Introduction: Hyponatraemia (serum sodium < 135mMol/L) is the commonest electrolyte imbalance encountered in clinical practice. It is associated with multiple poor clinical outcomes including increased mortality, longer hospital stay, falls and fractures. Prevalence is higher in frail patient groups, and elderly patients with fragility fractures (EPFF) are particularly susceptible. Euvolaemic hyponatraemia due to the syndrome of inappropriate anti-diuretic hormone (SIADH) is widely assumed to be the commonest cause. However, little is known about the epidemiology and aetiology of hyponatraemia in EPFF. This study examined the prevalence, incidence and aetiology of hyponatraemia in EPFF.
Methods: Prospective observational study of consenting adults aged >65 years admitted with a fragility fracture to Aberdeen Royal Infirmary between 7th January– 4th April 2013. Prevalence of hyponatraemia on admission and incidence of cases developing in hospital were reported. Aetiology of cases of hyponatraemia was determined by consensus of an expert panel using pre-specified data collected daily.
Results: 127/212 (60%) EPFF were recruited (mean age 79 yrs, 78% female); 2 participants withdrew mid-study. Of those not recruited, 66 had incapacity to consent and 19 refused participation. Point prevalence of hyponatraemia on admission was 13.4% and a further 12.6% developed hyponatraemia during admission. Hypovolaemic hyponatraemia was predominant (70%). 73% of cases were multi-factorial in aetiology. The commonest causative factors in cases of hyponatraemia were thiazide diuretics (76%), dehydration (70%), proton pump inhibitors (70%), SIADH (27%) and mirtazapine (15%).
Conclusion: Hyponatraemia is highly prevalent in EPFF, seen in 26% of cases. Dehydration and prescription of thiazide diuretics and proton pump inhibitors were the commonest causative factors, not SIADH.