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TECHNOLOGY, COMPUTING, AND SIMULATION

Continuous Epidural Infusion of Large Concentration/Small Volume Versus Small Concentration/Large Volume of Levobupivacaine for Postoperative Analgesia

Department of Anesthesiology, University Hospital Center, Charleroi, Belgium

Address correspondence and reprint request to Mira Dernedde, MD, Department of Anesthesiology, University Hospital Center, 92 Boulevard P. Janson, 6000 Charleroi, Belgium. Address e-mail to mira.dernedde{at}chu-charleroi.be

	Abstract

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In this randomized study, we evaluated the quality of postoperative analgesia and the incidence of side effects of continuous thoracic epidural levobupivacaine 15 mg/h in 2 different concentrations: 0.5%, 3 mL/h (n = 33) or 0.15%, 10 mL/h (n = 27). The following variables were registered within 48 h: sensory block, pain scores, rescue morphine consumption, motor blockade, hemodynamics, sedation, nausea and vomiting, and patient satisfaction. The two groups were similar with regard to demographics, cephalad level of sensory block, quality of analgesia, morphine consumption, side effects, and high satisfaction rate. Motor blockade was weaker in the 0.5% group (P = 0.025), with a significantly increased hemodynamic stability, compared with the 0.15% group (P = 0.004). In conclusion, the same dose of levobupivacaine provides an equal quality of analgesia in small- or large-volume continuous epidural infusion and decreases the incidence of motor blockade and hemodynamic repercussions. This is in accordance with the assumption that the total dose of local anesthetics determines the spread and quality of analgesia.

IMPLICATIONS: We demonstrated that a large concentration/small volume of levobupivacaine given as a continuous thoracic epidural infusion provided an equal quality of postoperative analgesia as a small-concentration/large-volume infusion and induced less motor blockade and fewer hemodynamic repercussions.

	Introduction

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The relative effects of the mass, volume, and concentration of local anesthetic solution used for epidural anesthesia and analgesia are still under debate. Clinical studies have shown discrepancies, probably because of limited consideration of total dose (1–5). Bromage (6) found that it is the total local anesthetic dose, and not the total volume, that determines the spread and quality of analgesia. This has been confirmed by others after both lumbar and midthoracic epidural administration (7,8). For continuous epidural postoperative analgesia, very few data are available considering the relative contribution of these factors. It is unclear whether concentration has any influence on the quality of pain relief during epidural analgesia when the total dose is held constant (9–11).

This prospective and randomized study was designed to evaluate the quality of analgesia and side effects produced by a continuous epidural infusion of 0.5% levobupivacaine compared with a dose-equivalent 0.15% after lower-abdominal surgery.

	Methods

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After approval by the Ethics Committee, written, informed consent was obtained from 70 consecutive ASA physical status I to III patients undergoing elective lower-abdominal surgery. Patients were included if they were 18–75 yr old, could read and understand French, had normal mental health, and were hospitalized for elective surgery. Exclusion criteria were sepsis, allergy to amide-type local anesthetics or morphine, and coagulopathy. At the time of the preoperative visit, patients were familiarized with a 10-cm visual analog scale (VAS) device for pain-intensity assessment (0 = no pain at all, 10 = worst imaginable pain) and nausea (0 = no nausea at all, 10 = worst imaginable nausea) (12).

Patients were premedicated with midazolam or alprazolam before the induction of anesthesia. In the operating room, a 20-gauge epidural catheter was inserted through an 18-gauge Tuohy needle into the epidural space at levels according to the site of surgery. The epidural catheter was directed cephalad for a distance of 4 cm and fixed to the back of the patient. As soon as the patient was in the supine position, a test dose of 3 mL of 0.5% levobupivacaine (Chirocaine®; Abbott, Louvain-la-Neuve, Belgium) was injected through the catheter as proposed by Murdoch et al. (13) and Daoud et al. (14).

Anesthesia was maintained with sevoflurane in 50% oxygen in air or nitrous oxide associated with sufentanil and myorelaxant. Three to 6 mL of 0.5% levobupivacaine were injected through the epidural catheter for the surgical procedure. If surgery lasted longer than 2 h, patients received a reinjection of half of the volume of the local anesthetic with the same concentration. After completion of the operation and tracheal extubation, patients were transferred to the postanesthesia care unit, where they remained under constant observation for approximately 4 h. The patients received, in a random fashion, either 0.5% levobupivacaine 3 mL/h (LV group; n = 33) or 0.15% levobupivacaine 10 mL/h (HV group; n = 27) for postsurgical pain relief. Patients were blinded to the drug concentration administered epidurally. No extra bolus injection or change of the infusion rate was allowed. For further postoperative pain relief, patients received IV propacetamol (2 g) every 6 h and, within 24 h, they received ketorolac (60 mg). Rescue medication by means of morphine was provided via a patient-controlled analgesia device (Abbott Lifecare PCA Infusor; Abbott Laboratories, North Chicago, IL) with 1.5-mg bolus doses, a 7-min lockout time, and a 25-mg dose limit over 4 h (multimodal analgesia) (15). The consumption of analgesic drugs was recorded during the 48-h study period. After 48 h, the infusion of levobupivacaine was discontinued, and alternative analgesia was provided.

Upon arrival in the postanesthesia care unit, patients were asked to rate their pain experience on the VAS device. This process was repeated every 2 h for the first 4 h, and when the patient moved to the general surgical ward, it was continued every 4 h for 48 h. Only rest pain was assessed, defined as the pain experienced by the patient while lying in bed. The pain threshold was set at 3 cm on the VAS scale (16). Nausea intensity was evaluated with a VAS device, and vomiting was recorded as either present or absent by direct observation or by spontaneous complaint of the patient. Nausea was defined as a patient’s rating score of >4 cm on the VAS (12). Rescue medications given for nausea or vomiting were recorded. The cephalad level of sensory block was evaluated by loss of sensation to cold by using ether swabs at the same time. If the levels of sensory block on the right and left sides were different, the most cephalad was recorded.

Motor blockade was assessed according to a modified Bromage scale (0 = no motor block, 1 = inability to raise extended legs, 2 = inability to flex knees, and 3 = inability to flex ankle joints) (17). Hypotension was defined as a 30% decrease of systolic blood pressure compared with baseline, bradycardia as a heart rate less than 50 bpm, and bradypnea as a respiratory rate <10 breaths/min. Sedation was recorded on a four-point scale (0 = no signs of sedation, 1 = mild sedation, 2 = moderate sedation, and 3 = severe sedation).

On Day 1 and Day 2, the patients were visited by a pain nurse from the Acute Pain Service who interviewed each patient regarding satisfaction with postoperative analgesia. The quality of pain management was judged by the patient on a four-point scale (1 = very dissatisfied, 2 = dissatisfied, 3 = satisfied, and 4 = very satisfied).

Results were expressed as means ± SD for quantitative variables, as median for the upper level of dermatomal sensory blockade, and as frequencies for categorical findings. Time-related VAS measurements were summarized by using a series of pain indicators as described elsewhere (18): area under the VAS-time curve (cm x h); mean VAS (cm); VAS_max, peak of VAS (cm); time of VAS_max (h); the persistence of VAS over 3 cm, i.e., the time period during which VAS was above the critical threshold (h); and pain duration, i.e., the time period during which the patient reported pain (VAS >0) over the 48 h (h). Comparison of mean values was done by means of the Student’s t-test, whereas proportions were compared by the classic ² test. The general linear model (GLM) was used to analyze repeated measures of continuous data. The GLM tests two null hypotheses as follows: 1) time has no effect on the variable, which means that the variable mean of the combined groups does not vary over time, and 2) the time patterns are equal between the two groups, which means that the difference between the mean of each group is the same at every time point. The Bonferroni test, based on Student’s t statistic, was used for post hoc testing. Upper dermatomal levels of sensory block were compared by use of the Mann-Whitney U-test. The number of patients included in the study was based on a power calculation assuming a 20% difference with = 0.05 and ß = 0.20. All statistical calculations were performed by means of the SAS package (Version 6.12; SAS Institute, Cary, NC) and always with all data available. Results were considered to be significant at the 5% critical level (P < 0.05).

	Results

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Ten patients were excluded because of protocol deviation, lack of information concerning the design of the study, or accidental removal of the catheter. In three of these patients, the continuous epidural infusion had been stopped in the HV group after 4, 8, and 12 h because of complete motor blockade. In two additional cases in the same group, the epidural infusion rate was decreased after 4 and 8 h, in regard to a unilateral Bromage score of 3. Sixty patients with complete case report forms were included in the study (27 in the HV group and 33 in the LV group). Patients’ characteristics and distribution according to the type of surgery are displayed in Table 1. The demographic data, baseline recordings, and type of surgery were similar in the two groups.

View larger version (13K): [in this window] [in a new window]   Figure 1. Evolution of the upper sensory dermatomal levels (median). No significant difference was found between the two groups of patients (general linear model statistics).

View larger version (16K): [in this window] [in a new window]   Figure 2. Evolution of the mean visual analog scale (VAS) scores. No significant difference was found between the two groups of patients (general linear model statistics). * P < 0.05 (Student’s t- and Bonferroni tests).

No difference could be found between the two groups for nausea and vomiting. Five patients in the HV group experienced nausea, compared with four in the LV group (P = 0.72). Vomiting was observed in two patients in the HV group and in one in the LV group (P = 0.58). Three patients in the HV group and four patients in the LV group received antiemetic drugs (P = 0.90).

The mean scores of motor blockade in the two groups are displayed in Figure 3. There was significantly less motor blockade in the LV group (P = 0.025; GLM statistics). There was a significant difference in the hemodynamic variables: systolic and diastolic blood pressures in the HV group were lower (P = 0.004). GLM statistics showed a highly significant time effect on the variables (P < 0.001), a significantly different time pattern (P < 0.001), and significantly different overall means of the groups (P < 0.001). Figure 4 displays the evolution of the systolic and diastolic blood pressure. Five patients in the HV group and two in the LV group experienced hypotension (P = 0.14). Bradycardia occurred in 3 patients in the HV group and in 11 patients in the LV group (P = 0.043). No vasoconstrictors or atropine were given during the study period. Twenty-two patients in the LV group and 13 patients in the LV group presented mild sedation (P = 0.15). No pruritus was observed in any patient. All patients of the two groups were satisfied or very satisfied regarding the quality of pain management.

View larger version (16K): [in this window] [in a new window]   Figure 3. Evolution of motor blockade (mean Bromage scores) in the two groups of patients (P = 0.025; general linear model statistics).

View larger version (32K): [in this window] [in a new window]   Figure 4. Evolution of mean systolic (SBP) and diastolic (DBP) blood pressure in the two groups of patients (P = 0.0044; general linear model statistics). *P < 0.05 (Student’s t- and Bonferroni tests).

	Discussion

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Our results are in accordance with previous studies (2,4,9–11). Duggan et al. (2) showed that the onset and recovery of surgical analgesia were similar with 0.75% and 0.5% bupivacaine solutions when these were administered at the same dose. Liu et al. (4) compared the effects of a threefold difference in concentration and volume of 2-chloroprocaine on epidural anesthesia in volunteers and demonstrated that the intensity of sensory and motor blockades were similar in both groups, depending primarily on the total milligram dose of the local anesthetic. Laveaux et al. (9) compared the analgesic efficacy and the side effects of a continuous thoracic epidural infusion of bupivacaine with those of sufentanil at large concentration/small volume versus small concentration/large volume in the postoperative period. They showed excellent analgesia and no difference in the incidence of side effects in both groups. These authors concluded that the total dose of the local anesthetic was more important than the concentration or the volume of the solution. Mogensen et al. (10) showed that pain relief and regression of analgesia were similar during continuous epidural infusion of either 8 mL/h of 0.5% bupivacaine or 16 mL/h of 0.25% bupivacaine. Recently, Murdoch et al. (13) observed that levobupivacaine 0.25% as a continuous epidural infusion provided better postoperative analgesia without any significant increase in motor blockade when compared with the 0.125% concentration.

However, there are discrepancies in the literature concerning the analgesic effects of large concentration/small volume of local anesthetics. Sakura et al. (5) demonstrated that lumbar epidural anesthesia with 10 mL of 2% lidocaine produced more intense blockade of sensory fibers than that with 20 mL of 1% lidocaine. No difference in the upper level of sensory block was observed between the groups. After thoracic surgery, Snijdelaar et al. (11) compared a continuous epidural infusion of a large volume of a sufentanil/bupivacaine mixture and a dose-equivalent small-volume infusion. The quality of analgesia at rest was less in the small-volume group, but for pain during exercise, no difference was found. In their study, they used a smaller amount of bupivacaine, i.e., 7.5–10 mg/h compared with the 15 mg/h in our study. This could contribute to the increased incidence of pain at rest found in this study. Liu et al. (21), using patient-controlled epidural analgesia (PCEA), observed that smaller concentrations of similar amounts of epidural ropivacaine/fentanyl provide equal analgesia with less motor block after lower-abdominal surgery. The use of PCEA rather than a continuous epidural infusion may explain the difference in the incidence of side effects such as motor blockade.

It is important to choose the epidural puncture site at a level appropriate to the innervation of the surgical incision. In this study, the epidural catheter was inserted at the thoracic level to deliver local anesthetics to the affected dermatomes (22). As Wheatley et al. (23) recently stated, "the use of the thoracic rather the lumbar approach to the epidural space has been one of the major changes in anesthetic practice over the last twenty years." The thoracic approach minimizes motor and sympathetic blockade of the lower limbs and could explain the small incidence of side effects encountered in our study. We placed our epidural catheters in low thoracic vertebral interspaces, which is typical practice for patients undergoing lower-abdominal surgery. However, placement of epidural catheters in such proximity to lumbar spinal segments providing motor innervation to the lower extremities appeared to increase the risk of motor block when compared with more cephalad placement, especially in the HV group (20). We suspected that more cephalad placement of epidural catheters would reduce the incidence and severity of the lower extremity motor block encountered in the LV group. The assessment of motor blockade was based on the original Bromage score (17). The Bromage score is not very sensitive for detecting subtle changes in motor function as compared with electromyography to measure the isometric maximal force contraction of the quadriceps (24).

The most frequently reported adverse event in our study was hypotension, which occurred in up to five of the patients in the HV group. Bradycardia was observed more frequently in the LV group. These results need to be elucidated, but it is likely that using a smaller volume of the local anesthetics may have reduced the occurrence of hypotensive episodes. The most important limitation related to the study design is that only rest pain was assessed. Further studies will now focus on pain during mobilization or coughing. Nevertheless, the goal of totally pain-free patients regardless of movement may not be realistic with an epidural pain program, as stated by Andersen et al. (25). The practice of adding epidural opioids to the local anesthetic infusion also needs to be evaluated (26). Dahl et al. (27) have shown that the addition of an opioid to an epidural local anesthetic has an appreciable benefit when the patient is actively mobilized, particularly for the first time in the postoperative period. Furthermore, our patients were treated with systemic analgesics, which might have masked small differences in the intensity of rest pain between the two groups.

Finally, the 0.5% levobupivacaine solution is ready to use. This could result in fewer administration errors and decreased nursing time and pharmacy preparation costs. Furthermore, with continuous administration, there is no need for sophisticated, expensive infusion devices such as PCEA pumps and disposable components.

In conclusion, continuous 0.5% levobupivacaine given epidurally at the thoracic level is equally effective compared with the same dose of 0.15% solution in achieving adequate analgesia with a less frequent incidence of motor blockade and reduced hemodynamic instability.

	Footnotes

 
Presented in part at the European Society of Anaesthesiologists Congress, Nice, France, April 6–9, 2002.

	References

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Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999