Analgesia, pruritus, and ventilation exhibit a dose-response relationship in parturients receiving intrathecal fentanyl during labor.

UNLABELLED: Several studies have characterized the 50% and 95% effective doses (ED50 and ED95, respectively) of intrathecal sufentanil for labor analgesia. Few have investigated these same criteria for the less expensive alternative, fentanyl. In addition, the ventilatory effects of intrathecal fentanyl at clinically relevant doses are unclear. We performed this study to establish the dose-response relationship of intrathecal fentanyl for both analgesia and ventilatory depression. Ninety parturients in active early labor (< or = 5 cm dilation) received intrathecal fentanyl 5, 7.5, 10, 15, 20, or 25 micrograms in a double-blinded, randomized fashion (n = 15 patients in each group). Parturients were monitored for degree of pain (measured using a 100-mm visual analog pain scale), blood pressure, arterial oxygen saturation (SaO2), respiratory rate, ETCO2, and fetal heart rate 0, 1, 5, 10, 15, 20, 25, and 30 min after the administration of intrathecal fentanyl. An absolute visual analog pain scale score < or = 25 mm was defined a priori as analgesic success. The percentage of parturients who achieved analgesic success was used to construct quantal dose-response curves, from which the ED50 and ED95 values were derived for the total population (mixed parity) and the nulliparous and multiparous subpopulations separately. Overall ED50 and ED95 values (95% CI) were 5.5 (3.4-7.2) and 17.4 (13.8-27.1) micrograms, respectively. Nulliparous values were lower (5.3 and 15.9 micrograms, respectively) than multiparous values (6.9 and 26.0 micrograms, respectively) but were within the 95% CIs of the total population. Pruritus incidence in parturients with analgesic success displayed a dose-response relationship identical to that seen for analgesia. ETCO2 displayed a dose-related increase, particularly at doses > or = 15 micrograms, without concomitant changes in respiratory rate or SaO2, which suggests a decrease in tidal volume. Even in the absence of overt signs or symptoms of somnolence, intrathecal fentanyl at doses within the effective analgesic range induced a change in ventilation that may last longer than the 30-min period we studied. IMPLICATIONS: Intrathecal fentanyl induces rapid and satisfying dose-dependent analgesia in early labor; however, it also produces dose-related decreases in ventilation in the absence of overt somnolence.

Field block for cranial surgery in World War II.

During World War II, physicians with minimal training were often thrust into the role of anesthetist. To educate these men, experts in anesthesia taught simple, conservative, and effective anesthetic techniques, such as the field block. Field blocks are the ideal "no frills" anesthetic because they are low-risk procedures that require minimal equipment. Unfortunately, many of the field blocks used during World War II are no longer taught. We present one technique that has fallen from favor, the field block for cranial surgery, both to educate about anesthesiology during World War II and to provide knowledge for the practicing military physician. The modern military anesthesiologist must be capable of anesthetizing patients under any conditions. First response care teams may find the technique of field block for cranial surgery useful in providing emergency anesthesia care.

Determination of the dose-response relationship for intrathecal sufentanil in laboring patients.

Multiple studies have investigated the efficacy of intrathecal opioids, particularly sufentanil, in laboring parturients. However, until the important pharmacological indices of the 50% and 95% effective doses (ED50 and ED95, respectively) are defined, reliable comparative studies among drugs at equipotent doses cannot be performed. This study was performed to establish the dose-response relationship of intrathecal sufentanil analgesia in labor. Sixty parturients presenting in active labor received intrathecal sufentanil 2.5 (n = 10), 5.0 (n = 10), 7.5 (n = 10), 10.0 (n = 10), 12.5 (n = 10), or 15.0 (n = 10) microg in a blind, randomized fashion. Patient 100-mm visual analog pain scale (VAS) scores, fetal heart rate (FHR), blood pressure, and heart rate were recorded at 0, 1, 5, 10, 15, 20, 25, and 30 min after administration of sufentanil and then again when the patient requested additional analgesia. Absolute VAS < or =25 mm was considered an analgesic success. Percent responders was used to construct a dose-response curve and calculate ED50 and ED95. The ED50 and ED95 for intrathecal sufentanil in laboring parturients were 2.6 (1.8-3.2, 95% confidence interval) and 8.9 (7.5-11.5) microg, respectively. There was a trend toward increasing analgesic duration with increasing sufentanil dose. The maternal side effect profile was not different among groups. FHR did not appreciably change for any group or individual studied. Assisted delivery and cesarean section rates were similar for all groups. Intrathecal sufentanil provides rapid onset of analgesia for labor. The ED50 and ED95 values established in this study should help to provide benchmarks both for the safe clinical use of intrathecal sufentanil for labor and for future comparison studies with other intrathecal analgesic techniques.