Post-operative orthopaedic hyponatremia: Etiology and clinical approach

Abstract

Hyponatremia is common after orthopaedic surgeries. The prevalence of hyponatremia in the post-operative period is 25-40% in elderly patients. It can cause serious and potentially life threatening complications. Identifying the cause (etiology) and providing appropriate treatment can mitigate the adverse effects of hyponatremia. Depending on the underlying cause, the treatment of hyponatremia can be markedly different. The aim of the study is to determine the cause of post-operative orthopaedic hyponatremia. Methods: This is a prospective study of adults aged more than 65 years admitted with major lower limb fractures who developed post-operative hyponatremia. ECF volulme status was assessed by clinical examination and biochemical parameters. Results: Thirty five patients developed post-operative hyponatremia. The most common cause of post-operative orthopaedic hyponatremia was hypovolemia 45.71% (n=16), followed by euvolemia (SIADH) in 25.71% (n=9). Acute kidney injury, hypervolemia and medications each in 3 cases (8.57% each), hypotonic fluids in one case. Etiology was multifactorial in 77.14% (n=27). Conclusions: Hypovolemia and euvolemia with SIADH are the two major causes of hyponatremia after orthopaedic surgery. The treatment requirements are exact opposites. Hypovolemia requires rehydration with IV fluids where as SIADH needs fluid (free water) restriction. Understanding the etiology of hyponatremia helps to treat hyponatremia with optimal use of IV fluids and avoids adverse outcomes.