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infant for this part of the examination. Another diagnostic clue is the presence of
prominent gastric peristaltic waves across the abdomen.
If the child has vomited for an extended period, he or she will show signs of
growth failure. There may be loose, hanging skin and an absence of subcutaneous
tissue. The infant may take on an “old man” appearance, with wrinkled skin on
the face and body. Weight gain is inadequate, which may be calculated by
knowing that the average child regains birth weight by 10 days of age and
thereafter 15 to 30 g (0.5 to 1 oz) per day. With severe dehydration, the infant
may be hypotonic and lethargic with poor feeding.
Serum electrolytes may be abnormal because of gastric losses. Accordingly, the
potassium and chloride are low, and serum bicarbonate is high. This
hypochloremic alkalosis may be profound with serum chlorides as low as 65
mEq/L. The patient can exhibit periods of apnea from the extreme metabolic
alkalosis. When dehydration becomes severe, the patient may then develop
acidosis, indicating an advanced and even more dangerous metabolic imbalance
(see Chapter 100 Renal and Electrolyte Emergencies ).
Management. Infants should be hospitalized and rehydrated with appropriate
fluid and electrolyte replacement. Initially, IV normal saline should be used
(lactated Ringer solution is contraindicated) to replenish intravascular volume and
supply adequate chloride. Potassium chloride should be added once urine output
has been established. If hypotonic solutions are used, there is significant risk of
causing hyponatremia.
Few pediatric surgeons will operate based on a typical history without US
imaging. The real-time US scanning not only increases the accuracy of the
diagnosis of pyloric stenosis, but can also localize the “olive.” The hypertrophic
pyloric muscle is seen as a thick hypoechoic ring surrounding a central echogenic
mucosal and submucosal region ( Fig. 116.13 ). The quantitative criteria for the
sonographic diagnosis of hypertrophic pyloric stenosis are 1.5 cm or longer
length of the pyloric canal/channel with 0.3 cm or greater thickness of the circular
muscle (institutions may vary slightly in exact measure used for diagnosis). The
ability of stomach contents to pass through the pylorus can be assessed

dynamically.