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Predicting Flap Failure Using Non-Invasive Perfusion Monitoring Devices
Neekita Jikaria*2, Ji Ho Park2, Shreeniket Pawar3, Bijay Ghimirey3, Allen Kunselman1, David Febre-Alemany2, Maryam Abdelaal2, Mary Landmesser2, Anilchandra Attaluri3, Mohammed-Reza Tofigh3, Dino Ravnic2
1Department of Public Health Sciences, Penn State Health Milton S. Hershey Medical Center, Hershey, PA; 2Department of Surgery, Penn State Health Milton S. Hershey Medical Center, Hershey, PA; 3School of Science, Engineering and Technology, The Pennsylvania State University, Harrisburg, PA

Introduction
Flaps are the cornerstone to reconstructive surgery. Unfortunately, they are prone to malperfusion and necrosis, especially in random pattern skin flaps. This adversely affects patient outcomes. Perfusion monitoring can potentially detect early flap failure. Currently, available non-invasive modalities include infrared thermography (temperature), oxygen saturation (SaO2), and tissue hemoglobin index (THI). However, the optimal device to predict impending flap necrosis remains unclear. We hypothesize that SaO2 upon flap elevation is the most sensitive predictor of subsequent necrosis.
Methods
Random pattern skin flaps (n=8) were elevated on the pig dorsum (2 flaps/pig; 2M:2F). Flaps measured 12x6 cm and were subdivided into 6 zones (2x6 cm), proximal (1) to distal (6). The contralateral skin served as control zones. Temperature, SaO2 and THI were measured immediately after flap elevation and in controls. On Day 7, skin was photographed for gross analyses. Then, full-thickness skin was harvested and hypoxia-inducible factor 1α (HIF-1α) expression was measured. Unpaired t-test, one-way ANOVA and linear mixed models were performed; p < 0.05 was considered statistically significant.
Results
At Day 0, significant differences were noted in temperature, SaO2 and THI between elevated flaps and corresponding controls (Figure 1A-C). At Day 7, flaps demonstrated an increase in injury/necrosis from proximal to distal compared to controls with 14.7% of distal flaps (zones 5 and 6) showing gross necrosis and zone 6 demonstrating the highest HIF-1α expression (Figure 1D). When comparing all monitoring modalities, THI appeared to be the most sensitive in predicting impending necrosis. (p=0.012). Furthermore, linear mixed models demonstrated a positive correlation between THI and HIF-1α in zone 6 (p=0.03), verifying ischemia.
Conclusion
THI appears to be the most sensitive modality in predicting impending flap failure. Hence, its utilization at the time of flap creation may provide surgeons the ability to alter their surgical approach to prevent downstream tissue necrosis.


Figure 1. A) Flap temperature was lower than controls at time of elevation. B) Flap SaO2 was lower than controls at time of flap elevation. C) Flap THI (signal of hemoglobin strength expressed in arbitrary units (AU)) was increased compared to controls at time of flap elevation. D) Flaps demonstrated increasing injury/necrosis and HIF-1α expression from proximal to distal compared to controls.
ns = non-significant, * = p<0.05, ** = p<0.01, *** = p<0.001, **** = p<0.0001
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