Regional Anesthesia for Anesthesia Technicians

Michael S. Axley

▪ INTRODUCTION

Regional anesthesia, the art and science of blocking nerve impulses in the peripheral nervous system, has a long and interesting history. 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 anatomical 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 can be found in early atlases, such as Regional Anesthesia: Its Technique and Clinical Application by Gaston Labat (Fig. 21.1).

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.

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 insensate 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.

▪ FIGURE 21.1 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.)

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.”

▪ INDICATIONS AND CONTRAINDICATIONS

In general, regional anesthesia may be indicated in patients who will 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.

Bleeding Disorders

Hereditary or iatrogenic bleeding disorders are common, as is the use of medications for anticoagulation, such as Coumadin, heparin, or Lovenox. 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. 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.

Pulmonary Function

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 collarbone) and infraclavicular (below the collarbone) 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. 21.2).

Preexisting Nerve Injury

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. At the same time, diabetics may be more susceptible to local anesthetic toxicity.

In another example, a patient with an injury to the common fibular of unknown etiology suffers from weakness in the lower leg. It would likely be unwise to ask this patient to submit to a nerve block, even if he or she is willing.

Local Anesthetic Reaction

Some patients are allergic to local anesthetics. True local anesthetic allergy is rare, but some types of local anesthetics can produce metabolites that cause a reaction. 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. 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.

▪ FIGURE 21.2 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.)

Patient Refusal

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, it may be advisable to have a complete discussion of risks and benefits with all patients who might benefit from a block prior to surgery. That way, even if they refuse a block initially, it remains an option for them, should their pain prove intractable in the postoperative setting.

Infection

Infection of the tissues at the site desired is a contraindication to block placement.

▪ PATIENT EDUCATION

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.

▪ BLOCK ROOMS, MONITORING AND POSITIONING, AND COMMON EQUIPMENT

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.

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