Hyponatraemia is one of the most common electrolyte disorders in the elderly and has considerable associated morbidity and mortality. In this study we report the prevalence and independent risk factors for the development of post-operative hyponatraemia after surgery for hip fracture.

We conducted a retrospective cohort study of 144 consecutive patients who underwent surgery after sustaining a hip fracture. Patient medical case-notes, operative notes and online biochemistry results were used to obtain relevant data which was entered into a database.

Pre-operative (30/144, 21%) and post-operative hyponatraemia (49/144, 34%) was common. However, most cases were mild (plasma sodium >130 mmol/l) and only 1% of pre-operative and 6% of post-operative patients had moderate/severe hyponatraemia (plasma sodium <130mmol/l). One of 3 post-operative deaths involved a patient with moderate hyponatraemia as a consequence of severe congestive cardiac failure. In order to determine the independent relationship between several reported risk factors and hyponatraemia we constructed a multivariable logistic regression model. Female gender, pre-operative hyponatraemia and hypotonic fluid administration were all significantly associated with the development of post-operative hyponatraemia. Age and thiazide diuretics both had positive risk associations however were not statistically significant.

Hyponatraemia is a common problem in hip fracture patients. While the majority of cases in this series were mild, 6% of patients suffered from moderate/severe hyponatraemia post-operatively. Female gender, pre-operative hyponatraemia and hypotonic fluid administration are all important and independent risk factors for the development of hyponatraemia. Hypotonic intravenous fluids should be avoided unless clinically indicated in this patient group.