The dose-response relation of intrathecal fentanyl for labor analgesia

Background: This study determined the dose-response relation of intrathecal fentanyl for labor analgesia and described the onset, duration, and quality of analgesia when used as the sole analgesic. Methods: Eighty-four parturients in active labor who requested analgesia were randomized to one of seven treatment groups. They received 5-45 mu g intrathecal fentanyl as part of a combined spinal-epidural technique. Visual analog pain scores were recorded before and at intervals after injection patients requested additional analgesia. The occurrence and severity of pruritus, nausea, and vomiting were also recorded. Maternal blood pressure was recorded before injection and at intervals after injection. Fetal heart rate was recorded before and 30 min after injection. Results: By 5 min after injection, pain scores mere significantly different among groups (P < 0.001). Mean duration of analgesia increased to 89 min as the dose increased to 25 mu g. Maternal diastolic blood pressure was significantly lower 10 and 30 min after injection. There was no difference among groups in the incidence of pruritus; nausea and vomiting were uncommon. Fetal heart rates did not change after injection. A dose-response curve indicates that the median effective dose of intrathecal fentanyl for labor analgesia is 14 mu g (95% confidence interval 13-15 mu g). Conclusions: Intrathecal fentanyl produces rapid, profound labor analgesia with minimal side effects. These data indicate that there is little benefit to increasing the dose beyond 25 mu g when it is used as the sole agent for intrathecal labor analgesia.