Clinical meaning
Electrolytes are charged ions essential for maintaining cellular membrane potentials, nerve impulse conduction, muscle contraction, acid-base balance, and enzymatic functions. The NP must understand the pathophysiology underlying each electrolyte disorder to prescribe appropriate correction and avoid iatrogenic complications. Potassium (K+, normal 3.5-5.0 mEq/L) is the principal intracellular cation; the Na+/K+-ATPase pump maintains the transmembrane potassium gradient that establishes the resting membrane potential (~-90 mV). Hyperkalemia reduces this gradient, making cells more excitable initially but eventually blocking depolarization entirely, producing the characteristic ECG progression: peaked T waves → prolonged PR → widened QRS → sine wave → VF/asystole. Hypokalemia increases the gradient, hyperpolarizing cells and producing muscle weakness, ileus, U waves, and predisposition to torsades de pointes. Sodium (Na+, normal 135-145 mEq/L) is the primary extracellular cation and the principal determinant of serum osmolality (calculated: 2×Na + glucose/18 + BUN/2.8). Hyponatremia is a water balance disorder, not a sodium deficit: excess free water dilutes serum sodium. Classification by volume status (hypovolemic, euvolemic, hypervolemic) and osmolality (hypotonic, isotonic, hypertonic) drives the diagnostic algorithm. The rate of correction is more dangerous than the...