CME Early Postoperative Subcutaneous Tissue Oxygen Predicts Surgical Site Infection Raghavendra Govinda, MD,*† Yusuke Kasuya, MD,†‡ Endrit Bala, MD,§ Ramatia Mahboobi, MD,§ Jagan Devarajan, MD,§ Daniel I. Sessler, MD,§ and Ozan Akc ¸a, MD† BACKGROUND: Subcutaneous oxygen partial pressure is one of several determinants of surgical site infections (SSIs). However, tissue partial pressure is difficult to measure and requires invasive techniques. We tested the hypothesis that early postoperative tissue oxygen saturation (StO 2 ) measured with near-infrared spectroscopy predicts SSI. METHODS: We evaluated StO 2 in 116 patients undergoing elective colon resection. Saturation was measured near the surgical incision, at the upper arm, and at the thenar muscle with an InSpectra™ tissue spectrometer model 650 (Hutchinson Technology Inc., Hutchinson, MN) 75 minutes after the end of surgery and on the first postoperative day. An investigator blinded to StO 2 assessed patients daily for wound infection. Receiver operating characteristic curves were used to analyze the performance of StO 2 measurements as a predictor of SSI. RESULTS: In 23 patients (20%), SSI was diagnosed 9  5 days (mean  SD) after surgery. Patients who did and did not develop an SSI had similar age (48  14 vs 48  15 years, respectively; P = 0.97) and gender (female:male, 15:8 vs 46:47, respectively), but patients who developed SSI weighed more (body mass index 32  7 vs 27  6 kg/m 2 ; P  0.01). StO 2 at the upper arm was lower in patients who developed SSI than in those who did not develop SSI (52  22 vs 66  21; P = 0.033), and these measurements had a sensitivity of 71% and specificity of 60% for predicting SSI, using StO 2 of 66% as the cutoff point. CONCLUSION: StO 2 measured at the upper arm only 75 minutes after colorectal surgery predicted development of postoperative SSI, although the infections were typically diagnosed more than a week later. Although further testing is required, StO 2 measurements may be able to predict SSI and thus allow earlier preventive measures to be implemented. (Anesth Analg 2010; 111:946 –52) S urgical site infections (SSIs) are perhaps the most common serious complication of anesthesia and sur- gery. They cause considerable morbidity and are expensive to treat. 1,2 The transition from contamination to established infection occurs during a decisive period that probably lasts only a few hours, even though infections are typically detected a week or longer after surgery. 3,4 If antibiotics are administered during this decisive period, they are more effective in reducing infection risk than when given later. 5 Tissue oxygen tension levels are one of the best factors established for predicting SSI. 6,7 Oxidative burst function of neutrophils is one of the primary defenses against SSI. 8 Oxidative burst depends on the Po 2 over the entire physiological range of tissue values. 9 Interventions to improve tissue oxygenation during or immediately after surgery are thus most likely to reduce the morbidity and mortality associated with SSI. 10,11 Tissue oxygenation has traditionally been measured with Clark-type electrodes or similar systems. However, these methods are invasive, expensive, and require exper- tise to use. 12,13 Near-infrared spectroscopy (NIRS) is an alternative noninvasive technique. 14 –17 We tested the hy- pothesis that tissue oxygen saturation (Sto 2 ) measured soon after surgery with NIRS predicts ultimate development of SSI. Confirming this hypothesis would allow early clinical interventions, which might reduce the risk of infection. METHODS With approval by the Human Studies Committees at the University of Louisville and the Cleveland Clinic, and written informed consent by the participants, we included 116 colorectal surgery patients. Forty-three of these patients had laparoscopic-assisted colorectal procedures; the re- mainder had laparotomies (Table 1). In a preliminary study, we found that patients who developed SSI had lower Sto 2 measurements at the thenar eminence 15% 20% (mean  SD) than those who remained uninfected postoperatively; the analogous abso- lute difference was 20% 30% at the upper arm. 18 Using these estimates, a sample size of 80 measurements at the thenar eminence and 132 at the upper arm was calculated to achieve 90% power with an  of 0.05. We therefore From the *Department of Anesthesiology, Tufts Medical Center, Boston, Massachusetts; †Department of Anesthesiology and Perioperative Medicine, and Neuroscience ICU, University of Louisville, Louisville, Kentucky; ‡Tokyo Women’s Medical University, Tokyo, Japan; and §Department of Outcomes Research, Cleveland Clinic, Cleveland, Ohio. Accepted for publication May 6, 2010. Supported in part by Hutchinson Technology Inc. (Hutchinson, MN) and the Joseph Drown Foundation (Los Angeles, CA). Data were presented in part at the American Society of Anesthesiologists Annual Meeting in Orlando, FL (October 2008). All authors are also affiliated with the Outcomes Research Consortium. Disclosure: The authors report no conflicts of interest. Address correspondence and reprint requests to Ozan Akc ¸a, MD, Depart- ment of Anesthesiology and Perioperative Medicine, University of Louis- ville Hospital, 530 S. Jackson St., Louisville, KY 40202. Address e-mail to ozan.akca@louisville.edu. Copyright © 2010 International Anesthesia Research Society DOI: 10.1213/ANE.0b013e3181e80a94 946 www.anesthesia-analgesia.org October 2010 • Volume 111 • Number 4