Regional Oxygen Saturation Index: A Novel Criterion for Free Flap Assessment Using Tissue Oximetry

Background: Tissue oximetry is a useful tool for postoperative free flap monitoring. Reported criterion values have been accurate; however, there are various complicated author-dependent criteria, and sometimes it is too late for flap salvage. The authors offer a new, simple criterion for faster and accurate detection of perfusion problems. Methods: Intraoperatively, perfusion areas of various free perforator flaps were assessed by both indocyanine green angiography and regional oxygen saturation. The elevated flap was categorized into the early-stained area, the delayed-stained area, and the no-stained area by indocyanine green angiography. The regional oxygen saturation index (regional oxygen saturation on the flap on the control nondissected portion) of each area was calculated. Postoperative continuous flap monitoring was conducted, recording the value of the regional oxygen saturation index at the early-stained area. The blood glucose measurement index was also recorded periodically. Results: In 60 cases of perforator-based free flaps, intraoperative indocyanine green areas were significantly correlated with the values of regional oxygen saturation index. The postoperative regional oxygen saturation index showed very stable values in various types of perforator flaps, provided that no vascular problem occurred, and it never went below 0.75. When vascular problems occurred, the regional oxygen saturation index dropped below 0.75 in all three cases before the blood glucose measurement index and the absolute value of regional oxygen saturation dropped below the criterion value. Conclusion: The regional oxygen saturation index may be a simple and fast criterion for detecting vascular problems following free flap reconstruction compared with existing criteria.