Effect of amniotic fluid on blood coagulation

Introduction

Amniotic fluid embolism (AFE) is a catastrophic complication of pregnancy. The incidence of AFE is very rare, and the clinical presentation; central hemodynamic data in humans are typically obtained more than 1 hour after the event and from only the subset of women who have survived the initial insult. This makes the exact pathophysiology remain elusive, despite numerous attempts at understanding AFE syndrome. We tried to evaluate the effect of amniotic fluid on blood coagulation by making a simple in-vitro model, using an activated clotting time (ACT) monitor.

Methods

Sixteen healthy women undergoing elective cesarean section under spinal anesthesia. A venous sampling line was inserted before induction of anesthesia. After artificial rupture of the membrane, amniotic fluid was carefully obtained by the surgeon. At the same time, 10 ml venous blood was obtained from the sampling line, and two series of samples were made; (1) 5 ml venous blood with 0.1 ml amniotic fluid (group 1), and (2) 5 ml venous blood alone (group 2 = control). ACT was measured using 2 ml sample in each group.

Results

The ACT was 66.5 ± 20.9 seconds in Group 1 versus 102.4 ± 15.8 seconds in Group 2 (P < 0.0001). Especially, there was one case that coagulated immediately after mixing the amniotic fluid and the ACT could not be obtained in Group 1 (excluded from analysis). The strong coagulation ability by amniotic fluid was induced immediately, even in very small doses.

Conclusion

A dose of 0.1 ml was enough to form the 5 ml venous blood thrombosis, which is thought to be a sufficient amount to cause AFE, and we consider that its pathophysiology resembles pulmonary embolism. We suggest that AFE may be induced by a smaller dose such as 0.1 ml amniotic fluid than it had been thought. A part of the mechanism of amniotic fluid embolism in humans can be explained by pulmonary embolism theory by making a simple in vitro AFE model.