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OBSTETRIC ANESTHESIOLOGY

A Randomized Controlled Trial of Three Patient-Controlled Epidural Analgesia Regimens for Labor

From the Department of Woman Anesthesia, KK Women's and Children's Hospital, Singapore.

Address correspondence and reprint requests to Mia Supandji, MD, Department of Woman Anesthesia, KK Women's and Children's Hospital, 100 Bukit Timah Rd, Singapore 229899. Address e-mail to miasupandji{at}gmail.com.

Abstract

BACKGROUND: Patient-controlled epidural analgesia (PCEA) is a safe and effective mode of maintaining labor analgesia; however, the ideal PCEA regimen is controversial.

METHODS: In this prospective, randomized, double-blind study, we examined the analgesic efficacy of demand-only PCEA and PCEA with background infusion. We recruited 300 nulliparous parturients. Analgesia was initiated with intrathecal ropivacaine 2 mg and fentanyl 15 µg and maintained with epidural ropivacaine 0.1% with fentanyl 2 µg/mL. Parturients were randomized to one of three groups. Group 0: demand-only PCEA, bolus of 5 mL, lockout interval of 15 min. Group 5: background infusion of 5 mL/h, bolus of 5 mL, lockout interval of 12 min. Group 10: background infusion of 10 mL/h, bolus of 5 mL, lockout interval of 10 min. The maximum dose of all groups was 20 mL/h. The primary outcome was incidence of breakthrough pain. Secondary outcomes included intrapartum pain scores, neuraxial blockade characteristics, side effects, the total and hourly volume of ropivacaine, neonatal outcomes, and obstetric outcomes.

RESULTS: The incidence of breakthrough pain and the maximum visual analog scale (0–100 mm scale) pain scores were higher in Group 0 versus Groups 5 and 10 (43% vs 17% and 11%, P < 0.001 and 37 ± 28 vs 22 ± 26 and 16 ± 25 [mean ± sd], P < 0.001), respectively. Group 10 had a longer duration of effective analgesia compared with Group 0 (mean 895 min, 95% CI 823–966 vs 565 min, 95% CI 454–677, P < 0.001) and increased ropivacaine consumption, and was associated with a longer duration of the second stage of labor.

CONCLUSION: Demand-only PCEA (5-mL bolus, 15-min lockout interval) resulted in less local anesthetic consumption but an increased incidence of breakthrough pain, higher pain scores, shorter duration of effective analgesia, and lower maternal satisfaction, when compared with PCEA with background infusion (5-mL bolus, 10–12-min lockout interval, and 5–10 mL/h infusion).

Patient-controlled epidural analgesia (PCEA) is a safe and effective method for maintaining labor analgesia. This method of maintenance has several advantages compared to continuous epidural infusion. It allows patient autonomy in determining level of pain relief, decreases local anesthetic consumption, decreases side effects (motor block), results in a higher patient satisfaction, and reduces the need for clinician supplementation of analgesia.1,2

Some studies have demonstrated that a background infusion as part of PCEA regimen improves pain scores.3,4 The lack of a background infusion in demand-only PCEA has also been associated with an increased incidence of breakthrough pain requiring unscheduled clinician administration of additional anesthetic.3–5 However, Boselli et al.6 found that there was a significant increase in overall local anesthetic consumption without improvement in pain scores or patient satisfaction with background infusion rates of 6 and 9 mL/h compared to 0 or 3mL/h. Thus, despite several randomized controlled trials that have compared demand-only PCEA and PCEA with background infusion for labor analgesia, results have been conflicting. The optimum bolus size, lockout interval, and background infusion rate, if required, remains uncertain.1–3,7–10

This randomized controlled study was designed to examine the incidence of intrapartum breakthrough pain provided by demand-only PCEA and PCEA with background infusion for labor epidural analgesia. We used bolus, lockout and background infusion settings based on our standard labor PCEA practice as suggested by a previous review.11 We hypothesized that there is no difference in the incidence of breakthrough pain between demand-only PCEA and PCEA with 5 or 10 mL/h of background infusion.

METHODS

After Hospital Ethics Committee approval and subjects written informed consent, 300 nulliparous parturients with ASA physical status I or II who requested epidural labor analgesia were recruited in this randomized, controlled double-blind study at the time they requested analgesia. Eligible parturients were older than 18 yr, >37 wk gestation with singleton pregnancy, cervical dilation <5 cm, and able to use the PCEA pump. Exclusion criteria were parturients who received any opioid injection <3-h before the initiation of labor epidural analgesia or parturients taking chronic pain medications.

Analgesia was initiated in all parturients using a combined spinal epidural technique at the L3–4 or L4–5 interspace in the right or left lateral position with ropivacaine 2 mg (Naropin, Astrazeneca, Sweden) and fentanyl 15 µg diluted with normal saline to a total volume of 2 mL (time 0). A multiorifice epidural catheter was then inserted 3 to 4 cm into the epidural space and tested with 3 mL of lidocaine 1.5% to exclude intrathecal placement. Parturients were withdrawn from the study for presumed intrathecal or intravascular catheter placement (blood or cerebrospinal fluid aspirated from the catheter or inability to flex the knees after the test dose) or for failure of pain relief (defined as visual analog scale [VAS] score >30; 100-mm unmarked line anchored with 0: no pain and 100: worst imaginable pain) 20 min after the intrathecal dose.

Thirty minutes after the test dose, parturients were randomized to a treatment group by shuffling and selecting a sealed opaque envelope containing the group assignment: Group 0 received a demand-only PCEA with demand bolus of 5 mL, lockout of 15 min, and maximum dose of 20 mL/h. Group 5 received PCEA with background infusion of 5 mL/h, bolus dose of 5 mL, lockout of 12 min, and maximum dose of 20 mL/h. Group 10 received PCEA with background infusion of 10 mL/h, bolus dose of 5 mL, lockout of 10 min, and maximum dose of 20 mL/h.11 All parturients received a mixture of ropivacaine 0.1% with fentanyl 2 µg/mL, administered via a PCEA pump (Rythmic^TM Plus, Pump Micrel Medical Devices S.A, Pollini Greece-European Union). The attending anesthesiologist who setup the PCEA pump was not blinded to group assignment; however, study subjects, the nursing staff, and resident anesthesiologists, who assessed study outcomes and treated breakthrough pain, were blinded to group assignment.

All parturients were given a handheld device and instructed to activate a self-administered epidural bolus dose when they experienced mild to moderate pain before the pain intensity became severe. They were told to inform the resident anesthesiologist if they experienced moderate or severe pain or had VAS >30 mm despite PCEA.

Breakthrough pain was defined as failure of the PCEA to provide adequate pain relief, necessitating a review by the attending anesthesiologist before delivery. The resident anesthesiologist assessed the pain scores and administered supplemental epidural ropivacaine 0.2%. If VAS remained above 30 mm, despite administering a total of up to 10 mL ropivacaine (in 5-mL aliquots over 30 min), analgesia was determined to be "ineffective" and the parturient was withdrawn from the study and replaced by another parturient via randomization.

The incidence of fetal bradycardia (defined as decrease in baseline heart rate by 50 bpm for 3 min or a decrease to below 100 bpm for 1 min) was monitored throughout labor. Maternal noninvasive arterial blood pressure was recorded at 5-min intervals for the first 30 min after initiation of analgesia and subsequently at 15-min intervals. Maternal hypotension, defined as a systolic blood pressure <100 mm Hg or a decrease of more than 20% from the baseline systolic blood pressure, was treated with IV ephedrine.

Baseline pain scores were assessed before initiation of labor epidural analgesia by the labor ward nurses. They also assessed neuraxial blockade characteristics, including pain scores, level of sensory block to cold and modified Bromage score (0 = no motor block, 1 = inability to raise extended leg, 2 = inability to flex knee or raise extended leg, and 3 = inability to flex ankles, flex knee, or raise extended leg) at 10 min, 30 min, and hourly after administration of intrathecal doses, and when breakthrough pain occurred.

The parturients were asked about the presence of pruritus and nausea at hourly intervals. The number of parturients with breakthrough pain, side effects (nausea and vomiting, shivering, pruritus, hypotension, and fetal bradycardia), the total and hourly volumes of ropivacaine, neonatal outcomes (Apgar scores and birth weight), and obstetric outcomes (duration of second stage of labor, duration of labor, and mode of delivery) were recorded. Maternal satisfaction with the labor analgesia was evaluated 24 h after delivery using a 0 to 100 verbal scale (0 = not satisfied at all, 100 = fully satisfied) by the resident anesthesiologist.

Our primary outcome was the incidence of breakthrough pain and secondary outcomes were intrapartum maximum pain scores, duration of effective analgesia, side effects, maternal satisfaction, and local anesthetic consumption. The assumed baseline incidence of breakthrough pain for the demand-only PCEA group was 35%. This was based on our previous study using a similar regimen.12 To detect a relative difference of 50% in the incidence of breakthrough pain between the demand-only PCEA group and PCEA group with background infusion, with = 0.05 and β = 0.02, in a two-sided test, 99 patients per group were required. Parametric and nonparametric data were analyzed with one-way analysis of variance and Kruskal–Wallis tests, respectively. If indicated, post hoc Bonferroni's correction was used for pairwise comparisons. Dichotomous data were analyzed with ² tests. The duration of effective analgesia, our secondary outcome, was analyzed with Kaplan–Meier survival analysis technique with log rank test; data from parturients who had vaginal or cesarean delivery before the loss of analgesia were censored. Because the number of censored parturients was expected to be high, we used a back-up Mann–Whitney U-test using the intent-to-treat approach. The dependent variable was "duration of effective analgesia," defined as the time from the induction of analgesia to the time of breakthrough pain or the time of delivery if breakthrough pain did not occur. The data were analyzed using SPSS versions 9.0 (Chicago, IL). A P value <0.05 was considered statistically significant.

RESULTS

Three-hundred parturients were enrolled in the study within 6 mo (October 2005 through March 2006). None of the parturients were excluded from the study because of inadequate analgesia in the first 20 min after intrathecal injection or because of intravascular or intrathecal catheter placement. There was no difference in parturients' demographic profiles and preblock characteristics (Table 1).

The incidence of breakthrough pain was significantly higher in Group 0 than in Group 5 or Group 10. The maximum pain scores were also significantly higher in Group 0 than in Group 5 or Group 10 (Table 2).

The mean duration of effective analgesia in Group 10 was significantly longer than in Group 0 (mean duration of effective analgesia: 895 min, 95% confidence interval [CI] 823–966 vs 565 min, 95% CI 454–677 min, P < 0.001) (Fig. 1). When analyzed with the intent-to-treat approach, the mean duration of effective analgesia in Group 10 was longer than in Group 0 (Table 3).

View larger version (10K): [in this window] [in a new window]   Figure 1. Kaplan–Meier survival curve of parturients with continuing effective analgesia (no break-though pain) versus time after intrathecal injection. Proportion of parturients: parturients delivering before loss of analgesia are included up to the time of delivery.

There was no difference in the incidence of side effects, such as hypotension, pruritus, nausea and vomiting, Bromage score, maximum sensory level, and maternal satisfaction among groups (Table 2).

The total amount of ropivacaine and hourly ropivacaine consumption was significantly lower in the demand-only PCEA group than in PCEA with background infusion groups (Table 2). The total duration of labor was similar among all three groups; however, the duration of the second stage of labor, defined as the time between full cervical dilation and the completion of vaginal delivery, was significantly shorter in Group 0 compared with Group 10 (Table 3).

There were no differences in neonatal outcomes (Table 3).

DISCUSSION

In this study, we demonstrated that PCEA with ropivacaine 0.1% and fentanyl 2 µg/mL administered via PCEA with a background infusion and 10 to 12-min lockout interval, provided better labor analgesia than demand-only PCEA with a 15-min lockout interval. The PCEA regimen with a background infusion of 5 and 10 mL/h provided longer duration of effective analgesia as evidenced by a reduced incidence of breakthrough pain, and improved pain scores compared with demand-only PCEA regimen. However, PCEA with background infusion increased ropivacaine consumption, and increasing the rate of background infusion to 10 mL/h was associated with increased duration of the second stage of labor.

Our results concur with those of several previous studies.3–5,13 In a large trial involving 300 laboring parturients, Campbell et al.14 compared demand-only PCEA and PCEA with background infusion of 10 mL/h. They demonstrated that other than reduced local anesthetic consumption, there were no benefits in using a demand-only PCEA regimen with respect to obstetric and neonatal outcomes.15 PCEA with background infusion of 10 mL/h provided more effective labor analgesia, decreased the incidence of anesthesiologist-administered supplemental "top-ups."14

The decreased requirement for clinician supplemental boluses also decreases the anesthesiologists' workload in a busy delivery suite. However, increasing the rate of background infusion from 5 to 10 mL/h did not provide any clinically important advantages and instead was associated with a longer second stage of labor.

Contrary to these results, a study conducted by Boselli et al.6 in 133 parturients demonstrated that the use of demand-only PCEA resulted in a less consumption of local anesthetic, reduced cost of analgesia, and provided good pain relief with no increase in the incidence of clinician boluses or compromised maternal satisfaction. The difference in results may be attributed to the difference in the PCEA settings (shorter lockout interval and difference in background infusion rate), shorter labor duration, and mixed parity study population.

We chose to have different lockout intervals for our three groups of parturients as these protocols constitute our institution's recommended PCEA regimens.11 Although the lockout intervals of Groups 0, 5, and 10 were different in our study, the hourly maximum dose was the same for all three groups. Previous studies, which compared the quality of labor analgesia between shorter and longer lockout intervals, did not demonstrate any differences in pain scores, physician interventions, side effects, and maternal and neonatal outcomes.9,10

A test dose of lidocaine 45 mg was used in all three groups in this study as it is a standard practice in our institution. This practice did not seem to contribute to motor blockade. In a previous study from our institution, epidural lidocaine did not affect the incidence of breakthrough pain or duration of analgesia but did increase the incidence of motor blockade.16 However, the study was performed with a higher dose of intrathecal local anesthetic, parturients were started on a continuous epidural infusion (10 mL/h), and the overall incidence of motor blockade was higher.

Although pain relief provided by PCEA with background infusion was superior, it was associated with significantly higher consumption of local anesthetic solution. We did not observe an increase in motor blockade among parturients on PCEA with background infusion; however, the increase in local anesthetic consumption may have contributed to the prolongation of the second stage of labor.17 This did not adversely affect the incidence of instrumental delivery or cesarean delivery; however, our study was not powered to detect this difference.

A limitation of our study was that cervical examinations were performed by the obstetric team at four hourly intervals and at the discretion of the obstetricians. We did not insist on regular cervical examinations at more frequent intervals, because we were concerned about our parturients' comfort. The lack of regular cervical examinations may have affected the recording of the first and second stage of labor. The diagnosis of full cervical dilation may occur later in a parturient with dense neuroblockade and thus spuriously shorten the calculated duration of the second stage of labor.

Based on our findings and under our study conditions, the use of ropivacaine 0.1% with fentanyl 2 µg/mL administered via demand-only PCEA without background infusion cannot be considered practical. Demand-only PCEA with a lockout interval of 15 min increased the incidence of breakthrough pain, resulted in a higher maximum intrapartum pain score, and decreased the duration of effective intrapartum analgesia, compared with regimens with background infusions and a shorter lockout interval. Although our study was under-powered to assess this outcome, it is likely that higher (10 mL/h) compared to lower (5 mL/h) background infusion rates are associated with less pain, but increased local anesthetic consumption and a longer second stage of labor. We recommend the use of ropivacaine 0.1% with fentanyl 2 µg/mL administered via PCEA with a background infusion of 5 mL/h for maintenance of labor analgesia.

Footnotes

Accepted for publication July 25, 2008.

There is no conflict of interests between authors and any company or organization.

We did not receive any financial support for this study.

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Lim, Y. Articles by Sia, A. T. Search for Related Content PubMed PubMed Citation Articles by Lim, Y. Articles by Sia, A. T. Related Collections Obstetrics Pain Medicine Regional Anesthesia Pain