Altered skin flap survival and fluorescein kinetics with hemodilution

Isovolemic hemodilution is known to reduce blood viscosity. Reduction of either the blood cell concentration or the serum total protein has been found to improve blood flow and ultimate survival of skin flaps. Nutritive blood flow and tissue survival were examined in dorsal pedicle skin flaps in three groups of rats at three hematocrit levels--44% (controls), 31%, and 19%. After hemodilution by phlebotomy and crystalloid replacement, the dye kinetics of intravenously administered fluorescein were measured with the fiberoptic perfusion fluorometer. Skin flap survival at the different hematocrits were also examined. Hematocrits and serum total protein were measured before and after hemodilution and the elevation of the flap. The rate of fluorescein elimination and ultimate flap survival were significantly augmented in the two hemodiluted groups. The maximum benefit was seen in the group of animals hemodiluted to 19%. However, significant improvement in blood flow and skin flap survival was noted in the group of animals that were hemodiluted to a more clinically acceptable level (31%). The decreases in serum total protein following flap elevation did differ among the groups. This study supports the hypothesis that isovolemic hemodilution may be a valuable technique for salvaging marginally ischemic tissues.