Post-operative hyponatraemia in orthopaedic injury

Post-operative hyponatraemia can be dangerous and can go unrecognised as the presenting signs and symptoms are often confused with post-operative or post-anaesthesia sequelae. Infusion of dextrose containing fluids in the peri-operative period is a well-documented cause of this electrolyte imbalance. We conducted a retrospective study to identify the incidence of hyponatraemia following surgery for orthopaedic injury. Medical notes and fluid charts of the patients were scrutinised. We detected 32 cases of post-operative hyponatraemia over a period of 1 year. Eleven hundred and thirty-one patients underwent orthopaedic surgery during this period. Calculated incidence of hyponatraemia was 2.8%. In the hyponatraemic group, the mean pre-operative sodium was 134 mmol/l and mean post-operative sodium was 126 mmol/l. There was a statistically significant difference between mean pre-operative and mean post-operative serum sodium concentration (P<0.0001, two sample t-test). The mean volume of dextrose containing fluids received by each patient was 3.26 l. There is a significant risk of hyponatraemia following orthopaedic surgery, especially in the elderly. Orthopaedic units need to be aware of this easily avoidable condition. Fluid infusion regimes should be carefully formulated with exclusion of dextrose containing fluids to prevent the danger of hyponatraemia.