Statistical Analysis of Total Labor Pain Using the Visual Analog Scale and Application to Studies of Analgesic Effectiveness During Childbirth

We recently evaluated statistical methodologies to measure from a societal perspective the cost-effectiveness of drugs and techniques to provide analgesia during childbirth [1]. Repeated measurements of pain using a visual analog scale (VAS) are probably not a valid method to measure the effectiveness of labor analgesia. First, missing VAS data are likely to be informative or directly related to the values that would have been observed (e.g., observations may be missing because some women in pain may refuse to complete the visual analog scale). Second, a woman's perception of "worst pain imaginable," the descriptive end point of the visual analog scale, may change over the course of childbirth. The single retrospective VAS may, in contrast, give accurate results. We agree with Dr. Cohen that additional studies are required. Patients' relative valuations for different magnitudes and durations of pain must be investigated. We considered cost-effectiveness measured from a societal perspective, as recommended by consensus reports [2]. Dr. Cohen states, "there is no cost incurred for analgesia until the patient … receives pain relief." By analogy, there would be no cost incurred for police protection until a citizen summons help. "There is no" direct medical "cost incurred for analgesia until the patient … receives pain relief." The greatest cost to society in providing labor analgesia to women is not the direct medical cost for epidural trays and drugs. Rather, most of the expense to society is for the availability (i.e., salary) of an anesthesiologist to provide the analgesia. Dr. Cohen maintains that the only appropriate period during which to evaluate the efficacy of analgesia is the period during which analgesia is administered. This may be true for the efficacy of a therapy; however, we considered the effectiveness of the therapy. Car safety belts are efficacious, but their effectiveness is decreased by people choosing to not use them. How a therapy is used, including when during labor a woman receives analgesia, can have as much or more profound an impact on the cost-effectiveness of a therapy than its efficacy. Franklin Dexter, MD, PhD Department of Anesthesia; University of Iowa; Iowa City, IA 52242-1079