Near-infrared Tissue Oximetry Predicts Outcomes Of Flap Preconditioning In Rodents
Pooja S. Yesantharao, Sarah Persing, MD, MPH, Nima Khavanin, MD, Justin M. Sacks, MD, MBA.
Johns Hopkins Medicine, Baltimore, MD, USA.
Purpose: The Intra.Ox is a novel, handheld device using near-infrared spectroscopy to quantify tissue oxygenation. This device may improve outcomes in Plastic Surgery, by reducing perfusion-related complications (flap necrosis) through early detection. Previous work by our lab has demonstrated that the Intra.Ox reliably predicts changes in flap necrosis in rodents after postoperative application of topical nitroglycerin. The purpose of this study was to further investigate the utility of the Intra.Ox device, in the context of preoperative intervention. In this study, we assessed the utility of near-infrared tissue oximetry in reliably predicting changes in flap necrosis as a result of flap preconditioning with negative pressure and local heat stress. By doing so, we hope to further understand the clinical efficacy of this technology.
Methods: This experimental protocol was approved by our institution's Animal Care and Use Committee. Twenty-four Sprague-Dawley rats were divided into three experimental groups: (1)heat stress preconditioning, (2)negative pressure preconditioning, and (3)unconditioned controls. All rats underwent elevation of a dorsal, cranially-based 10cmx3cm random pattern skin flap using the modified McFarlane technique. Tissue oxygenation was assessed preoperatively before and after preconditioning, intraoperatively following flap elevation, and at 24-hour and 7-day postoperative timepoints. All animals were euthanized on postoperative day 7 and flap survival was assessed clinically and histologically. Chi square and one-way ANOVA were used to study clinical variables. Pearson product-moment correlation coefficients were used to study tissue oxygenation. ROC curves were used to assess the utility of the Intra.Ox in predicting flap necrosis.
Results: Preoperative tissue oxygenation measurements recorded by the Intra.Ox device significantly increased 24-hours after negative pressure (51.2% versus 58.1%, p<0.01) and heat stress preconditioning (50.3% versus 57.1%, p<0.01). This correlated histologically to increased heat shock protein-32 staining from heat shocked tissue biopsied at this time point. In all animals, tissue oxygenation at all postoperative timepoints was negatively correlated with distance from the flap pedicle (r=-0.85 for postoperative day 7), with a statistically significant decrease in mean tissue oxygenation in the most distal centimeter of tissue compared to pedicle tissue (19.2% versus 48.9%, p<0.01). Preconditioning with negative pressure and heat demonstrated improved flap survival compared to unconditioned controls through histologic and clinical analysis (mean weight of non-necrotic tissue: 6 versus 5 versus 2.3 grams, p<0.01; Figure). Accordingly, near-infrared spectroscopy demonstrated a significant increase in intraoperative tissue oxygenation in preconditioned distal flap tissue compared to unconditioned controls, with negative pressure preconditioning demonstrating the greatest increase in oxygenation (+19.2%, p<0.001 for negative pressure, +15.4%, p<0.01 for heat. For all experimental groups, intraoperative tissue oxygenation predicted tissue necrosis (area under ROC curve: 0.922).
Conclusions: Near-infrared tissue oximetry may help in preventing flap necrosis, by accurately predicting tissue necrosis to allow for timely intervention. Improved flap survival after preconditioning strongly correlated with changes in tissue oxygenation. Transcutaneous tissue oximetry should be further studied in clinical settings, in order to assess its utility in patient care.
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