Postoperative Hyponatremia in the Orthopaedic Patient

Hyponatremia, defined as serum sodium less than 135 mmol/L, is associated with increased morbidity and mortality in the perioperative period. The most common etiological factor is preoperative hyponatremia, observed in 7% of orthopaedic surgery patients, and is associated with higher 30-day mortality, perioperative coronary events, wound infections, pneumonia, and prolonged hospitalization. Postoperative hyponatremia affects as many as 30% of patients and is linked to longer hospital stays, higher cost of care, and a greater risk of falls. The most significant pathophysiologic change due to hyponatremia is its osmotic effect on the brain. In the event of rapid fluid shift from the hypotonic extracellular compartment to the intracellular compartment, acute cerebral edema can occur, resulting in seizures, coma, and even death. The treatment strategy is rapidly raising serum sodium levels along with identifying and correcting underlying causes. In contrast, a rapid increase in serum sodium levels in patients with chronic hyponatremia can lead to catastrophic brain demyelination. Preventive measures should start preoperatively by suspending diuretics and other drugs that promote SIADH and addressing adrenal insufficiency, if any. Intraoperative preventive measures include limiting the infusion of hypotonic fluids and replacing volume with isotonic fluids. If a patient’s sodium level falls below 130 mmol/L, accompanied by symptoms including vomiting, confusion, somnolence, seizures, and coma, emergency care is necessary. Determining the etiology of hyponatremia and management typically requires expert consultation.