Background: Reliable detection of any circulatory issues threatening flap viability after free flap surgery is essential for prompt flap salvage. Currently, gold standard of flap monitoring is clinical monitoring. However, the method presents logistical challenges to insufficient trained personnel. Auxiliary methods are becoming increasingly vital.
Methods: To investigate developed monitoring parameters and vascular thrombosis in free flap model, twelve swine pedicle myocutaneous flaps were harvested and monitored using infrared cameras.
Results: The mean flap surface temperature after vein or artery occlusion decreased significantly, but the differences were relatively small with variability. As a result, the difference between recorded (Ts) and predicted (Tes) flap surface temperature was used as the parameter for pedicle thrombosis: ΔT = Ts–Tes. A ΔT <0.5oC was a vascular occlusion criterion; the sensitivity and specificity were 83% and 67%, respectively. The standard deviation of the surface temperature (SDT) was another indicator of vascular occlusion; with SDT drop more than 0.2oC, the estimated sensitivity and specificity for arterial occlusion were 83% and 100%, and 50% and 67% for venous occlusion.
Conclusions: The advantages of the infrared thermal imaging are that it is non-invasive, contact-free, continuous, and able to detect the whole flap surface area. We established two indicators, ΔT and SDT, for early prediction of flap pedicle thrombosis with high sensitivity and specificity. Further human studies are necessary to validate its clinical application.
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