Early detection of flap failure using a new thermographic device

Early recognition of perfusion failure is critical for free flap salvage. However, most of the different methods assessing perfusion have limitations and have not gain widespread acceptance. The aim of this study was to evaluate a novel system, a combination of a highly sensitive infrared camera with dynamic infrared image processing, in an animal flap model.

Flaps based on the inferior superficial epigastric vessels were raised bilaterally in 20 rats. One pedicle artery or vein was ligated and the contralateral side served as unligated control. Thermographic measurements were performed before and after ligation yielding a color map and a temperature recording. The macroscopic evolution of the flap was photographically documented.

All vascular occlusions were rapidly detected. In the artery ligated group, the disappearance of the hot spot, corresponding to the pedicle, was observed in absence of macroscopic changes of the flap. In animals undergoing venous ligation, changes in the thermographic image preceded clinical signs of congestion. Temperature recordings between arterial and venous ligation were not significantly different.

Vascular compromise was rapidly and consistently identified prior to appearance of macroscopic changes. This very sensitive system allows for a precise detection of small differences of infrared emission within the flap visualized as changes in the color map with disappearance of the hot spot on the color map. This is independent of absolute temperature values that are influenced by environmental factors. In addition to postoperative monitoring, the set-up may be a promising tool for preoperative planning of perforator flaps.