Effect of intrathecal fentanyl dose on the duration of labor analgesia

The short duration of effective analgesia produced by intrathecal fentanyl (ITF) at doses ranging from 5 to 25 micrograms limits the drug's use for the management of labor pain. The understanding of the potential of ITF related to duration of analgesia in the labor patient is derived from studies of and clinical experience with ITF at doses not exceeding 25 micrograms and less. We hypothesized that by increasing the dose beyond 25 micrograms, a prolonged duration of analgesia could be achieved. The purpose of the present study was to compare the difference in duration of effective analgesia and adverse effects produced by 25, 37.5, and 50 micrograms of ITF. A sample population of 60 term parturient women with uncomplicated singleton pregnancies who were in active labor and requesting pain control were randomly assigned to 1 of 3 groups: group 1, 25 micrograms (n = 20); group 2, 37.5 micrograms (n = 20); and group 3, 50 micrograms (n = 20). The ITF was then administered by an anesthesia provider blinded to the dose via a combined spinal epidural technique. The time from injection to the time of request for subsequent pain control (considered the duration of effective analgesia), maternal and fetal vital signs, and adverse effects were recorded at specific intervals until the patient requested activation of the epidural catheter or delivery occurred, ending participation in the study. Statistical analysis using a 1-way analysis of variance and considering a P value of < .05 to be significant revealed no difference in duration of effective analgesia between the groups. Statistical differences in the incidence of adverse effects, particularly uterine hyperstimulation, hypotension, pruritus, nausea, and fetal heart rate decelerations were not evident using the Fisher Irwin test and a significance of P < .05. The findings of the present study demonstrate that there is no real advantage of using doses of ITF greater than 25 micrograms in quality and duration of effective labor analgesia.