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 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