Halpern, Stephen H. MD, MSc, FRCPC*; Carvalho, Brendan MBBCh, FRCA†
Section Editor(s): Wong, Cynthia A.
Patient-controlled epidural analgesia for labor (PCEA) was first introduced into clinical practice by Gambling et al.1 in 1988. It has proven to be both safe and effective. PCEA has many advantages when compared with continuous epidural infusion (CEI) techniques. Although the analgesia provided is similar, PCEA reduces the incidence of unscheduled clinician interventions and the total dose of local anesthetic.2 PCEA also reduces the incidence of lower extremity motor block.3 Although PCEA has not consistently been associated with increased maternal satisfaction, this may be due to a lack of appropriate measuring tools. Theoretically, maternal satisfaction may be increased by allowing the parturient greater control over her analgesia.4 Compared with CEI, PCEA has no clinically significant impact on obstetric or neonatal outcomes.5
Clinical research has focused on refining PCEA techniques to further improve analgesia, reduce motor block, and increase maternal satisfaction, while reducing the frequency of unscheduled clinician interventions. In this overview, we will systematically review the current evidence to answer the following questions: 1) Should a background infusion be used? 2) Is ropivacaine superior to bupivacaine when used for PCEA in labor? 3) Can the volume of the PCEA bolus dose and lockout interval be manipulated to optimize analgesia? and 4) What is the impact of new techniques and technologies on current PCEA practice? In answering these questions, we hope to be able to suggest a range of appropriate settings for labor PCEA and present a glimpse into future techniques of labor analgesia maintenance.
To answer the above questions, we systematically reviewed all published, randomized, controlled trials on PCEA for labor. Studies were obtained from MEDLINE and EMBASE, published in English before April 1, 2008. We included studies that have the following intervention and control groups: 1) background infusion versus no background infusion; 2) ropivacaine versus bupivacaine; 3) high-volume bolus versus low-volume bolus and/or longer lockout interval versus shorter lockout interval; and 4) a novel approach to PCEA versus standard treatment. Each study included at least one outcome of interest: maternal analgesia, maternal satisfaction, motor block, and/or clinician workload. Many of the studies included data on maternal and fetal outcome, but none showed any difference between intervention and control groups. In addition, many of the studies reported differences in total drug dose and success:demand ratios. We considered these as surrogate outcomes and only reported them to explain any differences we found in the four outcomes outlined above.
THE USE OF BACKGROUND INFUSION
There are seven studies that compared PCEA with and without background infusions.6–12 All of these studies were randomized, controlled trials in low-risk parturients of mixed parity. The study characteristics are shown in Table 1. Of note, the infusion rates for most of the studies were quite low, with most <5 mL/h.
All of the four outcomes were reported in five of the studies.6,9–12 One study did not report maternal satisfaction,8 and one did not report clinician workload.7 Only one study found a difference in analgesia: patients who received PCEA without a background infusion reported a higher incidence of intense pain (>4/10) compared with those with a background infusion.7 Significant motor block was uncommon in all of these studies and was not significantly different between groups. In two of the studies, there were more clinician interventions in the no infusion group.8,9 One study noted that more local anesthetic was administered by clinicians to parturients in the no infusion group,11 implying greater workload. None of the studies noted any differences in maternal satisfaction between groups.
These data suggest that there may be a benefit for providing a continuous background infusion to PCEA. Of interest, none of the outcomes were better in patients who received PCEA alone. A meta-analysis of five of these studies6–9,12 reported in the American Society of Anesthesiologists' Practice Guidelines for Obstetric Anesthesia support the view that a background infusion provides better analgesia2 (Odds ratio = 3.33, 95% confidence interval 1.87–5.92), although the statistical significance was not stated. An additional study comprising 300 patients randomized to 0.08% ropivacaine and 2 μg/mL fentanyl PCEA with or without a background infusion of 10 mL/h, reported better analgesia scores in the group with a background infusion.* Although many of the studies reported reduced requirement of local anesthetics when the background infusion is omitted,6,10 there were neither reports of toxicity nor any impact on the incidence of motor block.
The most consistent benefit of a background infusion is to reduce the number of unscheduled clinician interventions. This is of greatest benefit in busy settings where clinicians are unable to reliably provide epidural clinician rescue bolus doses in a timely fashion. Under the study conditions reported above, there was no difference in maternal satisfaction related to delays in obtaining analgesia.
In summary, a background infusion reduces the incidence of unscheduled clinician interventions and may improve patient analgesia. None of the studies reported an increase in motor block associated with the background infusion.
ROPIVACAINE VERSUS BUPIVACAINE
There are 11 studies that compare ropivacaine with bupivacaine in parturients receiving PCEA.13–23 Five of these were in nulliparous patients,13,14,18,22,23 with one study separating the results of the nulliparous and parous patients.15 The investigators and patients were blinded to study drug in all of the studies.
The characteristics of the studies and measured outcomes are shown in Table 2. Of note, there was a wide range of PCEA settings. The concentration of bupivacaine ranged from 0.05% (with fentanyl) to 0.125%. The concentration of ropivacaine ranged from 0.05% to 0.20%. Two studies used different concentrations of ropivacaine and bupivacaine in an effort to reflect differences in potency.15,19
All of the studies measured maternal analgesia. Labor analgesia was similar between study groups.
All but one study reported the incidence of motor block.19 Of these studies, five reported an increased incidence of motor block associated with bupivacaine.13,15,16,18,20 These findings agree with data in the setting of CEI supplemented by clinician rescue bolus doses, suggesting that bupivacaine is associated with more motor block than ropivacaine.24 However, most studies did not account for relative differences in potency between ropivacaine and bupivacaine.25
Few studies measured maternal satisfaction.14,16,18,20 There were no differences in global satisfaction measures reported in any of the studies. One study found an increased satisfaction in analgesia at the time of delivery in parturients who received bupivacaine, but this was not reflected in the visual analog scale scores or global measures of satisfaction.18 The same study reported higher satisfaction scores for mobility in the ropivacaine group. Similarly, Fischer et al.16 reported increased maternal satisfaction with relief of contraction and delivery pain in patients receiving bupivacaine. These authors could not demonstrate a difference in visual analog scale scores between groups.
Six studies reported the incidence of clinician rescue bolus doses.14,16,18,20–22 There were no differences between groups in any of the studies. One study reported an increased incidence of clinician rescue boluses during the first stage of labor in patients who received bupivacaine, but the incidence was higher in the ropivacaine group during the second stage of labor.20
In summary, both ropivacaine and bupivacaine are well suited for PCEA in labor. The most consistent finding is an increased incidence of motor block in patients receiving bupivacaine compared with ropivacaine, but this difference may not be clinically significant, particularly for short labors. Flexibility in the PCEA settings may offset any advantage that drug selection may have.
BOLUS DOSE VOLUME AND LOCKOUT INTERVAL
There are wide variations in PCEA settings in clinical practice.26 Six studies have compared various PCEA settings to try to determine the ideal bolus dose and corresponding lockout time interval.27–32 The study characteristics are shown in Table 3. All of these studies were randomized, controlled trials in low-risk nulliparous or mixed parity populations.
Analgesia, maternal satisfaction, motor block, and clinician rescue boluses were reported in all of the studies. Studies used bupivacaine (0.0625%–0.125%) and ropivacaine (0.1%–0.2%) with fentanyl or sufentanil. Bolus volumes ranged from 2 to 20 mL and lockout intervals from 5 to 30 min. Three studies used a background infusion in addition to PCEA.29–31
Only one study found that increasing the bolus volume (4–12 mL, with corresponding lockout interval of 8–25 min) improved analgesia.32 A shorter lockout interval improved the PCEA success:demand ratio in one study,30 but this did not lead to a decrease in unscheduled clinician rescue boluses. None of the studies showed a significant difference in unscheduled clinician interventions. Significant motor block was uncommon in any of these studies and was not significantly different among PCEA settings. There were no reports of toxicity or increased side effects with the larger bolus volumes.
These data suggest that various regimens can produce effective labor analgesia. Most studies were underpowered to show modest outcome differences among the various settings. Bolus doses of 12 mL of dilute local anesthetic may provide better analgesia and maternal satisfaction than 4 mL boluses in parturients receiving PCEA without a background infusion.32 Large boluses improve spread in the epidural space and have been shown to improve epidural labor analgesia outside of the PCEA setting.33 There are insufficient data to comment on the safety of large volume patient-controlled bolus doses.
Although shorter lockout intervals may improve the success:demand ratios,30 this was not reflected in better analgesia or maternal satisfaction. Lockout intervals of up to 25 min did not result in any changes in either maternal satisfaction or unscheduled clinician interventions. This may have been due to the larger bolus doses used in these studies.
In summary, there remains no ideal bolus dose or lockout interval setting for labor PCEA. Large bolus doses of dilute local anesthetic may provide superior analgesia and maternal satisfaction compared with small boluses in patients who do not receive a background infusion.
Six studies have compared various local anesthetic concentrations using a PCEA technique for labor analgesia.17,28,34–37 The study characteristics are shown in Table 4. All of these studies were randomized controlled trials in low-risk nulliparous or mixed parity study populations. Studies used bupivacaine (0.0625%–0.25%) and ropivacaine (0.1%–0.2%) with fentanyl or sufentanil.
No differences in the efficacy of labor analgesia provided by the various solutions were reported in any of these studies. Four studies found increased local anesthetic use in the high-concentration local anesthetic groups.17,34–36 Local anesthetic dose reduction with the more dilute solutions ranged from 35% to 75%. The more concentrated solution groups resulted in significantly greater motor block in three of the studies.17,35,37 Two studies found less pruritus with local anesthetic without opioids.17,36 Two studies found higher PCEA success:demand ratios with the more concentrated solutions.35,37
These data demonstrate that the use of dilute local anesthetic solutions with opioids for labor PCEA results in less local anesthetic consumption and motor block without compromising labor analgesia. Reductions in local anesthetic consumption with more dilute local anesthetic solutions in these PCEA studies echoes the results of studies that compared high and low-dose solutions for initiation of epidural labor analgesia.33 For example, the minimum local analgesic dose (or ED50) of bupivacaine 0.125% was 25% lower than the minimum local analgesic dose of bupivacaine 0.25% for the initiation of labor analgesia.33 A possible explanation for this finding is that studies that used more dilute solutions also used larger volumes. The larger volumes may improve analgesia as a result of more uniform anesthetic spread in the epidural space.38 Similar to the finding that the addition of lipophilic opioids (e.g., fentanyl or sufentanil) to local anesthetics results in a dose-dependent reduction in the minimum local analgesic concentration of bupivacaine,39 their use also improves the quality of analgesia during labor PCEA.40 However, lipophilic opioids may result in dose-dependent pruritus.40
In summary, when using labor PCEA, dilute local anesthetic solutions should be used. The use of 0.25% bupivacaine and 0.2% ropivacaine will lead to an increased incidence of motor blockade without concomitant increases maternal analgesia or satisfaction. The lowest, clinically effective, concentration of lipophilic opioid should be added to avoid excessive pruritus.
Computer-integrated PCEA is a novel epidural solution delivery system that automatically adjusts the background infusion rate based on the number of PCEA demands.41,42 The authors who devised this system connected a laptop computer with a programmed algorithm to a standard epidural infusion pump. The computer-integrated PCEA algorithm adjusts the background infusion to 5, 10, or 15 mL/h if the patient require one, two, or three demand boluses, respectively, in the previous hour and decreases the background infusion by increments of 5 mL/h if there are no bolus demands in the previous hour.41 In theory, a system that responds to patient's analgesic requirements should improve efficacy while minimizing increases in local anesthetic use-associated background infusions. Initial studies with this system have been encouraging.41,42 One study compared demand-only PCEA with a similar PCEA regimen with the computer-integrated background infusion.41 The computer-integrated PCEA group had similar local anesthetic consumption compared with demand-only PCEA but was associated with increased maternal satisfaction. Another study found that computer-integrated PCEA reduced the incidence of breakthrough pain without increasing drug consumption when compared with CEI without PCEA for labor analgesia.42 Computer-integrated PCEA is not currently commercially available but may be incorporated in future epidural pumps.
Programmed Intermittent or Automated Mandatory Epidural Boluses
A recent development that may change the way PCEA is administered is programmed intermittent epidural boluses (PIEB). Instead of a CEI, the same total hourly amount of local anesthetic is administered as intermittent boluses (e.g., two boluses of 6 mL every 30 min vs 12 mL/h CEI). PIEB has been shown to be more effective than CEI for labor analgesia.43–45 The PIEB resulted in similar analgesia, higher maternal satisfaction, and less need for unscheduled clinician rescue boluses. The technique also resulted in less bupivacaine use for maintenance of epidural labor analgesia. A mechanism proposed for the local anesthetic-sparing effect of PIEB is a more uniform epidural spread of local anesthetics when large volumes of local anesthetic (with correspondingly high injectate pressures) are delivered.38 Recently, PIEB combined with PCEA were compared with PCEA with a standard continuous background infusion.46 The PIEB resulted in reduced consumption of ropivacaine and less PCEA demand boluses while maintaining similar analgesic efficacy. The PIEB function is currently not available, but the technology will be incorporated with future improvements in electronic epidural devices.
Disposable Epidural PCEA
The past decade has seen vast improvements in disposable local anesthetic infusion devices, driven mainly by the increase in ambulatory nerve block and wound instillation techniques. In the labor setting, a simple disposable PCEA device has been compared with a standard electronic PCEA device for labor analgesia.47 The authors found no significant differences in analgesic efficacy, maternal satisfaction, local anesthetic use, or side effects. Disposable devices are less bulky than electronic devices, which may facilitate ambulation during labor. The main disadvantages with disposable devices are the lack of programmability and potentially increased costs.
PCEA is a reliable and effective method of maintaining epidural labor analgesia. Provided that sufficient drug volumes are allowed, a wide variety of drug combinations and settings have been used successfully. Low concentrations of bupivacaine or ropivacaine with opioids provide excellent analgesia. Motor block can be minimized by using dilute local anesthetic solutions (up to 0.125% bupivacaine or 0.2% ropivacaine). A background infusion is suitable for most patients because it reduces the need for unscheduled clinician interventions and may provide better analgesia compared with when a background infusion is omitted. Background infusion rates between 2 and 10 mL/h have been used effectively. There remains no ideal bolus dose or lockout interval setting for labor PCEA. Larger bolus doses (more than 5 mL) of dilute local anesthetic may provide superior analgesia compared with small boluses. Research into new delivery strategies, such as mandatory programmed intermittent boluses and computerized feedback dosing, is ongoing.
*Campbell DC, Breen TW, Halpern S, Muir H, Nunn R. Determination of the efficacy of PCEA alone compared to PCEA + CEIA using ambulatory labor analgesics. Anesthesiology 2004;101:supp A1210. Cited Here...
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