USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

What electrolyte disturbance is characteristic of ischemia?

1. Bicarbonate accumulation

2. Intracellular calcium depletion

3. Na+ and Ca2+ leakage

4. Extracellular potassium increase

The correct answer is: Extracellular potassium increase

Ischemia, which is a condition characterized by insufficient blood flow to tissues, leads to a number of metabolic and cellular changes, including significant alterations in electrolyte distribution. One of the hallmark features of ischemic conditions is the increase of extracellular potassium. During ischemia, cells are unable to maintain normal ion gradients due to reduced ATP production, which hampers the function of sodium-potassium ATPase pumps. This disruption results in the leakage of potassium ions from the intracellular space into the extracellular fluid. The accumulation of potassium outside the cells is a direct consequence of cellular stress and injury, potentially leading to hyperkalemia. This increase in extracellular potassium can have critical physiological implications, such as affecting cardiac rhythm and excitability, which are vital to understand in clinical contexts involving ischemic events. The other options relate to different physiological processes. For instance, bicarbonate accumulation is usually seen in metabolic alkalosis rather than ischemia. Intracellular calcium depletion is more associated with cellular health and resilience rather than ischemia where calcium levels can actually rise due to cell injury. Lastly, while sodium and calcium leakage may occur, it’s not the hallmark characteristic compared to potassium changes during ischemia. Overall, the significant increase in extracellular potassium concentration represents a key electrolyte disturbance associated