Influence of bleeding on haemorheology and haemostasis in surgery

Changes in haemorheology and haemostasis may contribute to bleeding or thrombosis, which is of concern particularly in surgery. Blood loss itself has a major influence on both parameters being closely involved in the clinical outcome. In order to analyze the underlying interrelations, a prospective study with 122 patients (64 females, 58 males) aged between 18 and 83 years (mean: 51.8 years) was conducted. All patients were electively submitted to orthopaedic surgery. Haemorheological parameters included measurements of plasma viscosity, red body cell (RBC) and platelet aggregation index preoperatively, as well as by day 1 and day 7 after surgery. Additionally hematological and haemostaseological parameters including leukocyte and platelet counts, haematocrit and fibrinogen were investigated. Bleeding was defined as high (>500 ml) or low blood loss (≤500 ml) according to the drainage volume. High but not low blood loss was associated with an increase of RBC aggregation by day 1 and 7 after surgery. Plasma viscosity decreased significantly by day 1, returning to normal 7 days after surgery. Platelet count decreased significantly, concurrent with the haematocrit, by day 1 postoperatively, whereas by day 7 a significant increase was observed, being more distinct in high blood loss. Platelet aggregation index did not change under the influence of blood loss. Plasma fibrinogen, clearly corresponding to the extend of blood loss, showed a continuous postoperative increase, which was significantly higher at day 7. Leukocytes increased moderately but significantly in particular in high blood loss. In conclusion, the postoperative decrease of plasma viscosity and of platelet counts, concurrent with the haematocrit, provides evidence of being clearly dependent on blood loss which is regarded as a dilution effect corresponding with the haemorrhagic risk. The increase of RBC aggregation at the early postoperative stage is solely observed in high blood loss and is esteemed as a result of volume therapy. The marked increase of platelet counts and plasma fibrinogen at the late postoperative stage, being more pronounced in high blood loss, might contribute to an elevated prothrombotic risk and is ascribed to an inflammatory response to surgery. In summary, it is concluded, that bleeding tendency corresponding with haemorheologic parameters is enhanced in the early, whereas the prothrombotic risk, well correlating with haemostaseologic parameters, is elevated in the later stage after surgery.