A 2 week old male born at full term with no complications presents to your emergency department with 3 days of vomiting.  According to mother, the patient has had multiple episodes of forceful vomiting after feeds for the past 3 days.  After further history and careful physical exam you suspect pyloric stenosis and order an ultrasound which confirms the diagnosis.  Which of the following is the correct set of electrolyte abnormalities expected with pyloric stenosis?  (scroll down for the answer) 

A) hyponatremic, hypokalemic, hypochloremic

B) hypernatremic, hypokalemic, hypochloremic

C) hypernatremic, hyperkalemic, hypochloremic

D) hypernatremic, hyperkalemic, hyperchloremic

The correct answer is A) hyponatremic, hypokalemic, hypochloremic.

The classic electrolyte abnormalities associated with pyloric stenosis are hyponatremia, hypokalemia, and hypochloremia. 

Pyloric Stenosis Pearls

• >80% males
• Most cases diagnosed in first 10 weeks of life (most commonly from 2 weeks to 5 weeks old) 
• Pathophysiology: result of pyloric muscle hypertrophy that obstructs gastric outflow
• Clinical: nonbilious projectile vomiting immediately after feeds, continue to attempt eating (“hungry vomiter”)
• Diagnosis: Ultrasound
• Pathognomonic electrolyte abnormalities: hyponatremic, hypokalemic, hypochloremic, metabolic alkalosis 
• VIP to start correcting dehydration and electrolyte abnormalities in emergency department 

Stapczynski, J. Stephan,, and Judith E. Tintinalli. Tintinalli's Emergency Medicine: A Comprehensive Study Guide. 7th ed. New York, N.Y.: McGraw-Hill Education LLC., 2011.