N euraxial analgesia delays the active phase of spontaneous labor and flattens the slope. For example, Gambling and associates (1998) compared combined spinal epidural (CSE) labor analgesia against intermittent intravenous (IV) boluses of 50 mg meperidine in 1223 nulliparas in spontaneous labor at term. The active phase of labor was diagnosed when cervical dilation was 4 cm in the presence of regular uterine contractions. s shown in Table 23-5, mean cervical dilation at first pain aAdministered as intermittent intravenous boluses. bMedian value.
CPresented as number (%).
dpresented as mean ± standard deviation. Data from Gambling, 1998.
TABLE 23-6. 9000 Women Undergoing Primary Cesarean Delivery for Dystocia
Percentage of
Women with Noted Median (1st, 3rd 6 cm (5,s8) Augmentation to delivery time 9.3 hr (6, 13)
Data from Alexander, 2003.
relief was 5 cm in both study groups. Oxytocin augmentation rates were signiicantly greater in the CSE group. Also, the first analgesia-to-delivery interval was lengthened (5 versus 4 hours). However, cesarean delivery rates did not difer significantly.
Importantly, the efect of neuraxial analgesia to slow activephase labor should not negatively afect use of neuraxial pain relie. As described in Chapter 25 (p. 495), investigators at Parkland Hospital completed five randomized trials involving a total of 2703 nulliparas in spontaneous labor at term (Sharma, 2004). Various neuraxial techniques were compared with meperidine for pain relief. First-stage labor was significantly lengthened with neuraxial analgesia (8.1 versus 6.6 hours) but cesarean delivery rates for dystocia were unafected (9.i1 versus 8.1 percent).
In sum, neuraxial analgesia slows the active phase of firststage labor. his currently is empirically corrected by augmentation of uterine contractions. Thus, recommendations of the Consensus Committee regarding protraction disorders are correct. Second, the Consensus Committee (2016) suggests that cesarean deliveries for dystocia are being done before 6 cm cervical dilation. However, there is good reason to believe that all of the Committee's first-stage recommendations are actually already empirically in use but are concurrent with an overall cesarean delivery rate in excess of 30 percent. For example, Table 23-6 lists labor characteristics in 9000 women with primary cesarean deliveries for dystocia at 13 university hospitals between 1999 and 2000 (Alexander, 2003). Notably, the median cervical dilation at the time ofcesarean for dystocia was 6 cm. Moreover, Figure 23-4 depicts primary cesarean delivery rates for dystocia at Parkland Hospital between 1988 and 2017. The rate has not changed significantly in 28 years. Thus, Consensus Committee (2016) guidelines may fail to prevent additional cesareans for dystocia. Again, additional studies are needed.
Fetal descent largely follows complete dilation. Moreover, the second stage incorporates many of the cardinal movements necessary for the fetus to negotiate the birth canal (Chap. 22, p. 428). Accordingly, disproportion ofthe fetus and pelvis frequently becomes apparent during second-stage labor.
Similar to irst-stage labor, time boundaries have been supported to limit second-stage duration to minimize adverse maternal and fetal outcomes. he second stage in nulliparas is limited to 2 hours and extended to 3 hours when regional analgesia is used. For multiparas, 1 hour is the limit, extended to 2 hours with regional analgesia.