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Pyloric stenosis


Key points:

  • Think of pyloric stenosis in a vomiting infant.
  • Only about 1 in 7 cases will have the classic triad of projectile vomiting, visible peristalsis and the palpable “olive”.
  • Hypokalemia suggests several weeks of symptoms.
  • Ultrasound is the most common diagnostic modality, in addition to Hx & Examination.
  • Rehydrate and correct electrolyte disturbances before operative management.

Jackson is a 5-week-old baby brought into the emergency department by his mum Gina. Over the past four days he has had increasing vomiting, and today he seems lethargic. Gina tells you he hasn’t kept anything at all down in the past 24 hours, and has had only one slightly wet nappy since last night.

On examination, Jackson looks pale and mottled. His heart rate is 180 beats per minute, and his respiratory rate is 45. He is afebrile, and his central capillary return is around 3 seconds. You decide to organise an IV cannula for a fluid bolus while continuing to take more history from Gina.

What blood tests would you like to take as you cannulate? What further questions do you have for Mum?

Gina tells you Jackson is her first baby, he was born at term has been fully breast fed. She knows that lots of babies have small vomits after feeding, so wasn’t too concerned initially. The vomit is milky, with no blood or bile. Gina notes that as soon as Jackson vomits he seems hungry and extremely eager to feed again right away. Jackson usually has one or two soft yellow bowel motions a day, and hasn’t had any diarrhoea. Gina doesn’t know of any family history on her side, but isn’t sure about Jackson’s father’s side as they live overseas.

Happily, your cannula goes in beautifully, but yields only enough blood for a venous blood gas. Now what?

While you run through a fluid bolus of 10mL/kg of 0.9% sodium chloride, you take the opportunity to examine Jackson a little further. You find he has a slightly sunken anterior fontanelle. He is sleepy, but sucks vigorously at the pacifier Gina has provided. His abdomen is soft, and you can’t feel any masses in the supine position. There is no respiratory distress, and his lung fields are clear, with dual heart sounds and no murmurs.

What do you expect the gas to show?

As you finish your examination, your blood gas result becomes available. It shows a pH of 7.50, a pCO2 of 50, with a bicarbonate of 38, and a base excess of +5. The electrolytes provided on the gas readout show a sodium of 129, potassium of 3.6, and a chloride of 92.

Jackson has picked up following his fluid bolus, and is now looking for a feed. While keeping maintenance fluids running, you suggest to Gina that offering a breast feed might actually help you confirm the diagnosis. In the meantime, you decide to ask the sonographer if they can help out with an abdominal ultrasound.

As you head back to the room, you run into the surgical registrar and ask them to come and take a look at Jackson. You both note that after the feed, you can see waves of peristalsis across Jackson’s epigastrium going from left to right. You step away just in time to narrowly miss Jackson vomiting forcefully, with milky vomit making it across the cubicle to hit the wall 2 metres away!

The surgical registrar agrees this is very likely pyloric stenosis, and shows you how to palpate his right upper quadrant with Jackson resting prone on her hand. She is suitably impressed by Jackson’s presentation, and happily accepts his care, though she asks you to cancel the ultrasound as she is so confident of the diagnosis. She explains to Gina that Jackson will need surgery to release the muscle between his stomach and duodenum, but first he will need to be rehydrated over night.

Jackson went on to have a laparoscopic pyelomyotomy the following day, with no complications. As they are leaving, they come by to say goodbye, and to let you know it turns out Jackson’s dad also had pyloric stenosis at around about the same age.

What about POCUS?

Sivitz et al established a prospective study assessing the accuracy of POCUS for diagnosis of Pyloric Stenosis; it’s an interesting comparator, but essentially the vast majority of the scans were done by a only one of the participants. It’s also worth noting that the sonographic features become more marked as the stenosis progresses – in the study this meant that all POCUS-negative, sonographer-positive scans were given a free pass. The data suggest that POCUS is suitable as a rule-in test, but is not appropriate for excluding Pyloric Stenosis.

Practice Points

Idiopathic Hypertrophic Pyloric Stenosis typically occurs between 2 and 12 weeks of age, and is around 4-6 times more common in boys, particularly if they are first-born. A family history is often present.

Historically, the diagnosis was made clinically, with a ‘classic triad’ of projectile vomiting, visible peristalsis and a palpable ‘olive’ (the thickened pylorus) in the right upper quadrant at the border of the rectus abdominus muscle. More recently (possibly due to a trend toward earlier presentation to hospital), the ‘olive’ is often not easy to palpate, and ultrasound examination is often employed to confirm the suspected diagnosis. Gotley et al found At least one classic symptom or sign was present in 87% of infants but only 1 in 7 cases had the ‘classic triad’.

Blood gas analysis classically reveals a hypochloraemic metabolic alkalosis. Studies suggest hypokalaemia often doesn’t occur until 3 weeks worth of vomiting. A retrospective study of blood gas results showed that a pH of >7.45, a base excess of >+3, and a chloride of <98 were particularly useful in predicting the diagnosis in babies presenting with vomiting.

Metabolic disturbance needs to be corrected prior to surgery, as this dramatically reduces the risk of intra- and post-operative complications.



Gotley, LM, Blanch, A, Kimble, R, Frawley, K, and Acworth, JP, “Pyloric stenosis: A retrospective study of an Australian population” Emergency Medicine Australia 21 (2009) 407-413.

Taylor ND, Cass DT, Holland AJ. Infantile hypertrophic pyloric stenosis: has anything changed? J Paediatr Child Health. 2013 Jan;49(1):33-7. doi: 10.1111/jpc.12027. Epub 2012 Dec 2.

Sivitz et al. Evaluation of Hypertrophic Pyloric Stenosis by Paediatric  Emergency Physician Sonography Acad Emerg Med. 2013 Jul;20(7):646-51. doi: 10.1111/acem.12163. Epub 2013 Jun 19.

Oakley EA and Barnett PLJ, “Is acid base determination an accurate predictor of pyloric stenosis?” Journal of Paediatrics and Child Health 36 (2000), 587-589.


  • Erin is a Paediatric Endocrinology Fellow at one of the shiniest hospitals in the country, and has an interest in medical ethics. She’s heard it said that no-one has ever been happier to take a call about a blood sugar, and when she’s not working spends as much time snorkelling as possible. She believes the best hot chocolate in the world is from Quebec City on a -25◦C day, and challenges you to find a better one.



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4 thoughts on “Pyloric stenosis”

  1. Thanks for the comment Alan; I agree that a balanced discussion with parents around the merits, risks and benefits of macrolides in the eradication of pertussis is important.

    Several years ago, the BMJ published a huge Danish cohort study of nearly a million singletons reviewing the association between macrolide use, not only a) in the first 120 days of life, but also b) maternal usage in that same period as well as c) maternal usage during pregnancy. The paper makes for interesting reading and can be found here : Lund et al. BMJ 2014

    The discussion reads “In this nationwide cohort, macrolide use in infants was associated with a strongly increased risk of infantile hypertrophic pyloric stenosis (IHPS), including a 30-fold increased risk with use during the first two weeks after birth and a lower, but significantly increased threefold risk with use on days 14 to 120. Similarly, the risk of IHPS was increased more than threefold with maternal use of macrolides during the first two weeks after birth, but not increased with macrolide use thereafter. We found no evidence of an association between IHPS and maternal use of macrolides during gestational weeks 0 to 27, but a possible modest association with use during weeks 28 to birth.”

    It’s my understanding that there’s a reasonable volume of macrolides prescribed in pregnancy for the eradication of Group B Strep, although I’m not sure about the trend around this. Irrespective, it may further inform the incidence of IHPS.

  2. Along with the positive family history, another risk factor is the use of the macrolide medications, Erythromycin and Azithromycin, particularly in the first 2 weeks of life. Azithromycin is commonly used as prophylaxis against pertussis exposure and I feel that it’s use should include a discussion with the parents about this association.

    Azithromycin in Early Infancy and Pyloric Stenosis
    Matthew D. Eberly, Matilda B. Eide, Jennifer L. Thompson, Cade M. Nylund
    Pediatrics Feb 2015, peds.2014-2026; DOI: 10.1542/peds.2014-2026

  3. Pyloromyotomy, FYI. Definitely agree on the VBG being your baseline and monitoring tool, low chloride low sodium is what gives the anaesthetist headaches (the baby doesn’t wake up!).

  4. An eminent paediatric surgeon whom I have always hugely respected taught me that this was the only situation in which to examine the patient from their left hand side. Using your left hand you then aim to pull the ‘olive’ towards yourself and this makes it much easier to feel if it is present. Have always done so since.