Overview
Potassium (K⁺) is the primary intracellular cation, maintaining resting membrane potential in cardiac, skeletal, and smooth muscle.
Potassium (K⁺) is the primary intracellular cation, maintaining resting membrane potential in cardiac, skeletal, and smooth muscle. Normal serum K⁺ is 3.5–5.0 mEq/L. Dyskalemia at extreme ranges causes potentially fatal dysrhythmias — hypokalemia below 2.5 mEq/L and hyperkalemia above 6.5 mEq/L demand emergency intervention. Hypokalemia (K⁺ <3.5 mEq/L): Hyperpolarizes cells → muscle weakness, ileus, and ventricular ectopy. Life-threatening below 2.5 mEq/L. Missed hypokalemia in a patient on digoxin increases digoxin toxicity risk exponentially. Hyperkalemia (K⁺ >5.0 mEq/L): Depolarizes cells → cardiac conduction slows → bradycardia, heart block, sine wave, asystole. Peaked T waves are the first ECG sign. Ventricular fibrillation can occur without warning if K⁺ >7.0 mEq/L. Top 3 Nursing Priorities: 1. Continuous cardiac monitoring — identify dysrhythmias immediately 2. Establish IV access and confirm serum K⁺ before any replacement or shifting agent 3. Identify and treat the underlying cause (not just the electrolyte) Classic NCLEX Trap: Treating hypokalemia without simultaneously checking magnesium (Mg²⁺ <1.8 mEq/L blocks renal K⁺ retention — replacement fails without correcting hypomagnesemia first). On the exam, writers often pair stable-sounding options with unstable data—notice the...
