Monitoring of free flaps with combined tissue spectrophotometry and laser Doppler flowmetry in an animal experimental model

Background When mobilizing free flaps, postoperative monitoring of perfusion is crucial to detect ischemia. Continuous monitoring may be feasible by applying a combination of tissue spectrophotometry and laser Doppler flowmetry (oxygen-2-see [O2C]). Material and Methods On 10 pigs, two symmetrical myocutaneous flaps were mobilized on each side of the abdomen based on the deep inferior epigastric vessels. Flaps were randomized to clamp either the artery or the vein and measurements using O2C were performed before, during, and after the intervention yielding information on blood flow, saturation (sat), and relative tissue hemoglobin (rHgb) concentration. Results Baseline values were similar in all groups. Introduction of ischemia caused a rapid decline in arterial ischemic flaps which all reached threshold levels in 3 minutes, whereas that was only the case for three of six venous ischemic flaps. Venous clamping resulted in a decline in sat, while the response to arterial clamping was an initial decline followed by an increase in sat. In all arterial ischemic flaps, rHgb concentration either decreased or remained at baseline levels but increased in all venous ischemic flaps. The median time to a 30% rise was 1 minute at an 8-mm depth. The rate of decreasing flow along with the rHgb measurements made it possible to distinguish the arterial ischemia (AI) from the venous ischemia (VI) within the first few minutes. Conclusion In this animal experimental model, O2C measurements of blood flow reliably detected ischemia. By adding information about rHgb, it was possible to distinguish between AI and VI.