Limited mobility or prolonged immobility is common among elderly patients and, if severe, has negative effects on multiple organ systems. Some of these effects result in characteristic electrolyte disturbances. Two major complications related to immobility that have a direct effect on electrolyte levels are:

(1) Increased bone resorption

(2) Low cardiac output and muscle rigidity

Immobility related increased bone resorption results in liberation of calcium and phosphate from bone typically resulting in hypercalcemia and hyperphosphatemia, although serum calcium levels can be variable. Even though the patient has hypercalcemia, they will have a net negative calcium balance due to increased excretion rates, which can sometimes cause serum calcium levels to present as normal or even low. Low cardiac output and muscle deterioration results in increased total body water (hypervolemia) and lower serum sodium (hyponatremia).