We previously showed that epidural fentanyl or sufentanil, after a lidocaine-epinephrine test dose, provides approximately 2 h of analgesia, while allowing patients to ambulate (1–5). Fentanyl is the most commonly chosen opioid at our institution for ambulatory epidurals initiated during early labor, on the basis of its lower cost and similar analgesic efficacy when compared with sufentanil (3). Our usual institutional practice is to administer fentanyl after a lidocaine-epinephrine test dose and not to administer an epidural infusion, because of our concerns that this infusion would result in motor block. However, this concern, and the possible effect on time to epidural redose, have not been previously evaluated.
The aim of this study was to determine the influence of a continuous infusion of epidural fentanyl and bupivacaine on the degree of motor block when it is administered after fentanyl after a lidocaine and epinephrine test dose and to determine whether there is a different interval between initial dose and need for subsequent dosing in primigravid patients during the early first stage of labor.
Before this study was initiated, IRB approval was obtained. Fifty-one primigravid ASA physical status I or II obstetric patients at >36 wk of gestation who had requested labor analgesia gave written, informed consent. Patients were excluded if cervical dilation was >5 cm, if they had received IV opioid agonists or agonist/antagonists, if there was a diagnosis of preeclampsia, or if there was a contraindication to fentanyl or bupivacaine. A normal fetal heart rate pattern was required for inclusion in the study. A functioning epidural was required before inclusion in this study.
Before the procedure was begun, the patients’ vital signs (blood pressure, heart rate, and respiratory rate) were documented, and the patients were asked to relate any symptoms of pruritus, nausea, or vomiting. Each patient also completed a baseline assessment with a 100-mm visual analog scale (VAS) for pain, with 0 representing no pain and 100 being the worst possible pain. Each patient received from 500 to 1000 mL of lactated Ringer’s solution IV within half an hour of the epidural placement. All procedures were performed with patients in the sitting position. A lumbar epidural catheter was inserted approximately 5 cm into the epidural space by using a Tuohy-Schiff needle (B-Braun Medical, Bethlehem, PA). Each patient received a test dose of 3 mL of 1.5% lidocaine with 1:200,000 epinephrine. If the test dose was negative for intravascular injection (heart rate within 15 bpm of baseline values in 2 min of pulse oximeter monitoring) and intrathecal injection (no spinal block after 3 min of monitoring), the patient was given fentanyl 100 μg diluted in normal saline to a total volume of 10 mL. Once comfort was achieved, the patient then received one of two infusions in a double-blinded fashion, as follows: Infusion group (INF), a 10 mL/h infusion of 0.0625% bupivacaine with fentanyl (3 μg/mL); and Saline group (SAL), a 10 mL/h infusion of preservative-free normal saline.
The infusions were in a 60-mL syringe marked only with the patient’s name. Patients were placed in the recumbent position with left uterine displacement. VAS scores and the severity of side effects were recorded 10, 20, and 30 min after the administration of the study infusion and every 30 min thereafter. Observations were performed by an individual blinded to the analgesic technique. At the time of each assessment, vital signs, modified Bromage motor scale scores (6), pruritus, nausea, vomiting, and sedation were evaluated. Motor block was defined as none, partial (just able to move the knees), almost complete (able to move the feet only), or complete (unable to move the lower extremities). Pruritus was rated as none, minimal (present with minimal symptoms), moderate (bothersome but not requiring therapy), or severe (requiring therapy). Sedation was categorized as none (awake), mild (drowsy), moderate (sleepy), or severe (unarousable). The fetal heart rate pattern was evaluated at each interval, and any changes were documented. After the first 30 min, patients were allowed to ambulate with assistance, provided there was no detectable motor block and the fetal heart rate pattern was reassuring. The fetal heart rate was continuously monitored throughout the time of ambulation. The time at which each patient requested additional analgesia was recorded, vital signs were documented, pain and side effect assessments were performed, a cervical examination was performed, and the study period was concluded. Epidural analgesia was subsequently managed by the anesthesia team, as appropriate, for the remainder of labor. The length of labor, incidence of cesarean delivery, incidence of postdural puncture headache, and neonatal Apgar scores were recorded.
A plan for treating inadequate analgesia was standardized. If a patient did not experience adequate analgesia 20 min after the initial study dose, 15 mL of 0.125% bupivacaine was administered via the epidural catheter. If this did not provide relief after an additional 20 min, 10 mL of 2% lidocaine was administered. If this did not result in an adequate level of analgesia, then the epidural catheter was replaced.
Before this study was instituted, a power analysis was performed assuming a duration (defined as the time from initial dose to when additional analgesia was requested or to when delivery occurred) of fentanyl analgesia of 124 ± 42 min (3), an infusion analgesia duration of 165 ± 45 min, and an α of 0.05. This yielded a required sample size of 16 patients per group with an 80% power and 21 patients per group with a 90% power.
Demographic data were analyzed with analysis of variance. Pain scores were analyzed with the Mann-Whitney U-test. Presence or absence of side effects was analyzed by contingency testing. A Kaplan-Meier plot of the patients remaining comfortable over time was generated. Data are expressed as mean ± sd. Significance was determined at the P < 0.05 level.
Fifty-one patients agreed to participate in the study. All patients, except one, achieved adequate initial analgesia with the epidural fentanyl; this patient did not become comfortable after the administration of epidural local anesthetic, but did so after replacement of the epidural catheter; this patient was not included in the study. There were no differences in demographic variables, cervical dilation at the time of enrollment, rupture of membranes, or oxytocin use between the two study groups (Table 1). Baseline VAS pain scores and the incidence of nausea and pruritus were similar in the two groups. The median VAS scores were decreased 74% and 75% by the 10-min evaluation in the SAL and INF groups, respectively (P = not significant). At 20 min, VAS scores were reduced by 89% (SAL) and 93% (INF;P = not significant). There was no significant difference in pain scores between the groups at any of the time points (Fig. 1). The duration until redose, however, was significantly different between the SAL group (145 ± 50 min) and the INF group (198 ± 86 min) (P < 0.009;Fig. 2).
Before the administration of the epidural, six patients had experienced nausea (four in the SAL group and two in the INF group), and four patients had vomited (two in the SAL group and two in the INF group). During the entire study period, six patients experienced nausea (two in the SAL group and four in the INF group), and five patients vomited (one in the SAL group and four in the INF group). It is interesting that none of the patients who experienced nausea and vomiting before placement of the epidural experienced either of those symptoms once adequate analgesia was achieved. Six patients experienced mild sedation at least once during the study period (two in Group SAL and four in Group INF;P = not significant). No patient experienced moderate or severe sedation. At no time did any patient experience severe pruritus. No patient required specific treatment for nausea, vomiting, or pruritus. There was no significant difference between the groups with respect to occurrence of at least one period of mild pruritus (13 of 25 in the SAL group, 12 of 25 in the INF group;P = not significant). At 30, 60, 90, 120, 150, and 180 min, the respective numbers of patients with moderate pruritus were 0, 1, 3, 0, 0, and 0. Two patients delivered without the need for a redose (both in the INF group;P = not significant). The dose to delivery intervals in these two patients were 146 and 150 min. Cervical dilation was not significantly different between the groups at the time of redose. The incidence of cesarean delivery was not significantly different between the groups (nine in the SAL group and eight in the INF group). No patient had an inadvertent dural puncture, and no patient in either group had symptoms of a postdural puncture headache.
During the study period, motor block, as reflected by the Bromage Score, was absent (score of 0) in all patients. However, one patient (in the INF group) stated that her left leg felt weak 150 min after the start of the infusion. Although she did not have any clinically detectable motor block, she was nevertheless no longer allowed to ambulate. Twenty-six patients (52%) ambulated at least once during their labor (14 in the SAL group and 12 in the INF group). Of the patients who ambulated, 14 ambulated through the hallway (eight in the SAL group and six in the INF group); the remainder of the patients who ambulated walked either to the bathroom or to a chair. Apgar scores at birth were comparable between groups.
Epidural infusion of dilute local anesthetic solutions mixed with opioids is a popular epidural technique that provides satisfactory analgesia without a significant motor block. Analgesia allowing ambulation during labor is becoming increasingly popular, in part because of the perceived importance of preservation of motor power. In our institution, we prefer the epidural opioid technique, rather than the combined spinal-epidural (CSE) technique, because the former avoids an added step, the expense of a CSE needle, and the necessity of an intentional dural puncture (1–5). The accidental dural puncture rate with the epidural technique has been reported to be 0.69%–4.2%(7,8). However, no inadvertent dural puncture occurred in this study of 51 patients.
This study compared 100 μg of epidural fentanyl after a lidocaine plus epinephrine test dose in primigravid patients with and without a continuous infusion of 0.0625% bupivacaine plus fentanyl. The goal of a dilute epidural infusion of local anesthetic and fentanyl is to prolong the duration of analgesia without adversely affecting the ability to ambulate. As in our previous studies, only approximately half of our patients (52%) with a “walking epidural” did in fact ambulate. Anecdotally, the patients who did not ambulate were satisfied that they had the ability to get out of bed if they so desired (i.e., the patients who did not ambulate did not experience motor block; they simply chose not to ambulate). With the exception of one patient in the INF group who had a feeling of a weak leg and was required to remain at bed rest, the use of a small-concentration infusion did not result in any detectable motor block.
When epidural fentanyl (50 μg) was combined with clonidine (120 μg in a 10-mL total volume), the mean duration of analgesia was 80 minutes (9). In a study comparing CSE with epidural fentanyl, the mean duration of analgesia with epidural fentanyl (100 μg in 10-mL volume) was 83 minutes (10). In a study using 40 μg epidural fentanyl with 20 mL 0.08% bupivacaine, the analgesic duration was shown to be 91 ± 24 minutes (11). These times are less than the analgesic duration seen in this study (145 minutes). As compared with previous studies, it is possible that the more homogeneous nature of our patient population (primiparous patients in early labor) included fewer patients with rapid cervical dilation (e.g., multiparous patients) and thus resulted in a more consistent (and longer) duration until the need for additional analgesic medication.
Intrathecal sufentanil (2.5–10 μg) with bupivacaine (2.5 mg, as part of a CSE technique) provides approximately 95 minutes of analgesia (12). An infusion of a dilute epidural local anesthetic (0.1% ropivacaine at 10 mL/h) increases the duration of spinal analgesia provided by bupivacaine 2.5 mg with fentanyl 25 μg from 103 to 158 minutes (13). Similarly, we found that an infusion significantly prolonged the analgesia of our epidural technique. A concern of using an infusion is the development of motor block. Use of a lidocaine and epinephrine test dose has been implicated in a decreased ability for parturients to ambulate (14). However, this test dose was given immediately before a 12-mL epidural bolus of bupivacaine (0.0625% or 0.125%). Our use of epidural opioid after a test dose without the use of adjuvant local anesthetic did not result in significant motor block (1–5). We believe that when sufficient opioid is initially used, an initial bolus of local anesthesia is unnecessary, and ambulation can be achieved without eliminating the test dose. Epidural 0.1% bupivacaine with sufentanil, as part of a patient-controlled epidural analgesia technique (5-mL bolus, 10-minute lockout period), results in a detectable motor block in approximately 20% of patients (15). The decreased motor block rate in this study was presumably because we used a smaller concentration of bupivacaine and because of the absence of an initial bolus of local anesthetic.
Although only two of the patients in the current study delivered without the need for a redose (durations of 146 and 150 minutes), some have suggested that a small-concentration bupivacaine infusion can be sufficient for labor pain management (16). However, the quality of the analgesia and the criteria for a redose may not have been directly equivalent to those of this study.
The criteria for administering a redose in this study was the patient’s subjective desire for additional medication. Obviously, such a subjective assessment is influenced by institutional and subjective biases that affect the decision to redose patients. We have demonstrated satisfactory results with epidural fentanyl after a lidocaine and epinephrine test dose for the management of laboring patients. Furthermore, dilute infusion of bupivacaine and fentanyl maintains the analgesia longer while still allowing ambulation and causing no detectable side effects. When performing an ambulatory labor epidural with 100 μg fentanyl, after a lidocaine and epinephrine test dose, we currently recommend initiating an infusion of 0.0625% bupivacaine with fentanyl after initial analgesia is obtained.
The authors gratefully acknowledge the assistance of Anne Marie Moineau, RN, and Kelly Dixon, RN, for their help in data acquisition and analysis. The authors appreciate the secretarial assistance of Ms. Lynda Paglia. The authors also acknowledge the assistance of the obstetricians, midwives, and obstetric nurses for their professional care of our patients.
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