Pyloric stenosis is a medical emergency, not a surgical emergency. The patient should not be operated on until there has been adequate fluid and electrolyte resuscitation. According to Barash, the infant should have normal skin turgor, and the correction of the electrolyte imbalance should produce a sodium level that is >130 mEq/L, a potassium level that is at least 3 mEq/L, a chloride level that is >85 mEq/L and increasing, and a urine output of at least 1 to 2 mL/kg/hr. These patients need a resuscitation fluid of full-strength, balanced salt solution and, after the infant begins to urinate, the addition of potassium.
The cardinal findings in pyloric stenosis are dehydration, metabolic alkalosis, hypochloremia, and hypokalaemia. Loss of gastric fluid leads to volume depletion and loss of sodium, chloride, acid (H+) and potassium. This results in a hypokalemic, hypochloremic metabolic alkalosis. The kidneys attempt to maintain normal pH by excreting excess HCO3.The kidneys attempt to conserve sodium at the expense of hydrogen ions, which can lead to paradoxical aciduria. In more severe dehydration, renal potassium losses are also accelerated owing to an attempt to retain fluid and sodium.
According to Smith, “The initial therapeutic approach is aimed at repletion of intravascular volume and correction of electrolyte and acid-base abnormalities (e.g., 5% dextrose in 0.45% NaCl with 40 mmol/L of potassium infused at 3 L/m2 per 24 hours). Most children respond to therapy within 12 to 48 hours, after which surgical correction can proceed in a nonemergent manner. The use of cimetidine has also been shown to rapidly normalize the metabolic alkalosis in patients with hypertrophic pyloric stenosis."
In particular, semi-normalization of chloride may be important (and most relevant), as data suggest that 72% of patients with a chloride of 106 mEq/L have achieve resolution of their metabolic alkalosis.
D W Goh, S K Hall, P Gornall, R G Buick, A Green, J J Corkery Plasma chloride and alkalaemia in pyloric stenosis. Br J Surg: 1990, 77(8);922-3