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From the Department of Anesthesiology; University Hospital Hamburg-Eppendorf, Hamburg, Germany.
Address correspondence to: Dr. Thomas Standl, Department of Anesthesiology, University Hospital Hamburg-Eppendorf, Martini Strasse 52, 20246 Hamburg, Germany. Phone: +49 40 42803-4614; Fax: +49 40 42803-5024; Email: standl{at}uke.uni-hamburg.de
| Abstract |
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Methods: Twenty-eight women undergoing extended gynecological tumour surgery received postoperative CEI with 0.15 mLkg-1hr-1 0.2% ropivacaine (R: n = 14) or 0.125% bupivacaine plus 0.5 µgmL-1 sufentanil (BS: n = 14) during 24 postoperative hours. Twenty-four hours later, postoperative pain management was switched to PCEA without background infusion and 5 mL single bolus application of R or BS every 20 min at most. Visual analogue scales (VAS; 1100 mm) were assessed by patients at rest and on coughing after 24 hr of CEI and PCEA. Side effects, doses of local anesthetics and opioids were recorded and plasma concentrations of total and unbound ropivacaine and bupivacaine were measured.
Results: Patients required lower doses of each respective analgesic medication with PCEA (R: 108 ± 30 mL; BS: 110 ± 28 mL) than with CEI (R: 234 ± 40; BS: 260 ± 45; P < 0.01). Ropivacaine plasma concentrations were lower 24 hr after PCEA when compared with CEI (P < 0.01). No patient after PCEA but two after CEI (n = 4; NS) presented motor block. PCEA with R provided better postoperative pain relief than CEI (37 ± 32 vs 59±27, P < 0.05). No difference in parenteral opioid rescue medication between CEI and PCEA was seen.
Conclusion: PCEA in comparison to preceding CEI provides equivalent analgesia with lower local anesthetic doses and plasma levels, and without motor blocking side effects, irrespective of the applied drug regimen.
| Introduction |
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Patient-controlled epidural analgesia (PCEA) may offer the opportunity to reduce the incidence of side effects associated with CEI,7 since PCEA provides excellent postoperative analgesia with only minimal side effects when properly used.8 Both improved analgesia with similar doses of analgesics7 and dose-sparing effects with comparable analgesia9 have been shown for PCEA when compared with CEI.
The present prospective randomized double-blinded study examined the hypothesis that PCEA without background infusion provides comparable pain relief with lower doses of different analgesics when compared with a preceding 24 hr CEI using the same analgesics in women undergoing major abdominal surgery.
| Methods |
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A thoracic epidural catheter (22-G polyamide end-hole catheter, B. Braun, Germany) was inserted at T 8 ± 2 on the morning of the operation. Aspiration and injection of a 3-mL test dose with 2% mepivacaine excluded accidental intravascular or subarachnoid catheter position. General anesthesia was then induced with sufentanil (0.4 µgkg-1), etomidate (0.25 mgkg-1) and cisatracurium (0.15 mgkg-1) and maintained with 0.61.0 vol% isoflurane and nitrous oxide (FIO2 = 0.3). Sufentanil boluses (10 µg) were repeated if patients suffered from inadequate analgesia. Six to 10 mL of the respective LA (depending on the patients age: patients aged between 40 and 50 yr received 10 mL; between 50 and 60 yr 8 mL; and between 60 and 70 yr 6 mL) were injected in the epidural catheter at least 30 min prior to start of the operation, followed by a dose of 5 mL every 90 min. Patients were randomly allocated to receive ropivacaine 0.75% (AstraZeneca, Germany) in group R, or bupivacaine 0.5% (AstraZeneca, Germany) in group BS. Figure 1
shows a schematic flow-sheet of the protocol.
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50 mm. If the top-up did not result in a pain reduction of
20 mm an iv bolus injection of 3.75 mg piritramide was given (Janssen-Cilag, Germany; 15 mg piritramide are equivalent to 10 mg morphine).10 The analgesic technique was changed to PCEA 24 hr after the start of the CEI. The epidural catheter was connected to a patient-controlled analgesia (PCA) device (Graseby 9500, SIMS, Germany). All patients were allowed to inject themselves 5 mL of the respective analgesic (0.2% ropivacaine or 0.125% bupivacaine plus 0.5 µgmL-1 sufentanil) every 20 min with a four-hour maximum dose of 60 mL, irrespective of their age. No background infusion was administered. Rescue pain medication with 3.75 mg piritramide iv was administered on demand. After 24 hr of epidural infusion (= 24 hr after the end of surgery on POD 1) and after 24 hr of PCEA (POD 2), patients were examined by an investigator blinded to the study group. The quality of analgesia was assessed using a VAS (range from 0 mm = no pain to 100 mm = unbearable pain) by the patients at rest, during forced breathing or coughing and during mobilization out of bed. Motor function was assessed using the Bromage scale (0 = none, full flexion of both legs against gravity; 1 = partial, patient is able to move feet and knees but is not able to elevate his legs against gravity; 2 = almost complete, patient is able to move feet but not knees; 3 = complete, patient is unable to move feet or knees). Side effects such as nausea, emesis, respiratory depression (< 8 breathsmin-1) and pruritus were recorded every eight hours. The dose of epidural analgesic and of parenteral opioid was recorded at the end of the operation, after 24 hr of CEI and after 24 hr of PCEA. Before the first epidural injection (baseline), at completion of surgery, after 24 hr of CEI and after 24 hr of PCEA, central venous blood samples were taken for measurements of the plasma concentrations of the respective LA. All samples were centrifuged immediately, and the supernatant serum was frozen at -30°C until the day of measurement. Using high-pressure liquid chromatography, the total concentration and free (unbound) fraction of ropivacaine and bupivacaine were measured as described previously.11 The accuracy of this assay is 95% and the confidence interval is ± 1.25%.
Sample size calculation and statistical analysis
For sample size calculation of the main goal of the study (CEI vs PCEA), a power analysis was performed by using the cumulative consumption of administered study solution over 24 hr as the primary outcome variable on the basis of retrospective data from our institution in the same surgical population. We set 9 mLhr-1 as the mean dose of epidurally required analgesics, i.e., a cumulative dose of 216 mL over the first 24 hr. For calculation of the sample size we defined the smallest clinically significant difference between POD 1 and POD 2 as 25% (54 mL) of the cumulative amount of epidural analgesics over the first 24 hr. The anticipated pooled standard deviation was set at 40 mL. We would permit a type I error of
= 0.05, and with the alternate hypothesis, the null hypothesis would be retained with a type II error of ß = 0.1. This analysis reaches a power of 0.9 and indicated that a sample size of at least 13 patients per group was necessary.
In addition, patients were allocated to one of the two groups of analgesic regimen by a computerized randomization program (second goal of the study). A power analysis revealed that under the unexpected assumption of significant differences between the two analgesic regimens (VAS difference
30 mm), a sample size of 14 patients would be sufficient.
Data are reported as mean values ± SD if not stated otherwise. Differences within groups were tested by ANOVA for repeated measurements and post-hoc comparison by paired Students t test. Differences between groups were tested by the unpaired Students t test. Nonparametric data were tested by the Chi-square test. All differences were considered significant at P < 0.05.
| Results |
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| Discussion |
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There is a (randomization-related) trend to a higher mean age in group R when compared with group BS, although the difference was not statistically significant (P = 0.06) per study protocol, younger patients received a larger volume of LA solution. However, the higher age was not associated with a lower intraoperative mean dose of LA in group R vs BS (14 vs 15 mL), but was associated with a lower LA volume on POD 1 after 24 hr with CEI (R: 234 mL vs BS: 260 mL). The similar intraoperative dose of LA can be explained by the slightly longer duration of operation in group R which led to a higher percentage of reinjections during the case and may have counteracted the age difference. More importantly, the youngest women (45 and 48 yr) were included in group R leading to a higher LA dose of 10 mL in these patients. In addition, a higher cumulative top-up dose was required in the R group (89 ± 20 mL) when compared with the BS group (61 ± 18 mL) during CEI making the expected difference between R and BS on POD 1 smaller. This difference in required top-ups may probably be explained by the lower potency of R in comparison with BS. In a follow-up study we could show that 0.375% ropivacaine is equivalent to BS in patients undergoing major abdominal surgery.15 In this study we were investigating the opioid-free epidural administration of an LA solution, because epidural opioids can cause major problems in patients with sleep apnea syndrome or result in side effects like respiratory depression and sedation caused by the vascular uptake of the opioid. In identical concentrations, ropivacaine appears to be less potent than bupivacaine.16 Therefore we used a higher concentration of ropivacaine. Ropivacaine appears to have an advantage over other long acting LA because of a pronounced differential blocking effect17 and a lower severity of cardiac side effects in case of systemic intoxication.18
Irrespective of the applied drug regimen, comparable or even better pain relief could be obtained during PCEA with significantly lower doses of the respective analgesic than with CEI. This is reflected by the lower plasma concentrations of ropivacaine during PCEA when compared with CEI. In contrast, no significant decrease of the bupivacaine plasma concentrations could be detected, possibly due to the smaller amount of dose reduction during PCEA vs CEI and a longer plasma-half-life of bupivacaine in comparison to ropivacaine.19 Even when the higher concentration and doses of epidural ropivacaine are considered, the absolute plasma concentrations of ropivacaine were relatively higher than the plasma concentrations of bupivacaine. This result is consistent with other studies, which measured higher plasma concentrations of ropivacaine vs bupivacaine after equivalent epidural doses.20 However, all plasma concentrations of ropivacaine and bupivacaine, especially the unbound fraction, measured in this study were far below the threshold at which severe central nervous and cardiac side effects have been reported.21 The reduction of LA plasma concentrations may be an advantage of PCEA over CEI in terms of safety.
In contrast to CEI, no signs of motor block were observed with PCEA. Although an earlier study did not demonstrate a decrease in the incidence of motor block by using PCEA,9 a reduced rate of motor block may reflect an advantage of PCEA over CEI in postoperative pain management.
In accordance with other studies35 our results suggest that supplementation of a low concentration of LA with an opioid provides better pain relief than a LA used as the sole agent during the early postoperative period when patients are mobilized.
Increasing evidence suggests that epidural anesthesia and analgesia provide better outcomes after major surgical interventions2,8,22,23 and that epidural analgesia using thoracic catheters is more and more frequent.24 Although both CEI and PCEA have been shown to be safe and effective for the management of postoperative pain,25,26 we prefer to use PCEA whenever patients are able to use the device. This may help avoid unnecessarily high LA plasma concentrations and motor blockade. In addition, the unique advantage of PCEA over continuous infusion is the patients ability to obtain analgesia at the appropriate time, e.g., before physical exercise and mobilization. Only a few conditions may limit the use of PCA whether epidural or iv such as postoperative mechanical ventilation in highly sedated patients. Extremes of age should not be an exclusion criteria for PCEA, since the successful use of PCEA has been documented in elderly patients27 as well as in children.28 Further studies will be required to demonstrate whether the pain scores obtained with PCEA during stress and mobilization in our study can be improved by using low-dose background infusions13,29 or a low dose/high volume concept.30
| Acknowledgments |
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| Footnotes |
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The paper has been presented in part at the IARS meeting in Los Angeles, California, March 1216, 1999, and at the Annual Meeting of the American Society of Anesthesiologists, Dallas, Texas, October 913, 1999.
Accepted for publication August 29, 2002.
| References |
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2 Buggy DJ, Smith G. Epidural anaesthesia and analgesia: better outcome after major surgery? Growing evidence suggests so. BMJ 1999; 319: 5301.
3 Cooper DW, Turner G. Patient-controlled extradural analgesia to compare bupivacaine, fentanyl and bupivacaine with fentanyl in the treatment of postoperative pain. Br J Anaesth 1993; 70: 5037.
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