Tissue Oximetry Changes during Postoperative Dangling in Lower Extremity Free Flap Reconstruction: A Pilot Study

Background: Lower extremity free flap dangling protocols are still widely practiced, despite a paucity of evidence for their use. This pilot study investigates the use of tissue oximetry to provide further insight into the physiological effect of postoperative dangling in lower limb free flap transfer. Methods: Ten patients undergoing lower extremity free flap reconstruction were included in this study. Free flap tissue oxygen saturation (StO₂) was continuously measured using non-invasive near-infrared spectroscopy. Measurements were performed on the free flap and contralateral limb during dangling from postoperative day (POD) 7 until 11, according to the local dangling protocol. Results: StO₂ values measured in the free flap diminished to 70 ± 13.7% during dangling. This minimum StO₂ was reached significantly later, and correspondingly the area under the curve (AUC) was significantly larger on POD 11 compared to the start of the dangling protocol on POD 7, reflecting an improving free flap microvascular reactivity. The dangling slope was equal between the free flap and contralateral leg. The reperfusion slope was significantly flatter on POD 7 compared to the other PODs (p < 0.001). Thereafter, no significant differences between PODs were observed. Patients with a history of smoking had significantly lower tissue oximetry values compared to non-smokers. Conclusions: The application of tissue oximetry during dangling provides further insight into the physiological effect (i.e., changes in microcirculatory function) of the free flap of the reconstructed lower extremity. This information could potentially be useful to either revise or disrupt the use of such dangling protocols.