Calcium and Tetany

Calcium stabilizes excitable cell membranes and supports skeletal-muscle contraction, cardiac conduction, and coagulation. Tetany is the neuromuscular syndrome that appears when ionized calcium becomes too low: tingling progresses to painful spasms, carpopedal contraction, laryngospasm, seizures, or dysrhythmia. The clinical urgency depends less on an isolated number than on the combination of ionized calcium, symptoms, ECG findings, haemodynamic status, and the speed of the decline. An anxious, hyperventilating patient may report perioral tingling and develop hand spasms because alkalosis lowers ionized calcium. Those findings should not be dismissed as anxiety until airway status, breathing, circulation, ECG, and relevant laboratory results have been assessed. A patient with chronic kidney disease may have a different pattern: phosphate retention and impaired vitamin D activation gradually disturb calcium balance, and an acute illness can push a previously compensated patient into symptomatic tetany.