Intraoperative fraction of inspired oxygen is a modifiable risk factor for surgical site infection after spinal surgery

BACKGROUND: Surgical site infections (SSI) after spinal surgery increase morbidity, mortality, length of hospital stay, and costs. Most previously identified risk factors for these infections, such as severity of illness and procedure duration, are not amenable to intervention. This study sought to identify modifiable risk factors associated with SSI after spinal surgery. METHODS: This is a case-control study including case identification and review of medical records. A total of 104 patients with SSI after spinal surgery were compared to 104 randomly selected control patients without SSI after spinal surgery in a 926-bed tertiary care hospital in Baltimore, Maryland, between April 1, 2001 and December 31, 2004. RESULTS: Multivariate analysis identified independent risk factors for SSI after spinal surgery including prolonged procedure duration (odds ratio [OR], 4.7; 95% confidence interval [95% CI], 1.6-14; P < 0.001), American Society of Anesthesiologists score of 3 or greater (OR, 9.7; 95% CI, 3.7-25; P < 0.001), lumbar-sacral operative level (OR, 2.9; 95% CI, 1.2-7.1; P = 0.02), posterior approach (OR, 3.5; 95% CI, 1.2-9.7; P = 0.02), instrumentation (OR, 2.5; 95% CI, 1.1-6.0; P = 0.03), obesity (OR, 4.0; 94% CI, 1.6-10; P < 0.01), razor shaving before surgery (OR, 3.6; 95% CI, 1.2-11; P = 0.02), and intraoperative administered fraction of inspired oxygen of less than 50% (OR, 12; 94% CI, 4.5-33; P < 0.001). CONCLUSIONS: In addition to previously reported risk factors, this study identified intraoperative administered fraction of inspired oxygen of less than 50% as an independent, modifiable risk factor for SSI after spinal surgery. Intraoperative administration of at least 50% fraction of inspired oxygen should be tested prospectively as an intervention to prevent SSI after spinal surgery.