Why Does Prophylactic Epidural Blood Patch Fail to Demonstrate Efficacy in Preventing Post–Dural Puncture Headache in Parturients after Dural Puncture?

We read with interest the study by Scavone et al. 1that demonstrates the absence of efficacy of a prophylactic epidural blood patch after inadvertent dural puncture. We suggest that two factors could have influenced the negative result of this trial. First, inadvertent dural puncture could have been overdiagnosed, namely when loss of resistance to saline was used to locate epidural space. This could explain the lower incidence of post–dural puncture headache and less frequent realization of therapeutic epidural blood patch reported in this study compared with others.2,3Second, 20 ml may not be the adequate blood volume to test a prophylactic epidural blood patch. This volume has tended to increase over time to 20 ml or more, 23 ± 5 ml in a study by Safat-Tisseront et al. 3The optimal blood volume may be the volume at which pain in the back, buttocks, or legs occurs, which was only achieved for seven patients in the study of Scavone et al. This higher volume may lead to either a larger patch over the dural tear or a significantly higher increase in lumbar and intracranial pressure, leading to reduced cerebral vasodilation.*Hôpital Cochin Maternité Port-Royal, Assistance Publique–Hôpitaux de Paris, Paris, France. olivier.prus@club-internet.fr