What are the metabolic derangements and how are they treated?
The clinical symptoms of pyloric stenosis usually lead to hypovolemia and a hypochloremic, hypokalemic metabolic alkalosis. Since the vomitus consists only of gastric contents, there is a loss of hydrogen, sodium, potassium, and chloride ions. Initially, the renal response is to maintain acid–base balance. Alkaline urine is excreted because the bicarbonate load presented to the kidney exceeds the absorp-tion capability of the proximal tubules. Therefore, the excess bicarbonate is excreted in the urine. In addition, at the distal tubules aldosterone is secreted which increases sodium reab-sorption and potassium excretion. The loss of potassium is further exacerbated by the exchange of hydrogen ions for potassium ions in an effort to maintain acid–base balance.
As the infant becomes more dehydrated the renal response is aimed at maintaining intravascular volume. This is attained by secretion of aldosterone which will result in conservation of sodium ions and further loss of potassium ions. Furthermore, in the distal tubule sodium is conserved at the expense of hydrogen ions and an acidic urine is excreted.
The degree of dehydration should be assessed to guide fluid resuscitation. Sodium chloride is the isotonic fluid of choice for resuscitation. It may be necessary to rapidly correct hypovolemia with 10–20 cc/kg of normal saline if the patient is exhibiting signs of shock. Glucose should be administered as well. These infants may have depleted glycogen stores in the liver leading to the development of hypoglycemia if glucose is not provided.
Hypovolemia and electrolyte and acid–base derange-ments should be corrected prior to surgical intervention.