Massive blood transfusion can lead to hyperkalemia because stored red blood cells release potassium over time due to cell membrane breakdown. When large volumes of blood are transfused rapidly, this extracellular potassium load overwhelms the recipient’s capacity to maintain normal serum potassium, causing elevated potassium levels. Hyperkalemia is particularly dangerous as it can precipitate life-threatening cardiac arrhythmias. Understanding this risk allows for appropriate monitoring and management during transfusion therapy.

Reference: Miller's Anesthesia, 9th Edition.