Ans: C
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The most serious effects of hypokalemia are on the heart, a fact that necessitates frequent electrocardiography or cardiac telemetry. Hypokalemia produces a decrease in the resting membrane potential, causing prolongation of the PR interval. It also prolongs the rate of ventricular repolarization, causing depression of the ST segment, flattening of the T wave, and appearance of a prominent U wave. This supersedes the importance of fluid balance monitoring, arterial blood gases, oxygen saturation, or hemoglobin levels.