New-onset hyponatraemia after surgery for traumatic hip fracture.

BACKGROUND: hyponatraemia in orthopaedic patients is common but has been poorly investigated following surgery for traumatic hip fracture. The aims of this study were to define the incidence of new-onset post-operative hyponatraemia and to investigate associations between hyponatraemia and patient demographics, medication use and duration of hospital stay.
METHODS: all patients admitted to the Orthopaedic Unit for hip surgery following trauma in 2012 were retrospectively reviewed. Patients who developed post-operative hyponatraemia within 10 days of surgery were compared with patients who remained normonatraemic pre- and post-operatively.
RESULTS: a total of 254 patients were included. Overall, this study identified a significant (P =< 0.001) mean post-operative drop in serum sodium of 1.8 mmol/l (95% CI: 1.3-2.3%) compared with pre-operative levels. The incidence of moderate (<135 mmol/l) and severe (<130 mmol/l) post-operative hyponatraemia was 27% (95% CI: 21.7-32.5%) and 9% (95% CI: 5.7-12.8%), respectively. Statistical analysis revealed significant associations between the development of post-operative hyponatraemia and: (i) proton pump inhibitor use, (ii) selective serotonin re-uptake inhibitor use and (iii) increasing number of medications. Length of hospital stay was significantly increased in patients with moderate post-operative hyponatraemia compared with normonatraemic patients (30 versus 21 days; P =< 0.001). The incidence of new-onset post-operative hyponatraemia was not significantly increased by ethnicity, gender, fracture type, functional status or operative procedure.
CONCLUSION: hyponatraemia after surgery for hip fracture is common and results in longer hospital stay. This study provides evidence that an average post-operative drop in serum sodium concentration should be expected in this patient group. Moreover, patients taking SSRI or PPI medications may be at increased risk of post-operative hyponatraemia.