Near-infrared Tissue Oximetry Predicts Outcomes of Flap Preconditioning in Rodents

Abstract

Listen

Translate article

PURPOSE: Stress preconditioning of flaps is a potential strategy to mitigate risk of ischemia-reperfusion injury.1 The ability to reliably predict the impact of preconditioning on postoperative necrosis even before an incision is made would not only allow for improved operative planning but would also allow for better risk-stratification of patients. Although many devices have been developed to assess perfusion-related complications, they are limited by cost, intravenous dyes, and efficacy. This study assessed a novel, handheld, noninvasive and dye-less device using near-infrared spectroscopy to quantify tissue oxygenation in preconditioned tissue. By doing so, we determined the utility of near-infrared tissue oximetry in reliably measuring preoperative changes in flap oxygenation due to stress preconditioning, as well as this technology’s utility in predicting postoperative necrosis in preconditioned tissue. METHODS: Twenty-four Sprague-Dawley rats were divided into 3 groups: (1) heat stress preconditioning, (2) negative pressure preconditioning, and (3) unconditioned controls. All rats underwent elevation of a dorsal, cranially based 10 cm × 3 cm random pattern modified McFarlane skin flap. Tissue oxygenation was assessed preoperatively before and after preconditioning, intraoperatively following flap elevation, and at 24-hour/7-d postoperative time points. Flap survival was assessed clinically and histologically at postoperative day 7. Chi-square and one-way analysis of variance 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 time points 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 resulted in improved flap survival compared to unconditioned controls using histologic and clinical endpoints (mean weight of nonnecrotic tissue: 6 versus 5 versus 2.3 g; P <0.01). 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: Handheld near-infrared tissue oximetry may help in accurately predicting/preventing flap necrosis, as it was able to detect clinically relevant changes in rodent dorsal flap oxygenation even before a flap was raised. In fact, improved flap survival after preconditioning strongly correlated with preoperative changes in tissue oxygenation. Transcutaneous tissue oximetry should be further studied in clinical settings, in order to assess its utility in patient care. REFERENCE: 1. Krauss S, Rothenberger J, Mayer J, et al. Tissue conditioning-strategies to improve perfusion and reduce ischemia-reperfusion injury. Plast Aesthet Res. 2018;5:39.