Pyloric Stenosis

Question 1

An 8-week-old male patient is listed for a pyloromyotomy. He was admitted to hospital 3 days ago with vomiting and dehydration. You are asked to review him prior to his procedure.

What is a pyloromyotomy?

Answer 1

• Surgical procedure that is carried out in patients with pyloric stenosis, a condition caused by hypertrophy of the smooth muscles of the pylorus, which leads to a functional obstruction of the gastric outlet.
• The procedure can be performed open or laparoscopically, and involves dissecting the walls of the pylorus muscle down to the mucosa to relieve the obstruction.

Question 2

What are the risk factors for the development of pyloric stenosis?

Answer 2

• Incidence varies from 0.9-5.1 per 1000 live births.
• Overall unknown cause.
• Five times higher incidence in males compared to females.
• Increased risk with first-born babies, monozygotic twin concordance suggesting a genetic element, and premature infants.

Question 3

What are the typical signs and symptoms in a patient with undiagnosed pyloric stenosis?

Answer 3

• Most commonly present in the first 4–6 weeks of life.
• Projectile, non-bilious vomiting after feeding.
• Failure to thrive and poor weight gain.
• Dehydration, drowsiness and failure to engage.
• Palpation of an olive-like mass in the right upper quadrant of the abdomen.

Question 4

How would you assess this patient preoperatively?

Answer 4

History:

• Parental history: pregnancy, health conditions, medication and social history.
• Delivery: type, gestation and complications.
• Birth weight, current weight, APGAR scores at birth and events since birth.
• Any known medical conditions.
• Treatment so far and current medication.

Examination:
* Basic cardiovascular, respiratory and airway assessment.

• Fluid balance: the patient needs to be appropriately resuscitated prior to the procedure.

Investigations:

• Bedside observations to ensure adequate resuscitation and haemodynamic stability.
• Bloods to include urea and electrolytes and serial gases; babies commonly present with a hypochloraemic, hypokalaemic metabolic alkalosis secondary to vomiting and dehydration.
• Ultrasound to confirm the presence of pyloric stenosis.

Question 5

Why is this patient at increased risk of postoperative apnoeas?

Answer 5

• All babies under 60 weeks gestational age are at higher risk of apnoeas, and should be nursed in an appropriate setting with working apnoea monitors available.
• The vomiting of gastric contents leads to a hypokalaemic, hypochloraemic metabolic alkalosis and dehydration from water loss. The body compensates for this by:
• Excreting bicarbonate in the urine.
• Responding to reduced plasma volume by secreting aldosterone to favour retention of sodium and water and excretion of potassium by the kidneys.
• As dehydration progresses, this becomes the priority and hydrogen ions are excreted by the kidneys in exchange for sodium and water.
• Ventilation is stimulated by an increase in the concentration of hydrogen ions in cerebrospinal fluid, hence metabolic alkalosis
  can lead to respiratory depression.
• Even when the metabolic disturbance in the plasma is corrected, it can take hours before equilibration with cerebrospinal fluid takes place. This explains the higher risk of apnoea in these patients.

Question 6

How should induction of anaesthesia take place in this patient?

Answer 6

• This is elective surgery – induction should be undertaken after the patient is fully resuscitated and;
• pH 7.35–7.45.
• Bicarbonate equal to or under 30 mmol/L (or as per local guidelines).
• Chloride 95–112 mmol/L.
• Potassium 3.5–5 mmol/L.
• Base excess −4 to −2.5 mmol/L.
• Ensure parental consent, WHO checklist, AAGBI monitoring and patency of IV access.
• Preparation for the anaesthetic should include an experienced paediatric anaesthetist, trained assistant, availability of resuscitation/difficult airway trolleys and appropriate doses of routine and emergency drugs.
• Four-quadrant aspiration of nasogastric tube (should be in situ prior to induction). Consider an ultrasound of the stomach to ensure full emptying.
• Inhalational anaesthetic with sevoflurane in 100% oxygen followed by neuromuscular blockade and intubation with an appropriately sized endotracheal tube.
• Controlled ventilation, fluids and warming perioperatively.
• Check the blood glucose regularly perioperatively as the patient is in a starved state and is usually on a maintenance dextrose infusion, so is at a higher risk of hypo/hyperglycaemic episodes.

Question 7

What is your plan for analgesia in this patient?

Answer 7

• Postoperative pain is not usually severe
  .
• Regular paracetamol.
• Cautious intraoperative fentanyl.
• Local anaesthetic infiltration or consider regional anaesthesia – bilateral rectus sheath or transversus abdominis plane blocks.