A 1-month-old boy is brought to the office on a hot summer day due to vomiting and excessive sleepiness. He had been exclusively breastfeeding with normal feeding patterns until this afternoon, when he had 2 episodes of emesis and appeared much sleepier than usual. The infant was born at 41 weeks gestation after an unremarkable pregnancy. Newborn screening was positive for a homozygous F508 mutation affecting an epithelial transmembrane protein; further confirmatory testing is pending. Physical examination shows a somnolent boy with a sunken fontanelle and dry mucous membranes. Which of the following electrolyte disturbances is most likely responsible for this patient's current symptoms?

Question

A 1-month-old boy is brought to the office on a hot summer day due to vomiting and excessive sleepiness.  He had been exclusively breastfeeding with normal feeding patterns until this afternoon, when he had 2 episodes of emesis and appeared much sleepier than usual.  The infant was born at 41 weeks gestation after an unremarkable pregnancy.  Newborn screening was positive for a homozygous F508 mutation affecting an epithelial transmembrane protein; further confirmatory testing is pending.  Physical examination shows a somnolent boy with a sunken fontanelle and dry mucous membranes.  Which of the following electrolyte disturbances is most likely responsible for this patient's current symptoms?

Quizplus · Accepted Answer

Eductional Objective: Patients with cystic fibrosis (CF) produce eccrine sweat with higher-than-normal concentrations of sodium and chloride.  Exposure to high temperature or exercise can lead to hyponatremia and hypochloremia due to excessive sodium chloride loss through sweat; therefore, salt supplementation is recommended.

A 1-Month-Old Boy Is Brought to the Office on a Hot