Summary

Background and objective: Crystalloid haemodilution has been widely found to enhance coagulation onset, but the duration of this effect has never been documented. Methods: Twelve healthy, consenting volunteers had a rapid infusion of 14 mL kg−1 of normal (0.9%) saline. Blood samples were taken, prior to (control), and immediately after (30 min) the rapid saline infusion was completed (30 min). They were then repeated at regular intervals up to 120 min. Haematocrit/platelet counts were taken to determine the degree of dilution and thrombelastograms, with and without platelet antagonists (ReoPro, Abciximab), were measured in all samples. Antithrombin levels were selectively measured. Results: The haematocrit and platelet count showed a rapid dilutional decrease at 30 min (mean of −12.2% and −14.4%, respectively), with values returning towards baseline within 15 min after finishing the infusion. There was a significantly faster onset of coagulation (decrease in r-time) in the post-infusion sample (30 min) compared to control (P < 0.05), again returning towards normal as the dilution effect was reversed. Similar thrombelastograms findings were evident in the plasma factor only group (platelets inhibited by ReoPro). Antithrombin levels changed in keeping with the haemodilution effect (P < 0.0001). There was a linear relationship between antithrombin and thrombelastograms r-time (P = 0.012). Conclusion: The faster onset of coagulation brought on by haemodilution return towards normal as the dilutional effect is reversed. This effect is mediated through plasma clotting factors. Of interest is the significant inverse correlation of the onset of coagulation increasing as the antithrombin levels decreased with dilution.