Final answer:
Hyperkalemia after a burn injury is most commonly due to massive deep muscle injury as can occur with electric burns, which releases potassium from damaged cells into the bloodstream.
Step-by-step explanation:
A patient can be hyperkalemic following a burn injury due to massive deep muscle injury, as can occur with electric burns. When tissue is damaged, intracellular contents, including potassium, are released into the extracellular fluid, which can lead to hyperkalemia. This elevated potassium blood level can impair the function of skeletal muscles, the nervous system, and particularly the heart, potentially leading to life-threatening cardiac complications. In addition to muscle injury, conditions such as renal failure, severe dehydration, and adrenocortical insufficiency (e.g., Addison's disease) can decrease the excretion of potassium by the kidneys, further contributing to hyperkalemia after a burn.