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Pyloric Stenosis

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Pyloric Stenosis
Photo by Filip Mroz / Unsplash

Take home messages

  • Pyloric stenosis is a medical emergency, not a surgical one
  • It causes a hypochloraemic hypokalaemic metabolic alkalosis, sometimes with paradoxical aciduria
  • The definitive management is surgical pyloromyotomy
  • The main issues for the anaesthetist are the high risk of aspiration and electrolyte and acid-base disturbance

Podcast Episode

Two in one

The examiners over in FRCA-land thoroughly enjoy pyloric stenosis as an exam topic, because it allows them to test your knowledge on two topics at once:

  • Neonatal physiology and anatomy
  • Electrolyte and acid-base disturbances

One of the more common GI complaints presenting within an infants' first six months of existence, pyloric stenosis is of interest as it represents a medical emergency rather than a surgical one, however the definitive treatment is still an operation.

What are the key priorities for managing an infant with pyloric stenosis?

  • Fluid resuscitation and hydration
  • Electrolyte and acid-base abnormality correction
  • Prevent aspiration

Who gets it and when?

It's unclear exactly why babies develop pyloric stenosis. There appears to be a polygenic inheritance pattern and several theories as to the pathogenesis have been proposed, however no definitive aetiology has been found.

What we do know:

  • Male to Female 4:1
  • Runs in families
  • Caucasian infants more commonly affected
  • Generally affects full-term infants
  • 3/1000 live births worldwide, 1.5/1000 in UK

How does it present?

  • The textbook presentation is between weeks 3 and 5, but as always, it can vary widely
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The classic symptom is non-bilious projectile vomiting

This is because the obstruction is both profound and proximal to the biliary tree.

Clearly a baby that is projectile vomiting every feed is likely to be very hungry and failing to gain weight.

On examining the child, depending on how bad the situation has become, they may be:

  • Lethargic
  • Profoundly dehydrated
  • Hypovolaemic
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The classic examination finding is a distended upper abdomen with palpable peristaltic waves, and an olive-shaped mass

The baby may also be slightly jaundiced as a result of malnourishment causing a glucuronyl transferase deficiency.

How is pyloric stenosis definitively diagnosed?

  • The diagnosis can be made clinically
  • Ultrasound scan
  • Endoscopy
  • Barium swallow

Blood gas analysis will generally show a hypokalaemic, hypochloraemic metabolic alkalosis, as is to be expected with relentless vomiting. Severe dehydration in its own right can also contribute to the alkalosis.

What are the associated conditions with pyloric stenosis?

  • Congenital cardiac anomalies
  • Oesophageal atresia
  • Hirschprung's disease
  • Inguinal hernia
  • Anorectal abnormalities
  • Intestinal malrotation

Please explain the biochemistry

Here goes.

The alkalosis

If you block the stomach's exit to the duodenum, the gastric content, rich in hydrogen, chloride and potassium ions, is forced northwards onto the carpet.

Usually, vomiting includes some duodenal fluid, with its rich bicarbonate content, as well, which means hydrogen and bicarbonate is lost in relatively equal measure.

However because in this case there is an obstruction between stomach and duodenum, the vomiting means more gastric H+ is lost than duodenal HCO3-, producing a profound metabolic alkalosis.

The relatively high bicarbonate levels lead to alkaline urine, as the proximal convoluted tubule fails to keep up with reabsorption.

The hypokalaemia

We already have a mechanism for the hypokalaemia, through direct loss of gastric fluid, however it gets worse.

  1. We have a very dehydrated baby, who is very sensibly going to start producing vast quantities of aldosterone to conserve sodium and therefore water. But we have to swap the sodium for something, and this something ends up being potassium.
  2. Then to add insult to injury, in an attempt to fight the steadily worsening alkalosis, the kidney also gives up more potassium in an attempt to conserve some desperately needed hydrogen ions.
  3. Finally, there is intracellular shift of potassium in exchange for H+ ions, again in an attempt to normalise the pH.

Nightmare.

The hypochloraemia

This is less complex - there is lots of chloride in the stomach which is promptly removed, causing the recognisable hypochloraemia.

The paradoxical aciduria

Wait - aciduria in an alkalotic patient?

Yup.

This occurs later on, after all of the kidney's compensation mechanisms have been maxed out, and can simply no longer keep up with the messed up ion gradients.

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Once there isn't enough potassium left to exchange for sodium ions, the kidney is forced to give up hydrogen ions instead.

The urinary pH drops, the alkalosis gets worse, and things start to trend downhill rather rapidly.

How dehydrated is the child?

It's notoriously tricky working out just how bad a patient's dehydration is, but the following can provide a useful guide in infants:

Mild dehydration

  • <5% body weight loss
  • Normal fontanelle and eyes
  • Normal skin turgor
  • Moist membranes
  • Normal heart rate and respiratory rate
  • Urine output up to 2ml/kg/hour

Moderate dehydration

  • Up to 10% body weight fluid loss
  • Sunken fontanell and eyes
  • Reduced skin turgor and dry membranes
  • Tachycardia and tachypnoea
  • Urine output 1ml/kg/hour

Severe dehydration

  • 15% body weight fluid loss or worse
  • Very sunken fontanelle and eyes
  • Very dry membranes
  • Profound and feeble tachycardia
  • Rapid, deep respiration with air hunger
  • Oligoanuria - <0.5ml/kg/hour

Just remember that respiratory pattern can also be affected by the acid-base status

Hopefully you're seeing the child before it gets to the severe stage, however it's important to know the order in which the signs appear to accurately gauge the severity.

Fluids protocol

  • 20ml per kilogram initial fluid bolus of isotonic balanced crystalloid
  • Maintenance with 0.18% sodium chloride with 4% dextrose and 20mmol potassium at 4ml/kg/hour

Variations on this theme are acceptable - they just want you to appreciate the differences for resuscitation and maintenance.

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Plasma chloride concentrations of 106 mmol per litre or higher suggest adequate acid-base correction and fluid resuscitation

How do I anaesthetise it?

The definitive treatment for pyloric stenosis is surgical - pyloromyotomy - or 'cut a hole in it'.

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Pyloromyotomy is increasingly being performed laparoscopically

Of note - intra-abdominal pressure should be kept less than 10 mmHg and you may need to hyperventilate the infant to prevent CO2 build up from abdominal insufflation.

However the important thing to remember is that the emergency is medical, and the surgery is relatively elective, once the patient has been resuscitated and stabilised.

So before you reach for the laryngoscope:

  • Fill them up with fluid
  • Correct the electrolytes
  • Sort out the acid base balance
  • Empty the stomach with an NG tube

What on earth is four quadrant suctioning?

We don't tend to do this in adults, but it's far easier in an infant.

After inserting the NG tube, the infant is placed in the left lateral, right lateral, head down and supine positions, with NG suctioning occurring each time. The idea is complete emptying of every nook and cranny of the stomach before induction of anaesthesia.

You can even do gastric lavage if it makes you feel better, but the end result is if done properly, you can safely do an intravenous or gas induction.

Don't forget other sensible things

  • AAGBI monitoring
  • Keep patient warm
  • Regular NG suctioning
  • Consider atropine 20mcg per kilogram to reduce vagal response to intubation and surgery

Why avoid opioids?

Kids and heavy opioids are rarely a good mix, especially if they've had a recently corrected severe alkalosis, as well as intraoperative hyperventilation, because they stop breathing.

Plus, regular paracetamol in combination with judicious use of local anaesthesia - be that infiltration or a regional block - is usually sufficient for pain control and avoids the other unwanted side effects of opioids as well.

What else to watch for post operatively

  • Apnoea monitoring for up to 12 hours
  • Supplemental oxygen as required
  • Electrolyte monitoring
  • Glucose management*
  • Re-establish feeding cautiously after 12 hours or so

Remember these kids often have little to no glycogen stores left, so hypoglycaemia can be profound and sudden

Here's a free CRQ on neonatal anaesthesia from the lovely people at FRCA-revision.com

Useful Tweets and Resources

References and Further Reading

Infantile pyloric stenosis
D Fell, S Chelliah; Infantile pyloric stenosis, BJA CEPD Reviews, Volume 1, Issue 3, 1 June 2001, Pages 85–88, https://doi.org/10.1093/bjacepd/1.3.85
OUP AcademicD Fell

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