Physiology: hypertrophy of the pyloric sphincter with functional gastric outlet obstruction.
Onset: 2 to 6 weeks of age
Clinical findings (multiple P’s):
(1) persistent, progressive projectile nonbilious vomiting
(2) poor weight gain
(3) peristaltic waves visible across the abdomen with patient lying supine on back
(4) palpable “olive” at pylorus (midepigastrium)
(5) prominent metabolic alkalosis (from loss of gastric acid)
(6) paradoxic aciduria (despite alkalosis, see below)
If the clinical examination is questionable, ultrasonography can demonstrate muscle thickening at the pylorus. While contrast studies may be diagnostic, this results in additional fluid within the stomach
A number of fluid and acid-base disorders may be seen (Marshall):
(1) dehydration
(2) metabolic alkalosis from loss of gastric acid. Initially the kidneys excrete excess bicarbonate, but with dehydration and the need for sodium resorption there is resorption of the bicarbonate, yielding an acid urine.
(3) potassium depletion occurs, both from loss in gastric contents and from increase aldosterone secretion
(4) chloride depletion from loss of gastric acid
