Anaesthetic Considerations and Management for Neonatal Pyloromyotomy (Pyloric Stenosis)

1. Background and Pathophysiology

• Loss of gastric fluid containing H⁺, Cl⁻, K⁺, Na⁺
• Hypochloraemic, hyponatraemic, hypokalaemic metabolic alkalosis
• Initial renal compensation: NaHCO₃ excretion (alkaline urine)
• Late stage: kidneys conserve Na⁺ at the expense of H⁺ excretion → paradoxical aciduria (an ominous sign of severe depletion)
• Compensatory respiratory acidosis (hypoventilation) attempts to buffer the alkalosis

• Morgan & Mikhail's Clinical Anesthesiology, 7e
• Barash, Cullen, and Stoelting's Clinical Anesthesia, 9e

2. Preoperative Assessment and Resuscitation

Pyloric stenosis is a MEDICAL emergency, not a SURGICAL emergency. Surgery must NEVER proceed until fluid and electrolyte deficits are fully corrected.

Clinical Assessment

• Degree of dehydration: skin turgor, fontanelle, mucous membranes
• Serum electrolytes: Na⁺, K⁺, Cl⁻, HCO₃⁻ (bicarbonate is the key marker)
• Urine output: target ≥ 1-2 mL/kg/hr
• Blood gas analysis

Resuscitation Protocol

1. Initial bolus: Normal saline (NaCl 0.9%) 20 mL/kg IV - lactated Ringer's is not ideal as it does not correct chloride deficit
2. Maintenance: Once urine output is established - D5 ½ NS + 20 mEq/L KCl at 1.5× maintenance rate
3. Electrolytes rechecked every 6-12 hours

Targets Before Proceeding to Theatre

• Barash, Cullen, and Stoelting's Clinical Anesthesia, 9e
• Sabiston Textbook of Surgery, 21e
• Current Surgical Therapy, 14e

3. Aspiration Risk - The Central Concern

• Pass a large-bore orogastric (or nasogastric) tube and aspirate stomach contents with the patient in three positions: supine, right lateral, and left lateral
• This three-position suctioning technique removes approximately 98% of gastric contents
• Important: Even if an NGT was placed preoperatively, re-suction immediately before induction - NGTs may cause ongoing electrolyte loss and do not guarantee an empty stomach
• If contrast studies were done, all contrast material must be aspirated from the stomach before induction
• Miller's Anesthesia, 10e
• Morgan & Mikhail's Clinical Anesthesiology, 7e

4. Induction of Anaesthesia

Option A: Rapid-Sequence Induction (RSI) - Commonly Used

• Preoxygenation
• IV induction agent + neuromuscular blocking agent
• Concerns with classic RSI in neonates:
  • Cricoid pressure easily distorts the small, compliant infant airway and makes laryngoscopy difficult
  • Neonates and infants desaturate very rapidly with apnoea - attempting to avoid bag-mask ventilation is often not feasible
  • A modified RSI is usually employed: gentle mask ventilation with low pressure is often necessary before intubation

Induction Agents

• Propofol or thiopental are commonly used
• Atropine (0.02 mg/kg IV) should be given if succinylcholine is used (to prevent bradycardia)
• Succinylcholine 2 mg/kg IV (higher dose than adults due to larger volume of distribution in neonates) - if used, give after atropine pretreatment
• Non-depolarising agents (e.g., rocuronium) are an alternative
• IV induction with muscle relaxant leads to fewer intubation attempts and faster intubation compared to awake intubation

Option B: Awake Intubation

• Historically popular; now falling out of favour
• Associated with higher complication rates and is traumatic to the infant
• Appropriate only if IV access cannot be secured or the infant is severely compromised
• Fully resuscitated infants have little indication for awake intubation

Option C: Inhalation Induction

• Occasionally used by experienced clinicians in selected patients
• Nitrous oxide should be avoided (risk of bowel distension, especially for laparoscopic approach)
• Miller's Anesthesia, 10e
• Barash, Cullen, and Stoelting's Clinical Anesthesia, 9e
• Morgan & Mikhail's Clinical Anesthesiology, 7e

5. Airway Management

• Oral endotracheal intubation is the standard
• Use an appropriately sized uncuffed (or small cuffed) ETT - formula: (age/4) + 4 is unreliable in neonates; use weight-based charts
• Confirm tube placement clinically and with capnography
• Secure the airway carefully - position changes during laparoscopic surgery (Trendelenburg) can cause tube displacement

6. Maintenance of Anaesthesia

• Any volatile agent (sevoflurane, isoflurane) with oxygen in air can be used
• Nitrous oxide should be avoided - worsens bowel distension under laparoscopy
• Muscle relaxation: a short period of muscle relaxation is required for laparoscopy; controlled ventilation often reduces or eliminates the need for ongoing relaxants
• Laparoscopic considerations: Careful attention to ventilation and blood pressure during pneumoperitoneum insufflation - increased intraabdominal pressure impairs diaphragmatic excursion
• Normothermia must be maintained - neonates have a high surface area:volume ratio and lose heat rapidly; use warm blankets, warm IV fluids, and a warm OR environment

7. Analgesia (Multimodal)

1. Local anaesthetic infiltration of the wound (subcutaneous) - simple and effective
2. Transversus Abdominis Plane (TAP) block - ultrasound-guided; provides good somatic analgesia for port sites and the incision
3. Rectus sheath block - described for this procedure
4. Paracetamol (acetaminophen) - IV or rectal; dose 10-15 mg/kg
5. Opioids: used sparingly if at all; further blunts already-impaired respiratory drive

• Miller's Anesthesia, 10e
• Barash, Cullen, and Stoelting's Clinical Anesthesia, 9e

8. Extubation

• The patient should be fully awake and responding before extubation - do not extubate in a deep plane
• Confirm reversal of neuromuscular blockade if non-depolarising agents used
• Ensure adequate spontaneous ventilation before extubation
• Delayed extubation risk is elevated in infants with residual metabolic alkalosis - this is the strongest reason to correct electrolytes preoperatively

9. Postoperative Care

Apnoea Monitoring - Critical

• Postoperative apnoea occurs in approximately 9-10% of cases (Camporesi et al., 2022, PMID 36475052)
• Apnoea risk is increased by:
  • Residual metabolic alkalosis (CSF alkalosis outlasting plasma normalisation)
  • Postoperative anaemia (hemodilution reduces oxygen-carrying capacity)
  • Prematurity
• All infants should be monitored with apnoea monitors and pulse oximetry for a minimum of 12-24 hours postoperatively
• A high-dependency or ICU setting is appropriate for the first postoperative period

Feeding

• Most centres use a graduated feeding protocol post-pyloromyotomy
• Ad libitum feeding with a 60 mL limit, or incremental advancement
• Most infants tolerate feeds and are discharged within 36 hours

Complications to Watch For

10. Summary - Key Anaesthetic Principles

• Miller's Anesthesia, 10e (Pyloric Stenosis section)
• Barash, Cullen, and Stoelting's Clinical Anesthesia, 9e (Pyloric Stenosis + Anesthetic Management)
• Morgan & Mikhail's Clinical Anesthesiology, 7e (Pathophysiology + Anesthetic Considerations)
• Sabiston Textbook of Surgery, 21e (HPS Preoperative Management)
• Current Surgical Therapy, 14e (HPS Resuscitation targets)
• Camporesi et al. (2022): Postoperative apnoea after pyloromyotomy, PMID 36475052
• Youssef et al. (2025): Delayed extubation predictors in HPS, PMID 40656205

Rapid Sequence Induction (RSI) and Modified RSI

1. Definition and Purpose

• Miller's Anesthesia, 10e

2. Indications for RSI

• Miller's Anesthesia, 10e; Morgan & Mikhail's Clinical Anesthesiology, 7e

3. Classic RSI - The 6 Ps

• Current Surgical Therapy, 14e

Cricoid Pressure (Sellick Manoeuvre)

• Mechanism: The cricoid cartilage forms a complete, incompressible ring - pressure over it compresses the posterior wall against the cervical vertebrae, occluding the oesophagus and preventing passive regurgitation of gastric contents reaching the hypopharynx
• Force applied: 10 N while patient is awake → increased to 30 N after loss of consciousness
• Correct technique: Bimanual - one hand applies pressure on the cricoid anteriorly, the other hand supports the back of the neck

4. Drugs Used in RSI

A. Induction Agents

B. Neuromuscular Blocking Drugs (NMBDs)

Succinylcholine (Suxamethonium) - the "gold standard" NMBD for RSI

• Burns (>24-48 h old)
• Crush injuries / prolonged immobility
• Neuromuscular disorders (muscular dystrophies)
• Known or suspected myopathy / MH susceptibility
• Hyperkalaemia (can cause fatal cardiac arrest)
• Open globe injury
• Pseudocholinesterase deficiency
• Prior succinylcholine-induced hyperkalaemia

Rocuronium - preferred alternative when succinylcholine is contraindicated

• Miller's Anesthesia, 10e; Current Surgical Therapy, 14e; Morgan & Mikhail's, 7e

5. Classic RSI - What NOT to Do

• No bag-mask ventilation (BMV) between induction and intubation - avoids gastric insufflation and increases risk of vomiting/aspiration
• No delay between induction agent and NMBD - they must be given in immediate sequence
• Do not release cricoid pressure until ETT cuff is up and tube position confirmed

6. Modified RSI - Definition and Rationale

No standardised definition exists. The most commonly used definition (from surveys of anaesthesiologists) is: RSI with the addition of gentle positive pressure ventilation (PPV) with cricoid pressure applied.

Why Modify?

• Miller's Anesthesia, 10e; Barash Clinical Anesthesia, 9e

Core Modification: Gentle Mask Ventilation

• Allow gentle BMV with inspiratory pressure <20 cm H₂O while cricoid pressure is maintained
• This allows time to achieve adequate intubating conditions without the patient desaturating
• The theoretical risk (gastric insufflation) is mitigated by maintaining cricoid pressure during ventilation and keeping pressures low
• Morgan & Mikhail's, 7e: "A modification of the classic RSI allows gentle ventilation as long as cricoid pressure is maintained."

7. Spectrum of RSI Techniques

Classic RSI ←————————————————————————→ Standard Induction
   |               Modified RSI               |
No BMV          Gentle BMV + cricoid       BMV without cricoid
Strict apnoea   <20 cmH₂O pressure        Titrated depth
Succinylcholine Rocuronium + sugammadex    Any NMBD or none

Ultra-Modified RSI (THRIVE technique)

• Transnasal Humidified Rapid Insufflation Ventilatory Exchange (THRIVE): high-flow nasal cannula at 15-60 L/min applied during the apnoea window
• Prolongs safe apnoea time via apnoeic oxygenation through flow-mediated gas exchange
• Used as adjunct to both classic and modified RSI
• Barash Clinical Anesthesia, 9e

8. Cricoid Pressure - The Ongoing Controversy

Arguments FOR

• When correctly applied, compresses the oesophagus between cricoid and cervical vertebrae - prevents passive regurgitation
• Widely practised; approaches standard of care for full stomach

Arguments AGAINST

• MRI studies show cricoid pressure often causes lateral displacement of the oesophagus rather than true compression - so the theoretical mechanism may not work reliably
• Reduces lower oesophageal sphincter (LES) tone - paradoxically may increase regurgitation risk
• Worsens laryngeal view at direct laryngoscopy - can worsen Cormack-Lehane grade, prolonging time to intubation and increasing risk
• Can cause subglottic airway compression, especially in infants/children where the cartilage is softer and more compressible
• Too much pressure during active vomiting has caused posterior oesophageal rupture
• Evidence from RCTs and systematic reviews does not convincingly show reduced aspiration incidence

Practical Guidance

• In adults: Apply 10 N awake → 30 N at LOC; release immediately if it worsens laryngoscopy
• In children and neonates: Apply cautiously - less force than adults; the soft, compressible cricoid ring can obstruct the trachea if excessive pressure applied
• If laryngoscopy is impaired, partially or fully release cricoid pressure while maintaining airway management
• Do not apply during active vomiting
• Miller's Anesthesia, 10e; Morgan & Mikhail's, 7e; Barash Clinical Anesthesia, 9e

9. Modified RSI Specifically in Neonates and Infants (for Pyloric Stenosis Context)

1. Safe apnoea time is very short (45-90 s) - FRC is proportionally small, O₂ consumption is high (6-8 mL/kg/min vs 3 mL/kg/min in adults)
2. Cricoid pressure distorts the small, compliant airway - making laryngoscopy harder and potentially obstructing the trachea
3. Succinylcholine in neonates requires atropine pretreatment and a higher mg/kg dose
4. If intubation fails, gentle ventilation must be possible to rescue oxygenation

• Preoxygenate (100% O₂, even if infant uncooperative - do best you can)
• Gastric decompression first (three-position suctioning)
• Modified RSI: induction agent + NMBD → gentle BMV at <20 cmH₂O permitted while NMBD takes effect
• Cricoid pressure: applied gently - release or reduce if it worsens view or impairs ventilation
• Intubate once conditions are optimal
• Have sugammadex drawn up if rocuronium is used
• Miller's Anesthesia, 10e; Barash Clinical Anesthesia, 9e

10. Comparison Summary Table

11. Failed RSI - Rescue Strategy

1. Maintain cricoid pressure; attempt gentle BMV <20 cmH₂O to restore oxygenation
2. Call for help; switch to video laryngoscopy or bougie-assisted intubation
3. If rocuronium used: sugammadex 16 mg/kg for full reversal and return to spontaneous ventilation
4. If still cannot intubate or ventilate: declare CICO (Cannot Intubate Cannot Oxygenate) → front of neck access (surgical cricothyroidotomy / needle cricothyroidotomy in children)
5. Allow return of spontaneous ventilation → consider awake intubation

• Miller's Anesthesia, 2-Volume Set, 10e - RSI and Intubation chapter
• Barash, Cullen & Stoelting's Clinical Anesthesia, 9e - Full Stomach and RSI; Paediatric RSI
• Morgan & Mikhail's Clinical Anesthesiology, 7e - RSI technique and contraindications
• Current Surgical Therapy, 14e - 6 Ps of RSII in trauma