Reducing surgical site infections after spine surgery: the optimal amount of normal saline for intra-wound irrigation

Surgical site infection (SSI) following lumbar surgery can increase healthcare costs and lead to poor clinical outcome. Irrigation of wounds with saline solution is widely accepted globally and safe for nearly all kinds of surgery. However, the efficacy of different volumes of wound irrigation has not been addressed in elective spine surgery. The role and the optimal amount of intraoperative wound saline irrigation in preventing SSI in clean spinal surgery remain unclear.We aimed to investigate if insufficient intraoperative irrigation may be a risk factor for postoperative SSI. Additionally, we investigated the optimal amount of normal saline (NS) for irrigation to prevent postoperative SSI.This is a retrospective study of patients with degenerative spinal stenosis who were treated surgically. Patients were grouped according to the amount of intra-wound irrigation during surgery.We included 444 patients with degenerative lumbar spinal conditions who had undergone one to five level open spinal fusion surgeries from January 2015 through April 2020.The definition of superficial or deep SSI in this study was based on the Centers for Disease Control and Prevention criteria for SSI. The fusion status accessed was based on the Bridwell grading system at the final follow-up. Self-reported and clinical outcome measures include visual analog scale and Oswestry Disability Index.A total of 193 patients underwent irrigation with a bulb syringe with manual method (B group) with 2,000 mL NS; 251 patients underwent interpulse battery-powered device irrigation (P group) with >6,000 mL NS. Based on our protocolized departmental guidelines, all patients received the same preoperative preparation and standard surgical steps and postoperative care plan. Patients' demographic and surgical parameters were recorded. The main outcome measures included superficial wound infection, deep infection and overall infection.The incidence of overall SSI was 4.66% in the B group and 1.59% in the P group. The univariate analysis revealed a significant correlation with DM and irrigation amount per hour during surgery but not age, BMI, smoking, operative duration, fusion level, or blood loss. We determined the optimal irrigation amount during surgery as 1,400 mL per hour based on the receiver operating characteristic (ROC) curve (sensitivity, 92.3%; specificity, 44.1%). This was statistically significant (p=.033) with an odds ratio of 9.284 (95% confidence interval 1.2-72.0). In the analysis of surgical factors, the infection group had a significantly lower irrigation amount during surgery. To summarize, patients with diabetes and those receiving less than 1,400 mL of NS/hour had a higher likelihood of developing SSI.We observed that diabetes and lower volume of intraoperative irrigation were both risk factors for postoperative SSI following degenerative lumbar spine surgery. To reduce SSI in lumbar spine surgery, intra-wound irrigation with more than 1,400 mL/h of NS was recommended.