We thank Dr. Paech for bringing the results of his excellent work  to our attention, and we apologize for lack of citation of his paper in our list of references. However, we still must state that there are "little" data comparing demand dose and demand dose plus continuous infusion modes in patient-controlled epidural analgesia (PCEA) for labor and delivery [i.e., only two publications in the literature with differing conclusions [1,2]].
Exception must be taken with some of Dr. Paech's interpretations of our results. The results of our study never concluded that provision of a third of the hourly dose as a continuous background infusion was "optimal," but rather "appropriate" under experimental conditions . The results of the study suggest that use of the continuous infusion plus demand dose mode of PCEA for labor and delivery may be superior to demand dose alone. The preference for the continuous infusion plus demand dose mode of PCEA was based upon analgesic efficacy, dose-sparing effect, and the need for analgesic supplementation. It remains for further investigation to clarify the "optimal" amount of bupivacaine to be provided by a background infusion.
In our study, background infusions within the PCEA groups did not increase total cumulative or cumulative hourly bupivacaine dosage . (Please refer to Table 3 in the original publication.) In fact, use of PCEA with or without a background infusion provided a 35% dose-sparing effect as compared with a traditional continuous epidural infusion (CEI).
If all modes of PCEA were equianalgesic and provided a dosesparing effect as compared with CEI without an increase in total cumulative or cumulative hourly bupivacaine dosage, then one must ask how these results were achieved. They were achieved by an increase in requests for physician-administered supplemental bupivacaine by women receiving no or minimal background infusions. Definite statistical significance was achieved for an increased need for supplemental bupivacaine in these PCEA groups as compared with other experimental groups during the first stage of labor. A trend (P = 0.07) was noted over the entire course of labor.
The "difficulty" that readers may have with our results and conclusions is that they deny preconceptions regarding PCEA for the laboring patient that are drawn from the literature for intravenous patient-controlled analgesia (IV-PCA). Using opioids via IV-PCA in the postoperative patient, a concurrent background infusion increases cumulative dosage without affecting analgesia [3-5] and does not reduce the number of patient demands [3,4] or improve sleep at nighttime . Conclusions derived from the use of IV-PCA with opioids in postoperative patients may not necessarily be extrapolated to the use of PCEA with bupivacaine in the laboring patient. Moreover, the goal of PCEA with local anesthetics during labor and delivery is to maintain a level of sensory blockade. This is quite distinct from the requirement to provide systemic analgesia with opioids via IV-PCA or the requirement to provide postoperative epidural analgesia with PCEA. Thus, conclusions drawn from the literature of IV-PCA with opioids [3-5] or experience with PCEA for postoperative analgesia (opioids with or without local anesthetics)  are not necessarily applicable to PCEA with bupivacaine in the laboring patient.
As the literature is now conflicting as to the need for background infusions with PCEA in the laboring patient, clarification of this point must await further study with larger numbers of patients.
F. Michael Ferrante, MD, FACPM
Director, Pain Management Center
Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115
1. Paech MJ. Patient-controlled epidural analgesia in labour--is a continuous infusion of benefit? Anaesth Intensive Care 1992;20:15-20.
2. Ferrante FM, Rosinia FA, Gordon C, Datta S. The role of continuous background infusions in patient-controlled epidural analgesia for labor and delivery. Anesth Analg 1994;79:80-4.
3. Owen H, Szekely SM, Plummer JL, et al. Variables of patient-controlled analgesia. 2. Concurrent infusion. Anaesthesia 1989;44:11-3.
4. Parker RK, Holtmann B, White PF. Patient-controlled analgesia. Does a concurrent opioid infusion improve pain management after surgery? JAMA 1991;266:1947-52.
5. Parker RK, Holtmann B, White PF. Effects of nighttime opioid infusion with PCA therapy on patient comfort and analgesic requirements after abdominal hysterectomy. Anesthesiology 1992;76:362-7.
6. Parker RK, Sawaki Y, White PF. Epidural patient-controlled analgesia: influence of bupivacaine and hydromorphone basal infusion on pain control after cesarean delivery. Anesth Analg 1992;75:740-6.