Perfusion dynamics in lower limb reconstruction: Investigating postoperative recovery and training using combined white light photospectroscopy and laser Doppler (O2C(®)).

Background: Postoperative regimes designed to acclimatise lower limb free flaps to the changing flow dynamics of standing (flap training exercises) are widely employed despite a paucity of evidence for their use. This study utilises non-invasive monitoring of perfusion parameters to investigate flap training at the microcirculatory level.

Methods: Eight prospective patients undergoing lower limb reconstruction with anterolateral thigh fasciocutaneous free flaps were enrolled. Combined tissue photospectroscopy and laser Doppler (O2C, LEA, Germany) was used to assess perfusion during five days of postoperative limb elevation and a subsequent three day flap training regime. Superficial Oxygen saturation (SO2), Haemoglobin concentration (rHb) and Flow measurements were taken. Readings were compared to pre-training control measurements.

Results: In the first five postoperative days of limb elevation, there were no significant changes in perfusion parameters. On commencement of flap training, 5 min of leg dependency resulted in mean decreases in SO2 of 45% on day 1 (p = 0.05) and 56% on day 2 (p = 0.02). Haemoglobin concentrations increased by 20% on day 1 (p = 0.01) and 26% on day 2 (p = 0.02). Flow decreased by 67% on day 1 (p = 0.19) and 78% day 2 (p = 0.03). On day 3 changes were observed to a lesser degree and only rHb increases remained statistically significant (p = 0.01).

Conclusions: Prior to flap training, lower limb dependency causes reduced oxygenation, increased venous pooling and decreased flow consistent with venous congestion. Following a three day training regime, flap perfusion begins to accommodate for these changes. These findings provide a rationale for flap training, although further work is required to explain the mechanisms.