Epidural blood patches may be used to treat post-dural puncture headache following accidental dural puncture in parturients. Their mode of action and the optimum volume of blood for injection remain controversial, with the interaction between injected blood and cerebrospinal fluid unknown. We aimed to establish the effects of serial haemodilution of whole blood with cerebrospinal fluid from 34 pregnant patients compared with serial haemodilution with Hartmann's solution, using the thromboelastogram. Haemodilution with either cerebrospinal fluid or Hartmann's solution had significant procoagulant and clot destabilising effects, enhanced with progressive haemodilution up to 30%. The effect of cerebrospinal fluid was greater compared with Hartmann's solution (p < 0.001). Cerebrospinal fluid led to a mean (95% CI) decrease in r-time by 2.4 (1.6-3.2) min, a decrease in k-time by 0.6 (0.4-0.8) min, an increase in alpha angle by 7.3 (5.5-9.0)°, and a decrease in maximum amplitude by 2.0 (0.6-3.4) mm. This may have implications for epidural blood patch, as success may be reduced near the time of dural puncture when cerebrospinal fluid leak is at its greatest, and large volumes of blood may be required to reduce haemodilution and clot destabilisation by cerebrospinal fluid. In addition, blood patching should be performed at the level of the dural puncture in order to ensure that the maximum volume of blood comes into contact with the cerebrospinal fluid.
© 2014 The Association of Anaesthetists of Great Britain and Ireland.