The client presents to the emergency department (ED) with a 24-hour history of excessive vomiting. What is most concerning for the ED nurse?

Excessive vomiting causes a loss of hydrochloric acid (HCl) from the stomach, which leads to a decrease in hydrogen ions in the body. As H+ ions are lost, the blood becomes more alkaline, resulting in metabolic alkalosis. This is the acid-base imbalance most concerning after prolonged vomiting. The arterial blood gas in metabolic alkalosis would show an elevated pH (above 7.45) and an elevated bicarbonate level (above 26 mEq/L), with possible compensatory respiratory depression to retain CO2. Metabolic acidosis involves a gain of acid or loss of bicarbonate and would not result from vomiting; it is more associated with diarrhea, renal failure, or diabetic ketoacidosis. Respiratory alkalosis results from hyperventilation and excessive loss of CO2, not from gastrointestinal fluid losses. Respiratory acidosis results from hypoventilation and CO2 retention. Since vomiting primarily causes loss of gastric acid (H+ and Cl-), the dominant acid-base disturbance is metabolic alkalosis, which is the nurse's greatest concern because it can lead to electrolyte abnormalities such as hypokalemia and hypocalcemia, as well as serious cardiac dysrhythmias.