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J Thorac Cardiovasc Surg 1996;112:557
© 1996 Mosby, Inc.

LETTERS TO THE EDITOR

The benefit of heparin-bound circuits

Department of Cardiac Surgery
University Hospital of Antwerp
Edegem, Belgium

To the Editor:

We read with interest the recently published paper by Gorman and associates ¹ on surface-bound heparin in extracorporeal circuits. The study was well conceived and conducted. Several questions remain, however. The first question concerns the appropriateness of including several of the patients in the study. Four of the 20 patients, two in each group, underwent pulmonary arterial thrombectomy. Circulatory arrest of relatively long duration was applied in all, and at low body temperatures, varying from 12° to 14.9° C. Extreme hypothermia can result in severe disturbances in coagulation. ² The prolonged circulatory arrest in these patients suggests the presence of great quantities of thrombotic material. If these thrombi had been recently formed—and this was not stated in the paper—they may have resulted in significant consumption of coagulation factors. In our opinion these three patients should not have been included in the study.

Second, the authors state that a Cell Saver System (Haemonetics, Braintree, Mass.), was used in all patients, implying extensive contact between blood and uncoated synthetic material. Washing blood with normal saline solution results in removal of plasma, which would also greatly affect coagulation. In addition, no mention was made of how much blood per patient was so treated.

Third, experimental and clinical studies have shown that heparin-coated circuits yield some attenuation of inevitable damage to blood components, but that the difference with uncoated circuits is slight. We were therefore surprised that the study's conclusions correspond entirely with those of our animal experimental research, ^3,4 despite the possible shortcomings of the methods. Our study used a venovenous coated or uncoated circuit with low flow in unheparinized dogs. We, too, found some protection of circulating blood by coated circuits, and we also found no reduction in blood coagulability. We therefore agree with the authors' conclusion that reducing the dose of heparin when a heparin-coated system is used, as is advocated by some, ⁵ is unwise and even dangerous.

References

1. Gorman RC, Ziats NP, Rao AK, Gikakis N, Sun L, Khan MMH, et al. Surface-bound heparin fails to reduce thrombin formation during clinical cardiopulmonary bypass. J Thorac Cardiovasc Surg 1996;111:1-12.[Abstract/Free Full Text]
   
2. Yoshihara H, Yamamoto T, Mihara H. Changes in coagulation and fibrinolysis occurring in dogs during hypothermia. Thromb Res 1985;37:503-12.[Medline]
   
3. van der Hulst VPM, Henny CP, Moulijn AC, Engbers G, ten Cate H, Gründeman PF, et al. Veno-venous bypass without systemic heparinization using a centrifugal pump: a blind comparison of a heparin bonded circuit versus a non heparin bonded circuit. J Cardiovasc Surg (Torino) 1989;30:118-23.[Medline]
   
4. van der Hulst VPM, Gründeman PF, Moulijn AC, Rutten PJJM, Klopper PJ. Long-term extracorporeal blood bypas in dogs at low flows without systemic heparinization: heparin-coated versus uncoated circuits. Trans Am Soc Artif Intern Organs 1991;37:577-83.
   
5. von Segesser LK, Weiss BM, Pasic M, Garcia E, Turina MI. Risk and benefit of low systemic heparinization during open heart operations. Ann Thorac Surg 1994;58:391-8.[Abstract/Free Full Text]
   

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