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* From the Departments of Anesthesiology, Sapporo Medical University, School of Medicine, and
the Social Welfare Corporation, Hokkaido Social Work Association, Obihiro Hospital, Sapporo, Hokkaido, Japan.
Address correspondence to: Dr. Yukitoshi Niiyama, Department of Anesthesiology, Sapporo Medical University, School of Medicine, S1 W16 Chuou-ku, Sapporo, Hokkaido 060-8556, Japan. Phone: 81-11-611-2111, ext. 3568; Fax; 81-11-631-9683; E-mail; kawamata{at}sapmed.ac.jp
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Abstract |
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Methods: In this study, both observers and patients were blinded to patient group assignment. Sixty patients scheduled to undergo lower abdominal surgery were enrolled. Patients were randomized to one of three postoperative treatment groups: 1) combination group (a combination of 0.2% ropivacaine and 0.003% morphine); 2) morphine group (0.003% morphine); or 3) ropivacaine group (0.2% ropivacaine). Postoperatively, all solutions were administered epidurally at a rate of 6 mL·hr–1 for 24 hr. Patients were given iv flurbiprofen as a supplemental analgesic on demand.
Results: The combination group showed lower visual analogue scale scores than those of patients receiving either drug alone, both at rest and on coughing. The combination group showed a slight motor block at two hours after the continuous epidural infusion, while the ropivacaine and morphine groups did not show any motor block. The incidence of itching was significantly increased in the morphine and combination groups, compared to the ropivacaine group. There was no significant difference between the numbers of patients with nausea in the three groups. No hypotension or respiratory complications were observed in the three groups.
Conclusion: The combination of epidural 0.2% ropivacaine and 0.003% morphine has more effective analgesic effects than either of the drugs alone for postoperative pain relief after lower abdominal surgery.
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Introduction |
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Fentanyl is often used with epidural local anesthetics at a concentration of 2 or 4 µg·mL–1 for postoperative pain management.8 The use of fentanyl in combination with ropivacaine has been reported to improve postoperative pain at rest and on coughing without apparent motor block, compared to the effect of ropivacaine alone.8,9 However, the combination of fentanyl and ropivacaine frequently causes hypotension, nausea, and itching.8,9 Although epidural morphine has also been used commonly for postoperative pain management, there is little information about the analgesic effects and side effects of the combination of ropivacaine and morphine. Therefore, this study was designed to assess the analgesic and side effects of a continuous epidural infusion of 0.2% ropivacaine combined with morphine, as compared with the effects of morphine alone or of 0.2% ropivacaine alone, for pain management after lower abdominal surgery.
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Materials and methods |
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All patients were premedicated with oral zopiclone (7.5 mg) 60 min before entering the operating room. In the operating room, an epidural catheter was placed at the Th10–11 or Th11–12 level, and 3 mL of 1% lidocaine with 5 µg·mL–1 epinephrine were administered as a test dose. If there was no evidence of iv or subarachnoid injection five minutes after the test dose, 1.5% lidocaine with 5 µg·mL–1 epinephrine were administered in an initial volume of 6 to 10 mL. The spread of sensory analgesia was assessed using the skin prick method, and a minimum sensory spread from Th6 to L1 was required bilaterally for the patient to remain in the study. General anesthesia was induced with 2 mg·kg–1 iv propofol. Muscle relaxation was achieved by the iv administration of 0.1 mg·kg–1 vecuronium bromide, and the trachea was intubated. Anesthesia was maintained with sevoflurane (1–1.5%) in air (1 L·min–1) and oxygen (1 L·min–1). Additional doses of 5 to 8 mL 1.5% lidocaine with 5 µg·mL–1 epinephrine were administered epidurally at the discretion of the anesthesiologist. Analgesics other than sevoflurane and epidural lidocaine were not administrated during the period of anesthetic management.
After induction of anesthesia, the patients were randomly assigned to one of three groups by using a sealed envelope technique: a combination group, which received a continuous epidural infusion of 0.2% ropivacaine combined with 0.003% morphine; a morphine alone group, which received a continuous epidural infusion of normal saline combined with 0.003% morphine; and a ropivacaine group, which received a continuous epidural infusion of 0.2% ropivacaine. When closing the peritoneum, 6 mL of each solution were administered epidurally and the continuous epidural infusion was started using a disposable pump (Coordech SyrinjectorTM, Daikeniki Co., Osaka, Japan) at the rate of 6 mL·hr–1 for 24 hr. Fifty milligrams of iv flurbiprofen were given as a supplemental analgesic on patient demand. Non-invasive arterial blood pressure, heart rate, oxygen saturation and occurrence of untoward events were recorded at two-hour intervals postoperatively. Hypotension, defined as blood pressure below 90 mmHg, was treated with a vasopressor and/or iv fluid at the discretion of the investigator.
Intensity of postoperative pain was evaluated using the visual analogue scale (VAS) at rest and on coughing. The VAS consisted of a 100-mm horizontal line without gradation and with points marked as "0 mm = no pain" and "100 mm = worst possible pain." The patients were told to indicate how they felt at rest and on coughing by placing a mark perpendicular to the line. Motor blockade of the legs was evaluated using the Bromage scale (0 = no motor block; 1 = inability to flex knees 30°; 2 = inability to flex knees and ankle; 3 = complete motor block). VAS at rest and on coughing and Bromage scale were recorded at two, four, eight, 12, and 24 hr after starting the continuous epidural infusion. The occurrence of itching, nausea, and hypotension, were also noted.
On the basis of preliminary data from our institution in the same surgical population, a power analysis was performed using postoperative pain on coughing as the primary outcome variable. We calculated a sample size so that a between-group mean difference in VAS of 15 mm, with reduced pain scores in the combination group in comparison to the ropivacaine group, would permit a type 1 error rate of one-tailed 
= 0.05, and with the alternate hypothesis, the null hypothesis would be retained with a type error ß = 0.02. This analysis indicated 19 patients would be required in each group. Demographic data are presented as means ± SD. VAS data are presented as medians (25th–75th percentiles). Demographic data, the number of patients receiving supplemental analgesic, and the number of patients with nausea and itching were analyzed using the Chi-square test. VAS scores and Bromage scale were analyzed using the Kruskal-Wallis test followed by Scheffe’s test. P < 0.05 was considered to be statistically significant.
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shows the characteristics of the remaining 58 patients. There were no significant differences in gender ratio, age, height, weight, surgical procedures or total doses of epidural 1.5% lidocaine during surgery among the three groups.
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shows the VAS scores at rest and on coughing. There were significant differences between VAS scores at rest in the combination group and the ropivacaine group at four, eight, 12 and 24 hr after starting the epidural infusion. VAS scores at rest in the morphine group were significantly higher than those in the combination group at two and four hours after starting the epidural infusion but, thereafter, the morphine group showed VAS scores comparable to the combination group. VAS scores on coughing tended to be higher compared to VAS scores at rest in all three groups. VAS scores on coughing in the combination group were significantly lower than those in the ropivacaine group throughout the observation period. The combination group also showed lower VAS scores than the morphine group at two, four and eight hours after starting the epidural infusion.
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). The incidence of itching was significantly increased in the morphine and combination groups compared to the ropivacaine group, so that five patients in the combination group and nine patients in the morphine group complained of itching, while no patient in the ropivacaine group complained of itching. The degree of itch was self-limited, and no medication was required. No hypotension (Table III) or respiratory complications were observed in any of the groups.
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Discussion |
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The epidural infusion of 0.2% ropivacaine at the rate of 10 mL·hr–1 is thought to provide a good balance between analgesia and motor block of the lower limbs for analgesia after abdominal surgery.5,6 However, the incidence of significant motor block 21 hr after surgery is approximately 30 to 63% in patients receiving ropivacaine at the rate of 8 to 14 mL·hr–1.5 With the increasing emphasis on early postoperative ambulation, persistent motor blockade limits the usefulness of the epidural infusion of a local anesthetic. While the epidural infusion of 0.2% ropivacaine at the rate of 6 mL·hr–1 produces less motor block, it is less effective for postoperative analgesia than at the rate of 10 to 14 mL·hr–1.6 Therefore, we selected the rate of 6 mL·hr–1 to reduce the incidence of motor block in our study. However, patients receiving the combination showed a weak but significant motor block two hours after the start of infusion, while patients receiving only one of the drugs did not. It has been shown that epidural morphine does not affect motor function,10 and previous studies showed that the addition of morphine to local anesthetics did not increase the incidence or degree of motor block.11 We cannot explain the reason for the observed increase in the incidence of motor block in patients receiving the combination. However, the Bromage scale remained at 0 four hours after the start of the infusion until the end of the study. Therefore, the motor block observed in the combination group would not be clinically critical.
The incidence of nausea in the three groups was comparable, indicating that not only morphine but also other factors, for example patient-related factors, anxiety, type of surgery and nitrous oxide, contribute to postoperative nausea after major lower abdominal surgery.12 The incidence of itching in the combination group and the morphine group was higher than in the ropivacaine group. We used 0.003% (0.2 mg·hr–1) morphine because this dose of morphine, combined with a low dose of bupivacaine (10 mg·hr–1), has been shown to be effective for relief of postoperative pain at rest and during mobilization from the supine position to the sitting position and also on coughing after elective major abdominal surgery.13 A morphine concentration of less than 0.003% may significantly reduce the incidence of itching. Optimum drug combinations at minimal doses would produce powerful analgesia with lesser side effects. Further study is therefore needed to determine the optimum doses of ropivacaine and morphine in combination.
Although the addition of fentanyl to ropivacaine improves postoperative pain compared to ropivacaine alone,8,9 the combination of fentanyl and ropivacaine frequently causes hypotension in addition to nausea and itching.8,9 On the other hand, hypotension requiring specific treatment did not occur in any of the patients in the present study. Therefore, the combination of epidural morphine and ropivacaine may be more desirable than the combination of epidural fentanyl and ropivacaine.
In conclusion, the combination of epidural 0.2% ropivacaine and 0.003% morphine is more effective than either drug alone for postoperative pain relief after lower abdominal surgery without causing an increase in the incidence of nausea or hypotension, although the incidence of itching in the combination group was higher than that in the ropivacaine alone group.
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Footnotes |
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References |
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2 Reiz S, Haggmark S, Johansson G, Nath S. Cardiotoxicity of ropivacaine–a new amide local anaesthetic agent. Acta Anaesthesiol Scand 1989; 33: 93–8.[Medline]
3 Scott DB, Lee A, Fagan D, Bowler GM, Bloomfield P, Lundh R. Acute toxicity of ropivacaine compared with that of bupivacaine. Anesth Analg 1989; 69: 563–9.
4 Bader AM, Datta S, Flanagan H, Covino BG. Comparison of bupivacaine- and ropivacaine-induced conduction blockade in the isolated rabbit vagus nerve. Anesth Analg 1989; 68: 724–7.
5 Scott DA, Chamely DM, Mooney PH, Deam RK, Mark AH, Hagglof B. Epidural ropivacaine infsion for postoperative analgesia after major lower abdominal surgery–a dose finding study. Anesth Analg 1995; 81: 982–6.[Abstract]
6 Etches RC, Writer WD, Ansley D, et al. Continuous epidural ropivacaine 0.2% for analgesia after lower abdominal surgery. Anesth Analg 1997; 84: 784–90.[Abstract]
7 Berti M, Casati A, Fanelli G, et al. 0.2% ropivacaine with or without fentanyl for patient-controlled epidural analgesia after major abdominal surgery: a double-blind study. J Clin Anesth 2000; 12: 292–7.[Medline]
8 Scott DA, Blake D, Buckland M, et al. A comparison of epidural ropivacaine infusion alone and in combination with 1, 2, and 4 µg/mL fentanyl for seventy-two hours of postoperative analgesia after major abdominal surgery. Anesth Analg 1999; 88: 857–64.
9 Finucane BT, Ganapathy S, Carli F, et al. Prolonged epidural infusions of ropivacaine (2 mg/mL) after colonic surgery: the impact of adding fentanyl. Anesth Analg 2001; 92: 1276–85.
10 Niv D, Rudick V, Chayen MS, David MP. Variations in the effect of epidural morphine in gynecological and obstetric patients. Acta Obstet Gynecol Scand 1983; 62: 455–9.[Medline]
11 Niv D, Rudick V, Golan A, Chayen MS. Augmentation of bupivacaine analgesia in labor by epidural morphine. Obstet Gynecol 1986; 67: 206–9.[Medline]
12 Watcha MF, White PF. Postoperative nausea and vomiting. Its etiology, treatment, and prevention. Anesthesiology 1992; 77: 162–84.[Medline]
13 Dahl JB, Rosenberg J, Hansen BL, Hjortso NC, Kehlet H. Differential analgesic effects of low-dose epidural morphine and morphine-bupivacaine at rest and during mobilization after major abdominal surgery. Anesth Analg 1992; 74: 362–5.
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