Clinical meaning
Potassium homeostasis is critical for cardiac electrical stability — both hypokalemia and hyperkalemia can cause fatal arrhythmias. Normal serum potassium is 3.5-5.0 mEq/L. Hypokalemia (<3.5 mEq/L) most commonly results from diuretic therapy (loop and thiazide diuretics), GI losses (vomiting, diarrhea, NG suction), and renal losses (hyperaldosteronism, renal tubular acidosis). Every 0.3 mEq/L decrease in serum potassium represents approximately 100 mEq total body deficit. ECG changes progress with severity: U waves and ST depression (mild) → T-wave flattening and QT prolongation (moderate) → ventricular arrhythmias and cardiac arrest (severe, K+ <2.5). Hyperkalemia (>5.0 mEq/L) results from impaired renal excretion (CKD, ACEi/ARB, K-sparing diuretics, NSAIDs), cellular shift (acidosis, rhabdomyolysis, tumor lysis, succinylcholine), or excessive intake. ECG changes: peaked T waves (earliest, K+ 5.5-6.5) → PR prolongation and QRS widening (K+ 6.5-7.5) → sine wave pattern and cardiac arrest (K+ >8.0). The NP must calculate appropriate replacement rates, choose oral vs IV formulations, identify and treat the underlying cause, and implement cardiac monitoring when indicated. IV potassium administration: NEVER exceed 10 mEq/hour via peripheral IV (20 mEq/hour via central line with continuous cardiac...