Pyloric stenosis

Surgical approach

Operation: Ramstedt pyloromyotomy (splitting hypertrophied pyloric muscle down to mucosa to relieve gastric outlet obstruction).
- Approach: open (RUQ transverse incision) or laparoscopic (ports, insufflation).
- Key steps: identify pylorus (“olive”), longitudinal seromuscular incision, spread muscle fibres until mucosa bulges, ensure complete myotomy, check for mucosal perforation/bleeding.
- Post-op feeding: usually early graded feeds, vomiting can persist briefly despite adequate myotomy.

Anaesthetic management

Type of anaesthesia: General anaesthesia (no role for regional as sole technique).
Airway: cuffed ETT preferred, RSI with cricoid (modified for neonate/infant) due to full stomach/aspiration risk. Avoid SGA.
- Pre-induction: gastric decompression with wide-bore NG/OG, aspirate in multiple positions (supine, left, right, prone if safe) to minimise residual milk/secretions.
Duration: typically 30–60 min (longer if laparoscopic/complications).
Pain: usually mild–moderate, manage with paracetamol ± small-dose opioid, consider local infiltration/TAP block (operator dependent).
Key principle: resuscitation before anaesthesia (this is a medical emergency, not a surgical emergency).
Ventilation: avoid hyperventilation, aim normocapnia to reduce risk of post-op apnoea (alkalosis blunts ventilatory drive).

Definition &amp, epidemiology

IHPS = hypertrophy/hyperplasia of pyloric circular muscle causing gastric outlet obstruction in early infancy.
Typical age: 2–8 weeks, more common in males (classically first-born).
Associations: macrolide exposure (e.g. erythromycin/azithromycin) in early life, family history.

Clinical features

History: progressive non-bilious projectile vomiting after feeds, hungry after vomiting, poor weight gain, dehydration.
Examination: dehydration, visible gastric peristalsis, palpable pyloric “olive” (may be difficult).
Differential: sepsis, gastro-oesophageal reflux, milk protein allergy, intestinal obstruction (bilious vomiting suggests distal obstruction), raised ICP.

Investigations

Ultrasound: thickened pyloric muscle and elongated pyloric canal (diagnostic).
Blood gas/U&amp,Es: hypochloraemic, hypokalaemic metabolic alkalosis, may have paradoxical aciduria, assess glucose.
Assess hydration: weight trend, urine output, capillary refill, consider FBC/CRP if infection suspected.

Pathophysiology &amp, anaesthetic implications

Vomiting of gastric HCl → loss of H+ and Cl− → metabolic alkalosis + hypochloraemia.
Volume depletion → RAAS activation → renal Na+ retention with K+ and H+ loss → worsens hypokalaemia/alkalosis, can cause paradoxical aciduria.
Alkalosis reduces ionised calcium and can depress ventilation, in infants, alkalosis may increase risk of post-op apnoea (central drive blunted).
Stomach is full despite fasting → high aspiration risk, NG/OG decompression reduces but does not eliminate risk.

Pre-operative optimisation (core FRCA content)

Priorities: correct hypovolaemia, electrolytes, and alkalosis before theatre, treat hypoglycaemia.
IV access + monitoring, measure weight, strict fluid balance, consider warming measures early.
Fluid resuscitation: 0.9% saline boluses (e.g. 10–20 mL/kg) if shocked/dehydrated, then maintenance + deficit replacement with chloride-rich fluid.
- Add potassium only once urine output established and K+ known (typical 10–20 mmol/L in maintenance fluid, per local policy).
Targets often used before anaesthesia (institutional variation): Cl− ≥ 100 mmol/L, HCO3− &lt, 30 mmol/L (or base excess near normal), K+ corrected, clinically euvolaemic.
NG/OG tube: aspirate regularly, keep on free drainage until induction, remove/leave in situ per local practice (often left for decompression until after induction).
Fasting: treat as full stomach regardless, follow milk/clear fluid rules but do not rely on them to reduce aspiration risk.

Induction &amp, airway (RSI details)

Preparation: full monitoring, suction ready, difficult airway plan, pre-oxygenate (gentle CPAP if needed, avoid gastric insufflation if possible).
Modified RSI: gentle mask ventilation may be required in infants to prevent desaturation, keep pressures low, apply cricoid carefully (avoid airway obstruction).
Induction agents: propofol or thiopentone (haemodynamics/experience), ketamine may be considered if unstable, opioid sparing.
Neuromuscular block: rocuronium (rapid onset) or suxamethonium (if no contraindication), ensure full paralysis before laryngoscopy.
Tube: appropriately sized cuffed ETT, confirm with capnography, secure well (shared airway not typical but infant movement risk).

Maintenance

Anaesthesia: volatile (sevoflurane) or TIVA, maintain normothermia (forced-air warmer, warmed fluids).
Fluids: isotonic balanced crystalloid or 0.9% saline per local policy, avoid hypotonic fluids, monitor glucose (risk of hypoglycaemia).
Analgesia: paracetamol, local infiltration, small-dose opioid (e.g. fentanyl) if needed, avoid excessive opioids due to apnoea risk.
Antiemetic: variable, vomiting may occur post-op regardless, consider ondansetron per local practice.
Laparoscopy considerations: insufflation → reduced venous return, ↑ airway pressures, hypercarbia, adjust ventilation, watch for vagal bradycardia.

Emergence &amp, post-operative care

Extubation: fully awake with good tone/ventilation, ensure stomach decompressed, suction pharynx, consider lateral position.
Apnoea monitoring: consider HDU/appropriate monitoring, especially if premature, significant residual alkalosis, anaemia, sepsis, or opioid exposure.
Feeding: early feeds per surgical protocol, manage ongoing vomiting conservatively unless persistent/concerns for incomplete myotomy or mucosal perforation.
Complications: aspiration pneumonitis, mucosal perforation (peritonitis), bleeding, incomplete myotomy (persistent obstruction), wound infection.

Test yourself…

A 5-week-old, 3.8 kg infant with suspected pyloric stenosis is listed for pyloromyotomy. What are your immediate priorities before anaesthesia?

Focus on optimisation and making theatre safe, surgery should wait until resuscitated.

Confirm diagnosis and severity: history of non-bilious projectile vomiting, dehydration, weight loss, review ultrasound.
Assess and correct dehydration/hypovolaemia: clinical signs + urine output, IV access, consider 10–20 mL/kg 0.9% saline bolus if needed.
Correct biochemical derangements: hypochloraemic metabolic alkalosis ± hypokalaemia, repeat gases/U&amp,Es until acceptable.
Use chloride-rich fluids, add K+ only after urine output established and K+ known.
Treat/prevent hypoglycaemia: check glucose and give appropriate dextrose-containing maintenance if indicated (per neonatal policy).
Reduce aspiration risk: NG/OG decompression with repeated aspiration in different positions, treat as full stomach regardless of fasting time.

Explain the acid–base disturbance in pyloric stenosis and why it matters to the anaesthetist.

Link vomiting physiology to ventilation and peri-operative apnoea risk.

Vomiting gastric HCl → loss of H+ and Cl− → metabolic alkalosis + hypochloraemia.
Volume depletion → RAAS → renal Na+ retention with K+ and H+ excretion → worsens hypokalaemia/alkalosis, can cause paradoxical aciduria.
Alkalosis blunts ventilatory drive, infants are vulnerable → increased risk of post-operative apnoea, especially with opioids or residual alkalosis.
Hypokalaemia increases risk of arrhythmias and potentiates neuromuscular blockade, correct before GA where possible.

What biochemical targets would you like before proceeding to theatre?

State pragmatic targets commonly used, acknowledge local variation.

Clinically euvolaemic with adequate urine output.
Chloride corrected (commonly aim Cl− ≥ 100 mmol/L).
Alkalosis improved (commonly HCO3− &lt, 30 mmol/L or base excess near normal).
Potassium normalised (or trending to normal with safe replacement and ECG stability).
Glucose in acceptable range for age, normothermic.

Describe your induction technique and justify it.

High aspiration risk + infant physiology drives a modified RSI with careful preparation.

Treat as full stomach: NG/OG decompression immediately pre-induction, suction and assistance available.
Pre-oxygenate, consider gentle CPAP if needed, avoid excessive mask pressures to reduce gastric insufflation.
Modified RSI: induction agent + rapid NMBD, gentle ventilation may be required to prevent desaturation, apply cricoid carefully.
Intubate with cuffed ETT, confirm with capnography, secure tube, avoid SGA due to aspiration risk.

How do you decompress the stomach effectively and why might a single aspiration be inadequate?

Milk curds/secretions can remain despite fasting, position changes help empty dependent areas.

Use wide-bore NG/OG, aspirate until minimal return.
Repeat aspiration in different positions (supine, left lateral, right lateral, some also use prone with appropriate support).
Single aspiration may miss pooled contents or thick milk curds, pyloric obstruction prevents emptying into duodenum.
Even after decompression, aspiration risk persists → RSI strategy still required.

What are the key intra-operative concerns specific to pyloric stenosis?

Think aspiration, temperature, glucose, ventilation, and drug sensitivity.

Aspiration risk at induction/emergence, ensure suction, awake extubation, and gastric decompression.
Maintain normothermia (small infant, short surgery but high heat loss).
Monitor and manage glucose (limited glycogen stores).
Avoid hyperventilation, aim normocapnia to reduce post-op apnoea risk.
Cautious opioids due to apnoea risk, use multimodal analgesia.

The surgeon plans a laparoscopic pyloromyotomy. What additional anaesthetic considerations are there?

Insufflation effects are more pronounced in small infants.

CO2 insufflation → ↑ intra-abdominal pressure → ↓ venous return and potential hypotension, manage with fluids/anaesthetic depth.
CO2 absorption → hypercarbia, increase minute ventilation and monitor ETCO2 closely.
↑ airway pressures and reduced compliance, adjust ventilator settings and consider recruitment if needed.
Vagal responses/bradycardia with peritoneal stretch, be ready to ask for desufflation and treat with atropine if required.

How would you plan extubation and post-operative monitoring?

Aim to minimise aspiration and apnoea risk.

Extubate fully awake with good respiratory effort and tone, suction oropharynx, consider lateral positioning.
Ensure adequate analgesia with minimal opioids, use paracetamol and local techniques.
Monitor for apnoea (especially ex-premature infants, residual alkalosis, opioid exposure, intercurrent illness).
Observe for ongoing vomiting, small amounts can be normal early, persistent vomiting may indicate incomplete myotomy or other pathology.

What complications should you discuss in a focused consent/parental explanation from an anaesthetic perspective?

Keep it relevant: aspiration, airway, apnoea, common GA risks in infants.

Aspiration risk despite precautions, potential respiratory complications (desaturation, pneumonitis).
Airway complications: difficult intubation is uncommon but possible, sore throat/hoarseness (less common in infants).
Post-op apnoea/need for monitoring or temporary respiratory support.
Nausea/vomiting may persist for a short period after surgery.
General risks: IV access issues, temperature instability, rare drug reactions.

An infant arrives in theatre still alkalotic (HCO3− 36) but the list is pressured. What do you do and how do you justify it?

This tests prioritisation and patient safety: pyloric stenosis is not a surgical emergency.

Do not proceed routinely, request delay for further resuscitation/correction (patient safety, reduced apnoea/arrhythmia risk).
Explain risks: persistent alkalosis → ventilatory depression/post-op apnoea, associated electrolyte abnormalities (hypochloraemia/hypokalaemia) and aspiration risk remain.
Escalate appropriately: discuss with surgeon, paediatric team, anaesthetic consultant, document decision-making.
If exceptional circumstances mandate proceeding (rare): optimise as much as possible, plan HDU/PICU monitoring, minimise opioids, strict normocapnia, and correct electrolytes aggressively with senior support.