Journal of Clinical Anesthesia (2014) xx, xxx–xxx
Original Contribution
Effective low dosage of mepivacaine in ultrasound-guided axillary nerve block: a double-blinded, randomized clinical trial of efficacy in patients undergoing distal upper extremity surgery☆ Samuel Perov MD (Clinical Professor)a,b,⁎, Pranav Patel MD (Staff Anesthesiologist) b , Sanjeev Kumar MD (Staff Anesthesiologist)b, George M. McKelvey PhD (Research Associate)c, Elie Chidiac MD (Assistant Professor)b, Faisal Motlani MD (Staff Anesthesiologist)b a
Department of Anesthesiology, Wayne State University/Detroit Receiving Hospital, Detroit, MI 48201, USA Department of Anesthesiology, Wayne State University/Detroit Medical Center, Detroit, MI 48201 USA c Department of Anesthesiology, Detroit Medical Center, Detroit, MI 48201 USA b
Received 19 December 2012; revised 31 October 2013; accepted 5 November 2013
Keywords: Axillary plexus block; Ultrasound-guided; Functional block; Mepivacaine; Regional anesthesia; Surgical block
Abstract Study Objective: To evaluate two low-dose volumes (20 mL or 30 mL) of 1.5% mepivacaine solution used for ultrasound-guided axillary blockade for outpatients undergoing distal upper limb surgery. Design: Prospective, double-blinded randomized study. Setting: Outpatient surgical setting of a university-affiliated hospital. Patients: 64 adult, ASA physical status 1, 2, and 3 patients, aged 28-46 years, scheduled for upper limb surgery. Interventions: Patients were randomized to two groups to receive either 20 mL of 1.5% mepivacaine solution (n=31) or 30 mL of 1.5% mepivacaine solution (n=33) for ultrasound-guided axillary plexus blockade. Measurements: Block duration, proportion of surgical and functional successful blocks, onset of sensory and motor blockade measured from 0 to 30 minutes following final needle extraction, total amount of preoperative sedative (midazolam), and intraoperative propofol administered were recorded. Main Results: Following axillary plexus blockade, neither patient group showed any statistically significant difference in the percentage of functionally successful blockade (30 mL, 100%: 20 mL, 97%; P = 0.48), surgically successful blockade (30 mL, 100%; 20 mL, 94%; P = 0.23), cumulative sensory or motor blockade surgical time, block performance time, preoperative midazolam use, or intraoperative propofol use. Conclusion: Low volumes (30 mL or 20 mL) of 1.5% mepivacaine provides satisfactory anesthesia for ambulatory distal upper limb surgery with no significant difference in clinical outcomes. © 2014 Elsevier Inc. All rights reserved.
☆ This study was performed at the Detroit Medical Center, Detroit, Michigan, USA. ⁎ Correspondence: Samuel Perov, MD, Department of Anesthesiology, Detroit Receiving Hospital/Wayne State University, 4201 St. Antoine, Detroit, MI, 48201, USA. Tel: 313 745-2872; fax: 313 993-7729. E-mail address: [email protected] (S. Perov).
http://dx.doi.org/10.1016/j.jclinane.2013.11.016 0952-8180/© 2014 Elsevier Inc. All rights reserved.
2
1. Introduction The use of ultrasonography as an adjunct to regional anesthesia has increased significantly [1]. Brachial plexus blockade by an axillary approach is amenable to the use of ultrasound guidance. Real-time sonography of nerve structures ensures an optimal distribution of the block solution. When compared with other methods of nerve localization, sonography decreases failure rate [2,3], procedure time [4,5], and the onset time for blockade [6,7]. Furthermore, the use of ultrasound for peripheral nerve blockade demonstrates decreased procedure-related complications such as nerve injury and unintentional vascular puncture [8,9]. Traditional axillary nerve block techniques relying on surface anatomical landmarks require large volumes of local anesthetic, generally 40 mL and greater [10,11]. Local anesthetic concentration and volume significantly affect nerve block effects [12,13]. A local anesthetic shows large variations in analgesic effect depending on the infusion rate and bolus amount [14]. Using the increased accuracy offered by ultrasound, some studies have shown that lower volumes of local anesthetic can yield successful axillary plexus blockade [1,15–17] and interscalene brachial plexus block [18]. With smaller volumes of local anesthetic observed to be clinically effective, the tradition of using large volumes of local anesthetic for axillary blocks, even without ultrasound, may be unwarranted. Institutionally, 30 mL of a 1.5% solution of mepivacaine for axillary plexus blockade is clinically the most common volume we use. Therefore, in this study we used a 30 mL volume as the standard treatment to compare with 20 mL of a 1.5% solution of mepivacaine. Although recent investigations support using a low volume of local anesthetic for brachial plexus blockade [18], there is a lack of outcome data from blinded randomized trials. The primary objective of this study was to evaluate two different volumes of local anesthetic for axillary blockade: 1) 30 mL or 2) 20 mL. A 1.5% solution of mepivacaine was used due to its widespread clinical use in axillary blocks, which is secondary to rapid onset of action, intermediate duration of effect, and relative low cost. The primary outcome was block success rate for outpatients undergoing distal upper limb surgery. Secondary objectives included comparing the two volumes with respect to time required to perform the block and onset of sensory and motor blockade.
S. Perov et al. surgery in an outpatient setting. After giving their written, informed consent, patients were randomly assigned using a computerized number generator to receive either 20 mL (n=31) or 30 mL (n=33) of a 1.5% mepivacaine solution for axillary plexus blockade. All block placements used standard medical protocol. Nerve localization was performed using a GE LOGIQe ultrasound machine (GE Medical Systems, Milwaukee, WI, USA), with a 12L-RS transducer (42 mm x 7 mm footprint, 5-13 MHz). On identification of the axillary neurovascular bundle, a 22-gauge x 50 mm poly medic UPC electric stimulation needle was inserted and advanced along the longitudinal axis of the ultrasound transducer to visualize the entire shaft and tip. A peri-arterial injection of 1.5% mepivacaine near all the individual nerve sheaths was performed after negative aspiration, with the endpoint being the circumferential “donut sign” spread around the artery. Then the musculocutaneous nerve was identified and 1.5% mepivacaine injected around the nerve. Depending on the patient group allocation, there was infiltration of either 20 mL or 30 mL of 1.5% mepivacaine. For the group receiving 20 mL, 15 of the total 20 mL was spread around the axillary artery and 5 mL spread around the musculocutaneous nerve. For the group receiving 30 mL, 20 of the total 30 mL was spread around the axillary artery with 10 mL spread around the musculocutaneous nerve. By instituting this injection technique, there is extrapolation to non-ultrasound-guided axillary blocks. For preblock sedation all subjects were administered b 0.8 mg/kg of midazolam with no administration of preoperative opioids. All block procedure times were less than 10 minutes in duration. All subjects consented to light intraoperative sedation.
2.1. Inclusion criteria All subjects recruited into the study were patients undergoing forearm, wrist, or hand surgery in an outpatient setting. Other attributes were ASA physical status 1, 2, or 3; body mass index b 35 kg/m2, and age between 18 and 89 years. All subjects had no history of stroke, diabetes, anxiety disorder, obstructive sleep apnea, previous surgery or scarring in the axillary to elbow area, neurological impairment of either upper extremity, allergies to local anesthesia, coagulopathy, infection at site of block, chronic opioid therapy for chronic pain, or casts or dressing on the limb that would impair assessment of blocks.
2.2. Data collection
2. Methods and materials The current study had institutional review board approval and was registered at ClinicalTrials.gov NCT01485653. This study was a prospective, double-blinded, randomized trial of 64 patients recruited from the Detroit Receiving Hospital, Detroit, MI. All participating patients underwent upper limb
Preoperative variables, including demographics, ASA physical status, height, weight, surgical procedure, location of procedure (hand, wrist, forearm), sedation used in the preoperative holding area, amount of sedation used, block start and end time (duration of time taken between needle insertion and extraction), onset of sensory blockade, and onset of motor blockade were all recorded.
Low mepivacaine dose in US-guided nerve block Intraoperatively, conversion to general anesthesia, use of local anesthesia intraoperatively, total amount of propofol administered, surgical incision time, and surgery end times were recorded. Postoperative data included complications related to axillary block and discharge criteria met.
2.3. Block assessment An examiner who was blinded to the volume of injectate used for the axillary plexus block evaluated the onset of sensory and motor blockade and assessed whether the block was functionally successful and surgically successful.
2.4. Onset of sensory blockade This measure was examined every 5 minutes following needle extraction with the use of a blunt needle at 4 specific anatomic locations corresponding to radial, ulnar, median, and musculocutaneous distributions, and compared with the contralateral side using the same stimulus (normal pinprick sharp, 3; pinprick felt but not as sharp, 2; pressure felt but no pinprick felt, 1; no sensation at all, 0).
2.5. Onset of motor blockade This block was examined every 5 minutes following needle extraction at 4 anatomical locations (wrist flexion: median nerve; wrist extension: radial nerve; abduction of fifth finger or straight finger adduction: ulnar nerve; elbow flexion (with forearm supinated): musculocutaneous nerve. Normal strength, 3; decreased strength but moves against gravity or some resistance, 2; no movement against gravity or twitch, 1; no movement at all, 0).
2.6. Definitions of successful block Functional successful block was a sensory score of 0 - 1 in all 4 territories and a motor score of 0 - 1 in 3 of 4 territories within 30 minutes of needle extraction. A successful block required no intraoperative supplemental local anesthetic, light sedation b 25 μg/kg/min propofol, and absence of general anesthesia.
3 study groups on proportional differences were examined using a nonparametric Fisher’s Exact Chi-square test when applied to 2 x 2 and 2 x 3 tables. Statistical significance was set at a P-value ≤ 0.05. All continuous data are expressed as means ± standard deviation with 95% CIs [lower -upper]. All statistical procedures were performed using SPSS software (version 18.0; SPSS, Chicago, IL, USA). A binary outcome, non-inferiority power analysis based on a rate of 99% successful functional and surgical axillary plexus block for both anesthetic volumes (30 mL and 20 mL) concluded that 30 participants were necessary to achieve 80% power with a P-value b 0.05 (http://www. sealedenvelope.com/power/binary-noninferior/). These sample numbers determine the upper limit of a one-sided 95% CI excluding a difference in favor of the standard treatment (30 mL of mepivacaine) of more than 6.5% (noninferiority limit; d; http://www.sealedenvelope.com/power/ binary-noninferior/).
3. Results Six of the initial 70 patients recruited from data analysis were excluded due to incomplete data collection. Data from 64 subjects were analyzed in the two patient groups, 20 mL of mepivacaine (n=31) and 30 mL of mepivacaine (n=33). Demographic data, clinical characteristics, and surgical time were compared between the two groups (Table 1). Two patients necessitated conversion to general anesthesia, both in the 20mL group. One of the two patients had a functionally successful block as defined by our criteria. No patients required supplementation of block intraoperatively. No patients required more than 25 μg/kg/min of propofol infusion for light sedation intraoperatively. The median block performance time was 330 seconds for the 20 mL group and 342 seconds for the 30 mL group (Table 1). By 25 minutes following the axillary block, 97% of patients in both groups had attained onset of functionally significant sensory and motor blockade (Table 1). There were no reported adverse events relating to the block, and all patient discharge occurred on the same day of surgery.
4. Discussion 2.7. Statistics An unpaired Student’s t-test procedure (two-sample assuming equal variances, two-tail significance; P b 0.05, 95% confidence interval [CI]) was performed to examine mean differences between the two study groups on all continuously scaled variables. Repeated-measures analysis of variance was used to measure statistical differences for motor and sensory nerve block scores during the 30-minute assessment. Assumptions of normality and/or homogeneity of variance were checked and verified. Comparisons between
In this randomized, blinded study, ultrasound-guided axillary plexus blockade using 20 mL or 30 mL of 1.5% mepivacaine showed no statistically significant difference in operative data or block outcomes for patients undergoing distal upper limb surgery in an outpatient setting. By sonographically visualizing the axillary neurovascular anatomy in real time, the accuracy of needle placement and subsequent deposition and spread of local anesthetic is more precise. As a result, block success rate is improved and lower dose of local anesthetic is required [3,19]. Furthermore,
4
S. Perov et al. Table 1
Patient demographics, operative requirements, and study outcome parameters
Patient demographics
age (yrs) gender (M/F) ASA physical status (1 / 2 / 3) weight (kg) height (cm) surgical time (min) block performance time (sec) Operative data preop midazolam (mg) intraop propofol (μg/kg/min) Block outcome functional successful blocks (%) surgical successful blocks (%) peripheral nerve supplementation (%) conversion to general anesthesia (%) Sensory nerve block score 5 min 10 min 15 min 20 min 25 min 30 min Motor nerve block score 5 min 10 min 15 min 20 min 25 min 30 min
Mepivacaine 1.5% 20 mL (n=31)
30 mL (n=33)
35 [28-42] 14/17 6 / 23 / 2 80 [69-81] 169 [164-174] 34 [9-54] 330 [300-360]
38 [31-46] 18/15 1 / 27 / 5 82 [71-93] 165 [160-171] 31 [19-43] 342 [318-367]
20 mL (n=31)
30 mL (n=33)
P-value
2.5 [1.8-3.2] 10.2 [5.9-14.7]
3.2 [2.3-4.1] 7.2 [2.9-11.6]
0.06 0.12
20 mL (n=31)
30 mL (n=33)
P-value
97% (30/31) 94% (29/31) 0% (0/31) 6% (2/31)
100% (33/33) 100% (33/33) 0% (0/33) 0% (0/33)
0.48 0.23 0.99 0.23
20 mL (n=31)
30 mL (n=33)
P-value all 0.99
7.5 [6.4-8.6] 3.7 [2.6-4.8] 1.5 [0.6-2.5] 1.0 [0.2-1.9] 0.8 [0.6-0.9] 0.7 [0.5-0.8]
7.2 [6.1-8.3] 3.6 [2.4-4.8] 1.5 [0.6-2.5] 0.8 [0.2-1.5] 0.6 [0.4-0.8] 0.6 [0.5-0.8]
20 mL (n=31)
30 mL (n=33)
9.8 [8.9-10.7] 7.0 [6.0-8.0] 3.6 [2.3-4.8] 2.1 [0.9-3.4] 1.6 [0.6-2.6] 1.4 [0.4-2.4]
9.7 [8.8-10.6] 7.0 [6.0-8.0] 3.6 [2.3-4.8] 2.1 [0.9-3.3] 1.5 [0.4-2.6] 1.2 [0.3-2.1]
P-value all 0.99
Data are means ± SD with 95% confidence intervals [lower - upper]. Functional successful block=sensory score of 0-1 in all 4 nerve territories, and motor score of 0-1 in 3 of 4 territories within 30 minutes of needle extraction. Surgical successful block=no required intraoperative (intraop) supplemental local anesthetic, light sedation b 25 μg/kg/min propofol, and absence of general anesthesia. Scores for each measured time point=summation of scores from each of the 4 nerves/anatomical location. Sensory nerve block score=normal pinprick sharp, 3; pinprick felt but not as sharp, 2; pressure felt but no pinprick felt, 1; no sensation at all, 0. Motor nerve block score=normal strength, 3; decreased strength or some resistance, 2; no movement against gravity or twitch, 1; no movement at all, 0. preop=preoperative.
fewer injections result in shorter procedure times and less risk of injury [20]. A potential complication of regional anesthesia is the inadvertent intravascular injection of local anesthetic. Although infrequent, this event can lead to life-threatening complications such as seizures and cardiac arrhythmias. Since the toxic effect from local anesthetics is likely dosedependent [21], reducing the volume of local anesthetic injectate is a worthwhile endeavor. Reduction in local anesthetic volume by 50% may be of value in improving the safety profile of the axillary plexus block. A limitation of this study was that measurement of the onset of sensory and motor blockade for both groups was
made in 5-minute increments. As such, exact times for these variables could not be identified. Unavoidable variability in this study also occurred in terms of needle direction during the peri-arterial injection of the ulnar, radial, and medial nerves in order to ensure adequate spread of local anesthetic, and to obtain the sonographic endpoint of the “donut sign”. O’Donnell and colleagues have demonstrated successful axillary brachial plexus block by injecting volumes as low as one mL of 2% lidocaine per individual nerve [17]. However, this methodology necessitates sonographic guidance that is not a feasible option at all institutions. By injecting in a peri-arterial fashion, these results may be applicable to axillary blocks performed using a transarterial approach.
Low mepivacaine dose in US-guided nerve block In conclusion, real-time ultrasound-guided axillary plexus block with 20 mL or 30 mL of 1.5% mepivacaine provides satisfactory anesthesia for ambulatory distal limb surgery with no significant statistical or clinical difference in outcomes between both volumes. Given that any potential toxic effect from local anesthetics is dose-dependent [21], reducing the volume of local anesthetic injectate will improve the safety profile of the axillary plexus block without affecting clinical efficacy.
5
[9] [10]
[11]
[12]
Acknowledgments [13]
The authors wish to thank Drs. Ryan Guffey, MD, and Gokul Toshniwal, MD, for their technical assistance during this study.
References [1] Harper GK, Stafford MA, Hill DA. Minimum volume of local anaesthetic required to surround each of the constituent nerves of the axillary brachial plexus, using ultrasound guidance: a pilot study. Br J Anaesth 2010;104:633-6. [2] Sites BD, Beach ML, Spence BC, et al. Ultrasound guidance improves the success rate of a perivascular axillary plexus block. Acta Anaesthesiol Scand 2006;50:678-84. [3] Chan VW, Perlas A, McCartney CJ, Brull R, Xu D, Abbas S. Ultrasound guidance improves success rate of axillary brachial plexus block. Can J Anaesth 2007;54:176-82. [4] Williams SR, Chouinard P, Arcand G, et al. Ultrasound guidance speeds execution and improves the quality of supraclavicular block. Anesth Analg 2003;97:1518-23. [5] Spence BC, Sites BD, Beach ML. Ultrasound-guided musculocutaneous nerve block: a description of a novel technique. Reg Anesth Pain Med 2005;30:198-201. [6] Marhofer P, Sitzwohl C, Greher M, Kapral S. Ultrasound guidance for infraclavicular brachial plexus anaesthesia in children. Anaesthesia 2004;59:642-6. [7] Sandhu NS, Capan LM. Ultrasound guided infraclavicular brachial plexus block. Br J Anaesth 2002;89:254-9. [8] Stan TC, Krantz MA, Solomon DL, Poulos JG, Chaouki K. The incidence of neurovascular complications following axillary brachial
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plexus block using a transarterial approach. A prospective study of 1,000 consecutive patients. Reg Anesth 1995;20:486-92. Ben-David B, Stahl S. Axillary block complicated by hematoma and radial nerve injury. Reg Anesth Pain Med 1999;24:264-6. Casati A, Danelli G, Baciarello M, et al. A prospective, randomized comparison between ultrasound and nerve stimulation guidance for multile injection axillary brachial plexus block. Anesthesiology 2007; 106:992-6. McCartney CJ, Brull R, Chan VW, et al. Early but no long-term benefit of regional compared with general anesthesia for ambulatory hand surgery. Anesthesiology 2004;101:461-7. Ilfeld BM, Le LT, Ramjohn J, et al; PAINfRE™ Investigators. The effects of local anesthetic concentration and dose on continuous infraclavicular nerve blocks: a multicenter, randomized, observermasked, controlled study. Anesth Analg 2009;108:345-50. Le LT, Loland VJ, Mariano ER, et al; PAINfRE Investigators. Effects of local anesthetic concentration and dose on continuous interscalene nerve blocks: a dual-center, randomized, observer-masked, controlled study. Reg Anesth Pain Med 2008;33:518-25. Ilfeld BM, Morey TE, Enneking FK. Infraclavicular perineural local anesthetic infusion: a comparison of three dosing regimens for postoperative analgesia. Anesthesiology 2004;100:395-402. O'Donnell BD, Ryan H, O'Sullivan O, Iohom G. Ultrasound-guided axillary brachial plexus block with 20 milliliters local anesthetic mixture versus general anesthesia for upper limb trauma surgery: an observer-blinded, prospective, randomized, controlled trial. Anesth Analg 2009;109:279-83. O'Donnell BD, Iohom G. An estimation of the minimum effective anesthetic volume of 2% lidocaine in ultrasound-guided axillary brachial plexus block. Anesthesiology 2009;111:25-9. O’Donnell BD, Riordan J, Ahmad I, Iohom G. Brief reports: a clinical evaluation of block characteristics using one milliliter 2% lidocaine in ultrasound-guided axillary brachial plexus block. Anesth Analg 2010; 111:808-10. Gautier P, Vandepitte C, Ramquet C, DeCoopman M, Xu D, Hadzic A. The minimum effective anesthetic volume of 0.75% ropivacaine in ultrasound-guided interscalene brachial plexus block. Anesth Analg 2011;113:951-5. Casati A, Baciarello M, Di Cianni S, et al. Effects of ultrasound guidance on the minimum effective anaesthetic volume required to block the femoral nerve. Br J Anaesth 2007;98:823-7. Imasogie N, Ganapathy S, Singh S, Armstrong K, Armstrong P. A prospective, randomized, double-blind comparison of ultrasoundguided axillary brachial plexus blocks using 2 versus 4 injections. Anesth Analg 2010;110:1222-6. Mather LE, Copeland SE, Ladd LA. Acute toxicity of local anesthetics: underlying pharmacokinetic and pharmacodynamic concepts. Reg Anesth Pain Med 2005;30:553-66.
Original Contribution
Effective low dosage of mepivacaine in ultrasound-guided axillary nerve block: a double-blinded, randomized clinical trial of efficacy in patients undergoing distal upper extremity surgery☆ Samuel Perov MD (Clinical Professor)a,b,⁎, Pranav Patel MD (Staff Anesthesiologist) b , Sanjeev Kumar MD (Staff Anesthesiologist)b, George M. McKelvey PhD (Research Associate)c, Elie Chidiac MD (Assistant Professor)b, Faisal Motlani MD (Staff Anesthesiologist)b a
Department of Anesthesiology, Wayne State University/Detroit Receiving Hospital, Detroit, MI 48201, USA Department of Anesthesiology, Wayne State University/Detroit Medical Center, Detroit, MI 48201 USA c Department of Anesthesiology, Detroit Medical Center, Detroit, MI 48201 USA b
Received 19 December 2012; revised 31 October 2013; accepted 5 November 2013
Keywords: Axillary plexus block; Ultrasound-guided; Functional block; Mepivacaine; Regional anesthesia; Surgical block
Abstract Study Objective: To evaluate two low-dose volumes (20 mL or 30 mL) of 1.5% mepivacaine solution used for ultrasound-guided axillary blockade for outpatients undergoing distal upper limb surgery. Design: Prospective, double-blinded randomized study. Setting: Outpatient surgical setting of a university-affiliated hospital. Patients: 64 adult, ASA physical status 1, 2, and 3 patients, aged 28-46 years, scheduled for upper limb surgery. Interventions: Patients were randomized to two groups to receive either 20 mL of 1.5% mepivacaine solution (n=31) or 30 mL of 1.5% mepivacaine solution (n=33) for ultrasound-guided axillary plexus blockade. Measurements: Block duration, proportion of surgical and functional successful blocks, onset of sensory and motor blockade measured from 0 to 30 minutes following final needle extraction, total amount of preoperative sedative (midazolam), and intraoperative propofol administered were recorded. Main Results: Following axillary plexus blockade, neither patient group showed any statistically significant difference in the percentage of functionally successful blockade (30 mL, 100%: 20 mL, 97%; P = 0.48), surgically successful blockade (30 mL, 100%; 20 mL, 94%; P = 0.23), cumulative sensory or motor blockade surgical time, block performance time, preoperative midazolam use, or intraoperative propofol use. Conclusion: Low volumes (30 mL or 20 mL) of 1.5% mepivacaine provides satisfactory anesthesia for ambulatory distal upper limb surgery with no significant difference in clinical outcomes. © 2014 Elsevier Inc. All rights reserved.
☆ This study was performed at the Detroit Medical Center, Detroit, Michigan, USA. ⁎ Correspondence: Samuel Perov, MD, Department of Anesthesiology, Detroit Receiving Hospital/Wayne State University, 4201 St. Antoine, Detroit, MI, 48201, USA. Tel: 313 745-2872; fax: 313 993-7729. E-mail address: [email protected] (S. Perov).
http://dx.doi.org/10.1016/j.jclinane.2013.11.016 0952-8180/© 2014 Elsevier Inc. All rights reserved.
2
1. Introduction The use of ultrasonography as an adjunct to regional anesthesia has increased significantly [1]. Brachial plexus blockade by an axillary approach is amenable to the use of ultrasound guidance. Real-time sonography of nerve structures ensures an optimal distribution of the block solution. When compared with other methods of nerve localization, sonography decreases failure rate [2,3], procedure time [4,5], and the onset time for blockade [6,7]. Furthermore, the use of ultrasound for peripheral nerve blockade demonstrates decreased procedure-related complications such as nerve injury and unintentional vascular puncture [8,9]. Traditional axillary nerve block techniques relying on surface anatomical landmarks require large volumes of local anesthetic, generally 40 mL and greater [10,11]. Local anesthetic concentration and volume significantly affect nerve block effects [12,13]. A local anesthetic shows large variations in analgesic effect depending on the infusion rate and bolus amount [14]. Using the increased accuracy offered by ultrasound, some studies have shown that lower volumes of local anesthetic can yield successful axillary plexus blockade [1,15–17] and interscalene brachial plexus block [18]. With smaller volumes of local anesthetic observed to be clinically effective, the tradition of using large volumes of local anesthetic for axillary blocks, even without ultrasound, may be unwarranted. Institutionally, 30 mL of a 1.5% solution of mepivacaine for axillary plexus blockade is clinically the most common volume we use. Therefore, in this study we used a 30 mL volume as the standard treatment to compare with 20 mL of a 1.5% solution of mepivacaine. Although recent investigations support using a low volume of local anesthetic for brachial plexus blockade [18], there is a lack of outcome data from blinded randomized trials. The primary objective of this study was to evaluate two different volumes of local anesthetic for axillary blockade: 1) 30 mL or 2) 20 mL. A 1.5% solution of mepivacaine was used due to its widespread clinical use in axillary blocks, which is secondary to rapid onset of action, intermediate duration of effect, and relative low cost. The primary outcome was block success rate for outpatients undergoing distal upper limb surgery. Secondary objectives included comparing the two volumes with respect to time required to perform the block and onset of sensory and motor blockade.
S. Perov et al. surgery in an outpatient setting. After giving their written, informed consent, patients were randomly assigned using a computerized number generator to receive either 20 mL (n=31) or 30 mL (n=33) of a 1.5% mepivacaine solution for axillary plexus blockade. All block placements used standard medical protocol. Nerve localization was performed using a GE LOGIQe ultrasound machine (GE Medical Systems, Milwaukee, WI, USA), with a 12L-RS transducer (42 mm x 7 mm footprint, 5-13 MHz). On identification of the axillary neurovascular bundle, a 22-gauge x 50 mm poly medic UPC electric stimulation needle was inserted and advanced along the longitudinal axis of the ultrasound transducer to visualize the entire shaft and tip. A peri-arterial injection of 1.5% mepivacaine near all the individual nerve sheaths was performed after negative aspiration, with the endpoint being the circumferential “donut sign” spread around the artery. Then the musculocutaneous nerve was identified and 1.5% mepivacaine injected around the nerve. Depending on the patient group allocation, there was infiltration of either 20 mL or 30 mL of 1.5% mepivacaine. For the group receiving 20 mL, 15 of the total 20 mL was spread around the axillary artery and 5 mL spread around the musculocutaneous nerve. For the group receiving 30 mL, 20 of the total 30 mL was spread around the axillary artery with 10 mL spread around the musculocutaneous nerve. By instituting this injection technique, there is extrapolation to non-ultrasound-guided axillary blocks. For preblock sedation all subjects were administered b 0.8 mg/kg of midazolam with no administration of preoperative opioids. All block procedure times were less than 10 minutes in duration. All subjects consented to light intraoperative sedation.
2.1. Inclusion criteria All subjects recruited into the study were patients undergoing forearm, wrist, or hand surgery in an outpatient setting. Other attributes were ASA physical status 1, 2, or 3; body mass index b 35 kg/m2, and age between 18 and 89 years. All subjects had no history of stroke, diabetes, anxiety disorder, obstructive sleep apnea, previous surgery or scarring in the axillary to elbow area, neurological impairment of either upper extremity, allergies to local anesthesia, coagulopathy, infection at site of block, chronic opioid therapy for chronic pain, or casts or dressing on the limb that would impair assessment of blocks.
2.2. Data collection
2. Methods and materials The current study had institutional review board approval and was registered at ClinicalTrials.gov NCT01485653. This study was a prospective, double-blinded, randomized trial of 64 patients recruited from the Detroit Receiving Hospital, Detroit, MI. All participating patients underwent upper limb
Preoperative variables, including demographics, ASA physical status, height, weight, surgical procedure, location of procedure (hand, wrist, forearm), sedation used in the preoperative holding area, amount of sedation used, block start and end time (duration of time taken between needle insertion and extraction), onset of sensory blockade, and onset of motor blockade were all recorded.
Low mepivacaine dose in US-guided nerve block Intraoperatively, conversion to general anesthesia, use of local anesthesia intraoperatively, total amount of propofol administered, surgical incision time, and surgery end times were recorded. Postoperative data included complications related to axillary block and discharge criteria met.
2.3. Block assessment An examiner who was blinded to the volume of injectate used for the axillary plexus block evaluated the onset of sensory and motor blockade and assessed whether the block was functionally successful and surgically successful.
2.4. Onset of sensory blockade This measure was examined every 5 minutes following needle extraction with the use of a blunt needle at 4 specific anatomic locations corresponding to radial, ulnar, median, and musculocutaneous distributions, and compared with the contralateral side using the same stimulus (normal pinprick sharp, 3; pinprick felt but not as sharp, 2; pressure felt but no pinprick felt, 1; no sensation at all, 0).
2.5. Onset of motor blockade This block was examined every 5 minutes following needle extraction at 4 anatomical locations (wrist flexion: median nerve; wrist extension: radial nerve; abduction of fifth finger or straight finger adduction: ulnar nerve; elbow flexion (with forearm supinated): musculocutaneous nerve. Normal strength, 3; decreased strength but moves against gravity or some resistance, 2; no movement against gravity or twitch, 1; no movement at all, 0).
2.6. Definitions of successful block Functional successful block was a sensory score of 0 - 1 in all 4 territories and a motor score of 0 - 1 in 3 of 4 territories within 30 minutes of needle extraction. A successful block required no intraoperative supplemental local anesthetic, light sedation b 25 μg/kg/min propofol, and absence of general anesthesia.
3 study groups on proportional differences were examined using a nonparametric Fisher’s Exact Chi-square test when applied to 2 x 2 and 2 x 3 tables. Statistical significance was set at a P-value ≤ 0.05. All continuous data are expressed as means ± standard deviation with 95% CIs [lower -upper]. All statistical procedures were performed using SPSS software (version 18.0; SPSS, Chicago, IL, USA). A binary outcome, non-inferiority power analysis based on a rate of 99% successful functional and surgical axillary plexus block for both anesthetic volumes (30 mL and 20 mL) concluded that 30 participants were necessary to achieve 80% power with a P-value b 0.05 (http://www. sealedenvelope.com/power/binary-noninferior/). These sample numbers determine the upper limit of a one-sided 95% CI excluding a difference in favor of the standard treatment (30 mL of mepivacaine) of more than 6.5% (noninferiority limit; d; http://www.sealedenvelope.com/power/ binary-noninferior/).
3. Results Six of the initial 70 patients recruited from data analysis were excluded due to incomplete data collection. Data from 64 subjects were analyzed in the two patient groups, 20 mL of mepivacaine (n=31) and 30 mL of mepivacaine (n=33). Demographic data, clinical characteristics, and surgical time were compared between the two groups (Table 1). Two patients necessitated conversion to general anesthesia, both in the 20mL group. One of the two patients had a functionally successful block as defined by our criteria. No patients required supplementation of block intraoperatively. No patients required more than 25 μg/kg/min of propofol infusion for light sedation intraoperatively. The median block performance time was 330 seconds for the 20 mL group and 342 seconds for the 30 mL group (Table 1). By 25 minutes following the axillary block, 97% of patients in both groups had attained onset of functionally significant sensory and motor blockade (Table 1). There were no reported adverse events relating to the block, and all patient discharge occurred on the same day of surgery.
4. Discussion 2.7. Statistics An unpaired Student’s t-test procedure (two-sample assuming equal variances, two-tail significance; P b 0.05, 95% confidence interval [CI]) was performed to examine mean differences between the two study groups on all continuously scaled variables. Repeated-measures analysis of variance was used to measure statistical differences for motor and sensory nerve block scores during the 30-minute assessment. Assumptions of normality and/or homogeneity of variance were checked and verified. Comparisons between
In this randomized, blinded study, ultrasound-guided axillary plexus blockade using 20 mL or 30 mL of 1.5% mepivacaine showed no statistically significant difference in operative data or block outcomes for patients undergoing distal upper limb surgery in an outpatient setting. By sonographically visualizing the axillary neurovascular anatomy in real time, the accuracy of needle placement and subsequent deposition and spread of local anesthetic is more precise. As a result, block success rate is improved and lower dose of local anesthetic is required [3,19]. Furthermore,
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S. Perov et al. Table 1
Patient demographics, operative requirements, and study outcome parameters
Patient demographics
age (yrs) gender (M/F) ASA physical status (1 / 2 / 3) weight (kg) height (cm) surgical time (min) block performance time (sec) Operative data preop midazolam (mg) intraop propofol (μg/kg/min) Block outcome functional successful blocks (%) surgical successful blocks (%) peripheral nerve supplementation (%) conversion to general anesthesia (%) Sensory nerve block score 5 min 10 min 15 min 20 min 25 min 30 min Motor nerve block score 5 min 10 min 15 min 20 min 25 min 30 min
Mepivacaine 1.5% 20 mL (n=31)
30 mL (n=33)
35 [28-42] 14/17 6 / 23 / 2 80 [69-81] 169 [164-174] 34 [9-54] 330 [300-360]
38 [31-46] 18/15 1 / 27 / 5 82 [71-93] 165 [160-171] 31 [19-43] 342 [318-367]
20 mL (n=31)
30 mL (n=33)
P-value
2.5 [1.8-3.2] 10.2 [5.9-14.7]
3.2 [2.3-4.1] 7.2 [2.9-11.6]
0.06 0.12
20 mL (n=31)
30 mL (n=33)
P-value
97% (30/31) 94% (29/31) 0% (0/31) 6% (2/31)
100% (33/33) 100% (33/33) 0% (0/33) 0% (0/33)
0.48 0.23 0.99 0.23
20 mL (n=31)
30 mL (n=33)
P-value all 0.99
7.5 [6.4-8.6] 3.7 [2.6-4.8] 1.5 [0.6-2.5] 1.0 [0.2-1.9] 0.8 [0.6-0.9] 0.7 [0.5-0.8]
7.2 [6.1-8.3] 3.6 [2.4-4.8] 1.5 [0.6-2.5] 0.8 [0.2-1.5] 0.6 [0.4-0.8] 0.6 [0.5-0.8]
20 mL (n=31)
30 mL (n=33)
9.8 [8.9-10.7] 7.0 [6.0-8.0] 3.6 [2.3-4.8] 2.1 [0.9-3.4] 1.6 [0.6-2.6] 1.4 [0.4-2.4]
9.7 [8.8-10.6] 7.0 [6.0-8.0] 3.6 [2.3-4.8] 2.1 [0.9-3.3] 1.5 [0.4-2.6] 1.2 [0.3-2.1]
P-value all 0.99
Data are means ± SD with 95% confidence intervals [lower - upper]. Functional successful block=sensory score of 0-1 in all 4 nerve territories, and motor score of 0-1 in 3 of 4 territories within 30 minutes of needle extraction. Surgical successful block=no required intraoperative (intraop) supplemental local anesthetic, light sedation b 25 μg/kg/min propofol, and absence of general anesthesia. Scores for each measured time point=summation of scores from each of the 4 nerves/anatomical location. Sensory nerve block score=normal pinprick sharp, 3; pinprick felt but not as sharp, 2; pressure felt but no pinprick felt, 1; no sensation at all, 0. Motor nerve block score=normal strength, 3; decreased strength or some resistance, 2; no movement against gravity or twitch, 1; no movement at all, 0. preop=preoperative.
fewer injections result in shorter procedure times and less risk of injury [20]. A potential complication of regional anesthesia is the inadvertent intravascular injection of local anesthetic. Although infrequent, this event can lead to life-threatening complications such as seizures and cardiac arrhythmias. Since the toxic effect from local anesthetics is likely dosedependent [21], reducing the volume of local anesthetic injectate is a worthwhile endeavor. Reduction in local anesthetic volume by 50% may be of value in improving the safety profile of the axillary plexus block. A limitation of this study was that measurement of the onset of sensory and motor blockade for both groups was
made in 5-minute increments. As such, exact times for these variables could not be identified. Unavoidable variability in this study also occurred in terms of needle direction during the peri-arterial injection of the ulnar, radial, and medial nerves in order to ensure adequate spread of local anesthetic, and to obtain the sonographic endpoint of the “donut sign”. O’Donnell and colleagues have demonstrated successful axillary brachial plexus block by injecting volumes as low as one mL of 2% lidocaine per individual nerve [17]. However, this methodology necessitates sonographic guidance that is not a feasible option at all institutions. By injecting in a peri-arterial fashion, these results may be applicable to axillary blocks performed using a transarterial approach.
Low mepivacaine dose in US-guided nerve block In conclusion, real-time ultrasound-guided axillary plexus block with 20 mL or 30 mL of 1.5% mepivacaine provides satisfactory anesthesia for ambulatory distal limb surgery with no significant statistical or clinical difference in outcomes between both volumes. Given that any potential toxic effect from local anesthetics is dose-dependent [21], reducing the volume of local anesthetic injectate will improve the safety profile of the axillary plexus block without affecting clinical efficacy.
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[9] [10]
[11]
[12]
Acknowledgments [13]
The authors wish to thank Drs. Ryan Guffey, MD, and Gokul Toshniwal, MD, for their technical assistance during this study.
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