Critical threshold for tissue viability as determined by laser Doppler flowmetry.

As a noninvasive method for continuous evaluation of tissue perfusion, laser Doppler flowmetry fulfills many of the prerequisites of an ideal objective monitor. A critical threshold for insuring flap viability, however, has not been universally accepted. In this experimental design using pedicled epigastric flaps in rats, it was determined that if flow alterations in an otherwise healthy flap always exceeded 30% of the initial baseline value, consistent viability could be predicted. Although this relative critical index could be established, the variability of even intraspecies flow rates precluded defining any specific numerical index of flow that could always predict flap survival.