Effects of anaesthesia and surgery on the flow properties of blood.

The cardiovascular reaction to anaesthesia and surgery can be mediated through an effect on the heart, the calibre of the peripheral vessels and the physical flow properties of the blood. The last of these has been the most neglected and is the subject of this communication. The three principal primary determinants of the haemorheological properties of blood are the red cell concentration, the plasma protein concentration, in particular fibrinogen, the deformability of individual red cells and their aggregability. The general pattern of change following most operations under general anaesthesia consists principally of a rapid decrease in red cell deformability within the first 24 hours returning usually to normal range within two days, and an increase in whole blood viscosity reaching its maximum around four to five days following surgery and associated largely with a parallel increase in plasma fibrinogen and red cell aggregation. These changes may have a pathological significance, particularly in patients with pre-existing ischaemic disease. In these situations it may be desirable to modify the technique of anaesthesia and post-operative care to improve the patients' haemorheological response.