New Test Provides an 'Early Warning' for Surgical Site Infections
A simple technique for measuring subcutaneous (under the skin) oxygen concentrations may help to identify patients at high risk of developing infections after surgery, reports a study in the October issue of Anesthesia & Analgesia, official journal of the International Anesthesia Research Society (IARS).
The study, conducted at the Department of Anesthesia of the University of Louisville and the Department of Outcomes Research of the Cleveland Clinic, suggested that an inexpensive, non-invasive measurement an hour after surgery could identify patients at risk of developing wound infections, even though such infections were typically evident more than a week after surgery. By identifying patients who would benefit from aggressive preventative measures, this simple test could help prevent this potentially serious complication, according to the study.
Subcutaneous Oxygen Concentrations during Surgery Predicts Later Infection RiskThe study included 116 patients undergoing colorectal surgery, an operation associated with a high risk of surgical site infections. In each patient, a technique called near-infrared spectroscopy (NIRS) was used to measure the subcutaneous tissue oxygen saturation at three different sites under the skin.
Measured at a site on the upper arm about an hour after surgery, oxygen saturation was lower in patients who developed infections, even though the infections did not develop until an average of nine days later. The NIRS measurements were about 70 percent accurate in predicting which patients would go on to develop infections (sensitivity). And just as importantly, the test was about 60 percent accurate in identifying patients who did not develop infections (specificity). As a predictor of infection risk, NIRS was more accurate than widely-used risk scores.
"We know that high tissue oxygen saturation enhances the body's ability to fight infection, while low saturation prevents an effective immune response to infection," explains Dr. Steven L. Shafer of Columbia University, Editor-in-Chief of Anesthesia & Analgesia. “However, before NIRS, there was no practical, noninvasive technique for routine measurement of subcutaneous oxygen saturation.”
About 20 percent of patients developed surgical site infections. Surgical site infections continue to be a common, serious, and costly problem—despite preventive efforts. Each year, more than 290,000 surgical site infections occur, causing approximately 13,000 deaths. Effective approaches to prevention are urgently needed.
If the results are supported by future research, measuring tissue oxygen saturation could provide an important "early warning system" for identifying patients at high risk of surgical site infections, according to an editorial by Dr. Frank J. Overdy of Medical University of South Carolina. The NIRS technique may allow anesthesiologists to research new ways of optimizing oxygen levels during surgery, as well as new postoperative strategies for preventing infection in patients at high risk.
"This is an exciting finding that may help decrease the incidence of surgical infections," says Dr. Shafer. "However, we won't know for certain until a study compares patients whose treatment is adjusted based tissue oxygenation with patients who receive conventional preventative treatment."
"Wound infections remain a common and devastating surgical complication," comments Dr. Daniel I. Sessler, Professor and Chair of the Department of Outcomes Research at the Cleveland Clinic. "All wounds become contaminated, and what determines whether contamination progresses to clinical infection is how well the immune system fights the bacteria. Oxygen is the body’s main defense against infection. It is thus logical that low tissue oxygen saturation predicts which patients are at greatest risk. What is special about the system tested in this study is that the monitoring system is noninvasive and thus perfectly safe. Now we need a study to show that patients treated on the basis of tissue oxygen saturation actually have fewer infections."
Read the full study in Anesthesia & Analgesia
About the IARSThe International Anesthesia Research Society is a nonpolitical, not-for-profit medical society founded in 1922 to advance and support scientific research and education related to anesthesia, and to improve patient care through basic research. The IARS contributes nearly $1 million annually to fund anesthesia research; sponsors an annual forum for anesthesiology leaders to share information and ideas; maintains a worldwide membership of more 15,000 physicians, physician residents, and others with doctoral degrees, as well as health professionals in anesthesia-related practice; sponsors the SAFEKIDS initiative; and publishes the journal Anesthesia & Analgesia. Additional information about the society and the journal may be found at www.iars.org and www.anesthesia-analgesia.org.
About Anesthesia & AnalgesiaAnesthesia & Analgesia was founded in 1922 and was issued bi-monthly until 1980, when it became a monthly publication. A&A is the leading journal for anesthesia clinicians and researchers and includes more than 500 articles annually in all areas related to anesthesia and analgesia, such as cardiovascular anesthesiology, patient safety, anesthetic pharmacology, and pain management. The journal is published on behalf of the IARS by Lippincott Williams & Wilkins (LWW), a division of Wolters Kluwer Health.
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