Chapter 49. Peripheral Nerve Blocks

1. The duration of the surgical procedure, patient comorbidities, and postoperative factors, such as the early need for the use of the operative extremity and potential for significant postoperative discomfort, should all be used to determine the selection of local anesthetic and technique.

2. The lowest clinically effective dose of a local anesthetic should be used whenever possible to minimize toxicity.

3. Studies to date have shown that ultrasound decreases the time for placement of peripheral nerve blocks, increases the speed of block set-up, and improves the "quality" of the block by modest amounts when compared with the traditional landmark techniques or nerve stimulation.

4. Because the frequency of neurologic injury is low with peripheral nerve blocks, no single technique has been shown to be "safer" than another.

5. The use of ultrasound does not replace the need for a fundamental understanding of anatomy when placing peripheral nerve blocks.

6. The interscalene approach to the brachial plexus, unlike the supraclavicular approach, will most likely miss the ulnar distribution of the hand; thus it is not suitable as a complete anesthetic distal to the elbow.

7. Femoral nerve block is a relatively easy block to perform and its success rate is high. A femoral nerve block is usually performed in conjunction with other lower-extremity blocks.

8. The popliteal approach to the sciatic nerve can be done with the patient supine or prone and is ideal for surgeries involving the lower leg and/or foot. If the medial aspect of the lower leg or foot is required for surgical anesthesia, then the saphenous portion of the femoral nerve must be included.

Peripheral nerve blocks are a powerful component of the practice of anesthesia. No other anesthetic technique allows a precise targeting of anesthetic to the surgical site while sparing non–procedure-involved locations. This not only allows one to create tailored area of surgical anesthesia, but also to avoid, or reduce, the risk of systemic complications from general anesthesia such as nausea and vomiting.1,2 To perform a peripheral nerve block, one must have a local anesthetic, a means to administer the anesthetic, and a target nerve structure.

The modern knowledge of anatomy can be traced to the Renaissance, when scholars once again began using cadavers to teach their students anatomy after the Church banned cadaveric dissection during the Middle Ages. It was the "reawakening" of such scholars as Andreas Vesalius and the publication of his De Humani Corporis Fabrica (On the Structure of the Human Body) that shaped the modern day study of anatomy.3 However, the mapping of dermatomes and the understanding of peripheral nerve anatomy would not begin until the late 1800s. The combination of the observations of French neurologist Jean Martin Charcot and the American scholar Silas Weir Mitchell would begin to suggest the need for "cutaneous nerve mapping."4 Mitchell especially seemed to be a keen observer and was interested in peripheral nerve anatomy as he cared for injured veterans from the American Civil War.4 However, it was the English surgical registrar William Thorburn who published some of the first dermatomal maps in the 1880s based on observation of patients with spinal cord lesions.4

The discovery and development of local anesthesia can be traced back to the jungles of South America with the coca leaf, first described to the West by Amerigo Vespucci in the log of his 1499-1500 expedition.5 It was not until 1855 that the German chemist Friedrich Gaedke isolated the cocaine alkaloid, and it would take another 29 years before Karl Köller, a Viennese ophthalmologist, would use it first in a clinical setting in 1884.5 The early 1900s witnessed further local anesthetic discoveries, the most significant being procaine in 1904 by Alfred Einhorn. It was the Swedish chemist Nils Löfgren who synthesized lidocaine, the first of many amide local anesthetics.5

The invention of the hypodermic needle and syringe is credited to 2 individuals who developed their respective devices independently in 1853, the Scottish physician Alexander Wood and the French surgeon Charles Gabriel Pravaz. However, it was Wood who first published the medical use of the device when he used it to inject morphine to treat neuralgia.5,6

Modern day regional anesthesia techniques did not take foot in the United States until Gaston Labat published Regional Anesthesia: Its Technic and Application in 1922.7 Labat's book was written while he was teaching regional anesthesia techniques at the Mayo Clinic under the invitation of Charles Mayo. The text was the first of its kind published in the United States and would be the standard reference for the performance of peripheral nerve blocks through the first half of the 20th century.7,8 In deference to his contributions, it was proposed that the American Society of Regional Anesthesia be named the Labat Society when it was founded in 1923.9

Modern regional anesthesia techniques have grown from the solid and broad foundation established in the early 20th century with the further development and introduction of the amide local anesthetics and modern nerve localization techniques, such as nerve stimulation and ultrasound guidance. What has not changed is the dedication of anesthesiologists to their patients' safety and comfort.

The primary variable used in selection of local anesthetics is arguably the duration of the surgical procedure. It should be obvious that a peripheral nerve block that resolves before the conclusion of the surgical procedure has a negative clinical impact on the patient. A long-acting peripheral nerve block may not be ideal either, especially if a patient will need to ambulate or use the affected limb in the early postoperative period. Studies have also shown that total dosage or mass of local anesthetic is the primary contributor to block density.10-12 Thus a block with a higher concentration and lower volume of local anesthetic may provide a more profound block than a lower concentration, higher volume block.10

Another variable to be cognizant of when selecting a local anesthetic is toxicity. The overall volume and concentration of injected local anesthetic both contribute to the potential risk of toxicity (Table 49-1). Commonly cited maximum dosage limits (such as 3 mg/kg for bupivacaine and 4.5 mg/kg for lidocaine without epinephrine) have not been rigorously studied or confirmed except in the pediatric population.13 In addition, absorption of local anesthetics differs throughout the human body and from individual to individual. Therefore, the "toxic dose" in one location that has higher systemic absorption (eg, the intercostal space) may be much lower than an area with more limited systemic absorption (eg, around the sciatic nerve). Regardless, when injecting any local anesthetic for a peripheral nerve block, one should attempt to use the lowest dose possible for a successful block and perform the injection in a slow, deliberate manner with repeated aspiration during the course of injection to confirm that the needle has not migrated into a vascular structure. Traditionally, a vascular injection "indicator" such as epinephrine has been added to the local anesthetic solution to hint at an intravascular injection. The new technology of ultrasound guidance allows one to visualize the spread of local anesthetic to confirm correct placement and therefore may replace the need for an indicator in the future. Patients should also be monitored closely both during and after the injection for signs of toxicity. An unintended intravascular injection can show almost immediate signs of toxicity, whereas toxicity from systemic absorption (eg, a large volume placed correctly for a peripheral nerve block) may take 30 minutes to an hour to manifest.

Lidocaine has a fairly short onset and duration of action, making it ideal for stimulating surgical procedures of less than a couple hours duration. However, these properties are its weakness as well. It is not the best option for prolonged procedures or for postoperative pain control. Typically 2% lidocaine is the concentration selected for short-duration profound surgical anesthesia.

Bupivacaine has a slower onset of action compared with lidocaine. However, its duration of action can be up to 24 hours with an appropriate volume and placement. It is a good choice for peripheral nerve blocks placed for postoperative pain control or surgical anesthetics for procedures that are expected to be more than a couple of hours. Higher volumes and concentrations of bupivacaine may cause a profound block to be formed that can be used as a surgical anesthetic. Many early studies of peripheral nerve blocks typically used volumes of 30 to 40 mL of 0.5% bupivacaine; however, dosages of 0.25 mL/kg with the maximum of 30 mL are now being used. Bupivacaine does have serious toxic potential when contrasted with shorter-acting local anesthetics. Its affinity for blocking sodium channels in the cardiac conduction fibers resulting in sudden cardiac death should be approached with vigilance by practitioners. (Recent case reports and a small study in dogs have suggested that infusion with 20% lipid emulsion may rescue patients suffering from bupivacaine toxicity.14,15) Higher concentrations may also prolong a peripheral nerve block longer than intended, thus interfering with the patient's ability to ambulate or perform postoperative physical therapy. Typically 0.5% bupivacaine is used for a surgical anesthetic, with 0.2% to 0.3% used through a catheter or single shot for postoperative pain control in order to provide some muscle sparing.

Ropivacaine is an enantiomer of bupivacaine with similar properties as bupivacaine in terms of onset and duration of action. It has been suggested that ropivacaine provides more profound sensory than motor block as compared with bupivacaine, and ropivacaine has also been shown to have a slightly shorter duration of action as compared with bupivacaine.16 One potential advantage of ropivacaine compared with bupivacaine is that it is not as cardiotoxic as bupivacaine.17 Thus it is good selection for blocks that are placed with high volumes or for blocks where there is going to be significant systemic uptake. As with bupivacaine, 0.5% ropivacaine is a suitable choice for a surgical anesthetic, and 0.2% to 0.3% ropivacaine is a good choice for a continuous catheter or a single-shot block for postoperative pain control.

Chloroprocaine is a very short-onset and short-duration local anesthetic. It is a suitable choice for surgical procedures of 30 to 45 minutes in duration and for procedures with minimal expected postoperative pain. Chloroprocaine can also be bolused through a continuous nerve catheter to ensure proper function or as a "rescue" injection.

Mepivacaine 2% is also used for peripheral nerve blocks, as its onset is similar to lidocaine; however, its duration of action is longer. It is a good choice for surgical procedures in which a block of 2 to 3 hours duration is needed with postoperative return of limb function being necessary and postoperative pain not expected to be severe.

Additives can prolong the duration of the sensory component or both motor and sensory components of a peripheral nerve block. However, additives are not without their own side effects and contraindications; thus their selection must also be carefully considered before their inclusion in a local anesthetic "cocktail" for a peripheral nerve block.

Epinephrine is probably one of the most commonly used additives with peripheral nerve blocks. It is typically added in a concentration that is 1:200 000 to 1:400 000 parts per solution (5-10 μg/mL). It decreases the local anesthetic uptake by causing vasoconstriction at the site of injection, thus prolonging the duration of peripheral nerve blocks when added to the local anesthetic solutions of short- and mid-duration local anesthetics. Epinephrine is a potent vasoconstrictor, so it should be avoided in distal extremity blocks such as an ankle block or a forearm block. It also can cause systemic hypertension and tachycardia if injected intravascularly; thus it should be used with caution in patients with cardiac disease. However, it has been traditionally added to local anesthetic solutions as an indicator for intravascular injection because of these very properties.

Clonidine is an α2-agonist that has been shown to provide prolongation of peripheral nerve blocks when used in doses between 10 and 150 μg.18,19 This prolongation is more sensory than motor in nature and provides a relatively small increase in duration of bupivacaine when compared with the shorter-acting local anesthetics such as lidocaine and mepivacaine.18,19 The "ideal" dose has not been conclusively demonstrated; however, with increasing dosages, there are increasing side effects.19 Most notable are hypotension, bradycardia, sedation, and low body temperature.

Dexamethasone has been shown in a small study to prolong the duration of an axillary nerve block when used with lidocaine. However, this study did have a very small sample size.20 This has not been replicated in studies with bupivacaine except when the dexamethasone was combined with bupivacaine in microspheres.21 Although the exact mechanism of action is unknown, the prolongation of the nerve block with dexamethasone in microspheres can be several days. Thus this area of active research portends to have a potential significant impact on peripheral nerve blocks in the future.

Opioids have been routinely added to peripheral nerve blocks for their presumed synergistic effects; however, they have not been shown to increase the duration, onset, or quality of the block.22-24

Nonsteroidal anti-inflammatory drugs (NSAIDs) have been proposed to be added to peripheral nerve blocks to prolong the analgesic duration of the block. To date there have been very few studies to support the use of NSAIDS as additions to local anesthetic solutions for peripheral nerve blocks.23,25

The choice of technique has evolved over the last 30 years. Originally landmark techniques were the only methods for placing peripheral nerve blocks. In fact, the nomenclature that is used for the majority of peripheral nerve blocks owes its existence to the landmark technique. Descriptions of supraclavicular, infraclavicular, interscalene, and axillary do not correlate to a particular nerve structure, but to the area of the body where the brachial plexus will be encountered. The true landmark techniques are techniques where the needle is placed and directed into the body based on certain surface anatomical landmarks. The clinician, through tactile stimulation of "clicks and pops," ascertains whether he or she is in the correct position to inject local anesthetic. Daniel C. Moore, MD, astutely coined the phrase "No paresthesia, no analgesia" to describe the performance of these techniques.26

Nerve stimulation was the next "evolution" for facilitating the placement of peripheral nerve blocks. Nerve stimulation is founded on the landmark technique; however, an insulated needle is used, connected to a pulse generator with an additional lead attached to the patient to complete a circuit (Fig. 49-1). When the needle is advanced within the proximity of a nerve, a muscle twitch is witnessed in the distribution of the stimulated nerve. This helped increase the accuracy of peripheral nerve blocks; however, it still remains a blind technique. It also should be noted that there is a false-negative rate of between 10% and 15% when a nerve simulator is used.27

Ultrasound-guided regional anesthesia is the most recent technique used to place peripheral nerve blocks (Fig. 49-2). The technique uses ultrasound to identify the target nerve structure and the needle such that the needle can be guided near the nerve structure accurately. More importantly, ultrasound allows one to see the spread of local anesthetic around the target nerve structure. Ultrasound was first used to facilitate the placement of peripheral nerve blocks in 1978 by La Grange when he used a Doppler to map the subclavian artery when placing a supraclavicular nerve block.28 It would be another decade before the 2-dimensional ultrasound was used in the placement of peripheral nerve blocks.29 Currently the popularity of ultrasound-guided techniques is rapidly expanding. Studies to date have shown that ultrasound decreases the time for placement of peripheral nerve blocks, increases the speed of block set-up, and improves the "quality" of the block as compared with the traditional landmark techniques or nerve stimulation by modest amounts.30–32 It should be pointed out, however, that the available randomized, controlled studies have low patient numbers and that their overall number is rather limited. It also should be stressed that to date there has been no conclusive evidence that one technique is "safer" as compared with another because the number of patients that would need to be enrolled to ensure adequate power would be in the hundreds of thousands. Perhaps the greatest contribution of ultrasound is that it enables moderately experienced regional anesthesiologists to have success rates similar to those of expert regional experts.

With ultrasound there are 2 ways to orientate the needle with the beam of the ultrasound probe (Fig. 49-3). The in-plane technique has the needle imaged along its entire course from the hub to the point. It is believed that this adds safety because the needle is imaged its entire length, and thus objects such as veins and arteries can be avoided. The other technique is the out-of-plane technique, in which the needle is imaged in cross section. This technique demands vigilance by the operator to make sure that the needle tip is known because the needle could be bisected anywhere along the needle shaft. Thus it is possible that with this technique the needle may appear to be outside a vascular structure; however, in reality it may be lodged within it. To avoid this complication when using the out-of-plane technique, it can also be useful to slide the probe down the trajectory of the needle to help identify the needle tip. Another technique is to give a "puff" of saline while advancing the needle and look for the spread on the ultrasound image. If the needle is in view, but the saline puff is not visualized, then it is the needle shaft and not the tip that is being imaged. Echogenic needles with etched patterns at the tip that display a characteristic pattern on ultrasound have recently been developed to help the practitioner identify the needle tip as well (Fig. 49-4).

Regardless of which needle approach is selected, it is useless without an optimized ultrasound image with the target nerve structure and structures to avoid identified. The transducer manipulation technique by which an ultrasound image is formed and optimized has also been recently standardized as the PART maneuvers (Pressure, Alignment, Rotation, and Tilting)33 (Fig. 49-5). Pressure is applied to the patient to improve contact between the probe and the patient. Alignment relates to characterizing the course of the target nerve structure in a longitudinal axis. Rotation is achieved by rotating the transducer either clockwise or counter-clockwise to optimize the image of the target structure. Tilting describes the tilting of the transducer probe to improve the angle of incidence upon the target nerve structure.33 It is only after the ultrasound image has been optimized that the needle should be placed in the patient.

Only time will show whether the traditional landmark and nerve stimulation techniques will be completely replaced by ultrasound guidance or a new hybrid technique of ultrasound with nerve stimulation will become the new gold standard. It should be mentioned, however, that no matter what nerve location technique is used (ultrasound vs nerve stimulation vs landmark), none are a substitute for the fundamental knowledge of anatomy.

Needle selection for peripheral nerve blocks is not standardized. Certainly insulated needles are optimal for nerve stimulation techniques and there are ultrasound-lucent needles for ultrasound-guided techniques, although the clinical benefit over a standard needle has yet to be demonstrated. Touhy needles are great choices for placement of nerve catheters regardless of nerve localization technique used to place the block. We use B-bevel needles for single-shot nerve blocks because we believe the blunted bevel adds an extra degree of safety, although this has never been demonstrated. Lengths of 50 to 100 mm are usually more than adequate to place the standard blocks in all but the largest patients.

Nerve stimulators are modestly priced pulse generators that should be able to generate a current from 0.1 to 10 mA. A nerve stimulator should also have the ability to adjust this current in small 0.1-mA increments, thus allowing the practitioner to be able to adjust the needle for nerve localization with accuracy.

The purchase of an ultrasound machine is a major expenditure. There are stand-alone machines that must be wheeled to the patient and portable machines that can be carried. The images on the stand-alone tend to be of higher fidelity; however, this probably does not have a clinical impact except in the most difficult morphologic patients. Portable machines allow one to perform peripheral nerve blocks in other nontraditional locations in the hospital and can be moved easily and expeditiously between operating rooms as needed. The selection of transducer probe is also vitally important (Fig. 49-6). We prefer a linear probe that is 25 to 38 mm in length with the capability of 8 to 12 MHz at a minimum. The lower frequency allows deeper penetration for blocks of the lower extremity, and the higher frequency is better for more peripheral structures, such as the brachial plexus. Curvilinear probes are good for performing neuraxial blocks or very deep blocks in the extremities such as the infragluteal or transgluteal sciatic block. Generally the frequency of such probes is lower than 8 MHz, which is necessary to penetrate several centimeters of tissue.

There are many branch points that must be traversed in the decision-making process before placing a peripheral nerve block. The first question that must be answered is whether a regional anesthetic is appropriate to place in the selected patient. The patient may not wish to have a regional anesthetic, the surgical site may not be easily anesthetized with a regional technique, or the patient may have a high potential for a nerve injury either intraoperatively or postoperatively that could be masked by a peripheral nerve block. The next question is whether to sedate the patient for the peripheral nerve block. Our personal preference is to sedate the patient with a low-dose opioid and benzodiazepine (fentanyl and midazolam). This relieves the discomfort of placing the block as well as patient anxiety. However, be careful not to oversedate, as the patient then will not be able to help with positioning and more importantly will be unable to communicate discomfort with the block placement. It is because of this latter point that some practitioners refuse to sedate their patients before placing a regional anesthetic, as they would like the added safety measure of a responsive patient. Traditionally peripheral nerve blocks have not been placed in anesthetized patients due to the lack of input being perceived as a possible safety hazard. However, with the advent of ultrasound, placing peripheral nerve blocks in anesthetized patients has begun to emerge once again as a possibility. This has been demonstrated by several recent regional anesthesia studies in anesthetized pediatric patients.34-36

The next decision that has to be made is whether a single-shot or catheter is more appropriate for the patient. Single-shot blocks have variable durations depending on volume and selected local anesthetic agent. The continuous catheter, when functioning properly, gives the practitioner the ability to provide consistent regional anesthesia to a patient for several days. Potential drawbacks, however, remain infectious risks and follow-up.37-39 There is also the question of the safety of a continuous catheter in an anticoagulated patient.40-42

Selection of a local anesthetic also needs to address postoperative factors as well, such as need for ambulation, need for participation in physical therapy, and the need to perform tasks of daily living. Concentration appears to influence the duration as well as the quality of the block. Lower concentrations provide analgesia but have been shown to have some motor sparing, thus allowing the patient to ambulate or perform basic tasks sooner postoperatively, which may have benefits to the patient's overall outcome.43-47 Lower concentrations are predominately used in blocks primarily placed for postoperative pain control and for nerve catheter infusions. Likewise, higher concentrations may provide a more profound block and thus be more appropriate for blocks placed for a primary surgical anesthetic.

An additional factor for the selection of a local anesthetic is speed of onset of the block. This can have major clinical implications if not selected properly. If the operating room will be ready for the patient within 10 minutes and you are placing a block for a surgical anesthetic, then selection of a slower-onset local anesthetic may not be efficient enough, and thus a rapid onset local anesthetic should be chosen. The difficulty then is what to do with a patient who will be in the operating room shortly, but needs a prolonged block for postoperative pain control. Clearly bupivacaine would be ideal for its duration of action; however, its slower onset may not be efficient enough. Likewise, lidocaine's rapid onset may be necessary; however, its short duration of action would not be in the patient's interest. The mixing of local anesthetics has shown that their properties are affected by the presence of an additional local anesthetic.40 In the preceding combination of 1:1 bupivacaine and lidocaine, the resulting mixture would have an onset longer than lidocaine, but its duration of action would be reduced from that of bupivacaine. Other techniques that can be used to prolong block duration are the use of continuous catheters, the use of adjuvants within the local anesthetic solutions (eg, epinephrine), and the placement of the local anesthetic itself in relation to the target nerve structures.

Toxicity is another factor that needs to be addressed with the selection of a local anesthetic. The placement of large volumes in highly vascular areas increases the risk of toxicity from local anesthetics. Thus it may be wise to reduce volumes or use a less catastrophically toxic local anesthetic when performing a block that requires a large dose of local anesthetic. Typically volumes of 5 to 30 mL are used for placement of peripheral nerve blocks.

There is not a large volume of randomized controlled studies to support or refute the placement of peripheral nerve blocks in anticoagulated patients. For years some practitioners extrapolated the 2002 American Society of Regional Anesthesiologists (ASRA) consensus statement for placement of neuraxial anesthetics to peripheral nerve blocks.41 In 2010 ASRA submitted a practice advisory for the placement of a peripheral nerve block in an anticoagulated patient.42 Although these 2 documents only provide recommendations, it is in the regional anesthesia provider's and patient's interest to adhere to them when possible.

The brachial plexus is derived primarily from the cervical nerve roots of C5, C6, C7, C8, and T1, although there are variable contributions from C4 and T2 as well. As the roots emerge from between the anterior and middle scalene muscle, they form 3 trunks that are cephalad and posterior to the subclavian artery. At the level just above the clavicle, each trunk begins to transition to an anterior and posterior division; however, there is a high degree of variability between individuals at this level, and some continue to have trunks to just below the clavicle. Once the brachial plexus passes under the clavicle, at the lateral border of the first rib, the divisions combine to form the medial, posterior, and lateral cords around the subclavian artery. They then emerge from the lateral border of the pectoralis minor and become the peripheral nerves of the upper extremity. The ulnar, radial, and median nerves lie adjacent to the axillary artery in most individuals with the musculocutaneous between the muscle bellies of the biceps and the coracobrachialis (Fig. 49-7).

Cervical Plexus

Anatomy

The cervical plexus can be divided into the superficial and deep branches, both of which have their origins from the anterior rami of C2, C3, and C4 that lie directly under the sternocleidomastoid muscle. It is the superficial plexus that innervates the skin of the neck, posterior head, and superior shoulder. The deep cervical plexus innervates the muscles and other structures of the neck. It should be noted that C4 can participate in the formation of the brachial plexus in certain individuals. It also should be mentioned that with the deep cervical plexus block, it is possible to partially block the phrenic nerve because its origins are from C3, C4, and C5.

Technique

First position the patient supine with the neck turned away from the surgical site with the practitioner on the ipsilateral side. To block the deep cervical plexus, identify the mastoid process and the prominent transverse process of C6 (Chassaignac tubercle) (Fig. 49-8). The first of 2 lines is drawn from the mastoid to the Chassaignac tubercle. The C2 transverse process should then be palpated along this line approximately 1 cm caudal to the mastoid and then marked. This should be repeated with the C3 and C4 transverse processes as well by palpating down the line between the mastoid and the C6 transverse process. Once all of the processes are marked, a needle should be inserted over the C4 process until it contacts the C4 process at roughly 2 to 3 cm of depth (Fig. 49-9). A paresthesia may be obtained upon which 10 mL of local anesthetic should be injected with intermittent aspiration. If no paresthesia is obtained, then the needle can be walked along the line in a superior or anterior direction until a paresthesia is elicited. To block the superficial cervical plexus, asking the patient to lift their head should identify the lateral border of the sternocleidomastoid muscle. The midpoint of this border should be marked. The needle should then be advanced approximately 1 cm deep to the sternocleidomastoid muscle. It then can be withdrawn slightly and then redirected superior and inferior along the lateral border of the sternocleidomastoid muscle (Fig. 49-10).

The ultrasound technique requires one to identify the anterior scalene muscle and trace it cranially up the neck until it tapers off at C3 or C4. The longus capitus muscle should be anterior to the remnant of the anterior scalene at this level (Fig. 49-11). The needle should be directed into the longus capitus muscle and an injection of 5 to 10 mL should be performed.49 For the superficial plexus, the sternocleidomastoid muscle should be identified at the level of the interscalene groove. The needle should be directed immediately under the lateral border of the sternocleidomastoid muscle, and 10 mL of local anesthetic should be injected (Fig. 49-12).

Pearls and Pitfalls

Because the phrenic nerve will most likely be blocked with the deep cervical plexus block, it should go without saying that bilateral plexus blocks should be avoided. This block also is near several structures that must be avoided, such as the vertebral artery, the intrathecal space, and the spinal cord itself. Standard safety techniques should be used with vigilance, such as intermittent aspiration upon injection of local anesthetic and the use of epinephrine in the local anesthetic solution. This block provides excellent coverage for carotid endarterectomies and for supplementation for the superior shoulder if necessary after an interscalene block.

Interscalene

Anatomy

The C5, C6, and C7 nerve roots represent the brachial plexus at the level of the interscalene groove as they emerge from between the anterior and middle scalene muscles in the lateral neck. There are several documented variations to the brachial plexus at this level, one of the most common being perforation of the anterior scalene muscle by the C5 nerve root itself.50 The interscalene groove may be palpated by moving one's fingers posterior and laterally from the lateral edge of the sternocleidomastoid muscle at the level of the cricoid cartilage. To facilitate identification of these landmarks, the patient should be asked to turn their head away from the side to be blocked and should be asked to raise their head off of the bed momentarily in order to identify the lateral edge of the sternocleidomastoid muscle (Fig. 49-13).

Technique

With traditional landmark techniques initially described by Winnie, a needle is advanced in the interscalene groove at a 45-degree angle caudad and slightly posterior51 (Fig. 49-14). A contraction of the shoulder or arm should be elicited if using nerve stimulation or a paresthesia over one of the dermatomes of the plexus if using only a blunted needle.

To facilitate placement with the ultrasound technique, we place the patient in the full lateral position with the nonoperative side dependent or slightly rotated, with a bump under the operative side depending on patient body habitus. The ultrasound probe is then placed over the interscalene groove in a medial/lateral plane at the level of the cricoid cartilage (Fig. 49-15). The nerve roots of the brachial plexus should appear as 3 distinct hypoechoic or dark circles between the anterior and middle scalene muscles (Fig. 49-16). The needle should be advanced in-plane in a posterior to anterior direction with the needle tip aiming between the C5 and C6 nerve root. When a distinct "pop" is felt or observed into the fascia around the nerve roots and injection should commence after negative aspiration, local anesthetic should be observed surrounding the nerve roots.

For a continuous-catheter technique, the procedure is the same as a single shot; however, a 19-gauge Touhy needle should be used. Once the needle has penetrated the fascia between C5 and C6, a small bolus of 5 mL of normal saline should be placed to expand the sheath to facilitate catheter placement. Once the sheath has been expanded, a stimulating catheter should be inserted and visualized near the brachial plexus and potentially "hooking around" one of the nerve roots. This catheter will only be inserted 1 to 2 cm. Once in place, the needle is removed. Confirmation of correct placement comes with bolusing the catheter and watching the circumferential spread of local anesthetic during ultrasound imaging.52

Pearls and Pitfalls

With traditional techniques, if bone is contacted within 2 cm of the skin, it is likely that one has contacted the transverse process of a cervical vertebrae and the needle should be angled either more caudad or cephalad to find the plexus. If using nerve stimulation, beware of mistaking contraction of the diaphragm as the intended twitch, as this is an indication that the needle is located too anterior.

With ultrasound techniques, it is possible to approach with the needle from the medial to lateral direction. However, the medial approach should be avoided because the carotid artery and internal jugular vein are immediately under your insertion site and thus are at risk of puncture. Also the phrenic nerve lies on the anterior border of the anterior scalene muscle and may be injured with this trajectory.

Interscalene nerve block, if performed correctly, should spare the ulnar distribution; thus it is not an appropriate block for surgeries distal to the elbow. The interscalene block also carries an almost certain risk of transient ipsilateral diaphragm paralysis and thus should be avoided in patients whose respiratory mechanics are depleted to such an extent that the loss of diaphragm mechanics would cause them respiratory distress. There is also a risk of ipsilateral Horner syndrome (ptosis, miosis, anhidrosis). There is also a small risk of injection into the vertebral artery or the intrathecal space; thus equipment for emergent airway management should be readily available when performing this block.

Supraclavicular

Anatomy

Several authorities have referred to the supraclavicular block as "the spinal of the arm," as it is a very powerful technique for performing complete anesthesia distal to the elbow, as well as covering an upper-arm tourniquet site. In the supraclavicular fossa, the brachial plexus is transitioning between the trunks and the divisions; however, it is in a small, tight bundle, as it lies over the first rib cephalad and slightly posterior to the subclavian artery. The clavicle remains anterior to the neurovascular bundle. It should be stated that the first rib lies between the plexus and pleural space, and thus caution should be used when placing this block using traditional landmark techniques. However, with ultrasound the rib can be easily imaged and the needle can be directed away from the rib, thus potentially decreasing the risk of pneumothorax.

Technique

Patient positioning is once again a key component to success for placing this block. A 22-gauge 4-cm B-bevel needle is our choice for this block. The traditional landmark approach has the patient supine, with the arms at the sides and head rotated away from the side that the block is being placed. The needle should be inserted at the mid clavicle approximately 1 cm cephalad to the clavicle itself with a trajectory parallel with the patient's neck (Fig. 49-17). The end point will be either a paresthesia or nerve twitch of the muscles of the fingers if using a nerve stimulator. The insertion depth will be approximately 2 to 3 cm and should not be exceeded unless the patient is very large. Because there are several objects that should be avoided with this block (ie, the pleura and subclavian artery), if you fail to elicit either end point with your first pass and contact the first rib, withdraw the needle and recheck your landmarks. The needle can then be walked anterior or posterior along the rib in an effort to locate the brachial plexus. Do not direct the needle medially toward the apex of the lung.

The "plumb bob" or vertical technique is another landmark technique that was developed as a way to simplify the anatomical landmarks needed for the block. Once again the patient should turn his or her head away from the side being blocked and be in the supine position. The patient should be asked to raise his or her head off of the pillow in order to identify the insertion point of the lateral sternocleidomastoid muscle with the clavicle. The needle should be inserted directly superior to the clavicle at this point; however, unlike the classic approach, the needle will now be directed perpendicularly to plain of the floor (thus 90 degrees to the trajectory of the classic approach) (Fig. 49-18). Once again, a paresthesia or nerve twitch of the fingers should be elicited. If neither of these end points is achieved on the first pass, but the first rib is contacted, you may walk along the rib in an anterior-posterior direction. The needle should never be directed medially in order to avoid puncturing of the pleura.

The ultrasound technique is distinctly different from either landmark technique and was first described by Chan et al.53 The ultrasound probe should be placed on the patient immediately cephalad to the clavicle (Fig. 49-19). The subclavian artery should be imaged with the application of the PARTs maneuvers to form the subclavian artery into a circle.33 The brachial plexus should be located immediately lateral and slightly superior to the artery as 3 hypoechoic or dark circles (trunks) arranged in an inferior to superior direction or as a collection of 5 or 6 smaller hypoechoic circles or "cluster of grapes" that represent the divisions. The first rib will be immediately distal to the neurovascular bundle. In petite patients, the pleura may be imaged beyond the rib (Fig. 49-20). The rib is considered the "hard deck," and the needle should never be advanced beyond it in order to minimize the risk of pneumothorax. The needle will then be directed from the lateral to medial direction, in-plane with the ultrasound beam such that the needle can be seen in its entire course as it approaches the plexus. The first target should be the "corner pocket" or the extreme inferolateral border of the plexus adjacent to the rib. It has been observed in several institutions, including ours, that if this location is not addressed, then there is a high probability of missing the ulnar distribution.54 If spread of the local anesthetic appears to be spreading circumferentially within the nerve sheath, then one injection is necessary. Otherwise repositioning the needle cephalad to extend the local anesthetic placement in the sheath is recommended. Typical volumes for this block are 10 to 30 mL depending on duration needed for the surgical procedure.

Pearls and Pitfalls

Traditionally this block was avoided in favor of the axillary block for procedures distal to the elbow due to the risk of pneumothorax (reportedly between 0.5% and 5%) and the risk of phrenic nerve paralysis (between 30% and 50%). To avoid the risk of pneumothorax, the needle should never be walked medially along the first rib, only anterior or posterior. If a pneumothorax should occur, it will usually take several hours to establish; thus patients should be informed of possible signs and symptoms if they are to be discharged within 24 hours of block placement. The risk of pneumothorax with the ultrasound-guided technique appears to be lower and thus the supraclavicular block has become more common with practitioners using ultrasound-guided regional techniques. Lower volumes of local anesthetic can be used in an effort to avoid phrenic nerve paralysis. It also should be mentioned that patient selection is important, and this block should be carefully considered in those patients who have decreased pulmonary function. Vascular puncture of the subclavian artery is always a possibility as well; however, pressure can be applied to the site to minimize hematoma size, as the subclavian artery is superficial at this location.

With ultrasound-guided techniques, if you are having difficulty imaging the plexus in the supraclavicular fossa, find the plexus in the interscalene groove and trace it down to the supraclavicular fossa with the ultrasound probe. The first injection should always be as distal to the probe as possible, such as in the corner pocket. This allows one's remaining image not to be obscured and distorted by cavitations or air introduction from the first injection so that the remaining injections may be performed. We also do not recommend placing catheters at this level, as the plexus is fairly superficial and there is a fair amount of movement in this area from the neck and shoulder, thus making it very easy for a catheter to become dislodged.

Infraclavicular

Anatomy

As the brachial plexus descends below the clavicle, it becomes 3 distinct cords that are named in their relation to the axillary artery. The posterior divisions become the posterior cord, the anterior division of the inferior trunk becomes the medial cord, and the anterior divisions of the superior and medial trunks become the anterior cords. Several less prominent, but important neural structures branch from the brachial plexus at this level, they are nerves to the pectoralis major and minor, the subscapularis nerve, the medial brachial cutaneous nerve, medial antebrachial cutaneous nerve, and the axillary nerve. These "lesser" nerves are important to block in order to cover an upper-arm tourniquet site. It should be noted that the brachial plexus is now 5 to 6 cm deep to the patient's surface.

Technique

With a classic landmark technique, the patient should be placed supine, and the patient's arm can be abducted up to 90 degrees at the shoulder, but this is not necessary, although palpation of the coracoid process will be facilitated by arm abducted. The coracoid technique requires the coracoid process being palpated and marked. The insertion site will be 2 cm caudad and 2 cm medial to that mark at the coracoid process (Fig. 49-21). The needle should be directed posterior until a nerve twitch or the muscles of the hand or a paresthesia is elicited, which should occur at a depth of 4 to 5 cm.55 The modified Raj technique requires the jugular notch and the acromioclavicular joint be marked and a line drawn between the two. A second line should then be drawn perpendicular to this line, from the midpoint, approximately 2.5 cm in length, and a mark placed at the end. This will be the needle insertion site. The needle is then directed laterally toward the axilla with a nerve twitch or paresthesia being elicited at 5 to 6 cm of depth (Fig. 49-22). If the first pass fails to elicit the desired end point, the needle should be redirected cephalad or caudad.56

With the ultrasound-guided technique, the probe is placed below the clavicle and the PART maneuvers are used to form the subclavian artery and vein into circular cross sections. Color flow Doppler should be engaged to confirm the artery from the vein; however, the artery is usually the more cephalad structure. The needle should be inserted from the superior border of the ultrasound probe almost adjacent to the clavicle (Fig. 49-23). (If the probe is in direct contact with the clavicle, it should be moved slightly caudad to allow needle insertion.) The needle is then advanced in-plane with the ultrasound beam, with the target location being at the inferior border of the subclavian artery at the 7 o'clock position (Fig. 49-24). The cords remain perivascular at this location, so circumferential spread of local anesthetic around the artery should be sufficient, even if you are unable to visualize the individual cords.57 This approach also allows one to easily thread a catheter 2 to 3 cm such that the tip "hooks" around the artery and the tip lodges between the artery and vein. After the needle has been removed, catheter placement can be confirmed by visualizing circumferential spread around the artery with a small bolus of local anesthetic through the catheter.

Pearls and Pitfalls

The infraclavicular approach to the brachial plexus is usually the deepest block of the upper extremity and thus can be uncomfortable for patients if inadequate local anesthesia is given along the needle path. With the ultrasound-guided technique, the depth of the block will entail a lower frequency setting for adequate tissue penetration, thus decreasing the resolution. The reason for a superior opposed to an inferior approach for the ultrasound-guided technique is to facilitate catheter placement around the subclavian artery. With the inferior approach, one would have to aim between the subclavian artery and vein, which increases the risk of vascular puncture; however, this is still a viable option for a single shot as long as perivascular spread of local anesthetic is observed around the subclavian artery. The further lateral the block is placed, the higher the likelihood of missing the distribution of the musculocutaneous nerve, thus negating one of the advantages of the infraclavicular block over the axillary block.

The infraclavicular approach is excellent for catheter placement for surgical procedures distal to the elbow, regardless of what placement technique is selected. The added tissue between the patient's exterior and the plexus provides enough friction to maintain a catheter in place. The catheter exit is also in an area that can be cleaned and maintained with minimal annoyance to the patient.

Axillary

Anatomy

The brachial plexus finally evolves into the peripheral nerves of the upper extremity once it exits from under the lateral border of the pectoralis minor muscle. The radial, median, and ulnar nerves surround the axillary artery, with the musculocutaneous nerve now located between the bellies of the biceps and coracobrachialis muscles. Despite the classical teaching of the radial nerve being the nerve on the opposite side of the axillary artery from the axilla, the median nerve anterior and cephalad to the artery and the ulnar nerve anterior and caudad to the artery, recent ultrasound investigations have shown that there is a large degree of variability regarding where the nerves lie in relation to the artery58 (Fig. 49-25). It should also be mentioned that there is variability among the vascular structures at this level in the axilla as well in that we have seen patients with bifurcation of both axillary artery and vein at this level when using ultrasound. It also should be stressed that the neurovascular bundle at this level is not 1 contiguous compartment, but several different compartments. Thus multiple injections are usually required.

Technique

The axillary block is a good choice for those patients having surgery distal to the elbow. However, you must remember that the upper-arm tourniquet site will not be covered with this block, so an additional "ring block" may have to be placed subcutaneously in the axilla to cover the tourniquet site. All the different techniques require the patient to be placed supine with the ipsilateral arm abducted 90 degrees at the shoulder and the forearm flexed at the elbow such that the hand is almost behind the patient's head. The transarterial technique is a blind landmark technique that allows the perivascular placement of local anesthetic using a deliberate puncture of the axillary artery.59 If the transarterial technique is used, we would stress using epinephrine in the local anesthetic solution to indicate intravascular injection. With the transarterial technique, a small 25-gauge butterfly (or similar sized) needle is advanced toward the pulsation of the axillary artery. Once pulsatile blood is seen in the needle, the needle is advanced further until the blood stops being pulsatile. At this point the needle should be aspirated. If no blood comes back through the needle, then a 3-mL "test dose" should be injected and the patient monitored for increased heart rate or signs of an intravascular injection. If there are no indications of an intravascular injection, then half of the local anesthetic solution can be placed with intermittent aspiration. Once the injection is completed, the needle is slowly extracted with the return of pulsatile blood flow. Once the pulsatile blood flow stops, the needle should be aspirated and once again a 3-mL test dose should be administered. If the test dose is negative, the remainder of the local anesthetic solution can be deposited with intermittent aspiration.

Other methods using either nerve stimulation or blind techniques require the palpation of the axillary artery and marking its course on the skin (Fig. 49-26). A needle should be advanced on either side of the artery to either elicit a muscle twitch if using a nerve stimulator, in the appropriate peripheral nerve distribution, or a paresthesia if using the traditional technique.60 Five to 10 mL of local anesthesia can be deposited at each site. The musculocutaneous nerve will be blocked by a separate injection either in the body of the coracobrachialis muscle or in the antecubital fossa.

The ultrasound-guided approach requires similar patient positioning as the traditional approaches with the transducer placed over the patient's axilla and the PARTs maneuvers used until the axillary artery rests in the center and is in a circular cross section (Fig. 49-27). Because there is such a high degree of variability in the location of the different nerves in relation to the artery, a nerve stimulator may be helpful to confirm which nerve is being visualized and approached with the needle.61 Once again, this is an in-plane technique, with the needle advanced to each peripheral nerve, which should appear as a white, hyperechoic structure with black fascicles located in the interior, or a "popcorn" appearance. Once the radial, ulnar, and median nerves have been located and blocked, the probe should be moved cephalad and lateral to identify the musculocutaneous nerve, which has a similar popcorn appearance but is located in the body of the coracobrachialis muscle62 (Fig. 49-28).

Pearls and Pitfalls

The axillary approach to the brachial plexus was developed primarily as a means to provide anesthesia to the forearm and hand, but avoid the risk of pneumothorax and phrenic nerve paralysis. The drawback, however, is that the musculocutaneous nerve can be missed and that placement of the block requires several needle passes, which has shown to reduce patient satisfaction. Toxicity is also a factor, especially with the transarterial technique, because large dosages have traditionally been used in order to cover the musculocutaneous nerve as well as ensure circumferential spread around the axillary artery. The success rate of the axillary approach has also been called into question. Claims of 100% success are probably exaggerated, with more typical success rates of 60% to 80% being more typical. Whether the block is placed for surgical anesthetic or postoperative pain control and the very definition of "success" can all affect this number. Certainly the success rate is not as high as that of the supraclavicular block.

It is because of this last point that the axillary block has fallen out of favor with the ultrasound-guided regional anesthesiologist. When compared with the supraclavicular approach, the axillary block requires more time and more needle passes and has decreased fidelity with the higher likelihood of needing a "rescue block" distal to the elbow. All of these components contribute to a decrease in patient satisfaction. However, the axillary block still has some uses for patients when a supraclavicular or infraclavicular block is not a possibility.

Radial

Anatomy

The radial nerve supplies the dorsum of the thumb, index, and middle fingers, as well as the lateral half of the ring finger. The radial nerve leaves the axilla and courses between the brachialis and brachioradialis muscles before it emerges through the lateral intramuscular septum (Fig. 49-29).

Technique

With conventional landmark techniques, the radial nerve is approached in the antecubital fossa. A line should be drawn between the 2 epicondyles. The biceps tendon should be identified. The needle insertion site should be inserted 1.5 to 2 cm lateral to the biceps tendon along the line connecting the 2 epicondyles, and 3 to 5 mL of local anesthetic should be injected in a "fan" lateral to medial (Fig. 49-30).

With ultrasound, the nerve can be identified as the white, hyperechoic structure located between the brachialis and brachioradialis muscles proximal to the elbow. Its appearance is more oblong than circular at this location (Fig. 49-31). Once again, only 3 to 5 mL of local anesthetic needs to be injected.

Median

Anatomy

The median nerve leaves the axilla and it courses down to the elbow to lie medial to the brachial artery in the antecubital fossa. The median nerve provides the sensory component of the palm and the proximal fingers of the thumb to the radial half of the ring finger. The median nerve provides the motor component to the forearm flexors, the thenar eminence, and the lumbrical muscles of the first and second digits.

Technique

Once again, a line should be drawn between the 2 epicondyles. The traditional landmark technique requires the identification of the brachial artery by palpation or Doppler ultrasound. Once the brachial artery has been identified on the intercondylar line, 3 to 5 mL of local anesthetic should be injected medial to the brachial artery pulse (Fig. 49-32). A paresthesia or nerve stimulation of wrist flexors should be the end point before injection, although an injection in a fan pattern may be effective.

The ultrasound technique entails placement of the ultrasound probe over the antecubital fossa in a medial to lateral direction and identification of the brachial artery by color flow Doppler. The median nerve should appear as a white, hyperechoic structure immediately adjacent to the medial side of the artery (Fig. 49-33). Either an in-plane or out-of-plane technique can be used at this location. An injection of 3 to 5 mL of local anesthetic should be placed around the nerve. The median nerve can also be blocked at the wrist using ultrasound. Place the ultrasound probe approximately 1 to 2 cm proximal to the crease of the wrist. The surrounding tendons can be mistaken for the nerve; however, the nerve should be about 0.5 cm deep to the tendons and should not change its shape when the patient makes a fist. Either an in-plane or out-of-plane approach is acceptable to place 3 mL of local anesthetic solution.

Ulnar

Anatomy

The ulnar nerve leaves the axilla and courses to the posterior aspect of the medial epicondyle, where it lies in the ulnar groove. It then continues proximally, where it joins the ulnar artery approximately 5 cm distal to the elbow and continues down to the hand. The ulnar nerve supplies the sensory component of the ulnar side of the hand, the ulnar side of the ring finger, and the little finger. The ulnar provides the motor component of the all the remaining intrinsic muscles of the hand.

Techniques

Classic landmark techniques entail palpating the ulnar groove and then injecting 1 cm proximal to minimize the chance of nerve injury, as the ulnar groove is a tightly confined space. A paresthesia should be elicited without difficulty in this location (Fig. 49-34). There are descriptions of using very fine needles in this location to perform this block because of the almost certainty of entering the ulnar nerve when performing this block. The ulnar nerve can also be blocked at the wrist. The ulnar nerve lies between the ulnar artery and the pisiform bone. Both of these structures can be palpated, and 3 to 5 mL of local anesthesia can be placed in this location. With ultrasound, the ulnar nerve can be imaged 1 to 2 cm proximal to the wrist crease adherent to the ulnar artery on the ulnar side of the artery. The nerve should then be traced proximal, up the arm, to where it separates from the artery (Fig. 49-35). At this location using either an in-plane or out-of-plane technique, 3 to 5 mL of local anesthesia can be injected.

Pearls and Pitfalls

With any of the blocks of the distal upper extremity, it is important to be cognizant of the fact that the nerves in this location are in tighter anatomical compartments, and thus large local anesthetic doses should be avoided due to the risk of causing ischemia or nerve injury from increased compartmental pressure. Usually only 3 to 5 mL of local anesthetic is required for a successful block. It should also be noted that these tighter compartments make it more difficult for the nerve to "get out of the way" of a needle as it attempts to penetrate the nerve sheath, thus making it theoretically more likely to cause injury due to mechanical trauma. Even though relatively small volumes of local anesthetics are being used to perform these peripheral nerve blocks, many of these blocks are performed around vascular structures. Thus the practitioner should continue to remain vigilant for the possibility of an intravascular injection or vascular injury while performing these blocks.

Because many of these blocks distal to the elbow do not cover an upper-arm tourniquet site, we find these blocks for surgical anesthesia, by themselves, to be of limited value. Where these blocks add value are as supplemental blocks for missed distributions of more proximal blocks. A good example is blocking the ulnar nerve for a procedure on the hand after a supraclavicular block has failed to set up in the ulnar distribution. The other advantage of these blocks is for postoperative pain control when the motor block of the entire upper extremity from a more proximal block is to be avoided, yet preemptive pain control is necessary in a proximal nerve distribution in the hand.

There are several important considerations for regional anesthesia involving the lower extremity. First, it is important to clarify the goals of the block: a surgical block versus supplementation to a general anesthetic primarily for postoperative pain control. It is also important to consider the surgical use of tourniquets. This is especially important if the regional anesthetic goal is to provide a surgical block, as a tourniquet placed outside the field of the regional anesthetic will limit the time that a patient can tolerate the surgical procedure. Similar to upper-extremity nerve blocks, aseptic practice should be used during regional anesthesia involving the lower extremity. This includes use of sterile gloves, thorough cleansing of the skin, and barrier precautions when appropriate. In addition, one should always deposit local anesthetic at the site of needle entry. For the remainder of the discussion, we will assume that these considerations have been addressed.

Lumbar Plexus

A lumbar plexus block may be used as an analgesic option for surgeries of the hip, anterior thigh, and/or knee. It can provide anesthesia to the entire lower extremity when combined with a sciatic nerve block.

Anatomy

The lumbar plexus is primarily derived from the anterior or ventral rami of the L1 to L4 nerve roots, but there are also contributions from T12 in 50% of patients. This neural plexus is formed within the psoas major muscle63 and includes the iliohypogastric, ilioinguinal, genitofemoral, lateral femoral cutaneous, femoral, and obturator nerves. Local anesthetic blockade of the femoral, lateral femoral cutaneous, and the obturator nerves is most important for lower-extremity regional anesthesia. The sciatic nerve, discussed later in the chapter, receives contributions from the lower lumbar and sacral plexuses (Fig. 49-36).

Two basic approaches have been described for blockade of the lumbar plexus: (1) a posterior approach and (2) a perivascular approach. Although the posterior approach is most often used for procedures involving hip or femoral neck repair, the perivascular approach is most commonly utilized for surgical procedures involving the knee.

Technique

Psoas Compartment Block (Posterior)

With the patient in a lateral decubitus position (operative site up), the hips are flexed. A line connecting the iliac crests (Tuffier line) is drawn. The spinous process at midline is most often the L4. On the operative side, a line is drawn 5 cm parasagittal to the midline (Fig. 49-37). A point 3 cm caudal to the Tuffier line on this parasagittal demarcation is then made. This will be the entry point of a 10-cm, 21-gauge insulated needle for the purpose of nerve stimulation. The needle is inserted perpendicular to the skin until the L5 transverse process is encountered. The needle is then directed cephalad in a manner that allows the regionalist to walk off the transverse process. A quadriceps motor response confirms correct needle position, and approximately 30 mL of local anesthetic is then injected after careful, sequential aspiration attempts confirming that the needle is not intravascular.

A modification of the above technique involves use of a Touhy needle to identify the psoas compartment via stimulation and loss of resistance techniques. As above, this modified technique uses quadriceps contraction to signify proper location of the needle.64

Inguinal Perivascular Approach (Three‐in-One Block)

This block is based on the premise that injection of local anesthetic in sufficiently large amounts will track up fascial planes between the iliacus muscle and the psoas muscle, ultimately anesthetizing the nerves of the lumbar plexus that exit at the level of the inguinal ligament (the femoral, lateral femoral cutaneous, and the obturator). The approach is identical to the femoral nerve block described later, with the caveat that firm pressure is applied distal to the needle insertion to allow fascial tracking of the local anesthetic. Some authors have advocated high volumes of local anesthetic as a means of greater spread. Imaging studies have demonstrated that medial and lateral spread of the local anesthetic provide blockade of the obturator and lateral femoral cutaneous nerves, respectively.65

Pearls and Pitfalls

As with any regional anesthetic technique, local toxicity can occur secondary to vascular absorption and/or direct intravascular injection. The lumbar plexus block is associated with increased risk of local anesthetic toxicity due to proximity of vascular structures and use of large volumes of local anesthetics to obtain the desired spread.

It is important to note that the depth of the lumbar plexus for men and women can differ. Median depth for men is 8.5 cm and for women is 7.0 cm.66

Femoral

The femoral nerve block is used to provide analgesia to the lower extremity, often in combination with other nerve blocks. Occasionally, it may be used as the sole anesthetic for isolated procedures involving the thigh. More often, it is used for postoperative analgesia in cases of midshaft femoral fracture repair and/or after surgical procedures involving the knee.

Anatomy

The femoral nerve arises from the posterior branches of L2, L3, and L4 of the lumbar plexus. From the plexus, it travels between the psoas and iliacus muscles until it passes under the inguinal ligament. At this point, it assumes a position lateral and somewhat posterior to the femoral artery, where the division to anterior and posterior branches occurs. The anterior branches are largely cutaneous, whereas the posterior branches supply motor input to the quadriceps muscle and provide articular branches to the knee.

The terminal branch of the posterior division of femoral nerve is the saphenous nerve, which supplies sensory input to the medial aspect of the leg from the knee to the medial malleolus.

Technique

With the patient supine, the anterior superior iliac spine (ASIS) is identified on the ipsilateral side to be blocked. A line is then identified from the ASIS to the public tubercle. This is commonly known as the approach of Labat.67 After the skin is anesthetized, a 3- to 4-cm 22-gauge needle is inserted perpendicular to the skin at a point below the inguinal ligament and lateral to the pulse of the femoral artery. A path through the fascia iliaca will be denoted by a pop (Fig. 49-38). A contraction of the sartorius muscle in the medial aspect of the thigh will be appreciated if a nerve stimulator is being used. The path should continue deeper with redirection laterally. A patellar "snap" from contraction of the quadriceps muscle is confirmation that the posterior branch of the femoral nerve has been encountered.

An alternative approach to blockade of the femoral nerve is to elicit a paresthesia, which might be encountered using the nerve stimulation technique as well. Once a paresthesia is obtained, 20 mL of local anesthetic can be injected in a fan-like distribution.

Yet another approach to femoral nerve blockade is an ultrasound-guided approach.68,69

A linear transducer is placed at the level of the inguinal ligament in order to identify the femoral vessels and to achieve medial and lateral orientation. Using an in-plane technique, a 22-gauge bevel needle (2-4 cm) is used to approach the femoral nerve from the lateral aspect. The ultrasound is then used to guide the needle under the fascia lata, a linear, hyperechoic structure, toward the fascia iliaca (Fig. 49-39). Once the fascia iliaca is identified, the needle is advanced until a "pop" is felt and confirmed visually, indicating penetration of the fascia iliaca. The local anesthetic is then injected. Another finding consistent with correct needle placement is circumferential spread of the local anesthetic around the nerve after injection.

Saphenous Nerve

The saphenous nerve can act as a supplement to a sciatic nerve block for a lower-extremity surgery involving the medial portion of the leg or foot.

Anatomy

The saphenous nerve is the largest sensory component of the femoral nerve, and it is the only component to innervate below the level of the knee. The saphenous nerve courses through the femoral triangle and becomes more superficial as it travels between the sartorius and gracilis muscles in the thigh. The saphenous nerve also has a close relationship with the saphenous vein as it progresses caudally. Thus the trans-sartorial and perivenous are 2 common approaches to saphenous nerve blockade (Fig. 49-40).

Trans-Sartorial Approach to Saphenous

In the supine position with leg extension, the sartorius muscle is identified on the medial aspect of the upper leg. An 18-gauge loss-of-resistance needle is inserted 1 to 2 cm above the level of the patella, and with a posterior and caudad direction, it is passed through the body of the sartorius muscle. A sub-sartorial loss of resistance, usually achieved at 1.5 to 3.0 cm, indicates the usual plane where the nerve is located. Ten milliliters of local anesthesia is then deposited. This approach has been demonstrated to have an 80% success rate.70

Perivenous Approach to Saphenous

The patient is placed in the supine position and the tibial tuberosity identified. At this level, there is a close relationship between the saphenus nerve and tibial vein; the saphenous nerve lies medial and posterior to the vein. A tourniquet may aid in identification of the perivenous anatomy. Once identified, a small amount of local anesthetic is deposited on either side of the vein. Five to 10 mL of local anesthesia should be sufficient. This can also be done with ultrasound visualization (Fig. 49-41).

An alternative approach is a field block. With the tibial tuberosity identified, a subcutaneous wheal of local anesthetic is injected from the medial aspect of the tibial tuberosity to the medial portion of the gastronomies muscle.

Pearls and Pitfalls

The proximity of the femoral nerve to the vascular bundle generates some risk for vascular puncture and subsequent hematoma development. Thus special care should be taken to ensure proper understanding of the new anatomy in patients who have had femoral revascularization procedures. In fact, the presence of a new graft can be considered a relative contraindication if the anatomy cannot be identified using ultrasonography.

Femoral and lower-extremity nerve blocks have also been implicated as coexisting risk factors for falls.71 As such, patients, family, and health care providers should be informed of this potential risk in order to minimize the chance of a fall in the postoperative period.

In addition, because blockade of the femoral nerve is commonly used in conjunction with a sciatic nerve block to achieve complete lower-extremity analgesia, the total amount of local anesthetic used should be carefully considered in order to avoid local anesthetic toxicity.

It is important to also note that prolonged tourniquet time may increase the risk for nerve palsy,72 a complication that may be confounded by the addition of a local anesthetic.

Finally, continuous femoral nerve techniques, as compared with intravenous narcotics, have been shown to reduce hospital duration in patients undergoing total knee arthroplasty.73

Lateral Femoral Cutaneous

This block is used primarily in conjunction with other blocks of the lower extremity to offer complete lower-extremity analgesia. It may act as a supplement to skin graft harvesting, although it has been reported as the sole anesthesia for these procedures.74

Anatomy

The lateral femoral cutaneous nerve (LFCN) arises as a direct branch from the lumbar plexus (L2 to L3) and courses via the lateral edge of psoas muscle to enter the thigh deep to the inguinal ligament. It emerges from the fascia inferior and medial to the anterior superior iliac spine (ASIS). As it travels beneath the fascia lata, it divides into an anterior and posterior branch. The anterior branch provides sensory innervation to the anterolateral thigh, whereas the posterior branch provides sensory innervation to the true lateral portion and a small posterior portion of the thigh from the hip to the knee (Fig. 49-42).

Technique

Landmark

With the patient supine, the ASIS is identified on the ipsilateral side to be blocked. A mark approximately 2 cm medial and 2 cm caudad to the ASIS is made. A 22-gauge, 4-cm needle is advanced perpendicular to the surface of the skin until the fascia lata is encountered, as noted by a pop. Local anesthetic is then injected in a fan-like maneuver in a lateral to medial direction. Ten to 15 mL of local anesthetic should be sufficient.

Nerve Stimulator

There have been descriptions of using nerve stimulator techniques with improved success with localization.75

Ultrasound Guided

Ultrasound localization of the LFCN is possible with knowledge of its intrafascial location.

Pearls and Pitfalls

If the block is to be used as a sole anesthetic for a skin graft collection procedure, it is clearly important to determine the field of sensory blockade before starting the collection.

Obturator Nerve Block

The obturator nerve provides sensory innervation to the articular surfaces of the knee. Therefore, blockade of this nerve is an important consideration for total knee arthroplasties and anterior cruciate ligament repairs. However, obturator nerve blockade should not be thought of as a complete anesthetic for these procedures due to contributions from the femoral nerve.

Anatomy

The obturator nerve is formed from the anterior divisions of L2, L3, and L4 of the lumbar plexus. These anterior divisions organize within the body of the psoas muscle and emerge on the medial border as the obturator nerve. As such, the obturator nerve can be found situated within the obturator canal, where it divides into anterior and posterior divisions. The anterior division provides sensory innervation to the hip via an articular branch and motor supply to the adductor muscles of the thigh. The anterior branch also provides a highly variable sensory component to the medial thigh.76 The posterior division supplies the motor component to deep adductors and sensory innervation via an articular branch to the posterior knee joint.

Technique

The classic description involves nerve stimulator techniques, but paresthesias are not an uncommon associated finding. With a supine patient, the pubic tubercle is identified. A mark is placed 2 cm lateral and 2 cm caudad to the pubic tubercle.

A 22-gauge needle (8-10 cm) is then inserted perpendicular to the skin with a medial slant. When the inferior pubic ramus is encountered, the needle is withdrawn slightly and walked off caudad and lateral. The needle will walk off the rami into the obturator canal (after approximately 3 cm), identified by adductor contraction. Approximately 10 mL of local anesthetic should be injected.

Wassef77 described an interadductor approach. A skin mark delineating the obturator canal is made below the inguinal ligament and 1 to 2 cm lateral to the palpated femoral artery. The adductor longus tendon is identified near the pubic insertion and an 8-cm, 22-gauge needle is inserted behind the tendon, directed laterally and superiorly using the skin mark as a guide. Adductor contraction is the end point.

Ultrasound-guided obturator block has recently been used as an adjunct to femoral blocks for knee surgery (Fig. 49-43).

Pearls and Pitfalls

Neurovascular bundles place patients at risk for intravascular injections and/or hematoma formation. In the case of spasticity, obturator nerve blockade and/or neurolytics may be used. It may also prove useful as an aide in ascertaining patients who may benefit from additional modalities for relief of spasticity, such as Botox injections.

Sciatic

The sciatic nerve is the largest of the lower-extremity nerves and has several well-described levels that can be approached for blockade. Sciatic nerve blockade can be used as a complete anesthetic for surgeries of the foot or ankle where a lower-leg tourniquet will be needed and an ankle block would not be sufficient. However, a sciatic nerve block should be used in conjunction with a saphenous nerve block if the medial portion of the leg or ankle is in the surgical field.

Anatomy

The sciatic nerve is composed of the ventral rami from L4 to S3, which join on the anterior surface of the piriformis muscle. The sciatic nerve is the largest nerve in the body, with a width of 2.0 cm. As it passes through the greater sciatic foramen, it passes lateral to all of the other structures that emerge inferior to the piriformis (inferior pudendal vessels, pudendal nerve, inferior gluteal nerve and vessels) (Fig. 49-44).

The posterior femoral cutaneous nerve courses with the sciatic and the inferior gluteal nerves and vessels and is important because this nerve supplies the posterior portion of the thigh. It is important to note that the posterior cutaneous nerve will only be anesthetized via a high sciatic block.

The sciatic nerve courses inferolaterally deep to the gluteus maximus at a midpoint between the ischial tuberosity and the greater trochanter of the femur. The sciatic nerve itself is a combination of the common peroneal (lateral) and the tibial (medial) nerves joined by an epineurial sheath. These 2 nerves separate approximately 8 cm superior to the popliteal fossa.

Technique

There are many different approaches to the sciatic nerve. Several considerations are given to which technique is chosen: patient ability to roll over or aid in positioning, level of the surgery, and body habitus are important factors

Anterior Approach

With the patient supine and neutral position of the leg, a line connecting the pubic tubercle and the anterior superior iliac spine is drawn at the level of the inguinal ligament. A second parallel line is drawn inferomedially from the greater trichinae toward the lesser trochanter. A perpendicular line one-third the initial distance is then drawn perpendicular. This is the point of insertion for a 22-gauge, 10- to 15-cm needle. The lesser trochanter is contacted and the needle directed slightly medial. Five centimeters past the point of the lesser trochanter, a paresthesia or a contraction consistent with a sciatic nerve stimulation is encountered. Injection of 20 to 25 mL of local anesthetic is done incrementally (Fig. 49-45).

Posterior Approach (Classic Approach of Labat)

The positioning for the classic approach to the sciatic may make it impractical in patients who are suffering with a lower-extremity trauma. With the patient positioned in the lateral decubitus position (operative side up), the hip is flexed with the heel of the operative side resting on the nonoperative knee. Marking is done to identify the posterior superior iliac spine (PSIS) and the greater trochanter. A line connecting these 2 is bisected perpendicularly, and a point 5 cm caudad is identified (Fig. 49-46). This is the point of insertion with a 22-gauge, 10-cm needle. Paresthesia, sciatic motor response, and/or bone is contacted as the needle is advanced. If a paresthesia or motor response is elicited, then slow injection of 20 to 30 mL of local anesthetic is performed. If bone is contacted, methodical redirection of the needle is performed, with a medial and then lateral redirection until paresthesia or motor response is encountered.

Subgluteal Approach

A description of a subgluteal approach to the sciatic was given by Di Benedetto et al78 and has been used with success. With the patient in the lateral decubitus position, operative side up and hips flexed, and the operative knee at 90 degrees, a line is drawn connecting greater trochanter and the ischial tuberosity. At the bisection of this line, a perpendicular line is then drawn 4 cm caudal. This is the entry point of the 22-gauge, 10-cm needle. Surface anatomy indicates that this is below the bulk of the gluteal muscles in a depression that represents the biceps femoris and the lateral border of the vastus lateralis. In the original description, a nerve stimulator technique was used. However, several descriptions have recently been published discussing ultrasound-guided techniques.79-81 A curvilinear probe (2-5 MHz) with the patient in the above semilateral position has been used with an in-plane and out-of-plane approach to the nerve (Fig. 49-47). Single-injection and catheter-based techniques have been described.

Popliteal Fossa Approach to the Sciatic

Posterior Approach

For the posterior approach, the patient is positioned prone. With the knee in a flexed position, the base of a triangle is delineated by the skin crease of the posterior knee. The medial border of the triangle is the semimembranosus muscle and the lateral border is the biceps femoris muscle. In order to block the sciatic nerve before it separates into its 2 smaller components, it is recommended that the point of needle insertion be 7 to 10 cm above the skin crease.82 A paresthesia or muscle twitch confirming either sciatic component is accepted.

Lateral Approach

Ichiyanagi83 originally described a lateral approach to the popliteal fossa. The patient is supine with the leg in a neutral position. The leg may be supported so it is flexed at the knee to ease identification of structures (Fig. 49-48). The groove between the vastus lateralis and biceps femoris muscles is identified. A 22-gauge, 10-cm needle is inserted until contact with the femur is made. Once the femur is contacted, the needle is redirected posterior and the sciatic nerve should be encountered 1 to 2 cm beyond the femur contact distance. Acceptable nerve stimulation is either tibial nerve (plantar flexion at ankle, inversion of foot) or common peroneal nerve (ankle dorsiflexion or eversion of the foot).

Some authors84 have advocated for separate stimulation of each component of the sciatic, citing a greater success rate (88% for double stimulation vs 54% for only tibial). The volume of local anesthetic for the lateral and posterior approaches has widely varied in the literature from 20 to 40 mL.

Ultrasound in-plane techniques have also been used with great success for both the posterior and lateral approaches. The positioning for the lateral approach necessitates having the patient in 90-degree flexion in order to place the ultrasound probe on the posterior portion of the popliteal fossa. The entry point of the needle is exactly the same as in the lateral approach, but direct visualization of the local anesthetic ensures circumferential spread (Fig. 49-49).

Pearls and Pitfalls

Unlike other lower extremity blocks, the time required for the sciatic nerve analgesia to become apparent may be considerable. It is not unusual to have analgesia after 30 to 40 minutes. In contrast, femoral nerve sensory deficits can be appreciated relatively quickly.

As stated above, patient ability to position certainly guides the level at which the sciatic nerve is blocked. Patients with a body mass index greater than 35 may prove difficult for subgluteal approaches using ultrasound technology.

Ankle

The femoral and sciatic nerves terminate in the lower extremity into 5 terminal branches. The saphenous is the only contribution from the femoral nerve; the other 4 terminal branches—the deep peroneal, superficial peroneal, posterior tibial, and the sural—originate from the sciatic nerve.

The sensory innervation of the foot is provided by these 5 nerves (Fig. 49-50). Local anesthetic blockade of any one of these nerves or a combination will provide anesthesia and/or analgesia for surgery of the foot. Consideration must be paid to the possible use of a tourniquet. An ankle block is ideal for surgery on the toes or metatarsals.

Anatomy

The sciatic nerve branches into the common peroneal and the tibial nerves at the level of the popliteal fossa. The common peroneal further divides into the superficial and deep peroneal nerves. The tibial nerve is the larger of the 2 branches of the sciatic, and it terminates as the posterior tibial nerve and the sural nerve. It courses through the lower extremity in a neurovascular bundle accompanied by the posterior tibial artery and vein. At the ankle level, the posterior tibial nerve can be found posterior to the medial malleolus.

Technique

Posterior Tibial Nerve

Classic description is with a patient in the prone position, although this procedure can be accomplished in the supine position with the lower leg resting on a table or elevated. The posterior tibial artery is palpated, and a 22-gauge, 4-cm needle is inserted medial to the Achilles tendon, directed anteriorly toward the medial malleolus. If a paresthesia is elicited, a small volume of local anesthetic is injected (5 mL). In no paresthesia, then the needle is advanced until it contacts the medial malleolus and then the local anesthetic is deposited. This is essentially a field block.

Deep Peroneal and Superficial Peroneal Nerves

The patient is positioned as discussed earlier with the foot elevated, resting on a bump. Extension of the great toe identifies the extensor hallicis longus (EHL) tendon. A 22-gauge, 4-cm needle is inserted perpendicular to the skin lateral to the EHL tendon in the groove between the EHL and the extensor digitorum longus tendon (Fig. 49-51). The needle is advanced until bone is contacted, and then 5 mL of local anesthetic is injected as the needle is slowly pulled back. This raised skin wheal serves as an initiation point for the superficial peroneal nerve. A superficial wheal is made to the lateral malleolus, and then the needle is redirected toward the medial malleolus. Approximately 5 mL of local anesthetic should be appropriate.

Sural Nerve

An approach similar to the posterior tibial nerve is used for the sural nerve. A 22-gauge, 4-cm needle is inserted lateral to the Achilles tendon, directed anteriorly toward the malleolus, and approximately 5 mL of local anesthetic is injected.

Descriptions of the use of ultrasound guidance have been noted. A proposed use of ultrasound is in limiting the amount of local anesthesia necessary with deposition near nerves as opposed to the "field" block, where large volumes may be used to provide complete foot anesthesia. Specifically, ultrasound has been used to identify the sural nerve in association with the lesser saphenous vein. Injection of small amounts of local anesthetic (5 mL) according to these anatomical landmarks using ultrasound guidance has been shown to generate a denser and longer-lasting block as compared with traditional landmark techniques alone.85

Pearls and Pitfalls

As with all other blocks, knowing the anatomy is essential. Ankle blocks can be quite uncomfortable for patients, and they require multiple injection sites. Local anesthetic volumes need to be monitored.

The saphenous nerve is the only contribution from the femoral that has a terminal branch at the level of the ankle. For procedures on the medial aspect of the foot or ankle, this nerve is important to block.

Peripheral nerve blocks are being used more frequently in the pain literature for diagnostic86 and therapeutic87 purposes. As mentioned previously, interruption of obturator nerve conduction can aide in diagnosis or treatment of adductor spasm.

• Enneking FK, Chan V, Greger J. Lower-extremity nerve blockade: essentials of our current understanding. Reg Anesth Pain Med. 2005;30(1):4-35.
• Horlocker TT, Wedel DJ, Rowlingson JC, et al. Regional anesthesia in the patient receiving antithrombotic or thrombolytic therapy: American Society of Regional Anesthesia and Pain Medicine Evidence-Based Guidelines (Third Edition). Reg Anesth Pain Med. 2010;35(1):64-101.
• Neal JM, Brull R, Chan V, et al. The ASRA evidence-based medicine assessment of ultrasound-guided regional anesthesia and pain medicine. Reg Anesth Pain Med. 2010;35(2):S1-S9.
• Neal JM, Hebl JR, Gerancher JC, et al. Brachial plexus anesthesia: essentials of our current understanding. Reg Anesth Pain Med. 2002;27(4):402-428.