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* Departments of Anesthesiology and
Orthopedics, Baystate Medical Center and the Tufts University School of Medicine, Springfield, Massachusetts
Address correspondence and reprint requests to Scott S. Reuben, MD, Department of Anesthesiology, Baystate Medical Center, 759 Chestnut St., Springfield, MA 01199. Address e-mail to scott.reuben{at}bhs.org
| Abstract |
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2 agonist, and morphine, an opioid agonist, provide enhanced patient analgesia after arthroscopic knee surgery when administered via the intraarticular (IA) route. Clonidine potentiates morphine analgesia in the animal model. We designed this study to determine whether clonidine or morphine results in better analgesia and whether their combination would provide superior analgesia to either drug alone. We evaluated 60 patients undergoing arthroscopic knee meniscus repair under local anesthesia with sedation. After surgery, patients were randomized into four IA groups: Group B received 30 mL 0.25% bupivacaine; Group BC received 30 mL 0.25% bupivacaine and clonidine 1 µg/kg; Group BM received 30 mL 0.25% bupivacaine and morphine 3 mg; and Group BCM received 30 mL 0.25% bupivacaine, clonidine 1 µg/kg, and morphine 3 mg. This study revealed a significant benefit from the individual IA administration of both clonidine and morphine. The combination of these drugs resulted in decreased postoperative pain and analgesic use, as well as an increased analgesic duration compared with either drug alone. We conclude that IA clonidine and morphine improved comfort compared with either drug alone in patients undergoing knee arthroscopy. Implications: The intraarticular administration of both clonidine and morphine along with bupivacaine improves postoperative analgesia compared with either drug alone. There was an increased time to first analgesic request, decreased need for postoperative analgesics, and lower pain scores after arthroscopic knee surgery.
| Introduction |
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| Methods |
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After placement of routine monitors, patients received 30 mL IA bupivacaine 0.25% for their anesthetic. IV sedation was achieved with propofol (10100 µg · kg-1 · min-1) and midazolam (13 mg). Narcotics were not a component of the intraoperative sedation. After the surgical procedure, patients were assigned to one of four treatment groups in a double-blinded, randomized manner: Group B (IA bupivacaine) received 30 mL 0.25% bupivacaine; Group BC (IA clonidine) received 30 mL 0.25% bupivacaine and clonidine 1 µg/kg; Group BM (IA morphine) received 30 mL 0.25% bupivacaine and morphine 3 mg; and Group BCM (IA clonidine/morphine) received 30 mL 0.25% bupivacaine, clonidine 1 µg/kg, and morphine 3 mg.
Pain scores both at rest and with movement were recorded by a blinded observer in the postanesthesia care unit (PACU) at 1 and 2 h after injection of the study drug. A 10-cm linear visual analog scale (VAS) was used for this measurement with 0 = no pain and 10 = the worse imaginable pain. Patients received IV fentanyl (25 µg every 5 min as needed) in the PACU.
On discharge from the hospital, patients were instructed to take one acetaminophen 325 mg/oxycodone 5 mg (Percocet) every 3 h as needed for pain. The first time they required additional opioid analgesia (either IV fentanyl or oral analgesics) and the total analgesic requirement during the initial 24 h after surgery were documented (patients were contacted by telephone the following day). In addition, patients recorded their VAS pain scores both at rest and with movement 24 h after surgery. Pain scores at 24 h were returned to the surgeon during their follow-up visit. Analgesic duration was considered as the time from IA injection of the study drug to the first requirement of supplemental opioid analgesics.
Patients were discharged when they were oriented to time and place, were able to void, had stable vital signs, and could ambulate with the assistance of crutches. Discharge time was classified as the time from the end of surgery until the patients met the discharge criteria.
Demographic data were analyzed by using analysis of variance. Duration of procedure, time to discharge, analgesic duration, pain scores, and amount of postoperative analgesics were analyzed by using the Kruskal-Wallis test. When a significant result was obtained, Wilcoxons signed rank test was performed to determine significance between groups; a Bonferroni adjustment was made for multiple comparisons. Significance was determined at the P < 0.05 level. The following assumptions were made for the power analysis performed before the investigation: 1) for the pain scores, a 50% difference in pain scores; 2) for the analgesic consumption, a difference of two pills per 24 h; 3) for the time to first analgesic, a difference of 3 h. With these assumptions, a power of 90%, and an
of 0.05 of 6 (because there are six possible comparisons between the four groups), the pain score comparison required the largest number of patients. This figure was 15 patients per group. The power analysis performed at the conclusion of the study, by using an
of 0.05 of 6 and given 15 patients per group, revealed a power greater than 90%.
| Results |
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20% baseline), hypoxemia (SpO2
90%), or bradycardia (heart rate
60 bpm). No patient complained of sedation or other side effects.
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| Discussion |
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Several previous studies in the animal model have suggested a synergistic interaction between clonidine and morphine with respect to antinociception. Spaulding et al. (7) revealed that the antinociceptive activity of systemically administered clonidine was found to potentiate morphine analgesia in the rat tail flick assay. In this study, clonidines agonist activity was not reversed by naloxone, suggesting a mechanism of action independent of opioid receptor affinity. Murata et al. (12) also revealed that systemically administered clonidine and morphine have synergistic analgesic effects. These investigators demonstrated that subtherapeutic doses of clonidine and morphine by themselves were unable to elicit antinociceptive activity; however, their combination inhibited responses of wide dynamic-range neurons to thermal nociception. Ossipov et al. (13) and Wilcox et al. (14) reported the potentiation of clonidine and morphine when administered via the intrathecal route in the rat tail flick model. Drasner and Fields (15) demonstrated that systemic morphine and intrathecal clonidine also have synergistic antinociceptive activity in the same animal model. By using a more rigorous means to examine drug-drug interactions, Ossipov et al. (16) performed an isobolographic analysis of the dose-response curves of fixed ratios of morphine and clonidine. This study substantiated the reports that intrathecally administered morphine and clonidine act in a synergistic fashion. In addition, these authors revealed that the IV administration of these two drugs may be either additive or supraadditive, depending on the ratio of clonidine to morphine and the test used.
There have been no studies performed examining the antinociceptive effect of clonidine and morphine administered via the IA route in the animal model. Gentili et al (8). were the first investigators to study the analgesic effects of morphine and clonidine in humans when used alone and in combination after arthroscopic knee surgery. In this study, both clonidine 150 µg and morphine 2 mg resulted in equivocal analgesia, whereas the combination failed to demonstrate an enhanced analgesic effect. Similarly, we failed to demonstrate any significant difference in the analgesic efficacy between either IA morphine 3 mg or clonidine 1 µg/kg. However, at these doses, we revealed a significant analgesic benefit from the combination of these two drugs after arthroscopic meniscectomy. We used a smaller dose of clonidine in our study because when we previously administered IA clonidine doses
2 µg/kg, many of the patients experienced excessive sedation and hypotension. Likewise, Gentili et al. (8) reported either hypotension or bradycardia in 20% of the patients who received 150 µg (approximately 2 µg/kg) of IA clonidine.
It is possible that the different ratio of clonidine to morphine we used may have accounted for the observed difference in analgesic efficacy, as suggested by Ossipov et al. (16). We believe the more likely explanation is the result of including a more painful surgical procedure (meniscectomy) in our study group rather than a less painful procedure (diagnostic arthroscopy). In the study by Gentili et al. (8), patients reported very low postoperative pain scores (mean VAS
3) at all time intervals. In addition, >50% of the patients required no postoperative analgesics for the entire study period. Under these circumstances, sufficient analgesia was already achieved with either drug alone, thus making it difficult to detect a difference in analgesic efficacy from the combination. In contrast, we studied a more painful surgical procedure in which all patients required postoperative analgesics during the 24 h study period. In addition, we evaluated pain both at rest and with movement, which is a more sensitive measurement of analgesic efficacy.
In conclusion, we have shown that the IA administration of both clonidine and morphine, along with bupivacaine, improves postoperative analgesia compared with either drug alone. There was an increased time to first analgesic request, decreased need for postoperative analgesics, and lower pain scores after arthroscopic knee surgery.
| Footnotes |
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| References |
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