Relative Tissue Oxygenation Changes are More Reliable than Clinical Exam or Temperature Changes for Detecting Early Tissue Ischemia
Elizabeth M. Polfer, MD; Jennifer Sabino, MD; Isaac Fleming, CCRC, MD; Kenneth R Means Jr, MD
Union Memorial Hospital - The Curtis National Hand Center, Baltimore, MD
Introduction The clinical effect of not recognizing ischemia in post-traumatic and post-operative free tissue transfers can be devastating. In a prior study, it was demonstrated that increased skin pigmentation results in a significant difference in the ability for board certified plastic and orthopaedic hand surgeons to clinically assess an ischemic limb with physical exam alone. For example, when monitoring the posterior interosseous artery(PIA) skin territory with the tourniquet insufflated for 10 minutes, 92.9% of Caucasians were correctly identified as being ischemic compared to only 23.3% of African Americans. We hypothesized that there are non-invasive adjuvants to physical exam to better assess ischemia regardless of skin pigmentation.
Methods A prospective study of healthy controls exposed to limb ischemia was conducted to determine if adjuvants to physical exam are reliable methods to determine ischemia regardless of skin pigmentation. The subjects were classified based on skin pigmentation using a defined skin type assessment tool(Fitzpatrick Scale), a visual color scale(Von Luschan), and self-description of race. Ischemia was induced by tourniquet insufflation to 250mmHg. A surface temperature probe and a near-infrared spectroscopy(NIRS) monitor were placed on the skin in the PIA skin territory. The readings from both monitors were taken at baseline and every 15 seconds thereafter until 10 minutes.
Results We had 9 subjects enrolled, 2 Hispanics, 3 Caucasians, and 4 African-American. We found a consistently reliable decrease in the tissue oxygenation using NIRS in all patients regardless of skin pigmentation. On average, there was a decrease of 19.4% in tissue oxygenation(range 14%-25%) using NIRS with the starting oxygenation at 76.6%(range 66%-85%) and ending oxygenation at 57.2%(range 48%-67%). There was no such decrease in the temperature readings. There was no significant difference in the change in NIRS tissue oxygenation or temperature between patients with Fitzpatrick 3, 4, and 5 skin types or when patients were grouped into Fitzpatrick less than and equal to or greater than 3 or less than and equal to or greater than Fitzpatrick 4(p>0.05). There was also no significant difference seen in patients with Von Luschan scores less than and equal to or greater than 20(p>0.05).
Discussion In this study NIRS identified ischemia in all patients. It is a reliable way to non-invasively monitor tissue ischemia regardless of skin pigmentation. The surface temperature probes did not identify ischemia in any patient. Our study suggests that NIRS should be strongly considered in patients with increased skin pigmentation when evaluating tissue for ischemia.
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