Early detection onset of flap failure using near infrared spectroscopy

Background Near-infrared spectroscopy (NIRS) is widely used to assess flap perfusions by measuring tissue oxygen saturation (StO(2)). However, the StO(2) level for the onset of perfusion failure is still a controversial issue. Aim This study proposes a new threshold of StO(2) level for detecting the onset of perfusion failure as early as possible to increase flap salvage rates. Methods Twenty patients undergoing flap surgery were included in this study - 13 flaps were implemented to cover defects that occurred due to trauma and 7 flaps to hide imperfections that occurred after cancer treatment. Thirteen flaps were in the lower extremity, six in the mandible, and one in the breast. NIRS was used to measure StO(2) in 240 flap regions of the 20 patients to determine flap viability using descriptive statistics. Results The mean StO(2) values from healthy flap and control regions were obtained as 81.6% +/- 0.36 and 82% +/- 0.18, respectively. The lowest StO(2) value of 77.2% was defined as the onset of a vascular complication at a probability of 99.74% by subtracting three times the standard deviation from the mean StO(2) of healthy flaps. Vascular complications were observed from 21 regions in the four flaps with StO(2) values lower than 77.2%, but only one was lost. Conclusion The threshold value for the onset of perfusion failure was a 5% decrease from the expected value, much lower than previously described thresholds that may facilitate the detection of perfusion failure in the early stage and increase salvage rates in flap revisions.