Haemodilution and Coagulation: A Caveat

Introduction

Haemodilution with intravenous fluids will decrease the concentration of clotting factors in the blood, and intuitively it would be anticipated that this should induce some degree of impairment of coagulation. It has, however, been suggested that haemodilution may possibly provoke an increase in whole blood coagulation. In 1951 Tocantins [1] and in 1959 Monkhouse [2] reported that moderate haemodilution with crystalloids could induce a hypercoagulable state. This was later supported by Janvrin [3]in a clinical trial which suggested that the incidence of post-operative deep vein thrombosis increased with intra-operative fluid administration. Many of the studies which comment on the effects of colloids on coagulation have used a crystalloid control or have not made allowance for any crystalloid given to the patient in addition to the colloid, viz. cardio-pulmonary by-pass pump prime [4]. Vinnazzer and Bergmann in 1975 [5] performed a double-blind study which compared standard tests of coagulation as well as thrombelastographs pre- and post-operatively in two groups, one treated with Hydroxyethyl starch and the other with isotonic saline peri-operatively. Their findings show a post-operative hypercoagulable state in the control (saline) group, and an insignificant change in the test (Hydroxyethyl starch) group. As their study was done post-operatively, it does not show whether, or not, these changes on coagulability were already present after infusion of the intravenous fluid, before any surgical stress response occurred, which might further have influenced coagulation parameters. Tuman et al. [6] conducted an in vivo study in which they noted that patients receiving crystalloids demonstrated an increase in coagulability as measured by the Thrombelastograph (TEG), but they did not attribute this directly to the crystalloid infusions.

We, in a series of studies, set out to investigate the phenomenon that haemodilution per se would initiate enhanced coagulability.

References

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