LETTERS TO THE EDITOR Experimental anemia and patency of microvascular anastomoses To the Editor: The article entitled' 'The influence of experimentally induced amenia on the patency of microvascular anastomoses" by Buchler, Phelps , and Boswick l in the January issue of the JOURNAL was of particular interest to me. After reflecting a bit on the experimental methods used , I feel obliged to comment. We have shown in both published 2 and unpublished work that it is possible to obtain enhanced perfusion and survival in experimental skin flaps in anemic animals on both short-term and long-term bases. We have assumed, on the bases of these and other observations, that anemia may be beneficial in replantation surgery and so have chosen, whenever it seems to be reasonable, not to correct intraoperative anemia occurring during hand and digital replantation. It is well documented that blood viscosity is reduced in anemia. Buchler and his associates did not point out, however, that various blood fractions contribute differentially to the viscosity of the blood. 3 Thus in anemia depletion of the protein components-particularly globulin-contributes very significantly to reducing blood viscosity. To remove only the cellular components and return the protein components in the plasma to experimental animals after hemorrhage (as was done in the work described by Buchler and co-workers) thus may well reduce any improvement in blood flow that otherwise might have been observed in their experiments. Because of this, I believe that it is not correct to state "therefore, the hypothesis that anemia is a significant factor influencing the patency of microvascular anastomosis was not substantiated." Before such a statement can be made, evaluation should be carried out also in animals deprived of the protein components as well as the circulating red cells. A. Scott Earle. MD . Plastic and Reconstructive Surgery Cleveland Metropolitan General Hospital 3395 Scranton Rd. Cleveland. OH 44/09

REFERENCES I . Buchler U, Phelps DB, Boswick JA Jr: The influence of experimentally induced anemia on the patency of microvascular anastomoses. J HAND SURG 2:29-30, 1977 2 . Earle AS , Fratianne RB, Nunez FD: The relationship of hematocrit levels' to skin flap survival in the dog. Plast Recontstr Surg 54:341-344, 1974 3. Wells RE: Rheology of blood , in Winters WL, Brest AN, editors: The microcirculation: A symposium, Springfield, Ill. 1969, Charles C Thomas , Publishers

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Reply To the Editor: We thank Dr. Earle for his interest and comments. One must remember that patency of microvascular anastomoses and survival of revascularized tissues are not necessarily synonymous phrases. We are well aware of Dr. Earle's excellent experimental studies showing increased perfusion and survival of skin flaps secondary to anemia, and we suspect that alterations in blood viscosity which result from red cell depletion might favor the nutritional perfusion of replanted parts. Our study was not designed , however, to evaluate perfusion or survival rates, but rather to determine if anemia (and its concomitant lowering of viscosity) would favor the patency of small vessel anastomoses, a separate-but important-factor in the survival of replanted parts. We did not state, nor do we wish to imply, that anemia has no affect on the perfusion of tissues distal to the site of small vessel repair. Regarding the differential contributions of various blood components to viscosity , the importance of red blood cells-particularly in the microcirculation-is related primarily to the interaction of deformed red cells with the capillary endothelium. An additional factor is the tendency for red cells to aggregate. 1 Furthermore, blood viscosity is an extremely complex phenomenon, changing with alterations in velocity, shear stress, temperature, vessel size, disease states, blood additives, and measuring techniques . 2 To isolate the contribution of the globulin fraction alone would be a very difficult task. Since these proteins are replenished very rapidly in the serum following removal, one must question the assumption that their loss would result in more than a transitory effect. Studies on rats have shown that a turnover of approximately 25% of the total circulating proteins can occur each day. 3 Thus any protein effect on viscosity would be short-lived, while red cell effect would be expected to be present for 14 to 21 days . The conclusion that anemia did not significantly alter patency rates must stand. The experimental groups were identical in all aspects, with the exception of the depletion of red cell mass in one group, and yet the anastomotic patency rates were not significantly altered. There is a valid criticism of the study which has not been raised in Dr. Earle's letter: our results indicate that vessels measuring approximately 0 .5 mm in diameter can be joined with patency rates over 90% in both normal and anemic rats. It is possible that anastomoses performed on smaller vessels, which might show lower patency rates, could be benefited by anemia. In a clini-

September, 1977

Vol. 2, No.5, pp. 412-413