available elective list

Clinical Pearl: There is no benefit to operating overnight or emergently. Performing pyloromyotomy on an inadequately resuscitated infant increases anaesthetic risk. The pylorus will not decompress spontaneously - surgery can safely wait 24-48 hours for metabolic correction. [17,18]

---

Nasogastric Tube Aspiration

Importance

Despite adequate fasting, the stomach in pyloric stenosis contains residual gastric contents due to obstruction. Nasogastric tube aspiration is mandatory before induction of anaesthesia to reduce aspiration risk.

Technique

Equipment:

• Appropriately sized nasogastric tube (8-10 Fr for infant)
• 20-50 mL syringe
• Suction apparatus

Procedure:

1. Insert NG tube (confirm position by aspiration of gastric contents, auscultation)
2. Aspirate in supine position
3. Turn infant to left lateral position - aspirate
4. Turn infant to right lateral position - aspirate
5. Return to supine - final aspiration
6. Total aspirate may be 50-200 mL despite prolonged fasting
7. Leave NG tube in situ for induction (can aspirate again before RSI)

Awake vs Anaesthetised:

• Traditionally, NG aspiration performed awake
• Some institutions perform gentle aspiration under anaesthesia after RSI
• Awake aspiration preferred as allows more thorough emptying

Clinical Pearl: Four-quadrant aspiration is essential. Simply aspirating with the infant supine will not empty the stomach adequately as gastric contents pool in dependent areas. The "olive" creates a one-way valve preventing passive emptying. [19,20]

---

Anaesthetic Management

NOT an Emergency - Must Be Medically Optimised

Pre-anaesthesia Checklist:

• Electrolytes corrected (Cl- >100, K+ >3.5, HCO3- <30)
• Adequate hydration (urine output >1-2 mL/kg/hr)
• NG tube in situ and aspirated in all quadrants
• Appropriate monitoring available
• Temperature management (warming mattress, fluid warmer)
• Appropriately sized equipment selected
• Atropine drawn up (20 mcg/kg)
• Difficult airway equipment available

Preoperative Assessment

History:

• Duration and severity of vomiting
• Recent electrolyte results and trends
• Current hydration status
• Urine output in last 6-12 hours
• Birth history (gestational age, birth weight)
• Corrected gestational age (for ex-preterm infants)
• Any associated conditions

Examination:

• Weight (compare to birth weight)
• Hydration status
• Respiratory examination (baseline SpO2, respiratory rate)
• Cardiovascular examination (heart rate, perfusion)
• Airway assessment (though rarely abnormal)
• IV access (already established for resuscitation)

Monitoring

Standard Monitoring:

• Pulse oximetry (pre-ductal if <28 days)
• ECG (continuous)
• Non-invasive blood pressure
• End-tidal CO2
• Temperature (continuous)
• Inspired and expired oxygen concentrations

RSI vs Modified RSI Debate

This is a classic examination topic with ongoing debate regarding optimal induction technique.

Arguments for Classical RSI (with cricoid pressure):

Arguments Against Classical RSI / For Modified RSI:

Institutional Variation: Different institutions and anaesthetists have different approaches. The key is a systematic approach with:

1. Thorough NG aspiration
2. Adequate preoxygenation
3. Rapid induction with appropriate doses
4. Immediate securing of airway
5. Cricoid pressure applied (even if effectiveness debated)

Induction Technique

Standard Approach:

1. Preparation:

• Check equipment (ETT 3.0-3.5 uncuffed or 3.0 cuffed, laryngoscope, suction)
• Drugs drawn up: Atropine, induction agent, muscle relaxant
• Warming measures active
• NG tube aspirated in all quadrants

2. Preoxygenation:

• Apply oxygen via face mask
• 3 minutes tidal breathing or 4-8 vital capacity breaths
• Target FEO2 >0.85 (if monitoring available)
• Avoid positive pressure (stomach distension)

3. Atropine:

• 20 mcg/kg IV (some give IM if no IV access during gas induction)
• Given to prevent vagal bradycardia during:
  • Laryngoscopy
  • Pyloromyotomy (vagal manipulation)
  • Traction on stomach
• Controversial whether routine or only if bradycardia occurs

4. Induction:

• Propofol 3-4 mg/kg IV, OR
• Thiopentone 4-6 mg/kg IV, OR
• Sevoflurane induction (if no IV access - less ideal due to slower onset)

5. Cricoid Pressure:

• Apply immediately after loss of consciousness
• Maintain until ETT cuff inflated (or placement confirmed for uncuffed)
• Pressure approximately 10 N initially, increase to 30 N after paralysis

6. Muscle Relaxation:

• Rocuronium 1.0-1.2 mg/kg (RSI dose), OR
• Suxamethonium 2 mg/kg (traditional, but less favoured now)
• Wait 30-45 seconds (rocuronium) or 45-60 seconds (suxamethonium)

7. Intubation:

• Gentle laryngoscopy (Miller blade 1 preferred)
• Confirm tube position (bilateral air entry, ETCO2)
• Secure ETT

8. NG Tube:

• Re-aspirate NG after intubation
• Leave in situ or remove as per preference

Drug Dosing in Dehydrated Infant

Dehydration significantly affects drug pharmacokinetics:

Volume of Distribution (Vd):

• Vd reduced in dehydration
• Higher initial plasma concentrations for same dose
• Consider reducing induction agent dose by 20-30%

Protein Binding:

• Dehydration concentrates plasma proteins initially
• Later, albumin synthesis may be reduced
• Free drug fraction may be variable

Clearance:

• Reduced hepatic blood flow reduces clearance
• Reduced renal perfusion affects elimination

Practical Approach:

• Use lower end of dose range for induction agents
• Titrate to effect where possible
• Muscle relaxant doses unchanged (receptor blockade)

Clinical Pearl: A pale, tachycardic, dehydrated infant with a sunken fontanelle has a significantly reduced circulating volume. Standard induction doses may cause profound hypotension. Titrate induction agents carefully and have vasopressors immediately available. [21-24]

---

Intraoperative Considerations

Surgical Procedure: Ramstedt Pyloromyotomy

Approaches:

1. Open (traditional) - Right upper quadrant transverse incision or periumbilical
2. Laparoscopic - Increasingly common, similar outcomes, potentially reduced wound complications

Operative Steps:

1. Delivery of pylorus through incision
2. Incision along avascular line of pyloric serosa
3. Blunt spreading of hypertrophied muscle fibres
4. Separation of muscle down to mucosa (bulging mucosa indicates complete myotomy)
5. Check for mucosal perforation (air test)
6. Closure

Duration: 20-45 minutes typically

Anaesthetic Maintenance

Volatile Anaesthesia:

• Sevoflurane 2-3% in oxygen/air mixture
• Maintain normocapnia (ETCO2 35-45 mmHg)
• Avoid hyperventilation (worsens alkalosis if still present)

Opioid Analgesia:

• Minimal opioid often required
• Fentanyl 1-2 mcg/kg if needed for surgical stimulus
• Consider opioid-sparing given apnoea risk

Fluid Management:

• Maintenance fluids: balanced crystalloid or 0.9% NaCl with glucose
• 10 mL/kg/hr during surgery
• Replace blood loss mL for mL
• Blood loss usually minimal (<5 mL)

Temperature:

• Active warming essential (warming mattress, fluid warmer, theatre temperature >24 degrees C)
• Infants lose heat rapidly (high surface area:volume ratio)
• Hypothermia delays emergence, increases apnoea risk

Intraoperative Complications

Vagal Bradycardia:

• Occurs during pyloromyotomy (vagal afferents from stomach)
• More common during pylorus delivery
• Treatment: atropine if pre-emptive dose not given, surgical pause
• Usually resolves when stimulus removed

Duodenal Perforation:

• Occurs in 1-4% of cases
• Identified by air leak during intraoperative air test
• Requires primary repair
• May extend operative time
• Postoperative NG drainage, delayed feeding

Hypotension:

• Inadequate fluid resuscitation preoperatively
• Excessive depth of anaesthesia
• Blood loss (unusual)
• Treatment: fluid bolus, reduce volatile, vasopressor if needed

---

Postoperative Care

Immediate Recovery

Emergence and Extubation:

• Allow spontaneous ventilation to return
• Extubate awake with protective reflexes present
• Suction oropharynx gently before extubation
• Lateral recovery position
• Supplemental oxygen initially

Monitoring in Recovery:

• Continuous SpO2
• Apnoea monitoring (especially ex-preterm infants)
• Temperature
• Blood glucose monitoring

Feeding

Early Feeding Protocol:

• Most institutions now commence feeding within 4-6 hours
• Ad libitum feeding protocols show faster time to full feeds
• Traditional "graded feeding" regimens (start with small volumes, increase gradually) no longer recommended
• Vomiting in first 24-48 hours is common (up to 80%) and usually self-limiting
• No correlation between early vomiting and inadequate myotomy

Typical Protocol:

• 4-6 hours post-surgery: offer small feed (20-30 mL)
• If tolerated: ad libitum breastfeeding or formula
• Most infants on full feeds within 24 hours
• Discharge when tolerating feeds and parents confident

Analgesia

Multimodal Approach:

• Paracetamol 15 mg/kg IV/PR then 15 mg/kg 6-hourly (max 60 mg/kg/day)
• Local anaesthetic wound infiltration (bupivacaine 0.25% 0.5-1 mL/kg by surgeon)
• Rectus sheath block (ultrasound-guided)
• Minimal/no opioid usually required

Regional Anaesthesia Options:

• Wound infiltration by surgeon (most common)
• Ultrasound-guided rectus sheath block (bilateral for midline incision)
• Transversus abdominis plane (TAP) block (for laparoscopic port sites)

Apnoea Risk

High-Risk Groups:

• Ex-preterm infants (post-conceptional age <60 weeks)
• Infants <44 weeks post-conceptional age
• History of apnoea of prematurity
• Metabolic derangement not fully corrected
• Opioid administration

Apnoea Monitoring:

• Continuous SpO2 and apnoea monitoring for 12-24 hours
• Admission to high-dependency or special care nursery if high-risk
• Some institutions monitor all pyloric stenosis infants for 12 hours
• Caffeine citrate (10-20 mg/kg loading dose) may be considered in ex-preterm infants

Discharge Criteria

• Tolerating full oral feeds
• No significant vomiting (occasional vomiting acceptable)
• Adequate urine output
• Afebrile
• Parents comfortable with care
• Typically 24-48 hours postoperatively

---

Regional Anaesthesia for Pyloric Stenosis

Wound Infiltration

Technique:

• Performed by surgeon at wound closure
• Bupivacaine 0.25% or ropivacaine 0.2%
• Dose: 0.5-1 mL/kg
• Infiltrate subcutaneous tissue and rectus sheath

Efficacy:

• Provides 4-8 hours of analgesia
• Reduces opioid requirements
• Simple, low risk

Rectus Sheath Block

Indications:

• Open pyloromyotomy via midline or paramedian incision
• Provides sensory block to anterior abdominal wall

Technique:

• Ultrasound-guided (high-frequency linear probe)
• Identify rectus abdominis muscle and posterior sheath
• Deposit local anaesthetic between rectus muscle and posterior sheath
• Bilateral blocks for midline incision

Dosing:

• Bupivacaine 0.25%: 0.1 mL/kg each side (0.2 mL/kg total)
• Ropivacaine 0.2%: 0.1-0.15 mL/kg each side

Evidence:

• Reduces pain scores compared to wound infiltration alone
• Reduces rescue analgesia requirements
• Safe and effective in experienced hands [25,26]

TAP Block (Laparoscopic)

Indications:

• Laparoscopic pyloromyotomy (port site analgesia)

Technique:

• Ultrasound-guided TAP block
• Deposit in plane between internal oblique and transversus abdominis
• Cover port site locations

---

ANZCA Exam Focus

Classic Examination Topic

Pyloric stenosis is a perennial favourite for ANZCA Final examination as it combines:

• Paediatric physiology and pharmacology
• Metabolic derangement and correction
• Airway management decisions (RSI debate)
• Perioperative risk assessment
• Practical clinical decision-making

Common SAQ Patterns

Metabolic Questions:

• "Describe the metabolic derangement in pyloric stenosis and explain its pathophysiology."
• "What are your targets for metabolic correction before pyloromyotomy?"
• "Explain paradoxical aciduria in pyloric stenosis."

Anaesthetic Management Questions:

• "Describe your anaesthetic management for pyloromyotomy."
• "Discuss the arguments for and against rapid sequence induction in pyloric stenosis."
• "What preoperative preparation is required before pyloromyotomy?"

Pharmacology Questions:

• "How does dehydration affect drug pharmacokinetics in infants?"
• "Justify your choice of induction agent and dose in a dehydrated infant."

Clinical Viva Themes

Scenario Types:

• Preoperative assessment of infant with pyloric stenosis
• Inadequately resuscitated infant presented for surgery (should you proceed?)
• Intraoperative complications (bradycardia, hypotension)
• Postoperative apnoea in ex-preterm infant

Examiner Expectations:

• Clear understanding that surgery is NOT emergency
• Knowledge of metabolic targets and correction
• Systematic approach to anaesthetic management
• Understanding of RSI debate and ability to justify approach
• Awareness of postoperative complications

Key Examination Points

1. Medical emergency, not surgical emergency - never proceed without metabolic correction
2. Electrolyte targets: Cl- >100, K+ >3.5, HCO3- <30
3. NG aspiration in all four quadrants before induction
4. RSI debate - know arguments both ways, have defensible approach
5. Atropine for vagal reflex prevention
6. Drug dosing reduced in dehydration
7. Apnoea monitoring especially in ex-preterm infants
8. Early feeding is now standard practice [27-30]

---

Indigenous Health Considerations

Aboriginal and Torres Strait Islander Infants

Aboriginal and Torres Strait Islander infants may present with pyloric stenosis in contexts requiring specific cultural and clinical considerations:

Communication and Family Involvement: Discussions about the diagnosis, need for surgery, and anaesthetic risks should involve extended family members as appropriate to Aboriginal and Torres Strait Islander family structures. Aboriginal Health Workers (AHWs) or Aboriginal Hospital Liaison Officers (AHLOs) should be engaged early, particularly for complex discussions about risks and consent. Visual explanations using diagrams or models may be more effective than lengthy verbal descriptions. The concept of "medical emergency" versus "surgical emergency" should be explained carefully to ensure families understand why surgery is being delayed for fluid resuscitation. [31,32]

Higher Prevalence of Comorbidities: Aboriginal and Torres Strait Islander infants may have higher rates of conditions that can complicate anaesthesia and perioperative care:

• Prematurity and low birth weight (increased apnoea risk postoperatively)
• Respiratory conditions (bronchiolitis, pneumonia more common)
• Failure to thrive or malnutrition (may present more dehydrated)
• Later presentation due to geographic barriers to healthcare access

Remote and Rural Considerations: Many Aboriginal and Torres Strait Islander families live in remote communities where:

• Ultrasound diagnosis may not be available locally (clinical diagnosis may be necessary)
• Transfer to tertiary paediatric centre required (RFDS retrieval)
• Separation from family and Country causes significant distress
• Metabolic correction may need to commence before/during transfer
• Telemedicine consultation with paediatric anaesthetists advisable

Cultural Safety in Paediatric Care:

• Family presence during induction should be facilitated where safe and desired
• Accommodation for family members (especially mother if breastfeeding) essential
• Cultural protocols around infant care should be respected
• If complications occur or infant requires extended care, family support through AHLO critical
• Breastfeeding support and facilities should be provided to maintain milk supply during recovery

Maori Health Considerations (New Zealand)

Whanau Involvement: Maori families typically involve whanau (extended family) in healthcare decisions. Consent discussions should include key family members, and adequate time should be allowed for family consultation. Maori Health Workers can facilitate culturally appropriate communication.

Te Whare Tapa Wha Model: Consider all dimensions of health:

• Taha tinana (physical health) - the pyloric stenosis and anaesthesia
• Taha hinengaro (mental health) - parental anxiety and stress
• Taha whanau (family health) - impact on family, siblings
• Taha wairua (spiritual health) - cultural and spiritual needs

Practical Considerations:

• Karakia (prayer) may be requested before surgery
• Family presence during induction and recovery should be accommodated
• If infant unwell or requires prolonged admission, support from kaumatua (elders) may be requested
• Breastfeeding (important in Maori culture) should be actively supported and maintained [33,34]

---

Assessment Content

SAQ Practice Question (20 marks)

Question:

A 4-week-old male infant (3.8 kg) is referred for pyloromyotomy. He has had projectile vomiting for 5 days. He was born at 34 weeks gestation and is now 38 weeks corrected gestational age. He has a sunken fontanelle and reduced skin turgor.

Investigations show:

• Na+ 132 mmol/L
• K+ 2.8 mmol/L
• Cl- 82 mmol/L
• HCO3- 38 mmol/L
• pH 7.52
• Creatinine 65 μmol/L
• Urine output 0.5 mL/kg/hr

(a) Explain the pathophysiology of this infant's metabolic derangement. (6 marks)

(b) What are your targets for metabolic correction, and outline your fluid resuscitation plan? (6 marks)

(c) The surgical team request you proceed with surgery tonight as they have a busy elective list tomorrow. What is your response and why? (4 marks)

(d) Given this infant's gestational history, what additional postoperative considerations are required? (4 marks)

---

Model Answer:

(a) Pathophysiology of Metabolic Derangement (6 marks)

This infant has hypochloraemic hypokalaemic metabolic alkalosis, the classic metabolic derangement of pyloric stenosis. [1 mark for correct identification]

Mechanism:

1. Loss of gastric secretions [1 mark]

   • Gastric secretions are rich in H+, Cl-, K+, and Na+
   • Projectile vomiting causes selective loss of gastric contents
   • H+ and Cl- lost in excess of Na+ and K+

2. Development of alkalosis [1 mark]

   • Loss of H+ causes extracellular alkalosis
   • For each H+ lost, HCO3- is retained
   • Plasma bicarbonate rises (38 mmol/L in this case)

3. Renal compensation and paradoxical aciduria [2 marks]

   • Initially kidneys excrete HCO3- with Na+ and K+ (alkaline urine)
   • Volume depletion activates renin-angiotensin-aldosterone system
   • Proximal tubule HCO3- reabsorption increases with Na+
   • K+ is secreted in exchange for Na+ (worsening hypokalaemia)
   • Severe hypochloraemia limits Cl- for exchange
   • H+ secreted for Na+ in distal tubule despite alkalosis = paradoxical aciduria

4. Hypokalaemia mechanism [1 mark]

   • Loss of K+ in gastric secretions
   • Renal K+ wasting due to aldosterone and alkalosis
   • Intracellular K+ shift in alkalosis

(b) Correction Targets and Fluid Plan (6 marks)

Targets: [2 marks]

• Serum Cl- >100 mmol/L (currently 82)
• Serum K+ >3.5 mmol/L (currently 2.8)
• Serum HCO3- <30 mmol/L (currently 38)
• pH <7.45 (currently 7.52)
• Urine output >1-2 mL/kg/hr (currently 0.5)
• Correction of dehydration clinically

Fluid Plan: [4 marks]

1. Initial bolus (if haemodynamically unstable):

   • 0.9% NaCl 10-20 mL/kg over 30-60 minutes

2. Deficit + Maintenance:

   • Estimate 10% dehydration: Deficit = 0.10 x 3.8 x 1000 = 380 mL
   • Maintenance = 4 x 3.8 = 15.2 mL/hr
   • Total 24-hour requirement = 380 + (15.2 x 24) = 380 + 365 = 745 mL

3. Fluid choice:

   • 0.9% NaCl OR 0.45% NaCl with 5% dextrose
   • Add KCl 20-40 mmol/L once urine output established
   • Avoid rapid K+ correction (max 0.5 mmol/kg/hr)

4. Monitoring:

   • Electrolytes every 6-12 hours
   • Continuous ECG if K+ <3.0
   • Strict fluid balance
   • Blood glucose monitoring

(c) Response to Request for Emergency Surgery (4 marks)

I would decline to proceed with surgery tonight. [1 mark for clear answer]

Rationale: [3 marks]

1. Medical emergency, not surgical emergency: Pyloric stenosis requires metabolic correction BEFORE surgery. Proceeding with surgery in this metabolically deranged infant increases anaesthetic risk significantly.

2. Current status unacceptable for anaesthesia:

   • K+ 2.8 mmol/L - arrhythmia risk, respiratory muscle weakness
   • Cl- 82 mmol/L - alkalosis cannot be corrected without chloride repletion
   • pH 7.52 - respiratory depression, left-shifted oxygen dissociation curve
   • Dehydration - reduced cardiac reserve, altered drug pharmacokinetics
   • Oliguria - inadequate renal perfusion

3. Evidence supports delay: Historical mortality was 25-50% with emergency surgery on inadequately resuscitated infants. Modern mortality is virtually zero with appropriate preoperative preparation. The pylorus will not decompress spontaneously - surgery can safely wait 24-48 hours.

4. Safe to wait: Pyloromyotomy is semi-elective once diagnosis confirmed. Correct metabolic derangement, then proceed on next available elective list.

(d) Postoperative Considerations for Ex-Preterm Infant (4 marks)

This infant is ex-34 week preterm, currently 38 weeks corrected gestational age, placing him at high risk for postoperative apnoea. [1 mark]

Specific considerations: [3 marks]

1. Apnoea monitoring:

   • Continuous SpO2 and respiratory/apnoea monitoring for minimum 12-24 hours
   • Admission to Special Care Nursery or high-dependency unit
   • Staff trained to recognise and manage apnoea

2. Anaesthetic technique modifications:

   • Minimise opioid use (regional analgesia preferred)
   • Consider caffeine citrate 10-20 mg/kg loading if not already receiving
   • Extubate fully awake with robust protective reflexes

3. Duration of monitoring:

   • Current guidelines suggest monitoring until post-conceptional age >60 weeks for ex-preterm infants
   • At 38 weeks corrected, this infant requires extended observation
   • Document apnoea-free period before discharge

4. Other considerations:

   • Higher incidence of bronchopulmonary dysplasia in ex-preterm infants
   • May have altered respiratory drive and response to hypoxia
   • Ensure normothermia maintained (ex-preterm at higher risk of hypothermia)

Total: 20 marks

---

Viva Scenario (15 marks)

Opening Stem:

You are the anaesthetic registrar on call. A 5-week-old male infant (4.2 kg) is listed for pyloromyotomy. The paediatric surgical registrar requests you review the patient urgently as they want to proceed to theatre in the next hour. The infant was admitted 6 hours ago with a diagnosis of pyloric stenosis confirmed on ultrasound.

---

Expected Viva Progression:

Examiner: What information do you need before making a decision?

Candidate Response: [2 marks]

"I need to assess whether this infant is adequately resuscitated for surgery. Specifically, I need:

1. Current electrolytes: Na+, K+, Cl-, HCO3-, pH, creatinine
2. Electrolyte trends: Have they improved with resuscitation?
3. Clinical hydration status: Fontanelle, skin turgor, mucous membranes
4. Urine output: Ideally >1-2 mL/kg/hr
5. Current fluid regimen: What fluids, at what rate?
6. IV access: Is it adequate?
7. NG tube: Has stomach been aspirated?
8. Past medical history: Prematurity, other conditions

I also need to know why the surgeon feels this is urgent - there is no indication for emergency pyloromyotomy as this is a medical emergency requiring metabolic correction, not a surgical emergency."

---

Examiner: The electrolytes show: Na+ 134, K+ 3.0, Cl- 88, HCO3- 34, pH 7.48, creatinine 55. Urine output has been 0.8 mL/kg/hr. What do you do?

Candidate Response: [3 marks]

"This infant is NOT adequately resuscitated for surgery. My targets are:

• Cl- >100 mmol/L (currently 88)
• K+ >3.5 mmol/L (currently 3.0)
• HCO3- <30 mmol/L (currently 34)
• Urine output >1-2 mL/kg/hr (currently 0.8)

My response:

I would decline to proceed with surgery at this time and explain to the surgical team that:

1. This infant requires further resuscitation - likely another 12-24 hours
2. Proceeding with these electrolytes increases anaesthetic risk
3. The hypokalaemia puts the infant at risk of arrhythmias
4. The ongoing alkalosis affects respiratory drive and drug pharmacokinetics
5. The oliguria suggests inadequate volume resuscitation

I would recommend:

• Continue IV fluids with KCl supplementation
• Repeat electrolytes in 6 hours
• Plan for surgery on tomorrow's elective list
• Ensure NG tube in situ and regular aspirates"

---

Examiner: The surgeon is insistent - they say the baby has been vomiting and is losing weight, and they've always operated on these babies within 12 hours of admission. How do you handle this?

Candidate Response: [2 marks]

"I understand the concern about the infant's condition, but I would respectfully maintain my position. I would:

1. Escalate to consultants - involve my consultant anaesthetist and the paediatric surgical consultant to discuss
2. Explain the evidence - historical mortality was 25-50% with emergency surgery on inadequately resuscitated infants; modern mortality approaches zero with appropriate preparation
3. Emphasise the infant's safety - proceeding with K+ of 3.0 and significant alkalosis puts the infant at avoidable risk
4. Document the discussion - if there is disagreement, this should be documented

The pylorus will not spontaneously resolve - surgery can safely wait for metabolic correction. The risk of vomiting and aspiration while waiting (with appropriate NG drainage) is far lower than the anaesthetic risk of proceeding with this metabolic derangement."

---

Examiner: The consultant agrees to wait. The next day, the electrolytes are: Na+ 138, K+ 3.8, Cl- 102, HCO3- 28. Describe your anaesthetic induction.

Candidate Response: [4 marks]

"The electrolytes are now acceptable for surgery. My induction plan:

Preparation:

• Check all equipment (ETT 3.5 uncuffed or 3.0 cuffed, Miller blade 1, suction)
• Draw up drugs: Atropine 20 mcg/kg (84 mcg), Propofol 3 mg/kg (12.6 mg), Rocuronium 1.2 mg/kg (5 mg)
• Warm theatre, warming mattress on
• NG tube aspirated in all four quadrants (supine, left lateral, right lateral, supine)
• Standard monitoring applied

Induction:

1. Preoxygenation - 3 minutes tidal breathing, 100% O2
2. Atropine 84 mcg IV (to prevent vagal bradycardia)
3. Propofol 10-12 mg IV (starting at lower dose due to previous dehydration)
4. Apply cricoid pressure once unconscious
5. Rocuronium 5 mg IV
6. Wait 45-60 seconds
7. Laryngoscopy - gentle technique, Miller blade
8. Intubate, confirm position with ETCO2 and bilateral air entry
9. Release cricoid once tube placement confirmed
10. Secure tube, re-aspirate NG

Maintenance:

• Sevoflurane in O2/air
• Minimal opioid (fentanyl 1 mcg/kg only if needed)
• Active warming throughout"

---

Examiner: During the pyloromyotomy, the infant develops bradycardia to 70 bpm. What do you do?

Candidate Response: [2 marks]

"This is likely vagal bradycardia from surgical manipulation of the pylorus and stomach.

Immediate actions:

1. Alert the surgeon - request they pause manipulation
2. Check depth of anaesthesia (avoid excessive depth which worsens bradycardia)
3. Check for other causes (hypoxia, hypercapnia)
4. If already given atropine preoperatively, this is likely self-limiting when stimulus removed

If bradycardia persists or worsens:

• Atropine 10-20 mcg/kg IV (if not already given or insufficient effect)
• If hypoxia contributing - ensure adequate oxygenation and ventilation

Once the surgeon pauses manipulation, the heart rate should recover. This is a recognised complication due to vagal afferents from the stomach. Most institutions give atropine prophylactically for this reason."

---

Examiner: The surgery is completed without complication. What are your postoperative plans?

Candidate Response: [2 marks]

"Immediate recovery:

• Extubate fully awake with protective reflexes
• Lateral recovery position
• Supplemental oxygen initially
• Continuous SpO2 monitoring

Analgesia:

• Paracetamol 15 mg/kg IV/PR (63 mg)
• Surgeon to infiltrate wound with local anaesthetic
• Minimal opioid given apnoea risk

Feeding:

• Can commence ad libitum feeds from 4-6 hours post-surgery
• Some vomiting expected - this is normal
• Progress to full feeds as tolerated

Monitoring:

• Apnoea monitoring for 12-24 hours
• Not ex-preterm, so standard monitoring acceptable
• Monitor for wound complications

Discharge:

• Usually 24-48 hours once tolerating feeds
• Parental education regarding feeding and wound care"

---

Total: 15 marks

---

References

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

2. Sola JE, Neville HL. Laparoscopic vs open pyloromyotomy: a systematic review and meta-analysis. J Pediatr Surg. 2009;44(8):1631-1637. PMID: 19635316

3. Krogh C, Fischer TK, Skotte L, et al. Familial aggregation and heritability of pyloric stenosis. JAMA. 2010;303(23):2393-2399. PMID: 20551409

4. Pedersen RN, Garne E, Loane M, et al. Infantile hypertrophic pyloric stenosis: a comparative study of incidence and other epidemiological characteristics in seven European regions. J Matern Fetal Neonatal Med. 2008;21(9):599-604. PMID: 18828051

5. Lund M, Pasternak B, Davidsen RB, et al. Use of macrolides in mother and child and risk of infantile hypertrophic pyloric stenosis: nationwide cohort study. BMJ. 2014;348:g1908. PMID: 24618148

6. Eberly MD, Eide MB, Thompson JL, Nylund CM. Azithromycin in early infancy and pyloric stenosis. Pediatrics. 2015;135(3):483-488. PMID: 25687145

7. Hernanz-Schulman M. Infantile hypertrophic pyloric stenosis. Radiology. 2003;227(2):319-331. PMID: 12637675

8. Costello M, Elbertson M. Infantile hypertrophic pyloric stenosis: epidemiology, etiology and pathophysiology. Neonatal Netw. 2021;40(3):167-175. PMID: 33947738

9. Touloukian RJ, Higgins E. The spectrum of serum electrolytes in hypertrophic pyloric stenosis. J Pediatr Surg. 1983;18(4):394-397. PMID: 6620083

10. Breaux CW Jr, Georgeson KE, Royal SA, Curnow AJ. Changing patterns in the diagnosis of hypertrophic pyloric stenosis. Pediatrics. 1988;81(2):213-217. PMID: 3277085

11. Schwartz MZ. Hypertrophic pyloric stenosis. In: Pediatric Surgery. 7th ed. Elsevier; 2012:1021-1028.

12. Cook-Sather SD, Tulloch HV, Liacouras CA, Schreiner MS. Gastric fluid volume in infants for pyloromyotomy. Can J Anaesth. 1997;44(3):278-283. PMID: 9067047

13. Warner MA, Warner ME, Warner DO, et al. Perioperative pulmonary aspiration in infants and children. Anesthesiology. 1999;90(1):66-71. PMID: 9915314

14. Schmidt AR, Buehler P, Seglias L, et al. Gastric pH and residual volume after 1 and 2 h fasting time for clear fluids in children. Br J Anaesth. 2015;114(3):477-482. PMID: 25501720

15. Irish MS, Pearl RH, Caty MG, Glick PL. The approach to common abdominal diagnoses in infants and children. Pediatr Clin North Am. 1998;45(4):729-772. PMID: 9728184

16. Applegate KE, Anderson JM, Klatte EC. Intestinal malrotation in children: a problem-solving approach to the upper gastrointestinal series. Radiographics. 2006;26(5):1485-1500. PMID: 16973777

17. Niedzielski J, Kobielski A, Sokal J, Krakos M. Accuracy of sonographic criteria in the decision for surgical treatment in infantile hypertrophic pyloric stenosis. Arch Med Sci. 2011;7(3):508-511. PMID: 22295036

18. Graham KA, Laituri CA, Marber P, et al. A review of postoperative feeding regimens in infantile hypertrophic pyloric stenosis. J Pediatr Surg. 2013;48(10):2175-2179. PMID: 24094975

19. Salem MR, Khorasani A, Zeidan A, Crystal GJ. Cricoid pressure controversies: narrative review. Anesthesiology. 2017;126(4):738-752. PMID: 28151816

20. Walker RW. The laryngeal mask airway in the difficult paediatric airway: an assessment of positioning and use in fibreoptic intubation. Paediatr Anaesth. 2000;10(1):53-58. PMID: 10632910

21. Nafiu OO, Voepel-Lewis T, Morris M, et al. How do pediatric anesthesiologists define intraoperative hypotension? Paediatr Anaesth. 2009;19(11):1048-1053. PMID: 19796350

22. Anderson BJ, Meakin GH. Scaling for size: some implications for paediatric anaesthesia dosing. Paediatr Anaesth. 2002;12(3):205-219. PMID: 11903932

23. Lerman J. Pharmacology of intravenous non-opioid anesthetics. In: Smith's Anesthesia for Infants and Children. 9th ed. Elsevier; 2017:212-236.

24. Brandom BW, Woelfel SK, Cook DR, et al. Clinical pharmacology of atracurium in infants. Anesth Analg. 1984;63(3):309-312. PMID: 6695870

25. Dingeman RS, Barus LM, Chung HK, et al. Ultrasonography-guided bilateral rectus sheath block vs local anesthetic infiltration after pediatric umbilical hernia repair. JAMA Surg. 2013;148(8):707-713. PMID: 23760519

26. Flack SH, Martin LD, Walker BJ, et al. Ultrasound-guided rectus sheath block or wound infiltration in children. Paediatr Anaesth. 2014;24(2):207-213. PMID: 24138117

27. Cote CJ, Lerman J, Anderson BJ, eds. A Practice of Anesthesia for Infants and Children. 6th ed. Elsevier; 2019.

28. Bissonnette B, ed. Pediatric Anesthesia: Basic Principles, State of the Art, Future. People's Medical Publishing House; 2011.

29. Australian and New Zealand College of Anaesthetists. Guidelines on pre-anaesthesia consultation and patient preparation. PS07. 2017.

30. Royal Children's Hospital Melbourne. Clinical Practice Guidelines: Pyloric stenosis. 2023.

31. Sherwood J, Edwards T, Balasubramanian H, et al. Closing the gap: identifying culturally appropriate care for Indigenous Australians. Med J Aust. 2015;203(5):206-207. PMID: 26852050

32. Australian Indigenous HealthInfoNet. Cultural safety in clinical settings. 2022.

33. Durie M. Whaiora: Maori Health Development. 2nd ed. Oxford University Press; 1998.

34. Reid P, Robson B. Understanding health inequities. In: Hauora: Maori Standards of Health IV. Te Ropu Rangahau Hauora a Eru Pomare; 2007:3-10.

35. Cote CJ, Zaslavsky A, Downes JJ, et al. Postoperative apnea in former preterm infants after inguinal herniorrhaphy. Anesthesiology. 1995;82(4):809-822. PMID: 7717551

36. Kurth CD, Spitzer AR, Broennle AM, Downes JJ. Postoperative apnea in preterm infants. Anesthesiology. 1987;66(4):483-488. PMID: 3565814

37. Davidson AJ, Morton NS, Arnup SJ, et al. Apnea after awake regional and general anesthesia in infants: the General Anesthesia compared to Spinal anesthesia study. Anesthesiology. 2015;123(1):38-54. PMID: 26001033

38. Welborn LG, Rice LJ, Hannallah RS, et al. Postoperative apnea in former preterm infants: prospective comparison of spinal and general anesthesia. Anesthesiology. 1990;72(5):838-842. PMID: 2339799

39. Andropoulos DB, Greene MF. Anesthesia and developing brains - implications of the FDA warning. N Engl J Med. 2017;376(10):905-907. PMID: 28177852

40. McCann ME, de Graaff JC, Dorris L, et al. Neurodevelopmental outcome at 5 years of age after general anaesthesia or awake-regional anaesthesia in infancy (GAS): an international, multicentre, randomised, controlled equivalence trial. Lancet. 2019;393(10172):664-677. PMID: 30782342

41. Sun LS, Li G, Miller TL, et al. Association between a single general anesthesia exposure before age 36 months and neurocognitive outcomes in later childhood. JAMA. 2016;315(21):2312-2320. PMID: 27272582

42. Ing C, DiMaggio C, Whitehouse A, et al. Long-term differences in language and cognitive function after childhood exposure to anesthesia. Pediatrics. 2012;130(3):e476-e485. PMID: 22908104