To the Editor:—
We read with interest the article by Norris et al. , 1which compared combined spinal–epidural (CSE) to epidural analgesia. We congratulate the authors in revalidating the safety and low complication rates of these techniques in a large group of mixed-parity parturients; however, we differ in our interpretation of the impact of these techniques on the progress of labor. In our earlier report, 2we observed significantly faster initial cervical dilation and shorter times from analgesia induction to full cervical dilation in nulliparous women randomized to receive CSE versus epidural analgesia. Norris et al. interpret our findings as having “arisen by chance alone.” We believe this is unlikely given the statistical analysis we reported. CSE analgesia was associated with significantly faster time from analgesia initiation to full cervical dilation (P = 0.02) and rates of initial cervical dilation (P = 0.0013); the strength of these associations severely limits the possibility of chance being a major factor.
Instead, we suggest that our conflicting outcomes are the result of subtle but important differences. Parturients in the Norris study had analgesia initiated at a greater cervical dilation (4.0–4.5 ± 2 cm) than in our study (3 ± 1 cm), and as noted in a number of investigations, including the seminal work by Friedman, 3advanced labor alone is associated with faster dilation. This underlying dilation rate may have minimized the impact of analgesic technique. In addition, obstetrician management of labor, including using oxytocin for induction and assisting membrane rupture, which were not reported by Norris, may play significant roles in the progress and outcome of labor. 4
The medications used via the techniques also differed in a number of ways. Norris et al. allowed clinicians the ability to determine and provide different medication regimens based on a subjective diagnosis of “early”versus “advanced” labor, and epidural lidocaine was used, even in the CSE groups, for initiation of the analgesia. Moreover, epidural maintenance infusions were initiated in all groups immediately following the technique placement. By contrast, our groups received a single, standardized regimen based on the technique selected; used bupivacaine as the sole local anesthetic; and in our CSE group, received epidural medications, including the maintenance infusion, only when additional analgesia was requested. We recognize the techniques as employed by Norris et al. are popular, but the impact of such variations on progress of labor remains unknown. Since alterations in maternal catecholamines may be an important mechanism by which central neuraxial analgesia modulates uterine activity, 5,6these variations may play a significant role.
The effect of central neuraxial analgesia on the progress and outcome of labor remains controversial, and we commend Norris et al. for adding information to this discussion. However, we stand by the results of our previous study and encourage future investigation into the subtleties of patient selection, obstetric management, and anesthetic technique that may account for these differences.