Can introducing a direct endocrine pathway reduce hyponatraemia in elective knee and hip replacements? A closed-loop audit and service evaluation study.

Introduction: Hyponatraemia has a prevalence of up to 30% after orthopaedic surgery and is associated with poor outcomes, including around 20% mortality and longer hospital stays. This study assessed the prevalence of hyponatraemia following total hip and knee replacement, the causes, further tests, management, effect on length of stay, intensive care admissions and the impact of an endocrinology hyponatraemia protocol.

Materials and methods: Day one postoperative urea and electrolyte results for patients undergoing elective total hip and knee replacements were reviewed. Retrospective data was gathered through the web-based requesting and reporting system ICE. Parameters included demographics, procedure, sodium pre- and postoperatively, endocrine input, high-dependency admissions and length of hospital stay. Next, a hyponatraemia protocol based on NICE guidance was developed with the endocrinology department and a second audit cycle was initiated. SPSS software was used to analyse the data.

Results: Hyponatraemia occurred in 12% of patients, resulted in a significantly longer stay (7.7 days vs 4.6, t -4.6, p < 0.00001) and multiple critical care admissions (8 days). It was more common in total knee replacement (chi square 5.5194, p = 0.018807) and older age (t -2.81083, p = 0.002619). Prior to implementation of the endocrine pathway, hyponatraemia was under-investigated (38%). The precipitating factors such as age and use of diuretics corroborated with prior research. Implementation of the hyponatraemia protocol resulted in quicker endocrinology referrals (2.3 vs 3.6 days), reduced length of stay by 0.7 days (t -2.40973, p = 0.008144) and reduced intensive care days to 0 (chi square 4.6189, p = 0.031622).

Discussion: This study found a similar incidence of hyponatremia as earlier research with the same precipitating factors, the only exception being an increased incidence in patients undergoing knee compared with hip replacemenr The introduction of the direct endocrine pathway proved to be safe and effective without increasing local workload significantly. The main limitation in this project was the fact that it was carried out in a single unit, although this process could be easily replicated should other units wish to adopt it and compare results over a wider cohort.

Conclusions: This endocrine pathway is easily reproducible for other departments. It may help reduce waiting times and improve outcomes for total hip and knee replacements within the NHS.