Pyloric stenosis

Background

Congenital hypertrophic pyloric stenosis is thickening of the smooth muscle of the pylorus, which obstructs gastric outflow. It occurs in one in 300–400 children. There is a male predominance of 4:1. The condition has a polygenic mode of inheritance. The incidence is higher in the offspring of affected parents and is more common in autumn and spring. Caucasians are more likely to develop pyloric stenosis than Afro-Caribbean or Asian infants.

Learning outcomes

1 Understand the common presenting features of congenital pyloric stenosis

2 Ensure metabolic correction prior to surgery

3 Discuss an appropriate anaesthetic technique for a neonate with pyloric stenosis.

CPD matrix matches

2D02; 2D04

Case history

Baby M was born at 39 weeks’ gestation by spontaneous vaginal delivery following an uneventful pregnancy. There were no maternal risk factors for sepsis. He was the first born child, both parents being in good health with no significant past medical history. His birthweight was 3.2 kg, and the early neonatal period was uneventful.

On the 23rd day of life, baby M presented with a 1-day history of vomiting with feeds, mostly effortless, but occasionally forceful. He was still passing stool and urine, although his wet nappies had decreased in frequency. He had been feeding well (160 mL/kg/day) and was gaining weight. His current weight was 4.45 kg (50th centile). No close contacts had been unwell.

He was unsettled, but otherwise clinical examination was unremarkable.

What are the differential diagnoses?

◆ Gastro-oesophageal reflux

◆ Pyloric stenosis

◆ Viral illness

◆ Urinary tract infection (UTI).

What is your initial management plan?

◆ Admit for observation of feeds

◆ IV access and bloods: FBC, U&E, LFTs, CRP, capillary blood gas (CBG)

◆ Urinalysis

◆ If temperature >38°C: full septic screen.

Comment on the initial results

◆ Hb 14.2 g/L, WCC 14.3, Neutr 3.86, Lymph 9.58, Plt 376

◆ Na⁺ 140, K⁺ 5.2, urea 2.9

◆ Bil 21, ALT 20, ALP 219, γGT 44, Alb 44

◆ CRP <2

◆ pH 7.39, pCO₂ 6.72 kPa, BE 6 mmol/L, HCO₃^– 30.6

◆ Urinalysis: negative.

These results are essentially within normal limits.

Case update

The following day, this child appeared more settled. Overnight, a small posset was noted post-feeds. He was otherwise well, and there were no concerns regarding sepsis. Given that he was thriving and the short duration of symptoms, he was discharged with no further follow-up.

However, 5 days post-discharge, baby M was readmitted with a 3-day history of worsening vomiting, up to 1 hour following feeds. It was milky, non-bilious, and occasionally forceful. He had become increasingly agitated, and his wet nappies had decreased in frequency. He was constipated, and his weight had fallen to 3.96 kg. He remained apyrexic and had mildly sunken fontanelle but was well perfused. Clinical examination revealed a palpable mass to the right of his umbilicus, following a test feed.

What is the likely diagnosis?

◆ Congenital hypertrophic pyloric stenosis.

What is the initial management of this condition?

◆ Obtain IV access and baseline bloods, including CBG

◆ Nil by mouth (NBM); commence IV fluids

◆ Pass an NG tube

◆ USS to confirm the diagnosis.

Case update

The USS confirmed pyloric stenosis, and his initial CBG results were:

◆ pH 7.46, pCO₂ 6.27 kPa, BE 8 mmol/L, HCO₃^– 31 mmol/L, Cl^– 94 mmol/L, K⁺ 3.3 mmol/L, Na⁺ 138 mmol/L.

Comment on this CBG

There is a hypochloraemic, hypokalaemic metabolic alkalosis.

What IV fluid regime would you prescribe?

◆ Maintenance fluids with potassium chloride (150 mL/kg/day)

◆ NG losses: 0.9% normal saline (mL for mL).

Outline the ongoing management for your patient

◆ NBM

◆ Regular NG aspiration and replacement with 0.9% saline

◆ Continue maintenance fluids, guided by repeated CBGs

◆ Surgical pyloromyotomy only when the infant is adequately rehydrated and metabolic abnormalities corrected. This may take 24–28 hours or more.

Case update

A repeat CBG was taken 5 hours later, showing: pH 7.47, pCO₂ 5.9 kPa, BE 7.4 mmol/L, HCO₃^– 30.5 mmol/L, Cl^– 96 mmol/L, K⁺ 3.9 mmol/L, Na⁺ 133 mmol/L.

How would you interpret this CBG? Would you change the management plan?

◆ There is a persistent hypochloraemic metabolic alkalosis, with no improvement since commencing IV fluids

◆ Increase maintenance fluids to 180 mL/kg/day, then repeat CBG.

Case update

A repeat CBG 3 hours later shows: pH 7.48, pCO₂ 5.51 kPa, BE 6.6 mmol/L, HCO₃^– 29.9 mmol/L, Cl^– 94 mmol/L, K⁺ 4 mmol/L, Na⁺ 137 mmol/L. This demonstrates a persisting hypochloraemic metabolic alkalosis, some improvement in BE and HCO₃^–. However, full correction would not be expected in such a short time period, so the recommendation would be to continue at the current rate, and then to repeat CBG.

The CBG 12 hours later shows: pH 7.36, pCO₂ 5.69 kPa, BE –1.6 mmol/L, HCO₃^– 22.9 mmol/L, Cl^– 105.6 mmol/L, K⁺ 5.4 mmol/L, Na⁺ 141 mmol/L.

What is your interpretation of these results?

◆ Normal CBG.

It is now appropriate to proceed with surgical pyloromyotomy.

Describe the anaesthetic management of surgical pyloromyotomy

◆ Generally these infants have an IV cannula in situ and IV fluids running

◆ Aspirate the NG tube in left, right, lateral, and head-down positions. IV and inhalational induction are both safe techniques, following an NG aspiration

◆ Options for induction:

• RSI: thiopentone (5–7 mg/kg) and suxamethonium (2 mg/kg)

• IV induction and a non-depolarizing muscle relaxant

• Inhalational induction and a non-depolarizing muscle relaxant

• Inhalational induction, followed by intubation under deep volatile anaesthesia

◆ Intubate with an appropriately sized ETT (either uncuffed or microcuffed). Have a smaller sized ETT available.

◆ Pressure-controlled IPPV is the normal practice

◆ Maintenance is with volatile in oxygen and air

◆ The surgeon may ask for the stomach to be distended with 40–60 mL of air, injected through the NG tube, to check for mucosal perforation. The air is aspirated prior to wound closure

◆ Reverse the non-depolarizing muscle relaxants with neostigmine (50 micrograms/kg) and glycopyrrolate (10 micrograms/kg)

◆ Aspirate the NG tube at the end of surgery, and extubate the infant awake.

How would you control post-operative pain?

◆ Regular paracetamol

◆ Local anaesthetic infiltrated to the incision or laparoscopic port sites by the surgeon

◆ Bilateral rectus sheath blocks can be used for periumbilical incisions.

What post-operative instructions would you give?

◆ NBM

◆ Reintroduce feeds as per surgeon’s instructions (clear fluids initially, followed by milk, if tolerated)

◆ Continue maintenance fluids until feeding is re-established

◆ Overnight SpO₂ and apnoea monitoring.

Discussion

Infants generally present aged <12 weeks, commonly between the 3rd and 5th weeks of life. It usually affects full-term infants; only a small number of cases are premature infants. The infant presents with progressive non-bilious vomiting, following a feed, which may become projectile. Concurrent constipation is common. There may be mild jaundice, attributable to glucuronyl transferase deficiency which develops as a consequence of starvation.

Associated abnormalities are found in 6–20% of infants, including oesophageal atresia, congenital cardiac anomalies, Hirschsprung’s disease, intestinal malformation, anorectal anomalies, minor renal anomalies, and inguinal hernias. There is loss of weight or failure to thrive, and the infant is ravenously hungry. On clinical examination, varying degrees of dehydration and apathy may be present.

What are the clinical signs of dehydration in infants?

The diagnosis is made on history and examination. The upper abdomen may be distended, with visible gastric peristaltic waves moving from left to right during feeding. An olive-sized mass may be palpated to the right of the umbilicus, more apparent after vomiting. USS shows hypertrophy of the pylorus wall (thickness >4 mm or length >16 mm).

Gastric outlet obstruction initially produces regurgitation and eventually vomiting. Vomiting causes loss of fluid, H⁺, Cl^–, and a variable amount of Na⁺ and K⁺ Secondary hyperaldosteronism develops as a result of hypovolaemia. This causes the kidneys to avidly retain Na⁺ (to correct for intravascular volume depletion) and excrete increased amounts of K⁺ into the urine, thereby retaining Na⁺ and K⁺ ions. Infants may be dehydrated, with a hypochloraemic, hypokalaemic, hyponatraemic metabolic alkalosis. Increasingly, medical care is sought quickly, and many infants only have a mild metabolic derangement or none at all.

**Table 6.1** Definitions and grading of dehydration in children, and associated clinical signs

Prior to theatre, infants should be adequately rehydrated, with a urine output of >1 mL/kg/hour. Laboratory and CBG results should be monitored and the following targets achieved before surgery:

◆ Serum Cl^– >100 mmol/L

◆ Serum Na⁺ >135 mmol/L

◆ Serum HCO₃^– <26 mmol/L.

Summary

Pyloric stenosis is not a surgical emergency. Dehydration and metabolic abnormalities should be corrected prior to theatre. A 20 mL/kg bolus of 0.9% saline may be given for resuscitation, if necessary. Generally, infants receive maintenance fluids with added potassium chloride as 150% of their calculated maintenance requirements. An NG tube is passed, and losses are replaced, mL for mL, with 0.9% normal saline until volume and metabolic normality are achieved.