The Impact of Preoperative Dehydration on Outcomes After Single-Level Lumbar Fusion

Preoperative laboratory testing can identify patients with health conditions that increase perioperative risk and represent opportunities for optimization. To assess the effect of preoperative and postoperative day 1 (POD1) hydration status on outcomes after single-level lumbar fusion surgery. Retrospective cohort. Adult patients who underwent primary, elective, single-level lumbar fusion (2017-2021). Patients were excluded if they had chronic kidney disease (CKD) or end-stage renal disease (ESRD). Length of stay (LOS), transfusion requirements, discharge disposition, 90-day emergency department (ED) visit, 90-day readmission, and one-year spine reoperation. Patients were analyzed based on their preoperative and postoperative day 1 BUN/creatinine ratio. Patients with a ratio &#x2265;20 were considered dehydrated. Dehydrated patients were compared with hydrated patients preoperatively, postoperatively, and postoperatively within the group who were dehydrated preoperatively. Preoperatively, 281/752 (37.4%) patients were dehydrated (BUN/Cr: 24.2 vs . 14.6; P <0.001). Preoperatively dehydrated patients were more likely to be older, female, and less likely to be current smokers ( P <0.05). On multivariate regression, preoperative dehydration was independently predictive of reoperation and requiring a transfusion. Patients who remained dehydrated on POD1 were more likely to be older and have higher comorbidity burden. Among the full dehydrated group on POD1 (preoperatively either hydrated or dehydrated), patients were older, more commonly female, had higher comorbidity burden, and greater mean levels decompressed. On multivariate analysis, postoperative dehydration was independently predictive of transfusion need, but not non-home discharge or length of stay. Preoperatively dehydrated patients seem to be at increased risk of blood transfusion and spine reoperation after single-level lumbar fusion. Remaining or becoming dehydrated postoperatively, despite intraoperative rehydration, seems to be associated with increased age, female sex, more medical comorbidities, and more extensive surgical decompression. These results suggest that hydration status may be another useful marker to risk-stratify and optimize patients during the preoperative and in-hospital period.