Regional anesthesia, the art and science of blocking nerve impulses in the peripheral nervous system (PNS), has a long and interesting history. Local anesthetics were first demonstrated for topical use in the eye in 1884 by ophthalmologist Karl Koller. Practitioners began performing nerve blockade in the late 1800s, primarily in Europe, with physicians and anatomists mapping out and describing a wide variety of techniques and sites. At that time, the blocks were performed primarily by using anatomic landmarks; that is, prominent markers (e.g., the lateral malleolus of the ankle) would be identified and the subsequent placement of the needle guided by an invariant relationship to that marker.
The ankle block is a good example of one of the earliest described blocks. It is still often performed using a landmark technique. Today, the block often consists of five separate injections of local anesthetic at characteristic sites in a ring around the ankle. When performed correctly, it results in numbness of the foot from the ankle down. The ankle block allows comfortable surgical anesthesia for surgeries such as toe amputation or bunionectomy. Descriptions of the ankle block (Fig. 16.1) can be found in early atlases, such as Regional Anesthesia: Its Technique and Clinical Application by Gaston Labat, published in 1922.
FIGURE 16.1. Surgical anatomy for the ankle block technique. (Reproduced from Consins MJ, Bridenbaugh PO, eds. Neural Blockade. 3rd ed. Philadelphia, PA: Lippincott-Raven; 1998, with permission.)
Physicians with a grasp of the anatomy and practice of regional techniques, working primarily in Europe, were also able to provide some measure of solace to their patients. But these techniques required advanced study to perform, and few practitioners mastered them fully. In addition, many peripheral nerve blocks performed either by landmarks or by paresthesia (identification of the nerve by contacting it with the needle) tended to be unreliable. Anatomical variation and practical considerations such as time constraints tended to limit the overall utility of peripheral nerve blockade.
Even so, early practitioners, such as Gaston Labat, were enthusiastic and important advocates for regional anesthesia. Labat, instrumental in the introduction of regional anesthesia to the United States, was familiar with many of the blocks we use today—they are described in his textbook. Beginning in the middle of the 20th century, the technology applied to blocks changed. Blindly prodding an area with a needle to elicit pain (paresthesia) has drawbacks as a method of localizing nerves as does relying purely on regional anatomy. The use of a nerve stimulator allows a small electrical current to be passed through a block needle. If the needle is in close proximity to a nerve, the stimulus will cause the nerve to send an impulse (stimulate the nerve) and induce any muscles innervated by the nerve to twitch (elicit a motor response). Practitioners such as Dr. Alon Winnie were able to use the nerve stimulator to refine previously known blocks as well as describe new anatomical approaches that would become well used during the next 30 or so years.
More recently, regional anesthesiologists have widely adopted ultrasound-based techniques for block placement as it has several advantages when compared to nerve stimulators or anatomic-based techniques. Ultrasound allows real-time visualization of the block needle and its relationship to important structures, it allows visualization (and avoidance) of the nerve itself, and it allows more facile placement of perineural catheters. It can be used in conjunction with a nerve stimulator or alone. Anesthesia technicians and technologists should expect to be actively involved with ultrasound in most anesthesia practices and should understand its techniques and advantages.
Regional anesthesia can be used in conjunction with a general anesthetic to supplement the anesthetic and provide postoperative pain control. Regional anesthesia can also be used as the sole anesthetic for an operation (surgical anesthesia). Regional anesthesia used for surgical anesthesia can be of great benefit to patients who might have difficulty tolerating a general anesthetic. Currently used local anesthetics and adjuncts can render a limb pain-free for 12-24 hours. If a perineural catheter is placed, analgesia can be extended for as long as the reservoir of the attached pump lasts, usually 2-3 days.
The advances in regional anesthesia during the last century allow anesthesiologists to safely and reliably perform a wide variety of blocks to the benefit of patients both during and after surgery. Certain things, however, have not changed. Labat’s instructions to the staff and students at the Mayo Clinic in 1920 are still true today: “Gentleness is the first requisite of the anesthetist. Before anesthesia is begun, the patient should be warned that he will feel a few light pinpricks, but that all subsequent operative maneuvers will be painless, although the sense of touch and pull will not be abolished …The anesthetist should handle his needle and his patient with equal dexterity.”
In general, regional anesthesia may be indicated in patients who would have difficulty tolerating a general anesthetic and the surgical site is amenable to being anesthetized with a regional anesthetic. The other major indication for regional anesthesia, in combination with a general anesthetic or as the sole anesthetic, is to provide postoperative pain control. As described above, single injections of local anesthetics can provide postoperative pain control for 12-24 hours. The addition of a perineural catheter can extend postoperative pain control for a few days.
Despite the advantages in terms of postoperative comfort and stable surgical pain control associated with regional anesthesia, not all patients are appropriate candidates for a nerve block. Nor is blockade without risk. Use of regional techniques in patients who are inappropriate can lead to serious and potentially debilitating consequences.
Before placing a block, anesthesiologists carefully consider the type of surgery, the needs of the surgeon performing the procedure, and the wishes of the patient. They perform a complete history and physical of the patient, taking into special consideration their anatomy, airway, body habitus, and comorbidities. With regard to regional anesthesia, several important medical issues come into play and must be thoroughly investigated.
Hereditary or iatrogenic bleeding disorders are common, as is the use of medications for anticoagulation, such as Coumadin, heparin, or Lovenox. Anatomically, large nerves commonly run beside large vessels, and many of the commonly performed blocks are placed in close proximity to important and large vascular structures, such as the carotid or femoral arteries. In an anticoagulated patient, however, it is not necessary to lacerate a large artery to cause a hematoma. In these patients, disruption of smaller arteries or veins can cause significant bleeding. While anticoagulation is not an absolute contraindication to blockade, its presence does cause careful assessment of the risks and benefits of a given block. For some blocks, a small amount of bleeding is not necessarily a disaster. Access of the vessel for compression is important. The area around the femoral artery, for example, can be compressed until a small amount of bleeding slows and stops. This is not true for the tissue around the lumbar plexus, a deep structure well protected by thick musculature. Uncontrolled bleeding into the lumbar space is a dangerous affair and may require surgical intervention to control. The same consideration is true for the space around the spinal cord. Bleeding within the epidural space can cause compression of the spinal cord with disastrous consequences. Prior to performing a block, an evaluation of the patient’s coagulation status with lab tests may be required to determine if a block is contraindicated.
Many of the blocks used for analgesia of the upper extremity are placed in close proximity to the dome of the lung. This is particularly true of approaches used for supraclavicular (above the collar bone) and infraclavicular (below the collar bone) blockade. In some cases, the distance between the lung and the site where local anesthetic is deposited can be less than a centimeter. In these instances, the risk of pneumothorax (puncture of the pulmonary pleura) is a very real possibility. A pneumothorax is a complication that can have consequences ranging from overnight observation, to chest tube placement, to death. In a patient with compromised lung function, anesthesiologists carefully consider the implications of this complication before attempting to place one of these blocks. If the patient cannot tolerate even a small reduction in lung function, is it worth the risk of even trying to place the block?
Blocks of the brachial plexus (the nerves originating in the neck and traveling to the upper extremity) are common and also pose a hazard to pulmonary function, but for a different reason. Blocks of the brachial plexus performed above the clavicle or in the neck (interscalene or supraclavicular) usually involve injection of a volume and concentration of local anesthetic that will, almost universally, affect the phrenic nerve supplying the diaphragm, causing one-sided diaphragmatic paralysis. This, in turn, means that the lung on that side will lose much of its ability to participate in ventilation. This one reason is why some patients who have had an interscalene block may complain of shortness of breath. In patients who have reduced lung capacity, this reduction in ventilation may be sufficient to compromise their oxygenation (Fig. 16.2).
FIGURE 16.2. The interscalene approach to brachial plexus anesthesia. Position the patient supine with the head slightly rotated to the contralateral side. Identify the lateral border of the clavicular head of the sternocleidomastoid muscle. Roll the fingers posteriorly over the belly of the anterior scalene muscle and into the groove between the anterior and middle scalene muscles (interscalene groove). At the level of the cricoid cartilage (approximately C6), insert the block needle perpendicular to the skin in all planes and directed slightly caudad and slightly posterior. Advance the needle until paresthesias are elicited in the distal upper extremity or motor movement is obtained with a nerve stimulator. Inject 30-40 mL of local anesthetic after a negative aspiration for cerebrospinal fluid or blood. (From Bucholz RW, Heckman JD. Rockwood & Green’s Fractures in Adults. 5th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2001, with permission.)
As with bleeding disorders, preexisting nerve injury is not an absolute contraindication to nerve block. Consideration must be given to the cause of the previous injury and to the possibility that a block may exacerbate or reinjure the nerve. If, for example, a patient has a peripheral neuropathy caused by diabetes, it may be appropriate to perform a nerve block. The neuropathy caused by diabetes is more global—it does not affect a single region (see Chapter 12, Peripheral Nervous System). At the same time, diabetics may be more susceptible to local anesthetic toxicity. In another example, a patient with a nerve injury to the peroneal nerve, with foot drop and numbness, of unknown cause, suffers from weakness in the lower leg. Many anesthetists would not offer such a patient a nerve block, even if he or she is willing; some might, if there were reason to think it offered significant or unusual benefit.
As discussed in Chapter 12, Peripheral Nervous System, patients may be allergic to local anesthetics. Amide local anesthetic allergy is rare, but allergy to ester local anesthetics is more common; it is also relatively common for people to have reactions to preservatives in the local anesthetic solution. Local anesthetics are divided into two classes: amides and esters. Esters, such as chloroprocaine and tetracaine, are metabolized in the bloodstream by enzymes called pseudocholinesterases, and it is possible to have a hereditary or acquired pseudocholinesterase deficiency. Amides (lidocaine, mepivacaine, bupivacaine, ropivacaine), on the other hand, are metabolized largely in the liver. As a result, severe liver disease is a relative contraindication to their use.
It is not uncommon for patients to decline a block. Many feel that their pain tolerance will be sufficient for them to tolerate the postoperative discomfort of surgery. Others have had blocks previously and do not like the feeling of a numb limb; others are frightened of needles. Many of these patients will have correctly assessed their own pain threshold; some will not. Because it is difficult to predict who will tolerate pain and who will not, some centers plan to have a complete discussion prior to surgery of risks and benefits with all patients who might benefit from a block. That way, a postoperative block remains an option, should their pain prove intractable in the postoperative setting.
Infection of the tissues at the site desired is a contraindication to block placement. Needle passage or catheter placement may introduce infection or cause abscess around the nerve, which could cause permanent nerve injury.
The success of any given block is highly dependent on a willing and educated patient. The actual placement of a block is a technical skill; however, the anesthesiologist must also perform a thorough preblock assessment of the patient to determine the risks and benefits of performing the block, provide education to the patient, create a reassuring environment for placement of the block, and observe and reassess the patient following the block. These are the medical skills that make the regional anesthesiologist more than just a block technician.
Patients should understand the risks and benefits of peripheral nerve block, the process of block placement, and what to expect as a consequence of the block. This education must take place prior to the actual procedure. Methods of accomplishing this goal are in place at many institutions, which include a slide show, short video, or pamphlet detailing the actual procedure, followed by a personal discussion with the physician placing the block. The discussion will inevitably cover the risks of peripheral nerve blockade. As with all medical procedures, nerve blocks carry risks. Responsibly performed, the benefits will usually, but not always, outweigh the risks. Risks always include bleeding at the site or into tissues, infection, and nerve damage. Nerve damage is the most frightening possibility—but true, permanent nerve palsy as a result of regional techniques is a relatively rare occurrence. Most clinicians will combine their knowledge of published data with the monitoring they perform of their local and regional outcomes to provide their patients with an overall assessment of how often this can occur.
Most physicians take the opportunity to combine the discussion of risk and benefit with a site marking. Properly identifying the operative site and clearly marking it prior to the sedation or medication of the patient is an important part of maintaining patient safety. It cannot be omitted. As with site marking, it is also critical to obtain and clearly document the patient’s consent to the procedure prior to any sedation.
Regional anesthesia can be performed in almost any location, provided adequate equipment is readily available both to perform the block and to resuscitate the patient, if the need should arise. Practically speaking, most blocks are performed preoperatively in a dedicated block room or in a preoperative bay. Some are also performed directly prior to surgery in the operating room. Postoperative blockade is most commonly performed in the postanesthesia care unit (PACU).
Blocks are almost always done with the patient sedated but awake. Rarely, they can be performed on an anesthetized patient; however, this is not preferred because the patient cannot inform the physician of a paresthesia potentially signaling nerve injury. Because pediatric patients are often not able to cooperate with block placement, the majority of blocks in young children are placed in anesthetized patients despite the increased risk.
A dedicated block room, if available, is the most convenient location for block placement. It allows for consistent monitoring of the patient, standardization of the routine around regional practice, and a storage location for the different types of technical equipment associated with nerve blockade, including stools and tables, a block cart, an ultrasound machine, and the requisite monitoring devices. The current basic standard for monitoring patients undergoing anesthesia includes continuous evaluation of the patient’s oxygenation, ventilation, circulation, and temperature. In regional practice with an awake patient, this means, at a minimum, an electrocardiogram continuously displayed from the beginning to the end of the procedure, continuous pulse oximetry with adequate lighting of the patient to assess skin color, and determination and evaluation of blood pressure and heart rate at least every 5 minutes. It also means that the supervising physician must be in a position to readily assess and assist with the patient’s ventilation (i.e., providing a chin lift or a jaw thrust, or other maneuvers) if needed. As a matter of course, block rooms and other areas should be kept warm for optimal patient comfort. In the block area, most patients will rest either supine or prone on a hospital bed or gurney. The protective side rails of the bed are lowered so as to allow easy access to the patient and allow for appropriate monitor placement. An oxygen mask or nasal cannula is commonly used. If an ultrasound machine will be part of the procedure, it is placed on the side opposite the limb to be blocked. For example, if the patient’s right leg will be blocked with a femoral block, the ultrasound machine is placed on the left and the physician performing the block sits on the right. This type of positioning allows the anesthesia technician to operate the ultrasound machine, manipulate the nerve stimulator, give sedation or inject local anesthetic at the direction of the physician, and help monitor the patient.
Common equipment includes the ultrasound machine, a nerve stimulator if used, a block tray if a catheter is being placed, and a block cart. Not all institutions have block carts, but it is helpful to assemble all of the block equipment in one location. Block carts will contain local anesthetics, a variety of block needles (e.g., stimulating, single shot needles and needles for catheter insertion), other needles and syringes, extra block trays, ultrasound gel, ultrasound sheaths, gowns, gloves, masks, dressing materials, and emergency equipment (airway management) and medications (lipid infusion, resuscitation drugs).
It is easier for patients to tolerate the process of block placement if they are lightly sedated. Usually, this can be easily accomplished with a small amount of opioid and a benzodiazepine. Common medications for this purpose are fentanyl and midazolam. In small doses, both of these types of medication can help anxious patients be at ease as the block is placed. Most block placements should not be painful—often, the worst discomfort comes as the area is numbed with a local anesthetic skin wheal. In larger doses, both opioids and benzodiazepines cause respiratory suppression and the effect is synergistic. As a result, as with any attempt at sedation, physicians must carefully evaluate patients prior to administering these medications. Body habitus and airway concerns are particularly important. Is the patient obese? Do they have sleep apnea? Do they have a potentially difficult airway? All of these considerations come into play when determining whether or not a patient will tolerate even light sedation. In some instances, it is safer to offer a block with the understanding that no sedation at all will be provided and abort the block placement if it cannot be performed without medications.
Neuraxial regional anesthesia refers to blockade of nerves by introducing anesthetic agents into the spinal column and directly anesthetizing a portion of the spinal cord or the nerves as they exit the spinal cord. This is accomplished with two different techniques, spinal anesthesia and epidural anesthesia.
Spinal anesthesia, the administration of an anesthetic solution into the subarachnoid space, was initially performed on humans in Germany by August Bier in 1898. Because the solution is injected directly into the cerebrospinal fluid (CSF), the local anesthetic comes in direct contact with the spinal cord (see Chapter 11, Central Nervous System). Patients are placed in the sitting or lateral position, and a thin needle (26G-22G) is passed between the lumbar spinous processes and through the dura (Fig. 16.3). Proper positioning of the patient is important. If the patient is able to push his or her lower spine out toward the anesthesia provider (arch his or her back like a mad cat), it can open the space between the spinous processes and make access to the dura easier. The natural reaction of a patient is to pull away from the needle, and this will reduce the space between the spinous processes. Aspiration of clear CSF confirms proper needle placement. A solution of local anesthetic (sometimes mixed with opioid) is injected into the CSF. The onset of anesthesia is rapid and begins within just a few seconds. If the local anesthetic is hyperbaric (more dense than CSF), it will tend to fall with gravity. If the patient is in the sitting position, the local anesthetic will tend to sink toward the bottom of the spinal column. If the solution is hypobaric, it will tend to rise in the CSF. For example, a patient presenting for right hip surgery is placed in the left lateral position (on his or her left side). A hypobaric spinal would tend to rise and preferentially anesthetize the right side of the body. The baricity and position of the patient are used to provide a crude method of controlling the spread of the local anesthetic. The spread is important. The more spinal segments that are anesthetized, the greater the sympathetic blockade and the greater the hypotension caused by the spinal anesthetic. In addition, the anesthesia provider does not want the anesthetic effect to spread too high and involve the cervical portion of the spinal cord or even the brainstem. Anesthetizing the cervical spinal cord will produce diaphragmatic paralysis and apnea; anesthetizing the brainstem can produce loss of brainstem function with apnea, hypotension, bradycardia, and, rarely, cardiac arrest. When the spread of the anesthetic is too high, it is referred to as a high spinal, and the anesthesia team should be prepared to manage the airway and cardiovascular function. Spinal anesthesia is typically performed in the operating room because of its relatively rapid onset; preparation for surgery can usually proceed right away. It is also performed in the OR because patient vital signs may require prompt management quickly, and if so, it is preferable not to be in the hallway.
FIGURE 16.3. Lumbar puncture and epidural anesthesia. Because the spinal cord ends before the neural canal of the vertebral column constricts, a substantial amount of cerebrospinal fluid can accumulate in the lower lumbar regions of the subarachnoid space. Needles can be introduced in the space between L3 and L4 to sample the cerebrospinal fluid (a “spinal tap” or lumbar puncture) without risk to the spinal cord itself. Likewise, the anesthetic can be introduced into the epidural space at the same levels. (From Taylor C, Lillis CA, LeMone P. Fundamentals of Nursing. 2nd ed. Philadelphia, PA: JB Lippincott; 1993, with permission.)
Epidural anesthesia, like spinal anesthesia, also takes place in the neuraxis within the spinal column, as opposed to a peripheral nerve block, which is directed toward nerves after they have exited the spine. An epidural consists of a thin catheter that is placed in the epidural space, outside of the dura (the tough covering that envelops the spinal cord and the CSF) but inside the spinal column. It is placed using a special needle called a Tuohy needle, which has a dull point shaped somewhat like a spoon, specifically designed not to catch or cut the dura overlying the thecal sac, but rather to be able to stop in the epidural space (i.e., the space on top of the dura). The most commonly used technique for locating the correct placement of the epidural catheter is called the loss-of-resistance technique. Patients are placed in the lateral or sitting position. The anesthesia provider will detect the potential space superficial to the dura by attempting to inject a small amount of air or saline as he or she passes the Tuohy needle through the ligamentous structures surrounding the central bony canal of the spinal column, where the spinal cord sits inside its firm dural sac. As one enters this epidural space, the air and saline suddenly become easy to inject—one encounters a loss of resistance. The catheter is then threaded through the needle and the needle removed.
The segmental spread of anesthesia with epidural placement of local anesthetic is significantly less than with spinal anesthesia, despite 10 times the volume (and 10 times the dose) of local anesthetic being injected into the epidural space. For this reason, epidurals are commonly placed in the thoracic or lumbar spine depending upon which spinal segments are targeted for anesthesia. Cervical epidurals are rarely used outside of special injections for chronic pain management. It is important to note the large volumes and doses used in epidural anesthesia. It is possible for the epidural needle or catheter to be inadvertently placed in the subarachnoid space, or a blood vessel, rather than the epidural space. Injection of the usual epidural dose of local anesthetic into the subarachnoid space would produce a total spinal with potentially catastrophic consequences. Injection of the usual epidural dose of local anesthetic into the intravascular space could produce local anesthetic systemic toxicity (LAST), ventricular fibrillation, and cardiac arrest. For this reason, the first epidural dose administered through the catheter is a small “test dose” of local anesthetic that would not produce either high spinal or LAST. Most practitioners use a local anesthetic mixed with epinephrine for the test dose. The local anesthetic is enough to cause a predictable, uneventful spinal anesthetic, but not a high spinal. If the epidural needle or catheter has entered a blood vessel, the epinephrine should cause a tachycardia. If no signs of a spinal anesthetic or intravascular injection occur several minutes after injection of the test dose, the remaining dose of the local anesthetic is injected in increments. During the injection of epidural local anesthetics, the anesthesia provider must always be on the lookout to detect signs of intravascular injection or a high spinal. The incremental injection of every dose of epidural local anesthetic is another safeguard against producing a high spinal or an intravascular injection with local anesthetic toxicity.
Epidural and spinal anesthesia both provide a dense and reliable sensory and motor block of the lower extremities and the lower abdomen. Spinal anesthesia in particular has been adopted in Europe and the United States as a means of providing analgesia for many types of surgeries, particularly total joint replacement and cesarean section.
The interscalene block is one of the more frequently performed nerve blocks, most often for surgery of the shoulder or upper arm. The nerve roots of C4-T1 emerge from the spinal foramina and travel down the neck as trunks in the groove formed by the anterior and middle scalene muscles, underneath the sternocleidomastoid muscle. The location, seen on ultrasound in the midneck, is usually about 1 or 2 cm lateral to the carotid artery. Often, the roots or trunks will have a characteristic appearance, forming a pattern that almost looks like a traffic light, with three individual trunks resting one on top of the other. If using nerve stimulation, the physician will locate and mark the interscalene groove and then insert a needle 1 or 2 cm into the area between the muscles, until a deltoid (shoulder muscle) or arm muscle twitch is elicited (Fig. 16.4).
FIGURE 16.4. Ultrasound image of the brachial plexus in the interscalene region.
As previously noted, the interscalene block is associated with hemidiaphragmatic paralysis on the side of the block. It is also associated with Horner syndrome—ptosis, miosis, and anhidrosis. The eyelid droop (ptosis) and the small pupil (miosis) are often remarkable even to the layperson. Horner syndrome is not a complication; rather, it is innocuous and a sign of a successful block.
The interscalene block is often used for perineural catheter insertion. Because of the location on the neck, two technical problems are seen frequently: (1) leakage and (2) catheter movement. Even after surgery, patients will of course move their heads—this movement combined with injection of a bolus into an area of limited volume is often sufficient to cause the catheter to migrate. The bolus and ongoing administration of local anesthetic through a pump may also lead to a significant amount of leakage from the catheter entry site, enough to saturate and displace the dressing. It is best to make sure that the dressing is firmly buttressed and to instruct patients that some leakage is expected and not disastrous. They should also, of course, be able to contact a member of the anesthesia team at all hours until their catheter is removed.
With the advent of ultrasound, the supraclavicular block has become a popular block for surgery of the upper arm, elbow, and hand. The block can be performed with stimulation alone, but as the dome of the lung is very near to the divisions of the brachial plexus at this level, ultrasound may offer some protection from inadvertent pneumothorax. The location of the block (using ultrasound) is approximately midway along the superior aspect of the clavicle (collar bone). In this location, the anterior and posterior divisions of the brachial plexus tend to cluster in front of the subclavian artery, with both structures resting on the first rib. The lung lies very near to the nerves. In general, the supraclavicular block, like the infraclavicular block, tends to offer superior analgesia of the elbow and hand than does the interscalene block. The interscalene block can sometimes lead to incomplete anesthesia of the lower trunks of the plexus, with incomplete anesthesia in the distribution of the ulnar nerve. If nerve stimulation is used, alone or with ultrasound, a twitch at the level of the hand, fingers, or thumb is preferred.
The infraclavicular block is used for surgery of the elbow, forearm, and hand. As with the supraclavicular block, placement can be challenging and physicians should be skilled prior to attempting this technique. Because of its distance from the phrenic nerve, local anesthetic placed in this location is less likely to affect the diaphragm. It shares the risk of pneumothorax with other brachial plexus blocks. The placement of the block, with ultrasound, is underneath the clavicle, adjacent to the coracoid process. A hand, finger, or thumb twitch, when using nerve stimulation, is a predictor of a successful block. Some physicians will ask that the patient be positioned with the arm extended laterally and the forearm flexed and rotated above the head (as if the patient were saluting). This can sometimes bring the brachial plexus closer to the surface and make it more prominent under ultrasound, as well as draw it away from the lung (Fig. 16.5).
FIGURE 16.5. Ultrasound image of the brachial plexus in the infraclavicular region.
Unlike the supraclavicular block, at the level of the infraclavicular block, the brachial plexus tends to no longer be grouped in a single, discrete area. Instead, cords of the plexus are arranged in a triangular pattern around the artery. Because of the anatomy of the cords in this location, it may be necessary to direct injections around each cord in order to obtain adequate analgesia (Fig. 16.6).
FIGURE 16.6. Surgical anatomy for the axillary block technique. (From Doyle JR. Hand and Wrist. 1st ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2006, with permission.)
Both of the blocks around the clavicle lend themselves to a more secure dressing, in the event of catheter placement, than does the interscalene block. The distal location of the infraclavicular block may occasionally result in an unanesthetized musculocutaneous nerve, as this nerve splits off from the brachial plexus at about this level. In this case, a separate block can be directed at the musculocutaneous nerve directly, if needed, either at the time of the initial block or as a rescue after surgery.
The axillary block is performed for surgery of the elbow, forearm, or hand. It can be performed by landmark, using ultrasound or with nerve stimulation. The very top of the armpit is the site for this block (Fig. 16.6). At this level, the cords of the brachial plexus are becoming or have become the primary named terminal nerves (i.e., the median, radial, and ulnar nerves). The musculocutaneous nerve normally splits off prior to the site of axillary blockade.
As with the infraclavicular region, they are usually arranged around the artery, with the radial nerve being located posteriorly. Local anesthetic deposited posterior to the artery may sometimes travel around the vessel and anesthetize the two other desired nerves, but more often the anesthesiologist will perform multiple injections to ensure a good block of all the nerves. The musculocutaneous nerve will be injected separately, as it penetrates the substance of the coracobrachialis muscle (Fig. 16.7). Catheters are not commonly placed for continuous axillary block—the tissue of the axilla is too mobile, and the site is too inconvenient for the technique to be routine.
FIGURE 16.7. Formation of the brachial plexus. This large nerve network provides innervation to the upper limb and shoulder region. The brachial plexus is formed by the ventral rami of the 5th through 8th cervical nerves and the greater part of the ramus of the 1st thoracic nerve (the roots of the brachial plexus). Small contributions may be made by the 4th cervical and 2nd thoracic nerves. Observe the merging and continuation of certain roots of the plexus to three trunks, the separation of each trunk into anterior and posterior divisions, the union of the divisions to form three cords, and the derivation of the main terminal branches from the cords. (From Moore KL, Dalley AF. Clinical Oriented Anatomy. 4th ed. Baltimore, MD: Lippincott Williams & Wilkins; 1999, with permission.)
The lumbar plexus is a group of nerves that arise from the lumbar spine and supply the lower extremity. The performance of a lumbar plexus block is an advanced technique that requires ongoing practice to place safely. As a result, it is not performed with great regularity. When properly placed, however, it does offer some advantages over an epidural. These include unilateral as opposed to bilateral block and the lack of systemic effects such as hypotension. At the same time, because the lumbar plexus is located deep in the psoas muscle of the lower back, it is possible to have serious misadventures while searching for proper placement. Also, unlike most of the other routinely placed blocks, the lumbar plexus block may be uncomfortable during placement. Sedation and local anesthesia of the deep tissues of the back during the procedure require the close attention of the anesthesiologist if a successful block is to be completed (Fig. 16.8).
FIGURE 16.8. Constituents of the lumbar plexus. (From Campbell WE. DeJong’s The Neurologic Examination. 6th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2005, with permission.)
Some physicians may perform the entire block using ultrasound. More common practice, however, would be to use landmarks to define the proper location of the block, possibly using ultrasound as an adjunct to assess the likely depth of the lumbar plexus, and then use nerve stimulation to determine block placement. A patellar twitch is indicative of femoral nerve stimulation and likely block success. The lumbar plexus block, like a femoral nerve block, is usually indicated for surgery of the hip, medial and anterolateral upper leg, and knee. It does not cover the lower leg, except the cutaneous distribution of the saphenous nerve, nor does it cover the posterior aspect of the knee.
This nerve block is performed frequently due to its relative ease, safety, and versatility. A properly performed block will cover the anterior thigh and knee as well as the cutaneous distribution of the saphenous nerve. It will miss the medial thigh, innervated by the obturator nerve. It will also miss the posterior knee, which is innervated by the sciatic nerve, as well as the lateral thigh, which is innervated by the lateral femoral cutaneous nerve. Most of the time, this block is indicated for knee surgery—either total knee arthroplasty or knee arthroscopy involving substantial surgery on bone, such as anterior cruciate ligament repair. Most patients can tolerate routine knee arthroscopy without much postoperative pain. Femoral nerve block does offer some analgesia for hip surgery as well. Depending on the specific circumstances, many physicians will supplement femoral nerve block with a sciatic block to cover the posterior knee for total knee arthroplasty.
The site of the nerve block is just below the femoral crease, 1 cm lateral to the femoral artery. It is often shallow, perhaps 2-3 cm deep. The femoral artery is usually easily palpated and easily visualized if ultrasound is used. The nerve can also be seen quite readily. This is a common location for catheter placement. If nerve stimulation is used, physicians look for patellar (kneecap) movement as an indication of appropriate placement (Fig. 16.9).
FIGURE 16.9. Ultrasound image of the femoral nerve in the groin.
More recently, surgeries of the knee have benefited from the placement of adductor canal blocks. These ultrasound-guided blocks of the saphenous nerve are directed to the medical aspect of the thigh above the knee and below the midpoint of the leg. Blocking the saphenous portion of the femoral nerve at this location appears to have the benefit of lessened motor blockade to the components of the nerve that supply the quadriceps muscle. This means that patients may more easily complete the tasks of early physical therapy, with the goal of rapid recovery. As one might expect, most of the blocks that are performed with this goal in mind are single shot blocks, not catheters.
The sciatic nerve arises from a group of nerve roots originating in the lower spine (lumbar and sacral regions). As with most blocks, there are a number of approaches described to block the sciatic nerve in the upper, posterior leg. One such approach is the subgluteal technique, where the greater trochanter of the femur and the ischial tuberosity are identified and marked and a line is drawn between them. The sciatic nerve can often be found 3 cm distal to the midpoint of this line. Use of an ultrasound machine greatly simplifies this block, if the nerve can be seen. However, it is often deep enough that it cannot be readily identified with ultrasound. Because of this, a nerve stimulator is frequently used to verify that the structure in question is, in fact, the sciatic nerve. Physicians look for twitch of the foot or ankle to confirm identification of the sciatic nerve with a nerve stimulator.
Sciatic nerve blocks are suitable for surgery of the posterior knee, lower leg, and foot. The sciatic nerve does not cover the skin of the medial lower leg and ankle, the territory of the saphenous nerve. Catheters can be placed using high sciatic blocks, but they tend to be inconvenient. Most anesthesiologists will opt for a single shot technique in this location, placing catheters, if needed, lower down the leg, in the popliteal fossa.
The popliteal fossa block is a variant of the sciatic block. The block is performed at the top of the popliteal fossa, which is about 9 cm above the crease on the back of the knee where it flexes. The block can be placed easily with ultrasound and fairly easily using landmarks and nerve stimulation. Approaching the knee, the sciatic nerve divides into two terminal branches, the common fibular (peroneal) and the tibial nerves. These two nerves supply all of the lower leg, except the cutaneous distribution of the saphenous nerve (a terminal branch of the femoral nerve). Using ultrasound, it is often possible to observe the nerve divide as it is traced down the back of the leg toward the crease on the back of the knee.
The popliteal block provides excellent anesthesia for surgery of the lower leg and foot. If the surgery is medial, it can be supplemented with a saphenous nerve block to provide anesthesia to the skin. Catheters are frequently placed in this location. It should be noted that in addition to sensory block, most peripheral nerve blocks cause some degree of motor blockade. If either the femoral or sciatic distribution is blocked, it should be assumed that the patient’s leg will be weak and that he or she will not be able to walk without assistance. He or she will normally be placed in a brace and issued crutches. Surgery of the knee usually requires a subgluteal sciatic nerve block.
Anesthesiologists will often attempt to test a block’s function prior to the patient being taken to the operating room. This can be done in a number of ways: testing for sensory changes, such as pinprick or temperature, and testing for muscle weakness. Depending on the type of local anesthetic used and the location of block, analgesia can sometimes take 20 minutes or more to become established. Frequently used local anesthetics for regional anesthesia are lidocaine, mepivacaine, ropivacaine, and bupivacaine, listed in order from fastest to slowest onset and from shortest to longest acting.
Nerve blocks can fail for a wide variety of reasons. The needle may move during injection; the injectate may flow away from the nerve; the physician may have misidentified the nerve under ultrasound or accepted an incorrect twitch using nerve stimulation; the catheter, though placed correctly, may migrate; the patient may have underlying alterations in central pain processing, so that adequate relief requires treatment at both the PNS and central nervous system (CNS) levels. When a block fails, patient and provider can move forward with a noninvasive means of pain control, such as patient-controlled analgesia. Alternatively, the block can be performed a second time. Often, this takes place in the PACU after there has been ample opportunity to fully assess the patient and determine that the block is truly ineffective.
A failed block, of course, is not the same thing as a patient experiencing mild or even moderate pain after surgery despite a block. Blocks performed for analgesia postsurgery often do not completely eradicate pain. Rather, they ameliorate it, and allow reduced consumption of opioids, with an attendant reduction in side effects. Some blocks will never allow a patient to be completely pain-free (e.g., a femoral nerve block performed for a total knee arthroplasty). This is because the femoral nerve does not completely cover the knee. If a catheter has been placed but initially given a modest bolus, it may need to be rebolused after surgery to provide adequate pain relief.
Dressings or braces near, or over, the desired site of the block may complicate the performance of postoperative blocks. The surgical team can help determine whether these can be adjusted or removed safely. It is also incumbent upon the anesthesiologist performing the procedure to ensure that the patient is capable of giving consent. One method of handling this issue is to obtain consent for a postoperative block, if needed, prior to the surgery. Patient positioning can also be a challenge postoperatively. Prone blocks after knee or lower leg surgery may be difficult to perform because it may be painful for the patient to turn over. Often, it is possible to take an alternative approach to the nerve that will not involve as much motion on the part of the patient. In some instances, patient immobility may make a particular type of block impossible to perform.
Patients who have had nerve blocks need to be seen by a physician following surgery to assess their overall status as well as block function. If a patient has had a perineural catheter placed, he or she needs to be followed-up daily by a physician while in the hospital until the catheter has been removed. This allows observation of dressings and the catheter site, as well as titration of the pump dispensing the local anesthetic. If a patient has been allowed to go home with a pump, he or she should be followed-up by phone and have instruction to call either the physician who placed the pump or a covering service if the patient has any questions. Someone should be available at all hours to answer calls of this nature.
Regional anesthesia is a productive and compelling part of anesthesia practice. Correctly performed, it greatly reduces pain, one of the great fears people experience when facing surgery. Advances in imaging, such as ultrasound, and in equipment, such as perineural catheters, have extended the reach of nerve blockade in terms of both safety and duration. As more and more procedures are performed on an outpatient basis, the importance of this type of anesthesia will only increase. The anesthesia technician should be thoroughly familiar with the techniques and equipment to perform regional anesthesia in order to be an effective assistant.
1. Which of the following statements is FALSE regarding spinal anesthesia?
A) For placement, the patient is placed in the sitting or lateral position.
B) The needle is placed at the level of the lumbar spine.
C) The patient should have basic monitors placed prior to the injection of local anesthetic.
D) The spine should be as straight as possible to facilitate needle placement.
E) A “high spinal” may result in severe hypotension or apnea.
Answer: D
Proper positioning of the patient is important to facilitate needle placement. The space between the spinous processes can be very small. Having the patients arch their back can open the space and make proper placement of the needle easier. All of the other statements are true. Spinal needles are usually placed in the lower lumbar spine because the spinal cord usually ends above this level. If the needle is placed in the lower lumbar region, the risk of injuring the spinal cord is reduced. Because of the potential for hypotension even with properly placed blocks, and the risk of apnea and major cardiovascular changes with a high spinal, all patients should be monitored during block placement.
2. Which of the following would NOT be needed during placement of a routine peripheral nerve block?
A) Ultrasound machine with gel
B) Sterile prep
C) X-ray equipment (e.g., fluoroscopy)
D) Basic monitoring equipment
E) Peripheral nerve stimulator
Answer: C
The vast majority of peripheral nerve blocks are placed using ultrasound, anatomic landmarks, or peripheral nerve stimulators to locate the nerve. X-ray equipment would be necessary under very rare circumstances. The placement of nerve blocks requires a sterile prep and sterile technique to reduce the incidence of infection. Basic monitors should be applied because these patients are often lightly sedated and to monitor for the effects of inadvertent intravascular injection.
3. Which of the following is likely to be a complication from a peroneal sciatic block?
A) Intrathecal injection
B) Seizure
C) Pneumothorax
D) Hemidiaphragm paralysis
E) All of the above are potential complications
Answer: B
Seizure is a presenting sign of LAST, which can occur with intravascular injection of local anesthetic medications. Any peripheral nerve block can contain enough local anesthetic to cause CNS or cardiovascular toxicity. The sciatic nerve is located in the posterior part of the leg; the peroneal approach to it is just above the knee. Nerve blocks in the neck or upper arm can puncture the lung cavity, resulting in a pneumothorax. Nerve blocks in the neck can also block the phrenic nerve, resulting in paralysis of part of the diaphragm. Intrathecal injection is injection into the spinal fluid, not accessible from the peroneal space.
4. Which of the following statements is true?
A) Femoral nerve blocks provide complete pain relief for knee surgery.
B) Axillary nerve blocks can be used for shoulder surgery.
C) Femoral blocks can be used for pain relief for hip surgery.
D) Lumbar plexus blocks are commonly used for foot and ankle surgery.
Answer: C
Femoral blocks provide significant, but not complete, pain relief in hip surgery and can be used as part of a postoperative pain relief plan. The femoral nerve is more commonly used for pain relief in knee surgery but does not provide complete coverage of the knee: the posterior aspect of the knee is innervated by the sciatic nerve. The axillary nerve block does not cover the shoulder. The lumbar plexus block is technically challenging and typically would be replaced by a more distal block, such as a combined sciatic/saphenous, for a foot and ankle surgery.
5. Which of the following statements are true regarding a test dose of local anesthetic for an epidural catheter?
A) The test dose will detect a pneumothorax.
B) If the test dose produces anesthesia, the catheter is in the epidural space.
C) If the catheter is in a blood vessel, the patient will have CNS symptoms like tinnitus.
D) The test dose is used to detect intrathecal and intravascular injection.
E) Once the test dose is negative, the catheter is definitely not intravascular.
Answer: D
The test dose is used to detect intrathecal and intravascular injection. It will not detect pneumothorax, which would be a rare but not impossible complication of epidural placement. The epidural test dose usually contains a small amount of local anesthetic mixed with epinephrine. If the epidural catheter is inadvertently placed in the subarachnoid space, the local anesthetic will cause a spinal within 5 minutes; an immediate anesthetic level indicates intrathecal placement. Because the test dose is a small amount of local anesthetic, it should not cause a high spinal. If the catheter is placed inadvertently into a blood vessel, the epinephrine may cause tachycardia, but there is a significant false-negative rate. Similarly, there is a significant false-negative rate for CNS symptoms, especially in sedated patients. Thus, a negative test dose definitively rules out an intrathecal but not an intravascular catheter.
6. Which of the following statements is true?
A) A patient can go home with a continuous infusion of local anesthetic via a peripheral nerve catheter that she will remove herself, as long as she has a 24-hour contact person.
B) A patient who declines a block can give consent for a block after surgery if he is in intractable pain in the PACU.
C) Patients do not require EKG monitoring during block placement.
D) Bleeding disorders or anticoagulant medications are absolute contraindications to peripheral nerve blocks.
Answer: A
Patients can and do go home with peripheral nerve catheters infusing local anesthetic via elastomeric pumps, but should have rapid access to an anesthesia provider for questions and troubleshooting. This is now an important part of many fast-track outpatient recovery protocols. Obtaining informed consent for a patient is optimally performed prior to surgery, anesthesia, sedation, and acute pain, all of which can impair patient judgment (see Chapter 65, Legal and Regulatory Issues), and most regional anesthesia services would agree that it is optimal to discuss risks and benefits of blocks prior to surgery. Block placement requires ASA standard monitors. Bleeding abnormalities are relative contraindications and must be weighed carefully against the bleeding risk, compressibility of site, vulnerability of nerve (an ankle block is different from the neuraxis), and potential benefit.
American Society of Anesthesiologists. Standards for Basic Anesthetic Monitoring (Affirmed October 28, 2015). Available from: http://www.asahq.org/~/media/Sites/ASAHQ/Files/Public/Resources/standards-guidelines/standards-for-basic-anesthetic-monitoring.pdf
Auroy Y, Narchi P, Messiah A, et al. Serious complications related to regional anesthesia: results of a prospective survey in France. Anesthesiology. 1997;87(3):479-486.
Côté A, Vachon C, Horlocker T, et al. From Victor Pauchet to Gaston Labat: the transformation of regional anesthesia from a surgeon’s practice to the physician anesthesiologist. Anesth Analg. 2003;96(4):1193-1200.
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