Which electrolyte disturbance is a potential side effect of cardiopulmonary bypass (CPB)?

• A. Hyperkalemia
• B. Hyponatremia
• C. Hypokalemia
• D. Hypercalcemia

Answer: (C)

On cardiopulmonary bypass, the circulating blood is diluted by the bypass priming solution, which lowers the concentration of many electrolytes, including potassium. After bypass ends, ongoing diuresis and shifts of potassium into cells during reperfusion can further reduce serum potassium levels. The combination of dilutional effects and postoperative potassium losses makes hypokalemia a common and clinically important disturbance to monitor after CPB. While there can be intraoperative hyperkalemia due to potassium-rich cardioplegia, the postoperative tendency toward lower potassium is a key complication to expect and manage, which is why this option is the best fit. Hyponatremia and hypercalcemia can occur in other contexts, but they are less characteristic in this specific CPB setting.