Chapter 15 Peripheral Nerve Blocks
1. Name some types of peripheral nerve blocks.
2. Other than as anesthesia for a surgical procedure, what are some uses for peripheral nerve blocks?
3. What are some special considerations that should be made in the preoperative evaluation of a patient who is to undergo a peripheral nerve block?
Specific block techniques
7. What are some of the advantages of ultrasound-guided peripheral nerve blocks?
8. Describe the macroscopic cross-sectional appearance of peripheral nerves.
9. When using high-resolution ultrasound, what percent of the fascicles within a peripheral nerve are able to be visualized?
10. Describe the sonographic appearance of a proximal nerve.
11. What are the image characteristics of high-frequency ultrasound compared with low frequency?
12. What factors affect ultrasound visibility of needles?
13. Describe the short axis and long axis scanning orientations.
14. Describe the in-plane and out-of-plane needle approaches.
15. What is the significance of a paresthesia during block performance?
16. Describe cathodal stimulation and the significance of electrode reversal in evoking a motor response from a peripheral nerve.
17. What is an optimal stimulating threshold for nerve stimulator technique before injection of local anesthetic?
Brachial plexus block
23. For what surgical procedures is a brachial plexus block useful? What areas become anesthetized by a brachial plexus block?
24. What nerve roots form the brachial plexus?
25. What landmarks are used to locate the brachial plexus for blockade?
26. What are four different approaches to blockade of the brachial plexus?
27. How is a brachial plexus block via the interscalene approach achieved? What volume of local anesthetic is deposited with this approach to brachial plexus blockade?
28. What are some advantages of brachial plexus blockade via the interscalene approach?
29. What is a disadvantage of brachial plexus blockade via the interscalene approach?
30. What are some potential complications of brachial plexus blockade via the interscalene approach?
31. How is a brachial plexus block via the supraclavicular approach achieved? What volume of local anesthetic is deposited with this approach to brachial plexus blockade?
32. What are some advantages of brachial plexus blockade via the supraclavicular approach?
33. What are some potential complications of brachial plexus blockade via the supraclavicular approach?
34. Describe the in-plane ultrasound-guided technique for blockade of the brachial plexus via the axillary approach. What volume of local anesthetic is deposited with this approach to brachial plexus blockade?
35. Axillary block provides anesthesia for surgery in which regions of the upper extremity?
36. What nerves are blocked by injection superficial to the axillary sheath during the axillary brachial plexus block? How is this achieved?
37. What are some advantages of brachial plexus blockade via the axillary approach?
38. What are some potential complications of brachial plexus blockade via the axillary approach?
Distal nerve blocks of the upper extremity
39. What is the sensory distribution of the median nerve? How is it blocked at the forearm with ultrasound guidance?
40. What is the sensory distribution of the ulnar nerve? How is it blocked at the forearm with ultrasound guidance?
41. What is the sensory distribution of the radial nerve? What is the typical course of the superficial radial nerve through the forearm, and how is it blocked at the forearm with ultrasound guidance?
Blocks of the lower extremity
42. What are the challenges of lower extremity blocks relative to those of the upper extremity?
43. What are the four major nerves of the lower extremity?
44. What nerves form the sciatic nerve, and what are its approximate dimensions in the pelvis?
45. What area is anesthetized by sciatic nerve blockade and what additional blocks are usually necessary to provide lower extremity anesthesia?
46. How is sciatic nerve blockade achieved? What volume of local anesthetic should be deposited for sciatic nerve blockade?
47. What nerves form the femoral nerve? How does it reach the thigh? What is the terminal branch of the femoral nerve?
48. For what procedure is femoral nerve blockade a definitive anesthetic?
49. How is femoral nerve blockade achieved? What volume of local anesthetic should be deposited for femoral nerve blockade?
50. What nerve forms the saphenous nerve?
51. How is blockade of the saphenous nerve performed at the level of the thigh?
52. Where along the course of the sciatic nerve is the popliteal nerve block performed? What surgical sites are best covered by this block?
53. What supplemental blocks may need to be combined with popliteal nerve blockade?
54. What are the five nerves that supply the foot? What areas do each supply?
55. How is an ankle block achieved? What is the total volume of local anesthetic that is typically deposited in an ankle block?
Intravenous regional neural anesthesia
56. For what procedure types is intravenous regional neural anesthesia (Bier block) commonly used?
57. What are some contraindications for intravenous regional anesthesia?
58. How is a Bier block achieved? What volume of local anesthetic is used in a Bier block?
59. What local anesthetics are typically used for a Bier block?
60. What are some advantages of a Bier block?
61. What are some disadvantages of a Bier block?
62. What is a potential complication of a Bier block? How can this risk be minimized?
Answers*
1. Types of peripheral nerve blocks include blocks of the cervical plexus, brachial plexus, median nerve, ulnar nerve, radial nerve, sciatic nerve, femoral nerve, saphenous nerve, and ankle block. (285)
2. In addition to surgical anesthesia, peripheral nerve blocks may be used for postoperative analgesia and for the diagnosis and management of chronic pain syndromes. (284)
3. Considerations that should be made in the preoperative evaluation of a patient who is to undergo a peripheral nerve block include the patient’s coagulation status, the presence of any neuropathy in the involved nerves, the presence of any skin infection overlying the area where the needle will be inserted, and the presence of any anatomic abnormalities or difficulties with the usual landmarks for the performance of the nerve block. In addition, the patient should be evaluated in the usual manner with regard to history, physical examination, and laboratory analysis. The anesthesiologist must be prepared to administer another anesthetic in the event that the peripheral nerve block is not sufficient for surgical anesthesia and the surgery must proceed. (284-285)
Preparation for nerve blocks
4. Preoperative medication for patients who are to undergo a peripheral nerve block may reduce their level of anxiety. Patients are often more receptive to receiving a peripheral nerve block if they are assured they will be made comfortable during the anesthetic and surgical procedures. (284)
5. Peripheral nerve blocks that are not performed in the operating room should be performed in a block room with the appropriate monitors, drugs, equipment, and oxygen should their use become urgently necessary. (284-285)
6. The choice of local anesthetic agent for peripheral nerve blockade depends on a number of factors, including the desired onset, duration, and degree of conduction block (see Chapter 11). Lidocaine and mepivacaine, 1% to 1.5%, produce surgical anesthesia in 10 to 20 minutes that lasts 2 to 3 hours. Ropivacaine, 0.5%, and bupivacaine, 0.375% to 0.5%, have a slower onset and produce less motor blockade, but the effect lasts for at least 6 to 8 hours. (285)
Specific block techniques
7. High-resolution ultrasound imaging allows direct visualization of peripheral nerves, block needle placement, and the distribution of local anesthetic solution and thereby improves block success and minimizes local anesthetic volume (see Figure 15-1). In addition, ultrasound can also be used to visualize adjacent structures, such as blood vessels or pleurae, and may therefore reduce the risk for complications from peripheral nerve blocks. A major advantage of ultrasound imaging is that variability in surface landmarks, body habitus, and patient positioning can be appreciated. (285)
8. Peripheral nerves can be round, oval, or triangular in transverse cross section (short axis view) and can change shape along their nerve path.
9. About a third of the fascicles within a peripheral nerve can be seen with high-resolution ultrasound. (285)
10. Proximal nerves such as the roots and ventral rami of the brachial plexus appear dark, or hypoechoic, in their core but bright, or hyperechoic, in their outer mantle (Figure 15-1). This distinction occurs because incident sound waves reflect strongly off the connective tissue encasing nerve fascicles but pass through the inner portions of the fascicles undisturbed. (285-286)
11. High-frequency ultrasound provides better resolution but poor penetration into deeper tissue because of attenuation of the sound beam. (286)
12. Ultrasound visibility of needles for a regional block primarily depends on the gauge and insertion angle, such that larger needles parallel to the ultrasound transducer are seen most easily. (286)
13. In short axis imaging, cylindrical structures such as nerves appear as circles. Long axis imaging is achieved by placing the transducer longitudinally, or parallel to the course of a nerve, such that it appears as a linear structure. (286)
14. With the in-plane approach, the block needle is introduced within the plane of imaging, such that the entire needle and bevel are seen as a linear structure. The out-of-plane needle approach involves passing the needle from outside the plane of imaging so that it intersects the scan plane as an echogenic dot. (286, Figure 15-2)
15. A paresthesia is a radiating electric shocklike sensation that can occur during the performance of a peripheral nerve block, which indicates that the nerve has been localized by the needle tip. Local anesthetic solution should not be injected in the presence of persistent paresthesia because intraneural injection accompanied by intense pain increases the likelihood of permanent nerve injury. (286)
16. For nerve stimulation, the block needle is used as a stimulating cathode and another lead on the body serves as the anode to complete the electrical circuit (Figure 15-3). Cathodal stimulation is more efficient than anodal stimulation, so it is important to not reverse the leads during nerve stimulation–guided block procedures. The location of the surface anode (usually an electrocardiographic pad) on the patient does not alter the stimulation. (286)
17. A motor response evoked with currents of 0.3 to 0.5 mA indicates sufficient proximity of the block needle to the nerve for success of the block after the injection of local anesthetic solution. A motor response at a current of less than 0.2 mA may suggest an intraneural needle position. (286-287)
Peripheral nerve catheters
18. Continuous peripheral nerve blocks can be used in the hospital setting to facilitate vigorous early joint mobilization following orthopedic surgery. They can also be used to provide potent analgesia for outpatient surgery (also see Chapter 37). (287)
19. For placement of these catheters, the peripheral nerve should be first located in a fashion similar to that for single-injection blocks (typically nerve stimulation or ultrasound guidance with a large-bore needle), and then the catheter is threaded. Initially injecting a local anesthetic or dextrose solution to create more space adjacent to the nerve before catheter placement is useful. (287)
Cervical plexus block
20. The anesthesia produced by a cervical plexus block includes the area from the inferior surface of the mandible to the level of the clavicle. A cervical plexus block is used most often to provide anesthesia in conscious patients undergoing carotid endarterectomy. Although combined superficial and deep cervical plexus blocks have traditionally been used for this surgical procedure, studies have demonstrated that a superficial block alone is sufficient. (287)
21. The cervical plexus is derived from nerves C1 to C4. (287)
22. Blockade of the superficial cervical plexus can be achieved by infiltrating local anesthetic along the posterior border of the sternocleidomastoid muscle. (287)
Brachial plexus block
23. Brachial plexus blocks are useful for surgery on the shoulder or upper extremity. Areas anesthetized by a brachial plexus block include all the muscles and most of the sensation of the upper extremity. (287-288)
24. The brachial plexus is derived from the anterior rami of C5 to T1. (287-288)
25. Landmarks that may be used to locate the brachial plexus for blockade include the anterior and middle scalene muscles, the interscalene groove, the transverse process of C6, the clavicle, the axillary artery, and the subclavian artery pulse. With ultrasound use, these landmarks are the starting point for scanning. (287-292)
26. The four different approaches to blockade of the brachial plexus are the interscalene, supraclavicular, infraclavicular, and axillary approaches. (287-292)
27. An interscalene block of the brachial plexus is achieved by injecting local anesthetic solution into the interscalene groove adjacent to the transverse process of C6 (the external jugular vein often overlies this area) (Figure 15-7). An interscalene block of the brachial plexus should be performed with the arm at the patient’s side to relax the shoulder. High-frequency ultrasound can be used to image the brachial plexus within the posterior triangle of the neck. In this location, the nerves of the brachial plexus do not contain an abundance of connective tissue. Therefore, the nerves appear hypoechoic on ultrasound scans (see Figure 15-7). Using an in-plane technique, local anesthetic can be deposited adjacent to the brachial plexus between the anterior and middle scalene muscles. Injection of 20 to 30 mL of local anesthetic solution will anesthetize the cervical plexus and brachial plexus, and thus permit surgery on the shoulder and more distal upper extremity, although fibers that innervate the ulnar side of the forearm and hand (C8-T1, inferior trunk) may be spared (Figure 15-6). (288-289)
28. Advantages of brachial plexus blockade via the interscalene approach include a relatively low risk of pneumothorax, ease of palpation of necessary landmarks, and ease of nerve imaging with ultrasound. Additionally, it is possible to perform the block with the patient’s arm at his or her side. (288)
29. A disadvantage of brachial plexus blockade via the interscalene approach is the inconsistency with which the inferior trunk of the brachial plexus is blocked, making it possible that surgery involving the C8-T1 dermatomes will have inadequate anesthesia. (288)
30. Complications of brachial plexus blockade via the interscalene approach include phrenic and recurrent laryngeal nerve blocks; epidural, intrathecal, and intravascular injections; and nerve damage. (288-289)
31. Supraclavicular block of the brachial plexus is achieved by injecting 20 to 30 mL of local anesthetic solution around the brachial plexus where it is usually tightly bundled and adjacent to the subclavian artery, just cephalad to the clavicle. The supraclavicular block can be performed with a similar technique to interscalene blocks. The ultrasound probe is moved closer to the clavicle and faces caudally to facilitate imaging of the brachial plexus adjacent to the subclavian artery and over the first rib. In this location, almost all practitioners use the in-plane technique because of the proximity of the pleura. (289)
32. Advantages of a supraclavicular block are rapid onset and ability to perform the block with the arm in any position. Additionally the nerves are tightly bundled in this location. (289)
33. Complications of brachial plexus blockade via the supraclavicular approach include its relatively increased risk of a pneumothorax. In fact, the incidence of a pneumothorax with this technique is about 1%, making it a poor choice for patients with respiratory compromise. Other complications include phrenic nerve block, Horner syndrome, and nerve injury. (289)
34. An axillary brachial plexus block is achieved by injecting 30 to 40 mL of local anesthetic solution around the nerves that lie in close proximity to the axillary artery (Figure 15-9). At the level of the axilla, the terminal branches of the brachial plexus reside within the axillary sheath and in the tissue that immediately surrounds it (see Figure 15-9). The patient is positioned supine with the arm abducted to 90 degrees and externally rotated to gain access to the axilla. A high-frequency ultrasound transducer is placed in the axilla, showing the brachial artery and the surrounding nerves of the brachial plexus. A needle is advanced from superior to inferior within the plane of imaging so that the tip lies within the axillary sheath. Multiple injections of local anesthetic surround each of the nerves, including the musculocutaneous nerve, which lies lateral to the brachial plexus in the Five muscle. (290-292)
35. An axillary block can be used for anesthesia of the hand, forearm, and elbow. (290)
36. Five milliliters of local anesthetic solution is infiltrated into the subcutaneous tissue immediately superficial to the axillary artery to block the intercostobrachial, medial brachial cutaneous, and medial antebrachial cutaneous nerves. (292)
37. An axillary perivascular block has the advantage of being remote from the lung and neuraxis, and can therefore be performed with relative safety. (292)
38. Potential complications of brachial plexus blockade via the axillary approach include systemic local anesthetic toxicity as a result of intravascular injection and nerve injury from needle trauma, intraneural injection, and hematoma. (292)
Distal nerve blocks of the upper extremity
39. The median nerve provides most of the sensory innervation to the palm of the hand. The forearm is scanned in short axis with high-frequency ultrasound showing the median nerve with a fine fascicular appearance that is distinct from the surrounding muscles and tendons. Under continuous visualization, 3 to 5 mL of local anesthetic is injected around the median nerve. (292)
40. The ulnar nerve provides sensation to the dorsal and palmar sides of the ulnar aspect of the hand. The ulnar nerve is blocked by injecting 3 to 5 mL of local anesthetic solution around the ulnar nerve in the forearm, usually at a level in the forearm where the ulnar nerve is not in direct contact with the ulnar artery. (292)
41. Most patients have radial dominance of sensation on the dorsal aspect of the hand. The superficial radial nerve is the distal sensory branch of the radial nerve that follows the radial artery along its course through the forearm. It can be blocked by ultrasound-guided infiltration of 3 to 5 mL of local anesthetic solution anywhere along its course deep to the brachioradialis muscle or in a subcutaneous ring at the level of the anatomic snuffbox. (292-293)
Blocks of the lower extremity
42. Unlike the compactness of the brachial plexus, the lower extremity is supplied by nerves that are widely separated from each other as they enter the thigh. For many operations, it is easier to perform an epidural or spinal anesthetic than to attempt the same extent of anesthesia with multiple peripheral nerve blocks. (293)
43. The four major nerves of the lower extremity are the sciatic, femoral, lateral femoral cutaneous, and obturator nerves. (293)
44. The sacral plexus (L4-5, S1-3) gives rise to the sciatic nerve, which is nearly 2 cm wide as it leaves the pelvis. (294-296)
45. Sciatic nerve blockade provides nearly complete anesthesia of the foot and lower part of the leg. More often, a sciatic nerve block is combined with a femoral nerve block to provide more extensive anesthesia of the lower extremity. (294-296)
46. The classic approach to sciatic nerve blockade is with the patient lying on the side opposite the nerve to be blocked (Figure 15-14). A line is drawn between the posterior superior iliac spine and the greater trochanter of the femur. Using a peripheral nerve stimulator, the needle is inserted about 5 cm caudad from the midpoint of this line. Foot movement evoked by nerve stimulation is a satisfactory end point for needle placement before the injection of local anesthetic solution (about 25 to 30 mL is typically used). (294-296)
47. The femoral nerve is derived from L2, L3, and L4. The femoral nerve reaches the thigh by passing underneath the inguinal ligament just lateral to the femoral artery and vein, and separated from them by the iliopectineal ligament. The femoral nerve lies deep to the fascia iliaca, which invests the iliopsoas muscle. Along its course, the femoral nerve divides into multiple anterior cutaneous branches of the thigh and gives rise to the saphenous nerve of the medial aspect of the leg. (293-294)
48. Femoral nerve blockade is most often used together with other nerve blocks for surgery in the leg. Alone, femoral nerve blockade provides anesthesia of the anterior thigh and may be used for muscle biopsies in that area. (293)
49. Femoral nerve blockade is performed with the patient in the supine position and the thigh slightly abducted and externally rotated to improve access. The femoral nerve is appreciated on sonograms as a flattened bundle of fascicles lying between the hypoechoic subcutaneous tissue and the hyperechoic iliopsoas muscle (Figure 15-12). The block needle is advanced within the plane of imaging from lateral to medial until it punctures the fascia iliaca, with a distinct pop. The needle position is optimized to create the circumferential spread of 20 to 30 mL of local anesthetic around the femoral nerve. (294)
50. The saphenous nerve is a branch of the femoral nerve that contributes to innervation below the knee. (294)
51. The saphenous nerve is blocked at the midthigh level, where it lies anterior to the femoral artery (Figure 15-13). The femoral artery is a landmark for the saphenous nerve, both of which lie just deep to the sartorius muscle (see Figure 15-13). The block needle is advanced within the plane of imaging and 5 to 10 mL of local anesthetic is deposited deep to the sartorius muscle, adjacent to the femoral artery. (294-295)
52. Popliteal nerve blockade provides sciatic nerve anesthesia near the point where the sciatic nerve divides into its common peroneal and tibial nerve components in the popliteal fossa. It is most commonly used for foot and ankle surgery. (296)
53. Femoral or saphenous nerve blockade can be performed in addition to a popliteal nerve block to improve tourniquet tolerance and for surgery that involves the medial aspect of the leg. (296)
54. The tibial, sural, deep peroneal, superficial peroneal, and saphenous nerves supply the entire innervation to the foot. The tibial nerve innervates the sole of the foot, heel, and plantar portion of the toes. The sural nerve innervates the lateral portion of the foot and ankle. The deep peroneal nerve innervates primarily between the first two digits of the foot. The superficial peroneal nerve innervates the majority of the dorsum of the foot. The saphenous nerve innervates the medial foot and ankle. (296-297)
55. The tibial nerve lies on the heel side of the posterior tibial artery and can be blocked by infiltrating 3 to 5 mL of local anesthetic solution in a fanning pattern around this artery. The sural nerve can be blocked by injecting 5 mL of local anesthetic solution in the groove between the lateral malleolus and the calcaneus near the small saphenous vein. The saphenous nerve is blocked by infiltration of 5 mL of local anesthetic solution anterior to the medial malleolus near the great saphenous. The deep peroneal is blocked by injecting 5 mL of local anesthetic solution adjacent to the anterior tibial artery. Alternatively, if arterial pulsation is absent, the deep peroneal nerve can also be blocked deep to the extensor hallucis longus tendon and extensor retinaculum. The superficial peroneal nerve’s terminal branches are blocked by injecting a subcutaneous ridge of local anesthetic between the medial and lateral malleoli over the anterior surface of the foot. (296-297)
Intravenous regional neural anesthesia
56. Intravenous regional neural anesthesia (Bier block) is commonly used for anesthesia for short surgical procedures on an extremity, particularly those in which postoperative pain is not expected to be significant. (297)
57. Contraindications to a Bier block are essentially contraindications to tourniquet application (sickle cell disease, infection, ischemic vascular disease). Pain limits the effectiveness of exsanguination of extremities with fractures. Traumatic lacerations may allow escape of local anesthetic from the extremity. (297)
58. A Bier block is achieved by first placing an intravenous catheter distal in the extremity to be anesthetized. The extremity is then exsanguinated, a double tourniquet is placed proximal in the extremity, and the more proximal cuff is inflated. A dose of local anesthetic based on the patient’s weight is administered slowly. The volume of local anesthetic is 40 to 50 mL in the upper extremity. If the patient starts to develop tourniquet pain during the procedure, the distal cuff may be inflated and the proximal cuff deflated. (297)
59. Commonly used local anesthetic solutions for intravenous regional neural anesthesia are 0.5% lidocaine or prilocaine (plain solutions without epinephrine). Bupivacaine is avoided because of potential systemic toxicity, most notably malignant ventricular cardiac dysrhythmias leading to refractory cardiac arrest. (297)
60. Technically, a regional intravenous neural block is easier and faster to perform than a brachial plexus block or lower extremity block and is readily applicable to all age groups, including pediatric patients. (297-298)
61. Severe tourniquet pain and the maximum allowable tourniquet time limit the practical duration of the block. Because the duration of postoperative analgesia is also limited, this procedure is not usually performed when postoperative pain is a significant issue. (297-298)
62. A complication of a Bier block includes the risk of excessive, toxic doses of local anesthetic reaching the systemic circulation with accidental deflation of the tourniquet. This risk can be minimized at the conclusion of cases 20 to 40 minutes in duration by deflating the tourniquet in increments over time. This allows the local anesthetic to enter the systemic circulation over a greater period of time. (298)
