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REGIONAL ANESTHESIA AND PAIN MEDICINE

Small-Dose Clonidine Prolongs Postoperative Analgesia After Sciatic-Femoral Nerve Block with 0.75% Ropivacaine for Foot Surgery

Department of Anesthesiology, University of Milan, Milan, Italy

Address correspondence and reprint requests to Dr. A. Casati, Anesthesiology Department, IRCCS H San Raffaele, Via Olgettina 60, 20132 Milan, Italy. Address e-mail to casati.andrea{at}hsr.it

	Abstract

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To evaluate the effects of adding small-dose clonidine to 0.75% ropivacaine during peripheral nerve blocks, 30 ASA physical status I and II patients undergoing hallux valgus repair under combined sciatic-femoral nerve block were randomly allocated in a double-blinded fashion to receive block placement with 30 mL of either 0.75% ropivacaine alone (group Ropivacaine, n = 15) or 0.75% ropivacaine plus 1 µg/kg clonidine (group Ropivacaine-Clonidine, n = 15). Hemodynamic variables, oxygen saturation, and levels of sedation, as well as the time required to achieve surgical block and time to first analgesic request, were recorded by a blinded observer. Time to surgical blockade required 10 min in both groups. Patients in the Ropivacaine-Clonidine group were more sedated than patients in the Ropivacaine group only 10 min after block placement. No differences in oxygen saturation and hemodynamic variables, degree of pain measured at first analgesic request, and consumption of postoperative analgesics were observed between the two groups. The mean time from block placement to first request for pain medication was shorter in group Ropivacaine (13.7 h; 25th–75th percentiles: 11.8–14.5 h) than in group Ropivacaine-Clonidine (16.8 h; 25th–75th percentiles: 13.5–17.8 h) (P = 0.038). We conclude that adding 1 µg/kg clonidine to 0.75% ropivacaine provided a 3-h delay in first request for pain medication after hallux valgus repair, with no clinically relevant side effects.

Implications: This prospective, randomized, double-blinded study demonstrated that, when providing combined sciatic-femoral nerve block for hallux valgus repair, the addition of 1 µg/kg clonidine to 0.75% ropivacaine prolongs the duration of postoperative analgesia by 3 h, with only a slight and short-lived increase in the degree of sedation and no hemodynamic adverse effects.

	Introduction

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Hallux valgus repair is a minor surgical procedure, but it leads to significant pain in the postoperative period (1). For this reason, regional anesthesia with long-acting local anesthetics has been suggested (1–3).

The injection of an agonist along axons has been suggested to improve the nerve block characteristics of local anesthetic solutions through either a local vasoconstriction (4), a facilitation of C fiber blockade from the local anesthetic solution (5), or a spinal action caused by slow retrograde axonal transport or single diffusion along the nerve (6). Moreover, ₂ receptors have been directly isolated on peripheral nerves of the rat (7), whereas in clinical studies, the addition of clonidine to local anesthetic solutions improved peripheral nerve blocks by reducing the onset time, extending postoperative analgesia, and improving the efficacy of nerve block during surgery (8–10).

Ropivacaine is a new long-acting local anesthetic with a favorable profile for peripheral nerve blocks when used at 0.75% or 1% concentrations (2,3,11). However, little is known about the interaction between small-dose clonidine and ropivacaine when used for peripheral nerve blocks.

The aim of this prospective, randomized, double-blinded study was to evaluate the effects of adding 1 µg/kg clonidine to 0.75% ropivacaine during combined sciatic-femoral nerve block for hallux valgus repair.

	Methods

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The study protocol was approved by our hospital ethical committee, and informed consent was obtained from each patient. Thirty ASA physical status I and II patients, scheduled for elective hallux valgus repair under combined sciatic-femoral nerve block, were enrolled in the study. Patients receiving chronic analgesic therapy, as well as those with contraindications to regional anesthesia, severe cardiopulmonary disease, thyroid disease, diabetes, and central or peripheral neuropathies, were excluded.

The study size was calculated to detect a 5-min difference in the time required to achieve adequate surgical anesthesia between the two anesthetic solutions, accepting a one-tailed error of 5%, and a ß error of 10% (12), based on results of a previous study (2).

After an 18-gauge IV cannula had been inserted in the forearm, midazolam 0.05 mg/kg IV was given as premedication 10 min before block placement. Standard monitoring was used throughout the study, including noninvasive arterial blood pressure (B 606; Lohmeier, Munich, Germany), heart rate, and pulse oximetry. The surgical procedure was always performed by using a standard thigh tourniquet inflated 100 mm Hg higher than systolic arterial blood pressure. Hemodynamic variables were measured before block placement (Baseline) and every 5 min until the end of surgery.

By using a sealed envelope technique, patients were randomly allocated to receive sciatic-femoral nerve block with 30 mL of either 0.75% ropivacaine alone (group Ropivacaine, n = 15) or 0.75% ropivacaine plus 1 µg/kg clonidine (group Ropivacaine-Clonidine, n = 15). Sterile syringes with local anesthetic solution were prepared in a double-blinded fashion by one of the authors not involved in further evaluation of the patients. For the femoral block, 12 mL of anesthetic solution was used, and for the sciatic block, 18 mL of the same solution was used. Nerve blocks were performed with the aid of a nerve stimulator (Plexival, Medival, Italy) by using a short-beveled, Teflon^®-coated (DuPont, Wilmington, DE) stimulating needle (Locoplex, Vygon, France) (needle length/diameter were 3.5 cm/25-gauge for femoral nerve block and 12 cm/22-gauge for sciatic nerve block). Stimulation frequency was set at 2 Hz, while the intensity of stimulating current was initially set to deliver 1 mA and gradually decrease to <0.5 mA. Paresthesia was never intentionally sought. As routine at our department, a multiple-injection technique was used, eliciting specific muscular twitches on nerve stimulation to confirm exact needle location (2,3,13,14). First, we performed the femoral nerve block, which was immediately followed by the sciatic nerve block. For both femoral and sciatic nerve blocks, the total volume of anesthetic solution was equally divided among the acceptable twitches.

Sensory and motor blocks on the operated limb were evaluated at 2, 5, 10, 20, and 30 min after the completion of anesthetic injection by an independent, blinded observer. Further measurements were performed until surgical anesthesia was achieved. Sensory block was assessed by using the pinprick test (22-gauge hypodermic needle), and motor block was evaluated by asking the patient to move the ankle against resistance and to elevate the leg with the hip passively flexed. At the same time, arterial blood pressure, heart rate, hemoglobin oxygen saturation, and degree of sedation were also recorded. The degree of sedation was evaluated by using the Observer’s Assessment of Alertness/Sedation scale (15) (see Appendix 1). Clinically relevant hypotension (decrease in systolic arterial blood pressure > 30% of baseline) was treated with etilephrine (2 mg IV), bradycardia (heart rate decrease < 45 bpm) was treated with atropine (0.5 mg IV), and their occurrence was recorded. The time to surgical blockade was defined as the time from the end of anesthetic injection to loss of pinprick sensation on sciatic and femoral nerves distribution with the inability to move the ankle and toes of the operated limb.

Postoperative analgesia consisted of ketoprofen, 100 mg IV as required. Patients were given clear instruction for asking for a first postoperative analgesic as soon as they complained of discomfort caused by pain on the operated foot. When patients asked for the first postoperative pain medication, the degree of pain was measured by using a 100-mm visual analog scale. The time from the end of anesthetic injection to resolution of motor block at the ankle of the operated foot and first request for postoperative analgesic was recorded. At discharge from the orthopedic ward and 3 wk after hospital discharge (at the first routine postoperative orthopedic examination), patients were also evaluated regarding the occurrence of neurological complications.

Statistical analysis was performed by using the program Systat 7.0 (SPSS Inc, Chicago, IL). The Mann-Whitney U-test was used to compare continuous variables, and categorical data were analyzed by using the contingency table analysis with Fisher’s exact test. Duration of postoperative pain relief was also compared by using a log-rank test using the Kaplan-Meier estimation of survival analysis. Unless otherwise indicated, results were presented as median (range) or as number (percentage). A P value 0.05 was considered statistically significant.

	Results

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No differences in age (59 [29–74] yr in group Ropivacaine and 60 [21–74] yr in group Ropivacaine-Clonidine), weight (63 [52–80] kg in group Ropivacaine and 65 [49–86] kg in group Ropivacaine-Clonidine), height (162 [154–172] cm in group Ropivacaine and 165 [155–188] cm in group Ropivacaine-Clonidine), male to female ratio (2 to 13 in group Ropivacaine and 3 to 12 in group Ropivacaine-Clonidine), and ASA physical status were observed between the two groups. Successful surgical anesthesia not requiring analgesic supplementation to complete surgery was reported in 13 patients in each group (86%) (P = not significant). One of the two Ropivacaine-Clonidine patients requiring fentanyl supplementation showed inadequate surgical block as a result of unbearable tourniquet pain and required general anesthesia (fentanyl 0.15 mg and propofol 4 mg · kg^-1 · h^-1) to complete surgery. This patient was then excluded from the analysis.

No differences in the time required to achieve surgical anesthesia were observed between patients receiving only 0.75% ropivacaine (10 [5–20] min) and those receiving the ropivacaine-clonidine mixture (10 [5–30] min). Figure 1 shows the level of sedation measured according to the Observer’s Assessment of Alertness/Sedation scale during the first 30 min after the injection. Ten minutes after block placement, patients in Ropivacaine-Clonidine group were slightly more sedated than those patients receiving only 0.75% ropivacaine. However, no differences were observed at further assessments, and no clinically relevant decrease in oxygen saturation was observed in either group.

View larger version (40K): [in this window] [in a new window]   Figure 1. Sedation scores measured with the Observer’s Assessment Alertness/Sedation scale (OAA/S) before and 5, 10, 20, and 30 min after placing combined sciatic-femoral nerve block with either 0.75% ropivacaine (group Ropivacaine, n = 15) or 0.75% ropivacaine plus 1 µg/kg clonidine (group Ropivacaine-clonidine, n = 15). Patients receiving the ropivacaine-clonidine mixture were more sedated than the Ropivacaine group patients at 5 and 10 min after block placement (P = 0.07 and P = 0.02, respectively).

Resolution of motor block at the ankle of the operated foot required 10 (8–14) h in patients receiving ropivacaine alone as compared with 14 (8.5–22) h in those receiving the ropivacaine-clonidine mixture (P = 0.0016). The degree of pain measured with the visual analog scale at the onset of postsurgical pain was similar in the two groups (group Ropivacaine: 70 [10–100] mm; group Ropivacaine-Clonidine: 51 [10–90] mm). The mean time from block placement to first request for pain medication was shorter in group Ropivacaine (13.7 h; 25th–75th percentiles: 11.8–14.5 h) than in group Ropivacaine-Clonidine (16.8 h; 25th–75th percentiles: 13.5–17.8 h) (P = 0.038), and curves representing the Kaplan-Meier estimation of survival analysis for the first analgesic request were significantly different (P = 0.04) (Figure 2). No differences in postoperative consumption of ketoprofen were observed between patients receiving only 0.75% ropivacaine (100 mg [0–300]) and those receiving the ropivacaine-clonidine mixture (100 mg [0–300]). Four patients in group Ropivacaine-Clonidine (28.5%) did not require postoperative pain medication during the first 24 h after surgery as compared with only one patient (6.6%) in group Ropivacaine; however, the observed difference was not statistically significant (P = 0.17). No complications were reported at the postoperative follow-up.

View larger version (18K): [in this window] [in a new window]   Figure 2. Kaplan-Meier estimation of survival analysis for first request of postoperative pain medication. Percentage of patients not requesting analgesia after combined sciatic-femoral nerve block performed with either 0.75% ropivacaine (group Ropivacaine, n = 15) or 0.75% ropivacaine plus 1 µg/kg clonidine (group Ropivacaine-Clonidine, n = 15). The first postoperative request for ketoprofen constituted the response variable for the Kaplan-Meier survival analysis for the patient concerned. The log-rank curves representing the two studied groups are significantly different (P = 0.04).

	Discussion

Top Abstract Introduction Methods Results Discussion Appendix References

Bernard and Macarie (8), evaluating the effects of adding 30 to 300 µg clonidine to lidocaine for axillary brachial plexus anesthesia, reported that adding clonidine reduced block onset and improved the efficacy of surgical anesthesia. However, in agreement with our findings, other authors demonstrated that neither the onset nor the efficacy of nerve blockade was influenced by adding clonidine (4,16). These differences in the reported effects of small-dose clonidine on onset time and efficacy of nerve block may be explained by differences in the type of nerve block, mixture injected, and technique used to perform the block (single injection versus multiple injections). In fact, a multiple-injection technique was used, which is known to improve both onset time and quality of nerve block (8,13,17,18), and this could have reduced the differences in onset time between the two groups.

Duration of postoperative pain relief after sciatic-femoral nerve block performed with 0.75% ropivacaine alone is similar to findings reported in previous investigations (2,3), whereas small doses clonidine provided a nearly 20% prolongation of postoperative analgesia. Clinical relevance of a three-hour delay in first request for postoperative pain medication might be questioned, because no differences in total ketoprofen consumption or in the number of patients not requesting postoperative analgesics were observed between the two groups (also considering that postoperative pain lasts a few days after this surgical procedure). However, it should also be considered that the small size of the study prevents us from excluding a type two error when evaluating the number of patients not requesting postoperative analgesics during first 24 hours after surgery.

In a dose-finding study evaluating the minimum effective dose of clonidine required to prolong duration of analgesia after axillary brachial plexus block, Singelyn et al. (19) suggested that 0.5 µg/kg clonidine should be recommended, because significant prolongation of analgesia was provided without inducing sedation, hypotension, or bradycardia. Larger doses of clonidine were used in our investigation, but only mild, and short-lasting increases in the degree of sedation were observed 10 minutes after block placement, and no relevant cardiovascular side effects were reported. This may be related to the different type of peripheral nerve block, probably influencing the rate of absorption of the injected anesthetic solutions (20).

A control group receiving parenteral administration of the same dose of clonidine was not considered when designing our investigation; however, it has been widely demonstrated that subcutaneous or IM injection of clonidine was not as effective as the perineural administration (21,22), suggesting that the local anesthetic-prolonging effect of clonidine is probably mediated locally at the peripheral nerve (7). Even though injecting clonidine as the sole analgesic into the brachial plexus sheath did not provide clinically relevant analgesia (23), clonidine has been demonstrated to inhibit the action potential of A and C fibers in desheathed sciatic nerves (24). The ₂-adrenergic receptors activated by clonidine are located on primary afferent terminals, neurons in the superficial laminae of the spinal cord, and in brainstem nuclei implicated in analgesia (21): inhibition of noradrenaline release, mediated by an interaction with ₂-adrenergic presynaptic receptors, could be an alternative explanation for the enhancing effect of the peripheral administration of clonidine (25). Peripheral antinociception induced by clonidine has also been related to an ₂-adrenoceptor mediated local release of enkephalin-like substance (26).

Minor orthopedic procedures, such as hallux valgus repair, often produce significant postoperative pain that can be difficult to control with oral analgesics (1), and peripheral nerve blocks with long-acting local anesthetic have been advocated to improve the quality of postoperative analgesia (1–3). Results of this randomized, double-blinded study demonstrated that adding 1 µg/kg clonidine to 0.75% ropivacaine provided a three-hour delay in first analgesic request postoperatively, with only a light and short-lived increase in the degree of sedation and no hemodynamic adverse effects.

	Appendix

Top Abstract Introduction Methods Results Discussion Appendix References

 

	References

Top Abstract Introduction Methods Results Discussion Appendix 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