We appreciate the comments of Dr. Pruszkowski et al. regarding our recently published article.1Although we did not standardize epidural placement technique, it is standard practice at our institution to use loss of resistance to air to identify the epidural space, and it is unlikely that many, if any, procedures were performed using the loss of resistance to saline technique. Therefore, we do not believe this contributed to an overdiagnosis of inadvertent dural puncture, as suggested. In fact, the loss of resistance to air technique may be associated with a higher rate of post–dural puncture headache than the loss of resistance to saline technique.2The rate of post–dural puncture headache in our study (56%) corresponds closely with that found in a meta-analysis of dural puncture with an epidural needle in obstetric patients: 52.1% (95% confidence interval, 51.4–52.8%).3
We agree with the authors that the optimal volume of blood for an epidural blood patch is not known. Although approximately 20 ml seems to be the standard dose, volume of blood was not associated with epidural blood patch success in the retrospective study cited by the authors.4As noted, sacral pressure or pain was observed in only a small number of subjects who received a prophylactic epidural blood patch. This likely reflects the fact that the blood was, of necessity, injected through the 19-gauge, 88-cm epidural catheter at a much slower rate than is possible through a 17- or 18-gauge, 9-cm epidural needle, thus resulting in a smaller increase in epidural pressure during the injection. Although it is possible that modifications of the technique could result in a higher rate of efficacy of prophylactic epidural blood patch, our study clearly demonstrated no difference in the incidence of post–dural puncture headache using the technique as it is commonly practiced.
*Northwestern University Feinberg School of Medicine, Chicago, Illinois. email@example.com