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Patient-Controlled Epidural Analgesia During Labor: The Effects of the Increase in Bolus and Lockout Interval

Bernard, Jean-Marc MD, PhD*; Le Roux, Daniel MD*; Vizquel, Louis MD*; Barthe, Alexandre MD*; Gonnet, Jean-Marie MD; Aldebert, Alain MD; Benani, Reda M. MD*; Fossat, Christian MD; Frouin, Jacques MD*

doi: 10.1213/00000539-200002000-00017

Most studies use a bolus size of <6 mL of 0.125% bu- pivacaine for patient-controlled epidural analgesia (PCEA) during labor. In this double-blinded, randomized study, we compared the efficacy of a larger bolus injected via a PCEA pump to a conventional PCEA setting. By using a combination of 0.125% bupivacaine with 1:800,000 epinephrine and 0.625 μg/mL sufentanil, the first PCEA setting was typical (4 mL/8 min), whereas the other combined a 12-mL bolus dose and a 25-min lockout interval, i.e., similar maximal hourly dose. Rescue analgesia was provided with 6 mL of 0.25% bupivacaine. Patient satisfaction and pain were scored on verbal and visual analog scales. Data were analyzed from 103 parturients in the 12-mL/25-min group and 100 in the 4-mL/8-min group. In the 12-mL/25-min group, the median pain score on a 0- to 10-cm visual analog scale was lower at 6-cm cervical dilation (1 [range = 0–8] vs 3 [0–8]) and at delivery (1 [0–10] vs 2 [0–10]). Satisfaction was also better (70% vs 38% “excellent” opinions, at 6-cm cervical dilation). Use of the pump (ratio of successful and total demands) was high and similar in both groups. Rescue analgesia was comparable. Doses of analgesics were greater in the 12-mL/25-min group (hourly bupivacaine dose = 13.9 ± 5.3 [mean± SD] vs 9.4 ± 4.1 mg). No differences were noted between groups for the severity of hypotension, ephedrine requirement, outcome of the delivery, and Apgar scores.

Implications A patient-controlled epidural analgesia setting that allows a parturient to receive an increased analgesic dose improves satisfaction with patient-controlled epidural analgesia during labor.

*Département d’Anesthésie-Réanimation and †Clinique Gynécologique et Obstétricale, Polyclinique Jean-Villar, Bruges-Bordeaux, France

October 18, 1999.

Address correspondence and reprint requests to Dr. Jean-Marc Bernard, Département d’Anesthésie-Réanimation, Polyclinique Jean-Villar, BP 61, F-33520 Bruges-Bordeaux, France.

Presented at the Annual Meeting of the American Society of Anesthesiologists, Orlando, FL, October, 1998.

Most studies (1–8) of patient-controlled epidural analgesia (PCEA) for labor and delivery have used small bolus volumes, ranging from 3 mL of 0.25% bupivacaine (5) to 6 mL of 0.125% bupivacaine (7) plus or minus opioids. Although PCEA achieved a high level of parturient satisfaction, investigators chose to supplement patient self-administration with a continuous epidural infusion or staff-administered boluses as required or both, acknowledging implicitly some insufficiency in the PCEA technique during labor. However, the addition of a continuous background infusion did not consistently improve PCEA in this context (6,9), while supplements by the midwife mimicked conventional top-up regimens. For example, 20% (7) to 50% (8) of the parturients enrolled in these trials received one or several supplements of 9 (3,9), 10 (4,8), or 12 mL (7) of 0.25% (3,4,9) or 0.125% bupivacaine (7,8). The efficacy of PCEA with low bolus size may thus not be optimal.

We designed a study to assess whether the use of larger bolus size could improve the comfort of parturients and their satisfaction with analgesia during labor and delivery.

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After we received approval by our ethics committee and written, informed consent, 220 parturients of mixed parity, ASA physical status I or II, were enrolled in the study. Women with severe medical or obstetric complications, multiple gestation, contraindication to epidural analgesia, and those who were unable to use the PCEA pump were excluded. Instruction in the use of the PCEA pump took place during the preanesthesia visit, approximately 1 mo before delivery. Parturients were told to press the demand button whenever pain occurred and to expect some relief within 5 to 6 min. No comment was made about the prescribed interval between successful demands. If analgesia was deemed inadequate, supplements could be requested at any time.

Parturients received 500 to 1000 mL 0.9% NaCl IV infusion, followed by insertion of a five-port 20-gauge epidural catheter 4–5 cm into the epidural space at the L3-4 or L4-5 interspace. Catheters were carefully observed, aspirated gently for return of blood or cerebrospinal fluid, then tested by the injection of 2 mL, followed by 5 mL, of 2% lidocaine with epinephrine. After referring to a previously constructed randomization table, the attending anesthesiologist programmed the PCEA pump (APM Abbott, North Chicago, IL) to infuse either a 4-mL bolus dose with a lockout interval of 8 min (4-mL/8-min group;n = 110) or a 12-mL bolus dose with a lockout interval of 25 min (12-mL/25-min group;n = 110). To maintain blinding, the parturient, midwife, and obstetrician were unaware of the group assignment, and evaluation was performed by the midwife. As soon as the PCEA pump was attached to the epidural catheter, oxytocin IV infusion was begun at a rate of 2.5 mU/min, and the rate was increased by 2.5 mU/min every 30–45 min until an adequate labor pattern was achieved. All the epidural catheters were placed for the induction of labor before the onset of painful contractions. Both groups received an epidural solution containing 0.125% bupivacaine, 1:800,000 epinephrine and sufentanil 0.625 μg/mL. There was no background infusion or dose limit. A midwife again instructed the women on PCEA use when they entered the study. Rescue analgesia consisted of 6 mL of 0.25% epidural bupivacaine.

By using a 10-cm visual analog scale, pain was scored at 6- and 9-cm cervical dilation and at the expulsion phase. Satisfaction with labor analgesia was evaluated using a five-point verbal score (excellent, good, fair, bad, no opinion). The volume of bupivacaine and sufentanil required and the ratio of successful to total demands were obtained from the PCEA recordings. Time and number of supplemental bupivacaine injections given by the midwife were noted. Fetal heart rate, maternal heart rate, and arterial hemoglobin oxygen saturation were monitored continuously. Nursing personnel measured maternal blood pressure at regular intervals, at the time of fetal heart deceleration, or 5 min after each injection of 0.25% bupivacaine supplements. Hypotension was defined as systolic blood pressure of <100 mm Hg or a decrease of more than 25%. It was treated by 10-mg IV doses of ephedrine as needed and by assumption of the left lateral decubitus position. Episodes of arterial hemoglobin oxygen saturation lower than 90% were treated by oxygen administration via a face mask. Each fetal and maternal event, as well as therapeutic interventions, outcome of labor, and Apgar score, was recorded. Appropriate coordinated pushing was scored on a visual analog scale (no strength = 0 to maximal strength = 10) by the obstetrician at the end of the expulsion phase. Women were asked 1 to 2 h after the delivery whether they had criticisms about the epidural analgesia and whether they would be willing to use PCEA again in a future delivery.

Data were presented as mean ± SD, medians and ranges, or numbers and percentages of patients. Associations among discrete variables were tested by the χ2 test. The Mann-Whitney U-test was used for differences between the groups on data that were not normally distributed. Differences between the groups on continuous data that were normally distributed were tested by using Student’s t-tests with P < 0.05 considered significant.

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Of the 220 parturients enrolled in the study, 17 were excluded because the catheter was displaced and had to be replaced (3 parturients in each group) or because oxytocin failed to induce labor (7 cases in the 4-mL/8-min group and 4 in the 12-mL/25-min group; not significant). A total of 203 parturients completed the study : 100 in the 4-mL/8-min group and 103 in the 12-mL/25-min group. Patients did not differ in demographic or obstetric characteristics (Table 1). Duration of the labor (i.e., from the beginning of oxytocin IV infusion to the baby’s birth) was similar in both groups.

Table 1

Table 1

Pain was significantly lower at 6-cm cervical dilation and at the time of the delivery in the 12-mL/25-min group (Fig. 1). Satisfaction with labor analgesia was also better in this group (70% vs 38% and 72% vs 48% “excellent” opinions, at 6- and 9-cm cervical dilation respectively;P < 0.001). Fewer women in the 12-mL/25-min group had criticisms regarding the technique (15 vs 28;P = 0.02). However, the number of women unwilling to use a PCEA for a future delivery was similar in both groups (12 in the 12-mL/25-min group vs 16 in the 4-mL/8-min group; not significant).

Figure 1

Figure 1

The number of pump demands was greater in the 4-mL/8-min group, with a comparable ratio of successful and total demands in both groups (Table 2). Parturients in the 12-mL/25-min group received a greater dose of sufentanil (31 ± 12 vs 20 ± 9 μg) and bupivacaine (Table 2). Seventeen women in the 12-mL/25-min group and 22 in the 4 mL/12 min Group required supplemental bupivacaine injections (not significant).

Table 2

Table 2

Maternal blood pressure decreased similarly in both groups. Arterial hypotension requiring one or more ephedrine injections was observed in 8 parturients in the 4-mL/8-min group and in 13 parturients in 12-mL/25-min group (not significant). No maternal desaturation lower than 90%, as measured by pulse oxymetry, occurred. Five neonates required resuscitation for low Apgar scores. All recovered easily. No naloxone was required by any patient.

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In both groups, the proportion of successful demands was high and comparable, suggesting that, regardless of the PCEA group, patients were guaranteed immediate access to supplemental epidural medication. Periods where, despite patient pain, PCEA demands did not provide additional medication were also comparable, because the amount of rescue analgesics did not differ significantly. Consequently, improved satisfaction of parturients with analgesia was related to the possibility of obtaining more analgesics at each successful pump demand, suggesting that the drug mass is an important factor for inducing epidural pain relief during labor. This finding is supported by the study of Stainthorp et al. (10), who found that the failure rate of epidural analgesia was higher after 12 mL of a 0.125% plain bupivacaine solution than after 12 mL of 0.25% and 0.375% concentrations. In a recent study, local anesthetic consumption was greater, but the quality of pain relief improved during the second stage of labor when 0.25% bupivacaine was compared with similar volumes of a combination of 0.125% bupivacaine with 5 μg/mL sufentanil (11). However, these studies were not performed using PCEA. Clinical studies have not consistently found differences in analgesia among local anesthetic concentrations when added to opioids (12–14).

Bolus volume at each successful demand may also account for the observed difference in satisfaction. In the 4-mL/8-min group, the volume of each bolus might have been too small to ensure adequate filling of the epidural space, thus limiting analgesic spread. In a previous dose-range study (7), patients who received the largest bolus size at each PCEA demand had the highest sensory levels. However, the upper sensory level after a volume of 12 mL may be relatively low, reaching only the T10 dermatome in many parturients (15). Christiaens et al. (16) recently found that the uppermost sensory level is unchanged by the diluent volume when comparing an epidural injection of 20 mL of 0.10% bupivacaine and 10 mL of 0.20% bupivacaine. In addition, there were no differences between groups in the quality of analgesia in these previous studies (7,16).

PCEA can theoretically adjust for individual pain thresholds, allowing patients to use only the analgesic dose needed to control their pain. Parturients in the 4-mL/8-min group were potentially able to receive as large an amount of bupivacaine and sufentanil because the maximal dose per hour was equivalent in both groups. Despite a greater number of pump demands in the 4-mL/8-min group, this did not happen. Thus, our results suggest that the setting of PCEA may be restrictive despite the highest rates of successful demand. This calls into question the adequacy of PCEA in laboring women. Many women required rescue analgesia, a finding consistent with the observation of Paech et al. (17), showing that PCEA may result in a higher rate of supplementation and bupivacaine use when compared with midwife-administered intermittent bolus epidural analgesia. In our study, most rescue injections were given at the end of labor, suggesting that, regardless of the bolus-size, PCEA was inefficient at the end of the first stage of labor. Similar findings were recently reported by Capogna et al. (18), who found that advancing labor requires an increased concentration of epidural bupivacaine for pain relief. As analgesic concentration delivered by the pump was unchanged, this may account for part of the women’s discontent in our study.

The relevance of this study and the extent to which our results can be applied to other practices vary depending on case mix and institutional practices. This study was performed in a private institution where parturients insist on complete pain relief. Most labors are planned. As women had not experienced pain on commencing this study, they may have anticipated PCEA providing complete pain relief when accepting this technique. This is in contrast to most situations in which the patient is in active labor at the time of epidural activation. Another methodologic issue that could have influenced our study was that pain was only assessed twice, at approximately 6- and 9-cm cervical dilation. This may represent a limited assessment, and if timing were actually different between groups, it may represent a possible covariate. However, analysis of PCEA recordings was a valid means of assessing the pain relief. The few unsuccessful patient demands, associated with the few supplementations required during this period, indicate that analgesia was correctly provided throughout the first stage of labor.

No differences between groups in the severity of hypotension, ephedrine administration, outcome of delivery, and Apgar scores were observed in our study. No complications directly related to the large bolus were encountered. However, the small number of enrolled patients does not allow definitive conclusions. The possibility of extensive spinal block in the event of intrathecal displacement of the catheter remains a major concern. Hypotension or the development of lower limb motor deficit, which is unusual with 0.125% bupivacaine, should immediately alert nursing personnel. In the event of intravascular migration of the catheter, the dose of 15 mg, associated with the slow infusion rate of the device and a lockout interval of 25 min, is unlikely to produce systemic effects. Doses used in this study were lower than those reported in most studies (1,5,6,8,9,17). However, toxicity cannot be excluded as for any use of local anesthetics (19). Close patient monitoring therefore remains essential.

To conclude, this study suggests that a PCEA setting of a 12-mL bolus dose and a 25-min lockout interval can improve analgesia and patient satisfaction during labor, compared with a 4-mL bolus and 8-min lockout. The choice of a larger bolus volume and dose neither decreased the need for rescue analgesia, despite increasing analgesic consumption via the device, nor did it eliminate some discontent with the PCEA. Larger scale studies are needed to evaluate safety before concluding that the large bolus dose of 0.125% bupivacaine plus sufentanil and epinephrine is suitable for PCEA during oxytocin-induced labor.

We thank the midwife staff at the Polyclinique Jean-Villar for their patience with data collection.

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