The Effect of Normovolemic and Hypervolemic Hemodilution on a Microsurgical Model: Experimental Study in Rats

Background: Nowadays, postoperative flap perfusion impairment still occurs in free flap surgery; despite several studies on microcirculatory physiology, the effect of hemodilution is still extremely controversial. The aim of this study was to investigate the impact of acute normovolemic and hypervolemic hemodilution on the incidence of flap survival rate in a microsurgical rat model. Methods: Forty female Wistar rats were divided into four groups of 10 rats each: in group 1, a superficial inferior epigastric artery flap was elevated until femoral vessels were isolated, sectioned, and anastomosed without hemodilution; in group 2, surgery with previous acute normovolemic hemodilution was performed; in group 3, surgery with previous hypervolemic hemodilution was performed; and group 4, was used as a negative control to validate the microsurgical model. Normovolemic hemodilution was obtained, with simultaneous removal of an average of 2.25 cc of blood and replacement with an equal volume of isotonic sodium chloride 0.9 percent and hydroxyethyl starch 6 percent. Hypervolemic hemodilution was obtained by hemodilution and a 20 percent blood volume expansion. Microangiography of the flap and histopathologic analyses were performed. Results: Mean hematocrit values after the hemodilution were 26.80 0.05 percent for group 2 and 28.11 +/- 0.04 percent for group 3. Skin flap survival and vascularization after 7 days were significantly higher in both hemodiluted groups compared with the control group (p < 0.05). Conclusion: Hemodilution was an effective way of providing better microcir-culatory blood perfusion, increasing significantly the flap survival rate in the authors' microsurgical model.