Postoperative Hyponatraemia following Major Orthopaedic Surgeries: Incidence and Risk Factor Assessment

Abstract

Introduction: Postoperative Hyponatraemia (POH) commonly goes unrecognised and untreated. Previous studies have shown that POH is fairly common following orthopaedic surgeries. However, there are very limited prospective studies to estimate the incidence of POH, especially in the Indian scenario. Aim: To evaluate the serum sodium level change postoperatively in patients undergoing major orthopaedic surgeries and to evaluate its risk factors for the same. Materials and Methods: A prospective longitudinal study was conducted for a period of six months (September 2019 to February 2020) at a tertiary hospital in Sikkim, India. A total of 98 adult patients undergoing major orthopaedic surgical procedures of the lower limb and spine (fixation of long bones, joint replacement surgeries, spine fixation surgeries), were observed for development of early (day 1) and delayed (day 5) POH. Various risk factors (such as age, gender, preoperative sodium level, type of surgery, duration of surgery, co-morbidities, and perioperative fluid used) were analysed for the development of POH were evaluated. Results: The study found that 17 (17.3%) out of the total 98 patients, developed POH within 24 hours of surgery and no delayed POH was observed. Those who developed early POH started with low serum Na levels preoperatively and the mean change in Na level was significantly higher among them (5.42±1.4 mmol/L, p-0.001) as compared to postoperative normonatraemia patients (4.3±1.2 mmol/L). Increasing age, diabetes mellitus, preoperative sodium (Na) level, duration of surgery, and use of dextrose fluid intraoperatively were found to be significantly associated with developing early POH. After adjusting for the factors which showed a significance of p<0.1 in the univariate analysis, low preoperative Na (mmol/L) (AOR=0.48; 95% CI=0.32- 0.72; p<0.001) and duration of surgery (in hours) (AOR=1.8; 95% CI=1.04-3.2; p-0.035) were found to be the most statistically significant risk factors for POH. All of 17 patients with POH had normal sodium levels by postoperative day five, showing the transient nature of the drop in Na level. Conclusion: Although POH is fairly common after orthopaedic surgeries (17.3%), it is early and transient in nature and easily correctable. Preoperative sodium level, duration of surgery are the major risk factors for POH.