Key Concepts
Introduction
Potassium (K⁺) is the predominant intracellular cation (normal: 3.5–5.0 mEq/L in serum). Potassium imbalances — hypokalemia (< 3.5 mEq/L) and hyperkalemia (> 5.0 mEq/L) — are among the most dangerous electrolyte disorders because both extremes cause life-threatening cardiac dysrhythmias. Potassium is critical for maintaining the resting membrane potential of excitable cells (myocardium, skeletal muscle, neurons). The Na/K-ATPase pump maintains intracellular K⁺ at ~150 mEq/L versus extracellular ~4 mEq/L. This steep gradient drives the resting membrane potential (approximately –70 mV), which determines excitability. Any significant shift in serum K⁺ alters this gradient and disturbs electrical activity. For NCLEX-RN: know the ECG changes for each, understand medication causes, know IV potassium safety rules, and recognize the clinical sequelae. On the exam, writers often pair stable-sounding options with unstable data—notice the mismatch before you commit. If the stem names a license or role, reread that line; scope errors are classic trap answers even when the clinical topic is familiar. Run a 60-second scan: breathing work and oxygenation, perfusion and end organs, neuro baseline, likely infection sources, and devices that can fail quietly. When...