F. C. Mokken (Y) 7 C. P. Henny Department of Anesthesiology, Academic Medical Center, University of Amsterdam, P. O. Box 22700, 1100 DE Amsterdam, The Netherlands F. C. Mokken 7 F. J. M. van der Waart 7 P. T. Goedhart Laboratory of Clinical Hemorheology, Academic Medical Center, University of Amsterdam, The Netherlands A. W. Gelb Department of Anesthesia, University Hospital, London, Ontario, Canada Ann Hematol (1996) 73 : 135–137 Q Springer-Verlag 1996 ORIGINAL ARTICLE F. C. Mokken 7 F. J. M. van der Waart 7 C. P. Henny P. T. Goedhart 7 A. W. Gelb Differences in peripheral arterial and venous hemorheologic parameters Received: 12 February 1996 / Accepted: 3 June 1996 Abstract To evaluate the comparability of hemorheo- logic parameters in arterial and venous blood, we mea- sured hematocrit, whole blood viscosity, plasma viscosi- ty, erythrocyte deformability, erythrocyte aggregation, and erythrocyte indices in both arterial and venous blood from 20 consecutive patients scheduled for cor- onary artery surgery and/or valve replacement surgery. Hematocrit, whole blood viscosity at three shear rates (0.05 s P1 , 0.5 s P1 , and 70 s P1 ), plasma viscosity, and erythrocyte aggregation factor were statistically signifi- cantly higher in venous blood than in arterial blood. The differences may be explained by the difference in hematocrit. Erythrocyte deformability did not differ significantly. With the availability of more precise rheo- logical measurement techniques, differences such as those encountered in this study may be of importance in clinical studies. It is concluded that arterial and ve- nous blood samples are not entirely rheologically com- parable. Key words Arterial 7 Venous 7 Rheology 7 Viscosity 7 Erythrocyte deformability Introduction In recent years the study of blood flow in general and of hemorheologic parameters in particular has become of increasing interest to researchers and clinicians. As technology rapidly develops, many measurement tech- niques for rheological parameters are being developed. Methods are becoming increasingly accurate and intra- and interassay variability is decreasing. The need for standardization of these measurement techniques was recognized. In 1986, an expert panel for standardization in hematology issued guidelines for measurement of hemorheologic parameters to create clarity in this mat- ter. However, it did not state whether samples should be consistently taken from the arterial or venous side of the circulation. With the number of clinical investigations increas- ing, blood sampling is often facilitated by introducing an intra-arterial catheter. Additionally, such a catheter prevents prolonged venous stasis, erythrocyte damage, and hemolysis. The current literature lacks information concerning the comparability of hemorheologic results in arterial versus venous blood samples. The aim of the present study was to compare a number of hemorheo- logic parameters in arterial and venous blood. Materials and methods The institutionally approved study was performed with 20 conse- cutive patients scheduled for coronary artery bypass surgery and/ or aortic valve surgery who all gave written informed consent to their participation in this study. After an overnight fast, all pa- tients were premedicated with 4–6 mg lorazepam orally. In the operating room an arterial cannula was inserted into the radial artery, while an indwelling intravenous catheter was inserted into a large vein in the contralateral arm. After insertion, 10 ml of blood was withdrawn simultaneously from each catheter into va- cutainers containing solid disodium-ethylenediaminetetra-acetic acid for measurement of hemorheologic parameters. An addition- al 4 ml of blood was drawn from each catheter into vacutainers containing fluid potassium-ethylenediaminetetra-acetic acid for measurement of erythrocyte indices. No fluids were infused prior to blood sampling. Venous blood was collected with minimal ve- nous stasis, and the tourniquet had been removed at least 5 s pri- or to the actual blood withdrawal. Blood and plasma viscosity were measured in a Contraves LS30 rotational viscometer (Contraves, Basel, Switzerland) at 37 7C. Because it varies with the rate of shear, blood viscosity was measured at 81 different shear rates ranging from 100 to 0.01 s P1 . From this range three shear rates were selected, one representing a low shear rate (LS) at 0.05 s P1 , one a medium shear rate (MS)