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REGIONAL ANESTHESIA AND PAIN MEDICINE

Sedation with Sufentanil and Midazolam Decreases Pain in Patients Undergoing Upper Limb Surgery Under Multiple Nerve Block

Brian P. Kinirons, FFARCSI^*, Hervé Bouaziz, MD, PhD, Xavier Paqueron, MD, Adil Ababou, MD, Céline Jandard, MD, My Maï Cao, MD^§, Marie-Lorraine Bur, MD, Marie-Claire Laxenaire, MD, and Dan Benhamou, MD

*Department of Anesthesiology and Intensive Care, Centre Hospitalier Universitaire de Bicêtre, Le Kremlin Bicêtre Cedex; Department of Anesthesiology and Intensive Care, Hôpital Central, Nancy Cedex; Department of Anesthesiology and Intensive Care, Hôpital Antoine Béclère, Clamart Cedex; §Department of Clinical Epidemiology and Evaluation, Hôpital Marin, Nancy Cedex, France

Address correspondence and reprint requests to Dr. Hervé Bouaziz, Hôpital Central, 54035 Nancy Cedex, France. Address e-mail to h.bouaziz{at}chu-nancy.fr

	Abstract

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Multiple nerve blocks may be painful and a source of discomfort. We assessed the efficacy of sufentanil 5 µg combined with midazolam 1 mg in decreasing pain in outpatients after a midhumeral multiple nerve stimulation technique. Visual analog scores for pain were significantly lower in those patients who received sedation before the block, both at the time of block performance (14 ± 1 vs 27 ± 2 mm, P < 0.0001) and at discharge (11 ± 1 vs 24 ± 2 mm, P < 0.0001). We conclude that the association of sufentanil and midazolam produced minimal sedation while significantly reducing pain experienced by patients undergoing multiple nerve stimulation.

Implications: In a prospective trial of 168 patients, the use of sedation significantly reduced pain during a multiple-nerve stimulation block. The combination of sufentanil and midazolam produced either minimal or no sedation and allowed the performance of the block in awake and cooperative patients. Light sedation may improve patient acceptance of this technique

	Introduction

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Multiple-nerve localization provides a higher success rate than single-injection techniques (1–4). However, this technique requires serial withdrawal and redirection of the stimulating needle and may cause more pain and discomfort than a single-injection block. To decrease pain caused by this multiple nerve stimulation technique, it is common practice to administer IV sedation to patients receiving regional anesthesia. Nevertheless, sedation may obscure the recognition of adverse reactions, and some anesthesiologists believe that sedation should be avoided before performing a regional block.

To assess the efficacy and safety of light sedation on the perception of pain, we conducted a prospective, randomized, double-blinded study of the effect of an IV bolus of midazolam 1 mg combined with sufentanil 5 µg versus placebo in outpatients during upper limb surgery using a midhumeral block.

	Methods

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After institutional review board approval and written informed patient consent, 168 patients undergoing hand and forearm surgery under midhumeral block, were randomly allocated, by computer generated numbers, to one of two groups. Pain scales were explained to the patient during a preoperative visit. Patients were asked to score pain induced by IV cannulation (20-gauge) of a vein in the antecubital fossa by using a visual analog score (VAS) (0 = no pain, 100 = worst imaginable pain). Three minutes before the performance of the midhumeral block, patients received either an IV bolus of a combination of midazolam 1 mg and sufentanil 5 µg in 2 mL of saline (group sedation, n = 81) or 2 mL of saline in the placebo group (group placebo, n = 87). Patients received supplementary oxygen throughout the operative period. All blocks were performed by an anesthesiologist who was experienced in the technique and who was blinded to the drugs injected. A 22-gauge insulated needle connected to a peripheral nerve stimulator (Stimulplex^® Dig; Braun, Melsugen, Germany) was used to identify the following nerves according to their specific motor evoked response as follows: flexion + pronation of the wrist, flexion of the second and third fingers for the median nerve; arm flexion for the musculocutaneous nerve; wrist and finger extension for the radial nerve; and fourth, fifth finger flexion and thumb adduction for the ulnar nerve. Once the needle was inserted subcutaneously, the peripheral nerve stimulator was activated by using a frequency and intensity of 2 Hz and 1.5 mA, respectively. Evoked motor activity in all four nerves at 0.5 mA was required before the injection of local anesthetic solution. In both groups, the local anesthetic used was 40 mL of 1.5% mepivacaine. Five millileters of 2% lidocaine was injected subcutaneously on either side of the brachial artery to anesthetize the medial cutaneous nerve of the arm and forearm. The time to perform the block was defined as time from needle insertion to removal. The level of sedation was measured on a three-point scale (0 = no sedation, 1 = light sedation, patient opens eyes on verbal commands, 2 = deep sedation, patient opens eyes on tactile stimulation). No patient in the study groups received any IV medications during the procedure. To assess recall, all patients were interviewed before discharge by an anesthesiologist who was blinded to the drugs administered, and once more pain scores were recorded. Sedation scores were also measured at discharge.

We hypothesized that sedation before the block would reduce pain in a similar manner as when local anesthetics are applied before venous cannulation. In different studies, the application of EMLA cream and/or the subcutaneous injection of local anesthetics reduced the mean VAS scores of venous cannulation by 17 mm (5). VAS was chosen as the primary criteria for analysis. The number of patients required was calculated based on a power of 90%, an risk of 0.05, a standard deviation of 30 mm, and an expected difference between groups of 17 mm. Standard deviation (assumed equal between groups) and expected difference originated from previously published values (6). BMDP Statistical software package (Cork, Ireland) was used for statistical analysis. Differences in sex, anatomical site of surgery, and sedation scores were compared by using ² test. Student’s t-tests was used to compare the time to perform the midhumeral block and VAS values for pain and discomfort between the two groups. Bonferroni’s correction was used for multiple comparisons. P < 0.05 was considered statistically significant. Data were expressed as mean ± SEM.

	Results

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Both groups were similar with respect to age, ASA physical status, time taken to perform midhumeral block, and the type of surgery performed. Groups were dissimilar with respect to sex, with a higher proportion of men in the sedated group (Table 1). VAS pain scores for the initial venipuncture were similar in both groups, whereas the VAS scores for pain during performance of the block were significantly lower in the sedation group as compared with the placebo group (14 ± 1 vs 27 ± 2 mm, P < 0.0001) (Table 2). Before discharge, the VAS scores for the pain induced by the needle puncture for the regional block were again significantly lower in the sedated group (11 ± 1 vs 24 ± 2 mm, P < 0.0001).

	Discussion

Top Abstract Introduction Methods Results Discussion References

 
This study demonstrated that midazolam 1 mg combined with sufentanil 5 µg significantly reduced pain scores with no or minor sedation, thus allowing the performance of the midhumeral block in awake and cooperative patients.

A patient’s previous experience with regional anesthesia is a significant factor in acceptance of a regional technique for future surgery. Fear of needle puncture has been cited as a major cause for patient dissatisfaction or refusal of regional anesthesia. De Andrès et al. (7), in a review of patient satisfaction after regional anesthesia, reported that needle puncture was the greatest negative factor associated with the technique, and that pain after needle puncture was the most commonly reported complication. Their findings were confirmed by Gajraj et al. (8), who in a survey of obstetrical patients, cited fear of backache and needle puncture as the most common reasons for refusing regional anesthesia.

Multiple nerve stimulation in regional blockade is associated with reduced requirement for supplementary blocks and greater success rate than the conventional single injection technique (1–4). Nevertheless, the time required to complete a multiple nerve localization is longer (2), and thus muscle contractions and needle movements experienced during its performance may increase both patient discomfort and pain. Fanelli et al. (9), in a survey of 3996 patients who underwent multiple nerve injection technique for upper and lower limb blocks, demonstrated that, despite an overall success rate of 94%, only 74% of patients would request the same technique if they required similar surgery in the future. Discomfort during block placement was cited as the main factor in future patient refusal. They advocated the use of analgesic drugs in all patients undergoing multiple nerve stimulation block. Based on the above evidence, IV sedatives are frequently administrated before the performance of a multiple nerve stimulation regional block to decrease patient pain and/or discomfort and improve patient acceptance. Nevertheless, this practice has never been evaluated with respect to its safety or efficacy.

Although factors contributing to pain scores for venous cannulation vary widely, the VAS scores reported in our study are less than those reported in previous studies (10–12). This may be explained by the fact that both the site of needle insertion (antecubital fossa) and the size of the needle (20-gauge) were different from previous reports. There were no statistical differences in pain scores reported after venipuncture between the two groups.

Our study demonstrated that, in nonsedated patients (placebo group), the pain during performance of the block was 2-fold of that experienced during venipuncture. As most practitioners would accept that the pain of venipuncture should be reduced by local anesthesia, it would appear that prevention of regional anesthesia-induced pain is even more necessary. In contrast, pain scores at the time of the block were significantly lower in the sedated group and comparable to that experienced with venipuncture. Pain scores at discharge were similar to that measured immediately after the block in both groups. This finding was unexpected, because we anticipated an impairment of recall for pain at discharge in the group of patients that received midazolam/sufentanil, but not in the placebo group (13–15).

Although we did not perform a sedation dose response assessment in this study, the sedatives combination and doses used represent current practice in our institutes. Furthermore, the opioid and benzodiazepine combination was chosen because of its proven synergistic effect (16). Although the risks of excess sedation in regional anesthesia have been previously reported (17), the combination of midazolam 1 mg and sufentanil 5 µg induced a light sedation (Grade 1) in only 11% of patients in the sedated group, allowing the performance of a regional block on awake and cooperative patients able to inform the anesthesiologist of paresthesia or pain during the injection of the local anesthetic. Furthermore, no patient had amnesia of either the block performance or of surgery at discharge. This result differs from that of Fletcher et al. (18), who observed amnesia in 66% of patients premedicated with midazolam who underwent spinal anesthesia. This difference may be explained by the larger dose of midazolam (3.4 mg) used in their study. Our study suggests that a dose of midazolam as small as 1 mg does not induce amnesia, even when combined with sufentanil 5 µg. As previously reported, the use of sedation did not delay discharge of any patient in the sedation group (19). The time to perform the midhumeral block could also theoretically have altered the patient’s feelings of pain and discomfort. In the present study, the median time to perform block was similar for both groups. All patients were discharged four to five hours after performance of the block.

There were more men in the sedated group. This sex imbalance accounts for the differences in weight and height between the two groups. This difference could have induced a difference in pain scores; however, we were unable to demonstrate any statistical relationship between sex and pain scores.

As this study did not attempt to measure patient satisfaction, it remains to be demonstrated that patients who experience less pain are more willing to undergo a subsequent regional procedure. This should be the basis of future studies.

Although we agree with Fanelli et al. (9) that the role of needle movement may be important in patient acceptance of this technique, we do not believe that all patients require sedation. Moore et al. (20) demonstrated that premedication with fentanyl and midazolam reduced the local anesthetic toxicity symptoms in patients injected with IV lidocaine. We would advocate sedation in those patients who are anxious or who demonstrate needle phobia, trauma patients in whom multi-nerve stimulation may be particularly painful, and in teaching cases where, because of the inexperience of the anesthetist, the performance of the block may be prolonged.

In conclusion, the present study suggests that multiple nerve stimulation blocks are painful. Nevertheless, light IV sedation with midazolam 1 mg and sufentanil 5 µg provides satisfactory pain relief, without altering consciousness, thus allowing its safe use for ambulatory anesthesia.

	Acknowledgments

 
Authors would like to thank Dr. J. X. Mazoit for his assistance in reviewing this article.

	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