Analysis of hyponatraemia associated post-operative mortality in 3897 hip fracture patients.

Hyponatraemia is common in hospitalised patients. In recent years the relationship between hyponatraemia and bone metabolism, falls and fractures has become more established. This study evaluates the prevalence of hyponatraemia (plasma sodium<135mmol/l) in 3897 patients undergoing operative treatment for hip fracture and the relationship between hyponatraemia and mortality in these patients. Hyponatraemia was an independent risk factor for increased post-operative mortality on multivariate analysis. Median age at admission was 83 years. Hyponatraemia was present in 19.1% of patients with hip fracture on admission, 29.5% of patients in the first 24h post-operatively and 20% of patients at discharge. There was a significant association between hyponatraemia and time from admission to surgery indicating that patients admitted with hyponatraemia waited longer. The median follow-up time was 863 (range 0-4352) days. There were 2460 deaths (63.1% of the original 3897 patients) prior to the censor date. A total of 1144 patients (29.4% of the original 3897 patients) died within 12 months of discharge. Median time to death for patients with and without hyponatraemia on admission was 34 months (SE 1.7 months) and 41 months (SE 2.5 months) respectively (p=0.003). Median time to death for patients with and without hyponatraemia within 24h post-operatively was 35 months (SE 2.5 months) and 42 months (SE 1.7 months) respectively (p=0.004). Following elimination of other independent variables associated with increased mortality, hyponatraemia on admission was associated with an increased risk of death (adjusted HR 1.15, p=0.005). Post-operative hyponatraemia was also associated with an increased risk of death (adjusted HR 1.15, p=0.006). Trends suggested that hyponatraemia within 48h of discharge was associated with an increased risk of death (adjusted HR 1.15, p=0.636). Hyponatraemia is common in elderly patients with hip fractures both at initial presentation and during admission. In this vulnerable patient group, hyponatraemia may delay time to definitive surgery and is a potentially reversible cause of increased post-operative mortality. Every effort should be made to identify and correct hyponatraemia in hip fracture patients.