THE DOSE-RESPONSE RELATION OF INTRATHECAL FENTANYL FOR LABOR ANALGESIA

Background: This study determined the dose-response relation of intrat hecal fentanyl for labor analgesia and described the onset, duration, and quality of analgesia when used as the sole analgesic. Methods: Eig hty-four parturients in active labor who requested analgesia were rand omized to one of seven treatment groups. They received 5-45 mu g intra thecal fentanyl as part of a combined spinal-epidural technique. Visua l analog pain scores were recorded before and at intervals after injec tion patients requested additional analgesia. The occurrence and sever ity of pruritus, nausea, and vomiting were also recorded. Maternal blo od pressure was recorded before injection and at intervals after injec tion. Fetal heart rate was recorded before and 30 min after injection. Results: By 5 min after injection, pain scores mere significantly dif ferent among groups (P < 0.001). Mean duration of analgesia increased to 89 min as the dose increased to 25 mu g. Maternal diastolic blood p ressure was significantly lower 10 and 30 min after injection. There w as no difference among groups in the incidence of pruritus; nausea and vomiting were uncommon. Fetal heart rates did not change after inject ion. A dose-response curve indicates that the median effective dose of intrathecal fentanyl for labor analgesia is 14 mu g (95% confidence i nterval 13-15 mu g). Conclusions: Intrathecal fentanyl produces rapid, profound labor analgesia with minimal side effects. These data indica te 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.