A 32-year-old man comes to the emergency department due to a 12-hour history of poor oral intake and vomiting. He says that he feels "a little dizzy." He has had no abdominal pain or diarrhea. Medical history is unremarkable. Blood pressure is 110/70 mm Hg while supine and 100/60 mm Hg while sitting. Pulse is 90/min. Laboratory results are as follows: Which of the following is the most likely cause of the decreased chloride level in this patient?

Question

A 32-year-old man comes to the emergency department due to a 12-hour history of poor oral intake and vomiting.  He says that he feels "a little dizzy."  He has had no abdominal pain or diarrhea.  Medical history is unremarkable.  Blood pressure is 110/70 mm Hg while supine and 100/60 mm Hg while sitting.  Pulse is 90/min.  Laboratory results are as follows:  Which of the following is the most likely cause of the decreased chloride level in this patient?

Quizplus · Accepted Answer

This patient's laboratory results demonstrate hypochloremia, hypokalemia, and an elevated bicarbonate level. These findings are all consistent with gastrointestinal losses due to vomiting. Gastrointestinal fluid is rich in both hydrogen chloride and potassium chloride. Therefore, any process by which excessive gastric contents are lost (vomiting, nasogastric suctioning) may result in loss of hydrogen, chloride, and potassium ions. The results include hypochloremia and hypokalemia, as seen in this patient. Furthermore, the loss of hydrogen ions increases the concentration of bicarbonate. An arterial blood gas would be expected to confirm metabolic alkalosis in this patient (eg, elevated pH and elevated bicarbonate). Administration of isotonic sodium chloride and potassium is used to reverse these electrolyte abnormalities. A small anion gap elevation may occur in patients with metabolic alkalosis; one contributing factor is alkalemia causing albumin molecules to release hydrogen ions, which results in an increased anionic charge of albumin and a higher anion gap. (Choices B and E) For each hydrogen ion lost due to vomiting, a bicarbonate ion is produced. In addition, the volume contraction caused by vomiting leads to activation of the renin-angiotensin system, which stimulates bicarbonate reabsorption. Although volume contraction and bicarbonate reabsorption are increased in this patient, they are the result of hydrogen chloride loss not the cause of it. These answer choices reverse cause and effect. (Choice C) In this patient, vomiting has caused significant loss of hydrogen chloride, resulting in metabolic alkalosis. The metabolic alkalosis is the consequence, not the cause, of vomiting. (Choices D and F) Hypokalemia accompanies but does not cause this patient's hypochloremia. It is the primarily due to increased renal excretion of potassium caused by aldosterone, which is stimulated by the renin-angiotensin system as a means to retain fluid. Other contributing factors include gastrointestinal loss of potassium, and intracellular shift of potassium caused by alkalosis, Educational objective: Gastric contents are rich in hydrogen, chloride, and potassium. Therefore, vomiting causes hypochloremic metabolic alkalosis and hypokalemia. Bicarbonate levels rise as a result of hydrogen loss and activation of the renin-angiotensin system.

A 32-Year-Old Man Comes to the Emergency Department Due to a 12-Hour