Postoperative changes in blood viscosity and the influence of haematocrit and plasma-fibrinogen

Abstract

Abstract The blood of 25 patients undergoing surgery has been investigated for levels of whole-blood and plasma viscosity, haematocrit, and plasma-fibrinogen before and after operation. The whole-blood viscosity diminished by between 14 and 23 per cent after operation. The haematocrit fell from a mean preoperative level of 42.3 per cent (S.D. ± 5.2) to a mean postoperative level of 36.3 per cent (S.D. ± 5.5). When the effect on viscosity of this reduction in haematocrit was removed the blood viscosity rose after operation by 9–14 per cent. The level of plasma-fibrinogen rose from a mean preoperative level of 360 mg. per cent (S.D. ± 78) to a mean postoperative level of 714 mg. per cent (S.D. ± 155), an overall increase of 98 per cent. This postoperative rise in the plasma-fibrinogen concentration exerted an effect on the blood viscosity opposite to that of the haematocrit. The deleterious effects of a rise in blood viscosity on tissue perfusion and oxygenation are outlined, and the relevance of the reported findings to the maintenance of an adequate microcirculation in the postoperative period is discussed. Attention is drawn to the benefits of a slight fall in haematocrit during this period.