Pyloric stenosis

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  • See also

    Recognition of the seriously unwell neonate and young infant
    Intravenous fluids

    Key Points

    1. Classical clinical and biochemical features are unlikely in early presentations of pyloric stenosis
    2. Abdominal ultrasound may be equivocal in early presentations, and should be repeated if there is ongoing clinical suspicion
    3. Correction of dehydration, electrolyte disturbances and acid-base abnormalities is the priority of early management
    4. Surgical management can be delayed until the above are corrected


    Pyloric stenosis is caused by hypertrophy and hyperplasia of the muscular layers of the pylorus leading to gastric outlet obstruction. It usually presents between 2 and 6 weeks of chronological age with progressive non-bilious vomiting. It is unlikely after 12 weeks of age. Definitive treatment is by pyloromyotomy 

    Risk factors include:

    • Male
    • First born
    • Parental history of pyloric stenosis (especially maternal)
    • Pre-term birth
    • Younger maternal age
    • Postnatal exposure to macrolide antibiotics
    • Formula feeding
    • Maternal smoking during pregnancy




    • Recurrent and progressively more forceful. May be projectile
    • May occur shortly after feeding
    • Infant may appear hungry post-vomiting
    • Non-bilious
    • Blood-stained in less than 10%

    Weight loss or inadequate weight gain



    • Assess degree of dehydration
    • Weigh and plot on growth chart with previous weights if available

    Visible gastric peristalsis (may be more obvious following a feed)

    Pyloric mass

    • Olive shaped
    • Located in the right upper quadrant at the lateral edge of the rectus abdominis muscle 
    • Best felt from the left side with the infant settled and supine. May be difficult to palpate. May require repeated examinations or to wait for several minutes with hand on abdomen to feel

    Visible gastric peristalsis and pyloric mass can be difficult to appreciate and are unlikely to be present in early presentations. They are not required to consider a diagnosis of pyloric stenosis

    Differential diagnoses



    • Capillary or venous blood gas for electrolytes and glucose
    • Hypochloraemic hypokalaemic metabolic alkalosis may be seen with prolonged vomiting, the degree of abnormality is proportionate to the duration of symptoms
    • Abdominal ultrasound (95% sensitive in the diagnosis of pyloric stenosis). If ongoing clinical suspicion despite initial equivocal ultrasound, consider repeat study


    • Gain IV access
    • Correction of dehydration, electrolyte disturbances and acid-base abnormalities
    • Stop oral feeds
    • Insert a nasogastric tube if profuse vomiting continues despite stopping feeds

    Fluid management

    • Surgical correction of pyloric stenosis is usually delayed until after correction of dehydration, electrolyte disturbances and acid-base abnormalities
    • It is particularly important to await normalisation of serum bicarbonate before surgery because of the risk of hypoventilation/apnoea post-operatively in the setting of a metabolic alkalosis





    0.9% sodium chloride

    Fluid resuscitation as required. Not all infants will require fluid resuscitation


    0.9% sodium chloride + 5% glucose 

    Refer to dehydration and IV fluids guidelines
    Include potassium in IV fluids once urine output is adequate (1-2 mL/kg/hr)

    Maintenance (ongoing)

    0.9% sodium chloride + 5% glucose

    Consider consultation with local paediatric team when

    Pyloric stenosis is suspected

    Consider transfer when

    Confirmed or high suspicion for pyloric stenosis. Transfer to a paediatric surgical centre early, once an initial management plan is in place

    For emergency advice and paediatric or neonatal ICU transfers, see Retrieval Services

    Consider discharge when

    • Ultrasound is not consistent with pyloric stenosis
    • Differential diagnoses have been considered
    • Clinically well and tolerating oral feeds
    • Follow-up plan in place

    Parent information

    Pyloric stenosis

    Last updated March 2024

  • Reference List

    • Dalton, B et al 2016. Optimizing Fluid Resuscitation in Hypertrophic Pyloric stenosis. Journal of Paediatric Surgery, vol. 51, no. 8, pp. 1279 – 1282.
    • Hunter, C 2017. Pyloric stenosis. In: BMJ Best Practice. (Accessed March 2019)
    • Jobson, M 2016. Contemporary Management of Pyloric stenosis. Seminars in Paediatric Surgery, vol. 25, no. 4, pp. 219-224.
    • Olivé, AP et al 2023. Infantile hypertrophic pyloric stenosis. In: UpToDate, Post TW (Ed), Wolters Kluwer. (Accessed October 2023) 
    • Rich, BS et al 2021. Hypertrophic Pyloric stenosis. Pediatr Rev. 2021 Oct;42(10):539-545. doi: 10.1542/pir.2020-003277. PMID: 34599053.