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Department of Anesthesiology, Royal University Hospital, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
Address correspondence and reprint requests to David C. Campbell, MD, MSc, FRCPC, Department of Anesthesiology, Royal University Hospital, University of Saskatchewan, 103 Hospital Dr., Saskatoon, Saskatchewan, Canada S7N 0W8. Address e-mail to campbelld{at}sdh.sk.ca
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Abstract |
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5 cm) established labor received either 20 mL of 0.08% bupivacaine plus 2 µg/mL fentanyl (BF) or 0.08% ropivacaine plus 2 µg/mL fentanyl (RF) to initiate epidural analgesia. One woman (BF) required supplemental analgesia, and two (one BF and one RF) had visual analog scale scores > 0 but < 20 at 20 min. The time (mean ± SD) to visual analog scale score = 0 was BF (n = 18): 12.0 ± 4.5 min and RF (n = 19): 12.4 ± 4.0 min (P > 0.05). Spontaneous micturition was observed in 65% (13 of 20) BF compared with 100% (20 of 20) RF (P < 0.01), and ambulation was demonstrated in 75% (15 of 20) BF compared with 100% (20 of 20) RF (P < 0.03). The incidence of forceps delivery was 35% (7 of 20) BF compared with 10% (2 of 20) RF (P < 0.04). The results of this study indicate that dilute ropivacaine combined with fentanyl effectively initiates epidural analgesia while concurrently preserving maternal ability to void and ambulate.
Implications: As compared with a similar dilute concentration of bupivacaine, 20 mL of dilute (0.08%) ropivacaine combined with fentanyl (2 µg/mL) effectively initiates epidural analgesia in nulliparous women in early, established labor while preserving their ability to micturate and ambulate. Of importance, it appears that a true ambulatory epidural analgesic for women in labor is now possible.
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Introduction |
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This is the first prospective, randomized, double-blinded study designed to compare dilute concentrations of bupivacaine with ropivacaine (both combined with fentanyl) to initiate ambulatory LEA.
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Methods |
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5 cm and a reassuring fetal heart rate (FHR) tracing were considered for inclusion in the study. Determination of cervical dilation was required within 30 min of recruitment. Parturients were randomized, by using a computer-generated randomization table, to receive 20 mL of one of two study solutions to initiate LEA. The study solutions consisted of either (BF): 0.08% (16 mg) bupivacaine plus 2 µg/mL (40 µg) fentanyl; or (RF): 0.08% (16 mg) ropivacaine plus 2 µg/mL (40 µg) fentanyl. Each study solution was prepared by an anesthesiologist or nurse not involved in the study. The solutions were attained by adding 20 mL of 0.5% bupivacaine (100 mg) or ropivacaine (100 mg) and 5 mL of fentanyl (250 µg) to a 100-mL bag of preservative-free 0.9% saline. The resultant 125 mL had a concentration of 0.08% (bupivacaine or ropivacaine) plus 2 µg/mL fentanyl. A volume of 20 mL was then removed and given to the blinded investigator to initiate LEA. The remaining 105 mL of the study solution was then used for maintenance analgesia administered via patient-controlled epidural analgesia (PCEA).
On request for LEA, each parturient received IV 500-1000 mL of a balanced salt solution before the initiation of epidural analgesia. The procedure was performed at either the L3-4 or L4-5 interspace, with all patients in the sitting position. The epidural space was identified with a 17-gauge epidural needle by using a loss-of-resistance technique. A 20-gauge multiple-orifice epidural catheter was then inserted 4–5 cm into the epidural space. Aspiration was attempted from the epidural catheter in an effort to detect either intravascular or intrathecal placement of the catheter. The initial 5-mL bolus of the study solution was then injected. The epidural catheter was then secured and the parturient placed in the supine position with left uterine displacement with the head of the bed elevated 20–30 degrees. If no adverse sequelae were observed within 3 min, the remainder of the study solution was administered in three equal incremental boluses of 5 mL. The total time permitted to inject the entire 20-mL volume of the study solution was less than 5 min.
The epidural catheter was connected to the PCEA infusion pump 20 min after the administration of the study solution. Each parturient was instructed in proper PCEA use once analgesia had been established. The PCEA infusion device was programmed with the standardized parameters of a 5-mL bolus and a 10-min lockout period using the study solution. No continuous epidural background infusion of the study solution was administered. There were no hourly restrictions on the number of self-administered boluses that could be demanded or delivered. Further management of PCEA labor analgesia was left to the discretion of the anesthesiologist working on the labor and delivery floor.
The duration of epidural analgesia was defined as the time from the completion of the injection of the total volume (20 mL) of the study solution until the parturient pressed the demand button of the PCEA infusion pump.
Hypotension, defined as a systolic blood pressure of <90 mm Hg or a 20% decrease from baseline, was treated immediately with a fluid bolus and IV ephedrine as required.
After the administration of the study solution, each parturient was evaluated by an investigator blinded to the study solution. Assessments were made every 2 min for the first 10 min, then every 5 min until 30 min, and finally every 15 min until additional epidural analgesic study solution was delivered by the PCEA device. Parturient appraisal included demographics, assessment of vital signs, continuous pulse oximetry, and completion of a 100-mm linear visual analog scale for pain (VASP) at the peak of contractions (0 = no pain; 100 = worst pain imaginable). At the same time intervals, somnolence was assessed by using a 4-point ordinal scale for degree of sedation (0 = wide awake; 1 = drowsy; 2 = rousable; 3 = nonrousable), and weakness of the lower extremities by using the 4-point Bromage scale. Side effects, such as nausea alone, nausea and vomiting, and pruritus, were also recorded. The ability of the patient to micturate spontaneously was also recorded. The level of sensory loss to cold (ice) along the midclavicular line was assessed 30 min after the completion of the administration of the study solution. On delivery of the baby or when additional PCEA analgesia was self-administered, the patient was no longer required to complete the VASP score.
Effective labor analgesia was defined as a VASP score of <20 mm at 20 min after complete administration of the study solution.
Adequacy of motor function for ambulation was assessed 30 min after the administration of the study solution by using a modified Bromage scale (1). Parturients were asked to demonstrate straight leg raises, then sit at the edge of the bed, stand, and finally perform a deep knee bend. Ambulation was considered possible after three unassisted steps. Parturients were permitted to ambulate only after they successfully demonstrated three unassisted steps and only when accompanied by a responsible care provider (i.e., labor nurse). Once the parturient returned to bed, these assessments were repeated before permitting subsequent ambulation.
All parturients had continuous electronic FHR monitoring for 30 min after the initiation of LEA. Either continuous or intermittent FHR monitoring was subsequently done at the discretion of the obstetric care team. Any FHR abnormalities identified by the blinded obstetric team were recorded. Duration of the first and second stages of labor and the requirement for an instrumented (forceps) or cesarean delivery were recorded. Management of labor was left to the discretion of the obstetric caregivers.
Medication failure or technical failure was assessed if analgesia was inadequate (VASP > 20 mm) at 20 min. Failures were defined as medication-related if a symmetric sensory level was detected despite inadequate analgesia. Failures were considered technical-related if the level was undetectable, asymmetric with one side T10, or patchy. Parturients identified with either medication or technical failures were excluded from further data collection but included in the final data analysis.
Data were expressed as mean ± SD and were analyzed by using independent t-tests for continuous data and 
2 and Fisher’s exact proportion tests for categorical and nominal data. A P < 0.05 was considered statistically significant.
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Results |
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There was no significant difference in the VASP scores immediately before the initiation of LEA between the two groups. One woman in the BF group required supplemental epidural study solution at 20 min because of a VASP score of > 20 but < 30, even though cutaneous sensory levels were >T10 bilaterally. This patient experienced a rapidly progressive labor and complained primarily of perineal pressure. Two women (one BF and one RF) reported VASP scores > 0 but < 20 at 20 min but did not request additional epidural study solution. Both women experienced rapidly progressive labors and complained primarily of perineal discomfort (pressure). All three women were excluded in the determination of study solution analgesic profile and time to VASP score = 0. In the remaining women, the VASP scores did not differ between 0 and 20 min after the injection of the study solution (Figure 1).
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Unassisted maternal ambulation was observed in all women of the RF group but only 75% (15 of 20) of the BF group (P < 0.03). Of the five women (BF) who were unable to ambulate, one was unable to successfully complete a straight-leg raise, and four were unable to complete the partial deep knee bend as a result of motor weakness. None of the women experienced postural hypotension.
There was no evidence of excessive somnolence or desaturation after the administration of either study solution. Maternal ability to micturate spontaneously was demonstrated by all women in the RF group but only by 65% (13 of 20) in the BF group (P < 0.05).
Labor characteristics and incidence of cesarean deliveries did not differ between the two groups; however, the occurrence of forceps deliveries was elevated in the BF group compared with the RF group (35% vs 10%, respectively; P < 0.04) (Table 3).
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Discussion |
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The higher rate of unassisted ambulation is consistent with studies that have suggested less motor blockade associated with undiluted ropivacaine. This, however, is the first investigation to assess unassisted ambulation, considered the definitive assessment of lower limb motor strength (1).
The rate of spontaneous micturition was higher in the RF group. The mechanism for this observation requires further investigation. However, the ability of parturients to micturate spontaneously while receiving LEA has considerable cost implications, because of the reduction in the number of either intermittent catheterizations or continuous indwelling bladder catheters. Whether the reduced manipulation of the bladder significantly reduces the incidence of postpartum urinary tract infections requires further investigation.
Considering the routine practiced at our institution of maintaining LEA with a continuous epidural infusion (CEI) at 10–12 mL/h plus PCEA (5 mL; 10-minute lockout; no hourly limit), parturients in the present study received at least one-third less medication. These results concur with previous investigations (7–9) reporting that, with PCEA alone, analgesic requirements were reduced by approximately one-third to one-half compared with CEIs at 10–12 mL/h. Determinations of the optimal mode of delivery (PCEA versus CEI + PCEA) using dilute concentrations of these drugs merit further study.
Two recent publications suggested a difference in relative analgesic potency rather than chemical properties as the explanation for differences in both cardiotoxicity and motor blockade between bupivacaine and ropivacaine (10,11). These conclusions were based solely on the investigators’ determination of the concentration of 20 mL of each local anesthetic alone sufficient to initiate effective LEA in 50% of laboring parturients (MLAC). The MLAC, or 50% effective dose (ED50), of ropivacaine alone was reported to be 40% higher than for bupivacaine alone. Although these differences in ED50 might explain the observations of our investigation, the assertion that these local anesthetics are not equipotent based on determinations of the LEA ED50 (MLAC) requires critical appraisal. First, the full dose-response curves for LEA for both local anesthetics alone have yet to be determined. Consequently, it is possible that the 95% effective dose (ED95) of these drugs may, in fact, be similar, even though the ED50 values may be dissimilar. Although concentration response curves for each have been constructed (10), only the ED50 was actually measured. Thus, the curves were based primarily on derived estimates. Second, several similar investigations have indicated that the ED50 (MLAC) of epidural bupivacaine alone varies from 0.048% to 0.141% (6,10–14) suggesting that variations in study design may affect results. Third, we compared dilute concentrations of these local anesthetics in combination with fentanyl. There have been no dose-response determinations for either local anesthetic combined with fentanyl. Finally, the clinical relevance of ED50 (MLAC) determinations, without concurrent full dose-response curves remains suspect. In practice, only drug concentrations and combinations that provide labor analgesia with a minimum of ED95, are clinically relevant, and actually represent clinical potency. The concentration (0.08%) and combination with fentanyl (2 µg/mL) we used represents at least the ED95 of both drugs. Accepting for the moment the results of the ED50 (MLAC) investigations that bupivacaine is 40% more potent than ropivacaine, 0.048% bupivacaine and 2 µg/mL fentanyl should produce similar analgesic results. However, this concentration of bupivacaine, in fact, only produced effective analgesia in 50% of laboring parturients when combined with 2 µg/mL fentanyl (6). Moreover, Owen et al. (15) observed similar mean hourly use of either 0.125% bupivacaine or ropivacaine alone when administered by CEI and PCEA. This report concurs with our observation of an equivalent mean hourly PCEA utilization. Of note, our study design permitted precise parturient titration by not using a background CEI, as well as not limiting the hourly allowable dose. Further evidence of potential equipotency at clinically relevant doses was also provided by our observation of a similar mean duration of initial epidural analgesia. Although inequities in potency remain a possibility at the clinically relevant concentrations evaluated in the present investigation, the precise differences have yet to be determined.
The debate regarding the effect of ambulation (16,17) and LEA (18) on the progress of labor and labor outcome continues. The controversial report that LEA significantly slows the rate of cervical dilation during the first stage of labor and increases the cesarean delivery rate in nulliparous women in spontaneous labor has been highly publicized (19). In contrast, we observed rates of cervical dilation of 1.12 cm/h (BF) and 1.18 cm/h (RF), suggesting a lack of effect of LEA on the progress of labor. The observed mean duration of the second stage of labor (BF: 82 min; RF: 88 min) was less than that of 115 min previously reported (19). As well, cesarean delivery rates (BF: 5% vs RF: 10%) were also in contrast to the previous report of 25% (19). Our observations are of importance, as many of the nulliparous women enrolled had their labor induced (Table 3). Interestingly, the incidence of forceps delivery was significantly higher in the group receiving bupivacaine (35%) compared with those receiving ropivacaine (10%). The specific impact of ambulation and the method of LEA management we used requires further investigation.
In conclusion, the combination of ropivacaine (0.08%) and fentanyl (2 µg/mL) provides consistent, effective labor analgesia without causing clinically significant adverse maternal or fetal effects. This is the first report of dilute ropivacaine to initiate effective labor analgesia while preserving spontaneous micturition and unassisted ambulation of all evaluable parturients.
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Footnotes |
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Presented in part at the Society for Obstetric Anesthesia and Perinatology annual meeting, Denver, CO, May 21, 1999, and at the Canadian Society of Anesthesia annual meeting, Calgary, Alberta, Canada, June 21, 1999.
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