Approach To Hyponatremia In The Elderly

Abstract

Hyponatremia is a common and serious electrolyte abnormality particularly in the elderly.  It is often overlooked and is associated with a wide range of deleterious manifestations affecting different systems and is encountered in hospitalised and out-patients.  Since the level of sodium is the determinant of the osmolality of the ECF, changes in the level affect the internal milieu. It is the most common electrolyte disorder encountered in clinical practice affecting 15-30% of hospitalised patients at some time during hospital stay although, many may be asymptomatic. In institutionalised geriatric patients, the incidence may be as high as 50%. It is important to look for the same since it is an independent risk factor for morbidity and mortality. Pre-operative chronic asymptomatic hyponatremia is associated with increased perioperative complication rate and higher 30 day morbidity and mortality. The risk of death in a patient admitted to ICU with hyponatremia is at least 2 times higher than those admitted with normal levels of sodium. Increased mortality has been documented in patients with heart failure and cirrhosis when associated with hyponatremia. Abnormalities in gait and instability in walking observed in some elderly hyponatremic patients have been corrected following correction of hyponatremia. The gait instability translates into increased incidence of falls and fractures. The observation that elderly patients with fracture of pelvis and femur have intractable hyponatremia really raises questions on which occurred first? - hyponatremia or the fracture. The elderly have higher incidence of diabetes, hypertension and other co-morbidities which predispose to hyponatremia. They also have higher chances of hypopituitarism and secondary hypo-adrenalism. Elderly patients with cerebrovascular accidents develop ‘cerebral salt wasting’ characterised by loss of excessive sodium in urine resulting in hyponatremia.