Hypertrophic pyloric stenosis, RHC

Diagnosis

1. History/examination
2. Weight
3. Assess for clinical dehydration⁽²⁾ Capillary blood gas:
   1. Assess acid base
   2. Confirm hypochloraemic, hypokalaemic metabolic alkalosis
4. Calculate and document appropriate full milk feed compared to given feed ⁽³⁾, to ensure not being overfed
5. Ultrasound is the gold standard for diagnosis^(1-2)
   1. Discuss case with duty radiology registrar or consultant (requests for US should only be made after consultant review by parent team)
   2. Measurements: >3mm single wall thickness*, >14mm transverse diameter, >15mm length.
   3. Comment on passage of gastric contents through pyloric canal.
   4. In difficult cases, sterile water can be injected via the NG tube into the stomach to improve visualisation of the pylorus.
   5. *N.B. single wall thickness is the most specific measurement, and the scan should not be called normal if there is clear thickening of the muscle which does not quite reach these measurements.
   6. If US is equivocal (e.g. measurements not just reaching limits), a plan should be made for a period of clinical observation +/- test feed +/- re-imaging aftere a period agreed in concert with the radiologist (typically 24-48h). It may be appropriate to consider other diagnoses.
   7. Please ensure fluid resuscitation has been started and a nasogastric tube sited prior to transfer to the radiology department (see below).

Management

1. Fluid prescribing
   1. Resuscitate with 10ml/kg fluid bolus of 0.9% NaCl if clinically dehydrated
   2. Following resuscitation, the following fluid should be used until electrolyte correction(1,2,4,5):
      0.9% NaCl + 5% Dextrose + 10mmol KCl in 500ml
      Rate: 150ml/kg/day

2. Monitoring correction
   1. Capillary blood gas/blood test should be carried out a minimum of 12 hourly
   2. Aim for normal pH/H+ including the following 3 factors:
      1. Bicarbonate (HCO3) <28
      2. Chloride (Cl-) >100
      3. Potassium (K+) >3.1

3. Fluid adjustment
   1. Once achieved correction, reduce rate of same fluids to: 100ml/kg/day ⁽⁵⁾
4. Nasogastric tube placement ^(1,6,7)
   1. All patients should have NGT on admission, however this should be spigotted and advise nursing staff to aspirate when required (PRN)
   2. Occasionally babies will have significant losses by vomit or NG, for this small group the loss should be factored into the fluid replacement or increasing base rate of maintenance fluids
5. Proton pump inhibitor use (e.g. omeprazole as per BNF):
   1. Only required when blood-stained aspirates present
   2. Duration to be discussed depending on response and improvement in symptoms

Transfers from district general hospitals to RHC

Radiologically confirmed pyloric stenosis should be transferred safely to RHC for surgical management, following discussion with the on call surgical consultant (see Appendix 7). 

Recommendations

1. No out of hours transfers are recommended
2. Intravenous fluids should continue throughout the ambulance transfer
3. If ultrasound is not available, discussion with the surgical or medical team at RHC is recommended

Intra-operative 

1. All patients are given co-amoxiclav at induction (consult antibiotic guidelines if allergic)
2. All surgeons present to confirm palpation of pylorus
3. Surgical approach is at the discretion of the surgeon and should be discussed at consent.

1. NG to be removed at end of procedure
2. Cue driven feed
3. Stop IVF post-operatively
4. Advise parents to expect vomits
5. Consideration of feed thickeners if vomiting persistent
6. Can be discharged once two full feeds tolerated (as calculated pre-op)

1: Calculating appropriate feed

A common cause of non-bilious vomiting is overfeeding. The feed should therefore be calculated by weight (150ml/kg/day) and carefully explained to the parents or guardians ⁽³⁾. For reference 1 Fluid Oz is approximately 30ml. 

2: Use of Ultrasound in diagnosis

Historically, a test feed and palpation of an olive shaped mass in the epigastrium was used for diagnosis^(2,8). Ultrasound is widely accepted as a gold standard of diagnosis, to confirm hypertrophic pyloric stenosis (single wall thickness >3mm, transverse diameter >14mm) ^(2,5). It does not delay treatment given that the patient requires gradual restoration of their acid base balance and does not carry any risks to the child. None of our patients currently would proceed to the operating theatre without ultrasound confirmation.

If ultrasound has been carried out in a district general hospital, this should be discussed with the radiology department within the hospital. The scan should be repeated if any doubt on the diagnosis is present.

If a patient presents out of hours, there is limited benefit in imaging them at this time. A radiologist is always present on site 09:00 – 17:00, 7 days a week, therefore a plan should be made to carry out an ultrasound to look for pyloric stenosis within those hours. Given fluid resuscitation is required in the first instance, this should be initiated even prior to confirmatory ultrasound. A nasogastric tube should ideally be sited prior to transfer to the radiology department. 

3: Choice of Fluid

Fluid choice was based on the move towards standardisation ⁽⁹⁾, a safe balanced fluid to correct the alkalosis gradually, while also being universally available across different paediatric centres in the west of Scotland. Other fluid choices may be acceptable in correcting the acid base imbalance. 0.9% NaCl + 5% Dextrose + 10mmol KCl is based on a bag of 500ml volume. This is equivalent to 20mmol KCl in 1 litre (20mmol/L). Patients should not be admitted to the ward without secure intravenous access.

4: Electrolyte Threshold

Complete correction of the acid base imbalance should mean hydrogen ions, bicarbonate, base excess, sodium, potassium and chloride within the normal ranges. The main features of correction in pyloric stenosis should include bicarbonate <28, chloride >100 and potassium >3.1^(1,2,4,5). Hyperkalaemia is often detected in squeezed heel prick samples. Venous samples are preferable if possible.

5: Use of nasogastric tube

Nasogastric tube placement is indicated to prevent aspiration of gastric contents. It is not recommended to aspirate regularly or leave on free drainage, since this will lead to further acid loss(1,5,6,7). 

6: Use of PPI

Proton pump inhibitors such as omeprazole should be limited to usage in babies with significant concern for reflux. If treated successfully with a pyloromyotomy, some patients should not require PPI prescription. Blood stained nasogastric aspirates indicate a degree of gastric inflammation or erosion, which is an indication for PPI.

7: Transfers

All transfers should be discussed with the consultant surgeon on call. No transfers should happen outside daytime working hours. Out of hours transfers would pose an unnecessary risk to the infant given reduced staffing. Intravenous fluids should continue throughout transfer, necessitating appropriate staff to accompany the patient. This is due to the unnecessary risk posed by dehydration and electrolyte imbalance related to the condition, which can cause respiratory arrest and death ^(1,8).

8: Re-presentation with vomiting

Patients re-presenting with vomiting should be assessed by medical staff, and if appropriate, involve the surgical team. Other causes of vomiting should be excluded. If there is ongoing concern for recurrent pyloric stenosis, a barium meal study may help in the diagnosis.