Pyloric Stenosis - Pathophysiology

Pathophysiology

The gastric outlet obstruction due to the hypertrophic pylorus impairs emptying of gastric contents into the duodenum. As a consequence, all ingested food and gastric secretions can only exit via vomiting, which can be of a projectile nature. The exact cause of the hypertrophy remains unknown.

The vomited material does not contain bile because the pyloric obstruction prevents entry of duodenal contents (containing bile) into the stomach.

This results in loss of gastric acid (hydrochloric acid). The chloride loss results in hypochloremia which impairs the kidney's ability to excrete bicarbonate. This is the significant factor that prevents correction of the alkalosis.

A secondary hyperaldosteronism develops due to the hypovolemia. The high aldosterone levels causes the kidneys to avidly retain Na+ (to correct the intravascular volume depletion), and excrete increased amounts of K+ into the urine (resulting in hypokalaemia).

The body's compensatory response to the metabolic alkalosis is hypoventilation resulting in an elevated arterial pCO₂.