Results
Baseline characteristics for the 2 groups are shown in Table 1. Women receiving ITN were similar to the comparison group in mean age, marital status, and insurance type but were significantly more likely to be white. Women in the ITN group had less advanced cervical dilation on admission and were somewhat more likely to present with spontaneous rupture of membranes.
The technique of ITN administration was consistent. All procedures were performed by one of approximately 20 anesthesiologists in a private-practice group. The anesthesiologists used 25-gauge conical-tipped Whitacre spinal needles to puncture the dura at the L3-L4 interspace. Eighty-six percent of these women received both morphine and fentanyl, typically 0.25-mg and 25-mg doses, respectively. Fourteen percent received fentanyl only, a choice generally reserved for multiparous patients expected to have rapid labor progress. The mean cervical dilation at the time of ITN administration was 4.7 cm ± 1.4 cm. Six women required a second ITN procedure, and another 5 women received intravenous nalbuphine for pain after ITN (usually more than 4 hours after ITN administration).
Intravenous drugs administered for pain in the comparison group also followed a consistent pattern, with nalbuphine being the parenteral analgesic of choice. Forty-one percent of these women received one dose of intravenous nalbuphine ranging from 5 to 20 mg; an additional 3% required 2 doses. Overall, women receiving ITN were significantly less likely to receive nalbuphine than women in the comparison group (P=.000). A total of 17 women in the ITN group received nalbuphine (including both those who had it before and those after ITN) versus 41 in the comparison group.
Data on lengths of labor, oxytocin use, and delivery outcomes for the 2 groups are shown in Table 2. The mean length of active-phase labor was similar: approximately 4 to 5 hours in each group. However, women with ITN experienced significantly longer second stages. This difference remained significant after controlling with multivariate regression for the following confounders: ethnicity, parity, maternal age, cervical dilation on admission, nalbuphine use, oxytocin use, and infant weight (b coefficient=26.965; t=3.261; P=.001). When labor lengths were further analyzed by parity Table 3, the prolonged second stage in women receiving ITN was statistically significant among nulliparas and approached significance among parous women as well. Of note, the magnitude of prolongation was similar for both nulliparous and parous women; that is, the length of the second stage was increased by more than 50% in both groups receiving ITN.
Women in the ITN group were twice as likely to receive oxytocin augmentation during labor Table 2. This difference persisted in a logistic regression model taking into account ethnicity, parity, maternal age, cervical dilation on admission, duration of active-phase labor, nalbuphine use, and infant weight (b coefficient=1.55; P=.001). After controlling for confounders, the relationship between ITN and oxytocin use was strengthened, with women who received ITN more than 4 times as likely to receive oxytocin (odds ratio [OR]=4.69).
With regard to delivery outcomes Table 2, 8 women from both groups (4% of the total) required a cesarean delivery. Seven of these were in the ITN group, and 1 was in the comparison group. Six of the cesarean sections were performed for dystocia, 1 for fetal distress, and 1 for other reasons. Nine women (4.5%) had an instrumental vaginal delivery (6 with ITN, 3 without). Among instrumental vaginal deliveries, half were for maternal exhaustion, a diagnosis seen exclusively in nulliparous women. Differences between the groups in the rates of cesarean section versus combined spontaneous and instrumental vaginal delivery did not reach statistical significance.
Table 4 shows the frequency of ITN side effects gathered from the chart review. Among women receiving ITN, 2 side effects-urinary retention requiring urethral catheterization and pruritus-were recorded with significantly higher frequency than in the comparison group. Nausea or vomiting, generally viewed as a side effect of ITN, was equally common in both groups, as was maternal hypotension. To counter side effects, essentially all women who received ITN were routinely given 6.25 mg naltrexone sublingually immediately postpartum. Other than the naltrexone, medications to treat side effects were infrequently used. Diphenhydramine, hydroxyzine (for pruritus), and prochlorperazine (for nausea) were administered to 11 women in the ITN group. An additional complication seen only in the ITN group was the occurrence of a postdural puncture ("spinal") headache. Four spinal headaches were diagnosed, and 3 of them were treated with a blood patch. None of the women experienced respiratory depression following ITN.
Neonatal outcomes were similar in both groups. In the ITN group, the mean infant birth weight was 3491 ± 552 g compared with 3506 ± 454 g for the comparison group (P=.82). Four infants in the ITN group and none in the comparison group had 5-minute Apgar scores less than 7 (P=.12). There were no significant differences in the number of infants in each group requiring resuscitation beyond simple stimulation and blow-by oxygen (17 in the ITN group, 14 in the comparison group, P=.25) or admission to the neonatal intensive care unit (5 infants vs 3, P=.72). However, infants whose mothers were in the comparison group were more likely to be given naloxone postdelivery, presumably for prophylaxis against respiratory depression (10 infants vs 3 in the ITN group, P=.08).