Advanced Microcirculatory Parameters of Lower Extremity Free Flaps during Dangling and Their Influencing Factors.

Background: Dangling of the leg to habituate a free flap to the lower extremity is common practice. However, little is known about the microcirculatory changes in free flaps and the influence of comorbidities.

Methods: Tissue oxygen saturation (StO2) and hemoglobin content (tissue hemoglobin index [THI]) of 39 lower extremity free flaps was measured during dangling on postoperative days (PODs) 6 to 9. We assessed the maximal desaturation during dangling and re-elevation and the maximal increase in THI as well as the time required to reach a stable plateau during dangling, among others.

Results: All parameters showed significant changes during dangling (desaturation during dangling: 0.23 ± 10.7 vs. - 4.66 ± 12.6%, p = 0.001 for POD 6 vs. 7; further desaturation after re-elevation: - 11.1 ± 7.4 versus - 14.5 ± 7.8%, p = 0.001 for POD 6 vs. 9; THI increase during dangling: from 3.4 ± 1.6 to 4.2 ± 1.8 AU, p = 0.008, time to THI plateau: 1.7 ± 1.2 vs. 2.5 ± 1.7 minutes, p = 0.004 for POD 6 vs. 7). Age, gender, and smoking did not influence the mentioned parameters. Nondiabetic patients showed a significant increase of baseline StO2, whereas diabetic patients did not (p = 0.009 vs. 0.11). For THI, both diabetic and hypertensive patients showed a lower increase in THI on the first day of dangling (p = 0.056; p = 0.009) and significantly lower baseline values on the last day (0.046 for both).

Conclusion: Duration of dependency seems to have the greatest impact on microcirculation during dangling, although comorbidities may interfere with the adaptive processes. An earlier start of dangling could safely be applied in most patients. Special care needs to be taken in diabetic and hypertensive patients.