To the Editor:
Ferrante et al.  have furthered our knowledge and experience of patient-controlled epidural analgesia (PCEA) for labor. They are incorrect, however, in stating that "there are little or no data comparing… the two modes of delivery for PCEA" when introducing and discussing their clinical trial investigating the influence of a background infusion on demand dosing. This has been addressed before and the need for further investigation emphasized . In several respects the results obtained in two of Ferrante et al.'s groups (demand dosing only and demand dosing plus continuous infusion at 3 mL/h) confirmed those of my study using similar epidural solution and methodology.
It is true that, were a larger study to confirm their postulate that supplementary dosing is reduced by a concurrent infusion in addition to demand dosing, a logistic benefit would be confirmed where physicians administer supplementation. In our and most obstetric hospitals in Australasia, this is of no consequence, as epidural boluses are given by accredited attending midwives.
I believe that their conclusion (that a method in which approximately a third of the hourly maximum dose is infused continuously is optimal) may be premature. Background infusions increase cumulative drug dose [1,2], and the only potential benefit postulated (the abovementioned) was based on observation of a nonsignificant difference. Gambling et al.  reported no significant difference in rate of drug utilization or supplementation between various combinations of demand dose volume and lockout time. Ferrante et al. also found that cumulative hourly dose was the same for all PCEA methods. It is thus possible that the high incidence of supplementation they noted (86%) in the group self-administering 3 mL of 0.125% bupivacaine and fentanyl 2 micro gram/mL (which contrasts with a 40% incidence in the demand-bolus-only group receiving 4 mL of similar solution in my study) may have been reduced had a larger demand bolus been available.
Published experience confirms the efficacy and safety of demandonly PCEA in labor, and, until more convincing data supporting a concurrent infusion are presented, I believe that the former should remain the preferred method.
Michael Paech, MBBS
Department of Anaesthesia, King Edward Memorial Hospital for Women, Perth, Western Australia
1. 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.
2. Paech MJ. Patient-controlled epidural analgesia in labour--is a continuous infusion of benefit? Anaesth Intensive Care 1992;20:15-20.
3. Gambling DR, Huber CJ, Berkowitz J, et al. Patient-controlled epidural analgesia in labour: varying bolus dose and lockout interval. Can J Anaesth 1993;40:211-7.