Plastic Surgery Research Council

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Near-Infrared Tissue Oximetry Predicts Flap Necrosis in a Rat Dorsal Skin Flap
Nima Khavanin, MD, Halley Darrach, BA, Pathik Aravind, Franca Kraenzlin, MD, Tinglu Han, MD, Kevin Klifto, PharmD, Hamda Almaazmi, MD, Bashar Safar, Justin M. Sacks, MD.
Johns Hopkins University School of Medicine, Baltimore, MD, USA.

Purpose: The application of technology to predict and prevent perfusion related complications promises to revolutionize plastic surgery by improving patient care and preventing the downstream sequelae of flap necrosis. Although a myriad of devices have been developed toward this goal, their widespread application has been limited by cost, the need for potentially unwieldy machinery, the use of intravenous dyes, and questionable efficacy in human trials. The objectives of this study are to assess the potential efficacy of a novel, handheld, dye-less device utilizing near-infrared spectroscopy in quantifying tissue oxygenation, predicting the risk for flap necrosis, and preventing perfusion-related complications.
Methods: Twenty-four Sprague-Dawley rats underwent elevation of a dorsal, 10cm x 3cm cranially-based random pattern skin flap using the modified McFarlane technique. Rats were divided into 1 of 3 treatment groups: control, single-dose topical nitroglycerin, and two-dose topical nitroglycerin applied immediately post-operatively and again twelve hours later. Tissue oxygenation was measured intra-operatively following flap elevation and at 24-hours post-operatively. On post-operative day seven, the animals were euthanized, and flap survival was ascertained clinically and histologically. The Pearson product-moment correlation coefficient was used to correlate tissue oxygenation to distance from flap pedicle. Statistical analyses were performed using chi-squared tests and one-way ANOVA. ROC curves were used to evaluate the ability of intra-operative tissue oxygenation in predicting clinical flap necrosis.
Results: Tissue oxygenation was negatively correlated with distance from the flap pedicle (r = -0.798) with a statistically significant decrease in mean tissue oxygenation in distal tissues (p < 0.001). Necrotic tissue on post-operative day seven demonstrated a significantly lower intra-operative tissue oxygenation (32.1%) compared to healthy tissue (58.6%, p < 0.001). As a predictor for tissue necrosis, intraoperative tissue oxygenation demonstrated an area under the ROC curve of 0.969. Control rats demonstrated more tissue necrosis than those receiving a single or two doses of topical nitroglycerin (51.3% vs. 28.8% vs 18.8%, respectively; p=0.035). Near-infrared spectroscopy demonstrated a significant increase in tissue oxygenation between the intra-operative and 24-hours post-operative timepoints in ischemic tissue receiving nitroglycerin (+17.8%, p<0.001; figure).
Conclusions: Near-infrared tissue oximetry effectively detects clinically relevant differences in tissue oxygenation and is a strong predictor for flap necrosis in a rat model. The application of topical nitroglycerin ointment results in a measurable increase in tissue oxygenation that correlated to flap survival. Further translational studies are warranted in order to define the role of this techonology in patient care.


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