AN article in this issue reports that cervical dilation is more rapid in women receiving combined spinal–epidural analgesia (CSE) compared with epidural analgesia for the treatment of labor pain. 1A similar observation was reported recently in another article in ANESTHESIOLOGY that found more rapid cervical dilation with lumbar sympathetic block than with epidural analgesia. 2Neither study revealed a difference in the mode of delivery or obstetric outcome for the techniques studied, which could lead to the logical question, So what? I would like to address this question generally with a quick review of the history of obstetric anesthesiology research and more specifically regarding the progress of labor.
Obstetric anesthesiology research appeared as a real endeavor more than 30 yr ago, at a time when the pain of labor was largely ignored or treated with methods that were ineffective (small systemic doses of opioids) or entailed significant side effects to the mother (twilight sleep) or the fetus (paracervical block). Research in this area led rapidly to the provision of safe and effective analgesia in laboring women, with continuous epidural analgesia supplemented, more recently, by spinal injections. As with much of clinical medicine, a large area of research in obstetric anesthesiology focuses on the details of therapy (e.g. , the method of drug delivery, concentrations of local anesthetics, the use of adjuvants, and the prevention or treatment of side effects). These studies have clearly improved safety (by providing ways to avoid the catastrophic consequences of accidental intravenous and intrathecal injections of large doses of local anesthetics, and by helping us to understand the importance of patient positioning in maintaining uteroplacental perfusion) and patient comfort (by reducing dense motor block and even allowing ambulation).
No doubt that these studies have been useful in guiding therapy, but they clearly do not address fundamental questions of general importance and interest in perinatal medicine and anesthesiology. Indeed, we could argue that there has been a progressive decline in the quality of questions addressed by obstetric anesthesiologists in the past 30 yr, from a fundamental understanding of the regulation of uteroplacental perfusion and its alterations by regional anesthesia in the 1970s to the very narrow question of whether epidural analgesia causes cesarean sections or maternal fever in the 1990s (fig. 1).
We most certainly need both types of research: the what and the why. Unfortunately, the latter has, with the exception of efforts by a few persons, been rapidly dwindling.
To return to the current question, these studies suggest that, among nulliparous women who request more than systemic opioids for labor analgesia, cervical dilation occurs more rapidly with CSE (local anesthetic plus opioid) or lumbar sympathetic block (local anesthetic) than with epidural analgesia (local anesthetic plus opioid). Does this mean that CSE and lumbar sympathetic block speed labor, or that epidural slows it? Why? We can address this issue at a gross level (e.g. , the difference in motor block, sympathetic efferent block, and circulating drug concentrations) and, simultaneously, at a somewhat finer level (e.g. , on an endocrine, paracrine, or neural basis).
Asking why may lead to a better understanding of the regulation of the labor process, with important implications for major public health issues, such as the cause, prevention, and treatment of premature labor. Asking why may also change our role from that of primarily an important assistant (“merely” providing analgesia for labor) to that of a true consultant (diagnosing dysfunctional labor—whether too fast or too slow—and prescribing appropriate therapy). The clear relation between pain and obstetric outcome 3and the findings of the current study 1and that with lumbar sympathetic block 2suggest that pain and its treatment are central to obstetric management, and that this consulting role in labor management is not improbable. But why must be answered before how can be asked.
Anesthesiology is the practice of medicine. It involves diagnosis, prescription, and assessment, with research directed toward each of these activities. We need to know whether epidurals lead to cesarean section deliveries or neonatal sepsis workups, and whether it is better to use more opioid and less local anesthetic for epidural analgesia during labor. As physicians, however, we must also address the basic neurobiologic and perinatal issues that are at the center of our practice.
Neurophysiologic Basis of Labor Pain
What is the neuroanatomy of uterocervical nociception in labor, and why is the pain of labor so variable among women, when these same women differ little in response to experimental pain stimuli? What is the role of vagal afferents in labor pain? Is local inflammation important in uterocervical nociception of labor pain, and does clinical application of prostaglandins to ripen the cervix sensitize these afferents and increase pain?
Neuropharmacology of Visceral Afferents
What inhibitory receptors are expressed at the peripheral and central terminals of uterocervical afferents? Why is spinal morphine potency reduced so much for labor pain compared with postoperative pain? Can peripheral inhibitory mechanisms be harnessed to provide labor analgesia without spinal or epidural injections? What plastic changes occur in signaling or inhibitory mechanisms in uterocervical afferents during prolonged stimulation during labor?
Regulation of Labor
What is the role of neural influences on the regulation of labor, and what neuroanatomy does this reflect? What neuropeptides are present in peripheral afferent terminals, are they released during nociceptive stimulation, and do they regulate cervical remodeling? What is the role of uterine vagal afferents in the endocrine regulation of labor? How are these processes altered by our analgesic interventions?
Fetal Response to Asphyxia
Why does the fetal hormonal response to asphyxia differ so much from the adult? Are the stimuli for ischemic or programmed cell death identical in the fetus and the adult? How do mechanisms for redistribution of cardiac output during asphyxia differ between the fetus and the adult?
These are but a few questions. They may not be the best ones to ask. We could probably think of others. The point is that, in addition to knowing how to do things and what these interventions do to physiology (such as the progress of labor 1,2), we need to remember to ask why, or we stifle ourselves and reduce our field to a technical exercise.