- Email: [email protected]
Ultrasound-guided musculocutaneous nerve block: A description of a novel technique
Imaging Article
Ultrasound-Guided Musculocutaneous Nerve Block: A Description of a Novel Technique Brian C. Spence, M.D., Brian D. Sites, M.D., and Mike L. Beach, M.D., Ph.D. Background and Objective: Localizing the musculocutaneous nerve for neural blockade is crucial to providing surgical anesthesia for the distal forearm. We present a novel approach for localizing and anesthetizing the musculocutaneous nerve. Case Reports: Ten patients underwent successful ultrasound-guided musculocutaneous nerve blocks. In this technique, either a 10-MHz or a 12-MHz linear probe was placed at the junction of the pectoralis major muscle and the biceps muscle such that the axillary artery was visualized in cross section. The probe was moved towards the biceps muscle until the musculocutaneous nerve was visualized lying between the coracobrachialis and biceps muscles. A 22-gauge, 50-mm b-bevel needle was inserted under direct vision until the needle was adjacent to the nerve. Local anesthetic was then injected, which generated surgical anesthetic conditions in all patients. Conclusion: Ultrasound can facilitate the localization and local anesthetic block of the musculocutaneous nerve. Reg Anesth Pain Med 2005;30:198-201. Key Words:
Nerve block, Musculocutaneous nerve, Ultrasound, New technique.
C
urrently, multiple techniques are used to localize the musculocutaneous nerve for local anesthetic block. These techniques include direct injection into the corocobrachialis muscle, injection along the humerus, elicitation of a paresthesia, and generation of a biceps contraction by use of nerve stimulation.1,2 All of these techniques are based on anatomical assumptions of normal neural anatomy and on palpating internal landmarks. Ultrasound is becoming an increasingly popular technique to facilitate the performance of peripheral nerve blocks,3 partially because of improvements in ultrasound fidelity that allow the visualization of actual neural structures. Ultrasound guidance is an attractive option for neural structures, such as the musculocutaneous nerve, that do not have predictable relationships to easily identifiable vascular structures.
From the Department of Anesthesiology, Dartmouth Medical School, Dartmouth Hitchcock Medical Center, Lebanon, New Hampshire. Accepted for publication September 29, 2004. Reprint requests: Brian C. Spence, M.D., Assistant Professor of Anesthesiology, Dartmouth-Hitchcock Medical Center, One Medical Center Drive, Lebanon, New Hampshire, 03756. E-mail: [email protected] © 2005 by the American Society of Regional Anesthesia and Pain Medicine. 1098-7339/05/3002-0011$30.00/0 doi:10.1016/j.rapm.2004.09.009
198
In this article, we describe a technique of using real-time, high-resolution ultrasound guidance to facilitate the local anesthetic block of the musculocutaneous nerve.
Case Reports The data for this report were generated through our departmental regional anesthesia database. The Dartmouth College Committee for the Protection of Human Subjects (DCCPHS) approved the maintenance of a prospective database for quality improvement, billing, and research. The inclusion criteria for the query were as follows: patients who were scheduled to have hand surgery under an axillary plexus block, musculocutaneous sensory distribution involved in the surgical dissection, ultrasound used, and the musculocutaneous nerve block performed before the axillary plexus block. From January 2004 through August 2004, 10 of 76 patients met the above inclusion criteria.
Technique The operator in each case was either a staff anesthesiologist or a clinical anesthesia (CA) year 2 or year 3 resident. The residents were closely supervised by 1 of 3 staff anesthesiologists with experience in ultrasound-guided nerve blocks. Each pa-
Regional Anesthesia and Pain Medicine, Vol 30, No 2 (March–April), 2005: pp 198 –201
Ultrasound-Guided Musculocutaneous Nerve Block
tient was placed in a supine position with the arm abducted and externally rotated. The ultrasound probe (L12-5, 38 mm, 5 to 12 MHz [Envisor; Philips Medical Systems, Inc, Bothell, WA]; L25, 25 mm, 5-10 MHz, [iLook25; Sonosite, Inc, Bothell, WA]; or L38, 45 mm, 5 to 10 MHz, [Titan; Sonosite, Inc, Bothell, WA]) was placed at the junction of the pectoralis major and biceps muscles such that the axillary artery was visualized in cross section (Fig 1). While still imaging the axillary artery on cross section, the operator slowly moved the ultrasound probe toward the biceps muscle, until the musculocutaneous nerve appeared either in the body of the coracobrachialis muscle or in a plane between the coracobrachialis and the biceps muscles (Fig 2). At this point, a 22-gauge, 50-mm b-bevel needle (Stimuplex; B. Braun, Bethlehem, PA) was inserted on the biceps side of the probe and in the longitudinal axis of the ultrasound beam. The needle was visualized in its full course as it neared the nerve (Fig 3). The endpoint for injection was either the ultrasound image demonstrating proximity of the needle tip to the nerve or a biceps contraction of less than 0.5 mA of stimulation. The injection consisted of various volumes of 0.5% bupivacaine with 5 g/mL epinephrine. The injection and spread of local anesthetic was visualized under live ultrasound (Figs 4 and 5). All patients were assessed for the loss of sensation to cold before the performance of the axillary plexus block. Data collected for each
Fig 1. Technique of a real-time, ultrasound-guided musculocutaneous nerve block for the right-hand dominant individual. The operator holds the probe with the nondominant hand. The probe is placed at the junction of the biceps and the pectoralis muscles such that the axillary artery is imaged in cross section. The probe is then moved towards the biceps muscle until the musculocutaneous nerve is visualized in cross section. The needle is inserted with the operator’s dominant hand such that it is in plane with the longitudinal axis of the ultrasound beam.
•
Spence, Sites, and Beach
199
Fig 2. The left-hand dominant operator performs a realtime, ultrasound-guided musculocutaneous nerve block.
patient included time required to perform the block (defined as the completion of the sterile preparation until the last mL of local anesthetic was injected), time until sensory loss to an ice bag, degree of motor block (scale: 0 is no movement, 1 is weak movement, and 2 is normal movement), and any complications. The motor block was assessed after the axillary plexus block was placed. By our database convention, both the performance and the
Fig 3. A 12-MHz ultrasound image demonstrating the musculocutaneous nerve and surrounding structures. B, bone (humerus); Bi, biceps muscle; CB, coracobrachialis muscle; A, axillary artery; v, axillary vein. The musculocutaneous nerve is found in the juncture between the biceps and coracobrachialis muscles. The nerve, as does the median nerve, appears as a constellation of hypodense (dark) grapelike structures with hyperechoic (bright) rings.
200
Regional Anesthesia and Pain Medicine Vol. 30 No. 2 March–April 2005
Fig 4. A 10-MHz ultrasound image demonstrating the musculocutaneous nerve with the needle being inserted in the longitudinal plane of the ultrasound beam. B, bone (humerus); Bi, biceps muscle; CB, coracobrachialis muscle; A, axillary artery; , needle.
sensory loss onset times were rounded off to the closest minute. In all 10 cases, the musculocutaneous nerve was easily identified, and sensory loss to ice was documented before the performance of the axillary block. The average time to perform the musculocutaneous nerve block was 1.9 ⫾ 0.7 (SD) minutes. The average time to sensory loss to ice in the anterolateral forearm was 3.6 ⫾ 0.9 minutes. After the completion of the axillary blocks, 9 of 10 patients had their procedure performed under the nerve blocks and conscious sedation. One patient required conversion to general anesthesia secondary to tourniquet discomfort.
facilitate the performance of nerve blocks in both the upper and lower extremities.4,5 For this specific block, we found that a high-resolution ultrasound system is required to visualize the musculocutaneous nerve. The ideal probe would have resolution capabilities between 10 and 15 MHz. The more resolution a system has (higher MHz), the less the depth of penetration. Therefore, patients with thick arms from muscle or adipose tissue will be better served with a 10-MHz resolution. In patients who have thin arms, a 12-MHz resolution provides the best image of the musculocutaneous nerve. Because many ultrasound systems offer multiple resolution settings per probe, the operator must simply scroll through the different settings while examining the patient to determine which setting generates the best image. This ability to accurately visualize the needle and its tip may be crucial to safely and successfully completing various interventional ultrasound procedures. In our experience, the most successful nerve blocks occur when a structure such as the musculocutaneous nerve is imaged on axial section, and the needle is advanced in the longitudinal beam of the ultrasound machine. Although the needle may be brought into the ultrasound beam on axial section, a 22-gauge needle on axial section appears as a small dot that can be easily overlooked. In addition, when the needle is imaged on axial section, the operator may be visualizing a cross section of the needle shaft, rather than its tip. When the needle is advanced in the longitudinal plane of the ultrasound beam, the operator can see the entire needle and make adjustments as needed.
Discussion In this article, we describe a novel approach to localizing the musculocutaneous nerve at the axillary level. Historically, practitioners have utilized direct muscle injection with or without the application of either paresthesias or nerve stimulation. These techniques rely on the palpation of internal anatomy (coracobrachialis muscle, biceps muscle, and axillary artery) to guide needle placement. The degree to which these landmarks are appreciated depends on multiple variables, such as body habitus, prior surgical distortion of anatomy, ability to position the patient, and vascular disease. Therefore, alternative techniques for nerve localization may be clinically useful. Ultrasound offers the ability to visualize the target nerve of interest and direct the needle under live guidance. This technique has been shown to
Fig 5. Image represents the same patient as in Fig 4. The image demonstrates the local anesthesia being injected around the musculocutaneous nerve. B, bone (humerus); Bi, biceps muscle; CB, coracobrachialis muscle; L, local anesthesia; , needle.
Ultrasound-Guided Musculocutaneous Nerve Block
In conclusion, we describe a novel technique of localizing and anesthetizing the musculocutaneous nerve. Whether or not such a technique offers any advantages over conventional means of nerve localization will depend on the results of future controlled trials.
References 1. Brown D. Atlas of Regional Anesthesia. 2nd ed. Philadelphia: WB Saunders, Company, 1999:51-55 2. Gaertner E, Kern O, Mahoudeau G, Freys G, Golfetto T, Calon B. Block of the brachial plexus by the hu-
•
Spence, Sites, and Beach
201
meral route. A prospective study in 503 ambulatory patients. Proposal of a nerve-blocking sequence. Acta Anaesth Scand 1999;43:609-613. 3. Peterson MK, Millar FA, Sheppard DG. Ultrasoundguided nerve blocks. Brit J Anesth 2002;88:621624. 4. Marhofer P, Schrogendorfer K, Koinig H, Kapral S, Weinstable C, Mayer N. Ultrasonographic guidance improves sensory block and onset time of three-in-one blocks. Anesth Analg 1997;85:854-857. 5. Perlas A, Chan V, Simons M. Brachial plexus examination and localization using ultrasound and electrical stimulation. Anesthesiology 2003;99:429-435.
Ultrasound-Guided Musculocutaneous Nerve Block: A Description of a Novel Technique Brian C. Spence, M.D., Brian D. Sites, M.D., and Mike L. Beach, M.D., Ph.D. Background and Objective: Localizing the musculocutaneous nerve for neural blockade is crucial to providing surgical anesthesia for the distal forearm. We present a novel approach for localizing and anesthetizing the musculocutaneous nerve. Case Reports: Ten patients underwent successful ultrasound-guided musculocutaneous nerve blocks. In this technique, either a 10-MHz or a 12-MHz linear probe was placed at the junction of the pectoralis major muscle and the biceps muscle such that the axillary artery was visualized in cross section. The probe was moved towards the biceps muscle until the musculocutaneous nerve was visualized lying between the coracobrachialis and biceps muscles. A 22-gauge, 50-mm b-bevel needle was inserted under direct vision until the needle was adjacent to the nerve. Local anesthetic was then injected, which generated surgical anesthetic conditions in all patients. Conclusion: Ultrasound can facilitate the localization and local anesthetic block of the musculocutaneous nerve. Reg Anesth Pain Med 2005;30:198-201. Key Words:
Nerve block, Musculocutaneous nerve, Ultrasound, New technique.
C
urrently, multiple techniques are used to localize the musculocutaneous nerve for local anesthetic block. These techniques include direct injection into the corocobrachialis muscle, injection along the humerus, elicitation of a paresthesia, and generation of a biceps contraction by use of nerve stimulation.1,2 All of these techniques are based on anatomical assumptions of normal neural anatomy and on palpating internal landmarks. Ultrasound is becoming an increasingly popular technique to facilitate the performance of peripheral nerve blocks,3 partially because of improvements in ultrasound fidelity that allow the visualization of actual neural structures. Ultrasound guidance is an attractive option for neural structures, such as the musculocutaneous nerve, that do not have predictable relationships to easily identifiable vascular structures.
From the Department of Anesthesiology, Dartmouth Medical School, Dartmouth Hitchcock Medical Center, Lebanon, New Hampshire. Accepted for publication September 29, 2004. Reprint requests: Brian C. Spence, M.D., Assistant Professor of Anesthesiology, Dartmouth-Hitchcock Medical Center, One Medical Center Drive, Lebanon, New Hampshire, 03756. E-mail: [email protected] © 2005 by the American Society of Regional Anesthesia and Pain Medicine. 1098-7339/05/3002-0011$30.00/0 doi:10.1016/j.rapm.2004.09.009
198
In this article, we describe a technique of using real-time, high-resolution ultrasound guidance to facilitate the local anesthetic block of the musculocutaneous nerve.
Case Reports The data for this report were generated through our departmental regional anesthesia database. The Dartmouth College Committee for the Protection of Human Subjects (DCCPHS) approved the maintenance of a prospective database for quality improvement, billing, and research. The inclusion criteria for the query were as follows: patients who were scheduled to have hand surgery under an axillary plexus block, musculocutaneous sensory distribution involved in the surgical dissection, ultrasound used, and the musculocutaneous nerve block performed before the axillary plexus block. From January 2004 through August 2004, 10 of 76 patients met the above inclusion criteria.
Technique The operator in each case was either a staff anesthesiologist or a clinical anesthesia (CA) year 2 or year 3 resident. The residents were closely supervised by 1 of 3 staff anesthesiologists with experience in ultrasound-guided nerve blocks. Each pa-
Regional Anesthesia and Pain Medicine, Vol 30, No 2 (March–April), 2005: pp 198 –201
Ultrasound-Guided Musculocutaneous Nerve Block
tient was placed in a supine position with the arm abducted and externally rotated. The ultrasound probe (L12-5, 38 mm, 5 to 12 MHz [Envisor; Philips Medical Systems, Inc, Bothell, WA]; L25, 25 mm, 5-10 MHz, [iLook25; Sonosite, Inc, Bothell, WA]; or L38, 45 mm, 5 to 10 MHz, [Titan; Sonosite, Inc, Bothell, WA]) was placed at the junction of the pectoralis major and biceps muscles such that the axillary artery was visualized in cross section (Fig 1). While still imaging the axillary artery on cross section, the operator slowly moved the ultrasound probe toward the biceps muscle, until the musculocutaneous nerve appeared either in the body of the coracobrachialis muscle or in a plane between the coracobrachialis and the biceps muscles (Fig 2). At this point, a 22-gauge, 50-mm b-bevel needle (Stimuplex; B. Braun, Bethlehem, PA) was inserted on the biceps side of the probe and in the longitudinal axis of the ultrasound beam. The needle was visualized in its full course as it neared the nerve (Fig 3). The endpoint for injection was either the ultrasound image demonstrating proximity of the needle tip to the nerve or a biceps contraction of less than 0.5 mA of stimulation. The injection consisted of various volumes of 0.5% bupivacaine with 5 g/mL epinephrine. The injection and spread of local anesthetic was visualized under live ultrasound (Figs 4 and 5). All patients were assessed for the loss of sensation to cold before the performance of the axillary plexus block. Data collected for each
Fig 1. Technique of a real-time, ultrasound-guided musculocutaneous nerve block for the right-hand dominant individual. The operator holds the probe with the nondominant hand. The probe is placed at the junction of the biceps and the pectoralis muscles such that the axillary artery is imaged in cross section. The probe is then moved towards the biceps muscle until the musculocutaneous nerve is visualized in cross section. The needle is inserted with the operator’s dominant hand such that it is in plane with the longitudinal axis of the ultrasound beam.
•
Spence, Sites, and Beach
199
Fig 2. The left-hand dominant operator performs a realtime, ultrasound-guided musculocutaneous nerve block.
patient included time required to perform the block (defined as the completion of the sterile preparation until the last mL of local anesthetic was injected), time until sensory loss to an ice bag, degree of motor block (scale: 0 is no movement, 1 is weak movement, and 2 is normal movement), and any complications. The motor block was assessed after the axillary plexus block was placed. By our database convention, both the performance and the
Fig 3. A 12-MHz ultrasound image demonstrating the musculocutaneous nerve and surrounding structures. B, bone (humerus); Bi, biceps muscle; CB, coracobrachialis muscle; A, axillary artery; v, axillary vein. The musculocutaneous nerve is found in the juncture between the biceps and coracobrachialis muscles. The nerve, as does the median nerve, appears as a constellation of hypodense (dark) grapelike structures with hyperechoic (bright) rings.
200
Regional Anesthesia and Pain Medicine Vol. 30 No. 2 March–April 2005
Fig 4. A 10-MHz ultrasound image demonstrating the musculocutaneous nerve with the needle being inserted in the longitudinal plane of the ultrasound beam. B, bone (humerus); Bi, biceps muscle; CB, coracobrachialis muscle; A, axillary artery; , needle.
sensory loss onset times were rounded off to the closest minute. In all 10 cases, the musculocutaneous nerve was easily identified, and sensory loss to ice was documented before the performance of the axillary block. The average time to perform the musculocutaneous nerve block was 1.9 ⫾ 0.7 (SD) minutes. The average time to sensory loss to ice in the anterolateral forearm was 3.6 ⫾ 0.9 minutes. After the completion of the axillary blocks, 9 of 10 patients had their procedure performed under the nerve blocks and conscious sedation. One patient required conversion to general anesthesia secondary to tourniquet discomfort.
facilitate the performance of nerve blocks in both the upper and lower extremities.4,5 For this specific block, we found that a high-resolution ultrasound system is required to visualize the musculocutaneous nerve. The ideal probe would have resolution capabilities between 10 and 15 MHz. The more resolution a system has (higher MHz), the less the depth of penetration. Therefore, patients with thick arms from muscle or adipose tissue will be better served with a 10-MHz resolution. In patients who have thin arms, a 12-MHz resolution provides the best image of the musculocutaneous nerve. Because many ultrasound systems offer multiple resolution settings per probe, the operator must simply scroll through the different settings while examining the patient to determine which setting generates the best image. This ability to accurately visualize the needle and its tip may be crucial to safely and successfully completing various interventional ultrasound procedures. In our experience, the most successful nerve blocks occur when a structure such as the musculocutaneous nerve is imaged on axial section, and the needle is advanced in the longitudinal beam of the ultrasound machine. Although the needle may be brought into the ultrasound beam on axial section, a 22-gauge needle on axial section appears as a small dot that can be easily overlooked. In addition, when the needle is imaged on axial section, the operator may be visualizing a cross section of the needle shaft, rather than its tip. When the needle is advanced in the longitudinal plane of the ultrasound beam, the operator can see the entire needle and make adjustments as needed.
Discussion In this article, we describe a novel approach to localizing the musculocutaneous nerve at the axillary level. Historically, practitioners have utilized direct muscle injection with or without the application of either paresthesias or nerve stimulation. These techniques rely on the palpation of internal anatomy (coracobrachialis muscle, biceps muscle, and axillary artery) to guide needle placement. The degree to which these landmarks are appreciated depends on multiple variables, such as body habitus, prior surgical distortion of anatomy, ability to position the patient, and vascular disease. Therefore, alternative techniques for nerve localization may be clinically useful. Ultrasound offers the ability to visualize the target nerve of interest and direct the needle under live guidance. This technique has been shown to
Fig 5. Image represents the same patient as in Fig 4. The image demonstrates the local anesthesia being injected around the musculocutaneous nerve. B, bone (humerus); Bi, biceps muscle; CB, coracobrachialis muscle; L, local anesthesia; , needle.
Ultrasound-Guided Musculocutaneous Nerve Block
In conclusion, we describe a novel technique of localizing and anesthetizing the musculocutaneous nerve. Whether or not such a technique offers any advantages over conventional means of nerve localization will depend on the results of future controlled trials.
References 1. Brown D. Atlas of Regional Anesthesia. 2nd ed. Philadelphia: WB Saunders, Company, 1999:51-55 2. Gaertner E, Kern O, Mahoudeau G, Freys G, Golfetto T, Calon B. Block of the brachial plexus by the hu-
•
Spence, Sites, and Beach
201
meral route. A prospective study in 503 ambulatory patients. Proposal of a nerve-blocking sequence. Acta Anaesth Scand 1999;43:609-613. 3. Peterson MK, Millar FA, Sheppard DG. Ultrasoundguided nerve blocks. Brit J Anesth 2002;88:621624. 4. Marhofer P, Schrogendorfer K, Koinig H, Kapral S, Weinstable C, Mayer N. Ultrasonographic guidance improves sensory block and onset time of three-in-one blocks. Anesth Analg 1997;85:854-857. 5. Perlas A, Chan V, Simons M. Brachial plexus examination and localization using ultrasound and electrical stimulation. Anesthesiology 2003;99:429-435.