We maintain our full support of the numeric pain rating scale (NPRS) as our primary outcome measurement given its wide acceptance, easy administration, and demonstrated objectivity and validity in multiple studies of labor analgesia.3,4 NPRS is the standard method for comparing the onset and effectiveness of different labor neuraxial techniques, and the selected threshold of NPRS ≤ 1 is relevant to the patient and provider; using this threshold, Beilin et al3 demonstrated only 2% of parturients desired additional neuraxial analgesia medication. By contrast, the use of a surrogate such as the absence of “top-up medication requests after block initiation” would yield less information on the quantitative and qualitative subtleties between techniques including analgesia onset (eg, time to NPRS ≤ 3 versus NPRS ≤ 1), as well as maintenance (eg, the degree of discomfort at the time of supplemental medication request). To this end, our selection of survival analysis a priori enabled the use of the full time-to-event data, acknowledging that not all women (8/120 patients) would achieve our primary outcome (ie, time to NPRS ≤ 1 between the DPE and epidural [EPL] groups).
Moreover, we continue to value the incidence of asymmetric blockade >2 dermatomes as an important research and clinical outcome. Although no catheters in our study were replaced or manipulated, the number of top-up interventions and the degree of motor block can be directly influenced by the presence of asymmetric blockade. In addition, the presence of an asymmetric analgesic blockade of 2 to 3 dermatomal levels can result in the conversion of neuraxial to general anesthesia for operative deliveries,5 which has associated maternal and fetal implications. To emphasize the relevance of these findings, we analyzed physician top-ups as a binary outcome of having satisfactory analgesia or requesting a top-up; using this definition, Halpern et al6 found that those with >1 clinician top-up had significantly higher failure rates for conversion of epidural labor analgesia to surgical anesthesia. Our finding of lower top-up rates in the DPE group remains unchanged even after a multivariable adjustment for duration of infusion (Table; duration of infusion data in Table 32).
Although Richardson and Baysinger summarized our work as suggesting that combined spinal epidural (CSE) “is the technique of choice when rapid sacral block is needed,” we urge our colleagues to consider the full implications of their analgesic selections. We found the CSE technique to be associated with a significantly higher incidence of combined uterine tachysystole, hypertonus, and need for uterine relaxation, as well as progression of National Institute of Child Health and Human Development category I to II fetal heart rate tracings, when compared to EPL and DPE techniques.2 While the incidence of emergency cesarean delivery did not differ between groups, this may not hold true in parturients or fetuses with comorbid conditions.
The presence of early sacral coverage may be an important prognosticator of ongoing sacral analgesia. In our study, all parturients undergoing DPE and CSE techniques achieved bilateral and ongoing S2 blockade within the first 30 minutes, whereas 5% of patients undergoing EPL never achieved sacral blockade.2 It is possible that the analgesic medication volume (20 mL) used in our study, as well as at many other institutions,7 was at least partially responsible for the sacral analgesia observed; future studies will need to determine the contribution of volume, pressure, and local anesthetic concentrations as well as the optimal combination of these elements to the qualitative aspects of the DPE technique.