The Effect of Normovolemic and Hypervolemic Hemodilution on a Perforator Flap with Twisted Pedicle Model: Experimental Study in Rats

Background: Several studies showed the detrimental effect of pedicle torsion on flap survival; however, the impact of hemodilution in this peculiar condition has never been investigated. This study evaluated the effect of acute normovolemic and hypervolemic hemodilution on flap survival in a perforator flap with twisted pedicle model.Methods: Sixty-three female Wistar rats were divided into three groups of 21 rats each: group 1, superficial inferior epigastric artery flap, which was elevated bilaterally and transposed back to the abdominal wall with different angles of rotation (i.e., 90, 180, 270, and 360 degrees); group 2, surgery with previous acute normovolemic hemodilution; and group 3, surgery with previous acute hypovolemic hemodilution. Normovolemic hemodilution was obtained, simultaneously removing 2 cc of blood and replacing it with an equal volume of isotonic sodium chloride 0.9% (two-thirds) plus hydroxyethyl starch 6% (one-third). 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 hemodilution were 27.80 0.04 percent for the acute normovolemic hemodilution group and 27.01 +/- 0.03 percent for the acute hypovolemic hemodilution group. Twisting the pedicle at 90, 180, and 270 degrees had no effect on flap survival in all groups. However, 360-degree pedicle torsion showed flap edema, congestion, and necrosis.Conclusions: The authors' hemodilution protocol is an effective and reliable method that could be used to further investigate the impact of the hemodynamic changes that occur during hemodilution on flap microcirculation. The results obtained sustain the existence of a strong correlation between necrosis rate and hemodilution.