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

Sir: We would like to thank Drs. Qi and Wang for their appropriate and very interesting comments regarding our recent publication.1 In our study, the protective effect of hemodilution when a rotation of 360 degrees was applied to the flap pedicle was quite evident. Because our study is the first and only experiment evaluating the impact of hemodilution on a pedicle perforator flap with twisted pedicle, these results do not allow us to recommend hemodilution in humans undergoing reconstruction with perforator propeller flaps. An experimental animal study with a larger population and larger animals and prospective and retrospective clinical studies in human subjects are needed. Replying to Dr. Qi, more than one formula has been used in the literature to calculate total blood volume in rats.2–4 However, the most trustworthy formula is 64 ml/kg of body weight (i.e., for a 350-g rat: 64 × 0.35 = 22.4 ml) (according to the United Kingdom’s National Centre for the Replacement, Refinement and Reduction of Animals in Research).5 In disagreement with the statement by Dr. Qi, withdrawing 2.58 ml of blood (1 ml/minute) in a 200-g rat and simultaneously replacing the blood removed allows maintaining normovolemia, reducing the hematocrit level. Blood loss during surgery, and artery catheterization, were absolutely not relevant. The blood removed during the hemodilution process was used as the first blood sample. Blood replacement was performed for the blood sample obtained after hemodilution. Dr. Wang stated in his letter that “hemodilution improved the arterial inflow in subgroup IV, but had no significant effect on venous congestion.” In this study, we were able to evaluate the overall microcirculatory blood perfusion. Microangiography of the flap and the histopathologic analyses we performed could not discriminate the flap failure cause, whether related to arterial or venous ischemia. As for the other degree of rotation, twisting the pedicle at 90, 180, and 270 degrees had no effect on flap survival and no differences were found among the three main groups. The abbreviation AHH (acute hypervolemic hemodilution) has been mistakenly substituted with “acute hypovolemic hemodilution” because of a misprint that occurred in the editing process. As in our previous experiment,6 the choice of the degree of hemodilution (the mean hematocrit value after hemodilution) was based on the relationship existing between viscosity and hematocrit. Viscosity is greatly increased above the hematocrit of 40 percent. Thus, hematocrit of approximately 30 percent appears to be one that offers the best balance between viscosity and oxygen-carrying capacity. Further reductions in hematocrit may decrease oxygen-carrying capacity.7 Concerning the microangiography process, a 30% solution of lead oxide was prepared mixing lead oxide (30 mg) with warm water (100 ml) to create a radiocontrast to be injected, with each flap usually requiring 20 to 25 ml of solution. The solution was administered slowly, with low pressure, through a catheter placed in the common carotid artery to fill up the entire vascular system with radiopaque material. The flap was then dissected and the lead oxide infusion was stopped when the yellow solution began to ooze from the edges of the flap. DISCLOSURE The authors have no financial interest to declare in relation to the content of this communication. Matteo Amoroso, M.D.Sant’Andrea HospitalSchool of Medicine and Psychology“Sapienza” University of RomeRome, Italy Özlenen Özkan, M.D.Department of Plastic, Reconstructiveand Aesthetic Surgery Cumhur İbrahim Başsorgun, M.D.Pathology Department andDepartment of Plastic, Reconstructive, andAesthetic Surgery Önur Ögan, M.D. Kerim Ünal, M.D.Department of Plastic, Reconstructive, andAesthetic SurgeryAkdeniz University School of MedicineAntalya, Turkey Benedetto Longo M.D., Ph.D. Fabio Santanelli Di Pompeo, M.D., Ph.D.Sant’Andrea HospitalSchool of Medicine and Psychology“Sapienza” University of RomeRome, Italy Ömer Özkan, M.D.Department of Plastic, Reconstructive, andAesthetic SurgeryAkdeniz University School of MedicineAntalya, Turkey