Regional Anesthesia of the Thorax and Extremities

Virtually every peripheral nerve can be blocked at some point along its course from the spine to the periphery ( to ), but digital nerve blocks (e.g., fingers and toes) are more commonly used than proximal blocks. Other common applications include femoral blocks for fractures of the femur, ankle blocks for foot injuries and infections, intercostal blocks for rib fractures, and wrist blocks for injuries to the palm.

The preparation, technique, choice of anesthetic, precautions, and complications are similar for all nerve blocks and are described in general in the following sections. The clinician is encouraged to use the same basic techniques and precautions for all nerve blocks. Specific precautions unique to a particular nerve block are included with the description of that block. Obvious precautions, such as aspiration before injection when the needle is in close proximity to a vascular structure, are not restated to avoid redundancy.

General Concepts

Indications

For most lacerations and injuries seen in the emergency department (ED), local infiltrative anesthesia is adequate and more efficient than using a nerve block (see Chapter 29 ). Patients who require extensive repair and anesthesia of the entire extremity are often referred to a specialist, who may prefer to examine an unanesthetized limb. A nerve block is indicated when it will provide advantages over other techniques. Scenarios in which this requirement is met include the following:

When distortion from local infiltration hampers closure (e.g., facial wounds) or compromises blood flow (e.g., fingertip)
When anesthesia is required over a large area and multiple injections would be painful or when the large amount of anesthetic needed for local infiltration exceeds the recommended dose
When a nerve block is the most efficacious form of treatment, such as an intercostal block for treating a rib fracture in a patient with chronic obstructive pulmonary disease (COPD)
When local infiltration of the wound would be more painful than a regional nerve block, such as in the plantar surface of the foot or the palm of the hand
When the block is performed to decrease pain during reduction of a finger or toe dislocation
When extensive limb surgery or manipulation is required (e.g., extensive tendon repair) and other options are not available

Preparation

A brief history, including drug allergies (particularly to local anesthetics), medications, and systemic illnesses, should be taken from the patient. Peripheral vascular, heart, and liver disease may increase the risk for severe complications. Therefore information about the existence of these diseases should also be sought.

Instructions

Explain the procedure to the patient, including the pain of needle insertion, paresthesias, and possible complications that may occur. Discuss the potential need for additional anesthetic or alternative procedures if the nerve block fails. Be sure that the patient understands that the additional administration of an anesthetic is part of the normal procedure rather than an attempt to correct an improperly performed nerve block. It is not standard to obtain written informed consent for nerve blocks performed in the ED.

Equipment

For most nerve blocks performed in the ED, the following equipment is required: latex gloves, an antiseptic solution (e.g., chlorhexadine), a 10-mL syringe, an 18-gauge needle for drawing the anesthetic from the vial, and a 3.75-cm, 25- or 27-gauge needle for the nerve block. Note that the needle sizes given in text are general recommendations, but for the majority of blocks, a 25-gauge needle is ideal. In addition, keep standard resuscitation equipment for advanced cardiac life support readily available any time that local anesthetic agents are given.

Choice of Anesthetic

Factors influencing the choice of anesthetic agent for nerve blocks are similar to those for local infiltration (see Chapter 29 for extensive discussion). In general, most nerve blocks are done for the repair of painful traumatic injuries that are likely to cause pain long after the repair is completed. In such cases, select the anesthetic with the longest duration of action to maximize the patient's analgesia. Buffering the anesthetic is strongly encouraged to lessen the pain of infiltration (see Chapter 29 ). For most of the blocks described in this chapter, buffered 0.25% bupivacaine is suggested as the anesthetic of choice, but equal volumes of 1% lidocaine with epinephrine can be substituted to provide faster onset of relief. The use of epinephrine on end-organ areas has traditionally been discouraged (e.g., tip of the nose, peripheral ear pinna, distal end of the penis), although the theoretical risk is unsubstantiated in clinical practice. Literature from 2010 describes the use and confirms the safety of lidocaine with epinephrine (1 : 100,000 concentration) for digital blocks. It would be prudent to avoid epinephrine-containing anesthetics in injuries involving vascular compromise or for those patients with peripheral artery disease. Higher concentrations of lidocaine (≤ 2%) or bupivacaine (0.5%) are commonly used for large nerves. Ropivacaine is another anesthetic with a rapid onset and a long duration of action (several hours). It has been reported to have fewer cardiotoxic and central nervous system effects than bupivacaine. Take care to avoid exceeding the recommended dosages of the anesthetic chosen.

Positioning the Patient

When possible, perform nerve blocks with the patient in the supine position to minimize the vasovagal syncope that may occur when the patient is in an upright position. When drawing up the anesthetic from the vial, hide this anxiety- and fear-inducing portion of the procedure from the patient.

Preparation of the Area to Be Blocked

To limit the incidence of infection, prepare the field in aseptic fashion before needle puncture. Allow the antiseptic solution to dry fully to achieve its maximal antibacterial effect. Sterile drapes and gloves are not routinely required but may be considered in addition to aseptic skin preparation for the initiation of blocks that (1) are close to large joints, vessels, and nerves; (2) are located in inherently contaminated areas of the body (e.g., groin, perineum); or (3) require simultaneous palpation of the underlying structures while injecting.

Choosing the Nerves to Block

Successful anesthesia requires appropriate knowledge of the relevant anatomy. Most areas to be anesthetized have overlapping sensory innervation and therefore require two or more nerves to be blocked. In addition, the cutaneous distribution of the various peripheral nerves differs slightly from patient to patient. Use a liberal margin of error when determining which nerves supply the desired area of anesthesia.

Locating the Nerve

When locating a nerve to be blocked, approach it from a site with easily identifiable anatomic landmarks. The best sites are those with good structural landmarks (e.g., prominent bones or tendons) immediately next to the nerve. For example, the four digital nerves are reliably found at the 2, 4, 8, and 10 o'clock positions around and just superficial to the proximal phalanx, whereas the median nerve lies between the palpable palmaris longus and flexor carpi radialis tendons at the proximal wrist crease. Nerves that course adjacent to easily palpable arteries, such as in the axilla and groin, are also easy to locate and are good sites for performing nerve blocks. Nerves that do not have adjacent structural or vascular landmarks are much more difficult to block.

Blocking nerves with good structural or vascular landmarks is straightforward: palpate the landmarks and follow the course of the nerve in relation to these landmarks. After visualizing the anatomy in the mind's eye, insert the needle in close proximity to the nerve.

Blocking nerves with poor landmarks, such as the radial nerve at the elbow, requires skill, practice, and some degree of luck. To increase the likelihood of successfully blocking these nerves, consider using ultrasound-guided techniques (see Ultrasound Box 31.1 ).

Nerve Stimulator

A nerve stimulator is commonly used by anesthesiologists but has never gained popularity among emergency clinicians. Nevertheless, it helps locate nerves that do not have adjacent structural or vascular landmarks, which greatly increases the chances of successfully blocking these nerves.

Ultrasound

Use of ultrasound to identify injection sites for peripheral nerve blocks has gained popularity. Ultrasound has been used successfully to locate and block nerves in the neck (e.g., interscalene, axillary, and brachial plexus), lower extremity (e.g., femoral and saphenous nerve blocks), upper extremity (e.g., radial, ulnar, and median nerve blocks at the elbow and forearm), and the lumbar plexus. Ultrasonographic guidance negates the effects of anatomic variability, provides real-time needle guidance, and allows the operator to visualize the “spread” of local anesthetic. The use of ultrasound is associated with superior success rates with fewer attempts, less time to perform the block, and fewer complications compared to anatomic nerve blocks or use of nerve stimulators.

There are two basic ultrasound techniques used to facilitate nerve blocks; the in-plane and out-of-plane techniques. Using the in-plane technique, the needle is inserted at the side of the probe and advanced toward the target. With this technique, the entire needle is visualized as it traverses the plane of ultrasound. With the out-of-plane technique, the needle enters the skin away from the probe and is aimed at the plane of sound. As the needle moves toward the target, only the needle tip is visualized. Detailed descriptions of ultrasound-guided nerve blocks can be found later in this chapter (see Ultrasound Box 31.1 ).

Paresthesia

A common technique to ensure that the tip of the needle is in close proximity to the nerve is to elicit a paresthesia. Touching and mechanically stimulating the nerve with movement of the needle tip produces a tingling sensation or jolt known as a paresthesia , and it is felt along the distribution of the nerve. In practice, the jolt of a true paresthesia is often difficult to distinguish from the “ouch” of a pain-sensitive structure. When blocking proximal nerves at the elbow or axilla, the paresthesia travels far enough away from the injection site that it can be reliably distinguished from locally induced pain. Paresthesias at the level of the hand and wrist are more difficult to distinguish from pain. In both cases, paresthesia is a subjective feeling that requires intelligent and cooperative patients to understand what they are expected to feel and to remain relaxed and attentive so that they can distinguish an “ouch” from a jolt. Before the procedure, a simple explanation of what the patient should or may feel will facilitate cooperation. Although eliciting paresthesias is generally reliable in demonstrating that the needle is close to its target, some authors believe that it may theoretically increase the rate of complications as a result of mechanical trauma or intraneural injection. Once the paresthesia is elicited, it is important to withdraw the needle 1 to 2 mm before injecting the anesthetic. If a paresthesia persists, stop the injection and reposition the needle.

Injecting the Anesthetic

Strive to ensure that the anesthetic agent is not inadvertently injected into a vessel or nerve bundle. In practice, a misplaced intravascular injection is usually of minimal consequence, but small amounts of epinephrine may cause systemic symptoms such as tachycardia or anxiety. Intraarterial injection, theoretically, is more dangerous than intravenous injection. Either way, aspirate the syringe to check for blood before injection. If no blood is aspirated, inject the anesthetic while observing the extremity for blanching, which suggests intravascular injection. If blanching occurs, reposition the needle before further injection.

Nerve bundle injection has the potential to cause nonspecific nerve injury. Severe pain or paresthesia during injection or resistance to depressing the plunger suggests the possibility of intraneural placement of the needle. If any of these problems occur, immediately stop injecting and reposition the needle.

The onset and duration of anesthesia are both greatly influenced by how close the injected anesthetic is to the nerve. Onset occurs within a few minutes if the anesthetic is in immediate proximity to the nerve. Onset takes longer or may not occur at all if the anesthetic must diffuse more than 2 to 3 mm, which underscores the importance of locating the nerve before the injection.

More anesthetic is required if it must diffuse a long distance to the nerve. A range of suggested volumes of anesthetic is given with each nerve block description. For blocks in which a definite paresthesia is elicited or a nerve stimulator or ultrasound is used, the minimal recommended amount of anesthetic suffices. For blocks of smaller nerves, paresthesias are often not easily elicited, and the anesthetic must be injected in the general vicinity of the nerve. For these blocks or when doubt exists about the proximity of the needle to the nerve, larger amounts of anesthetic are recommended. This point cannot be emphasized strongly enough. The difference between a successful and an unsuccessful block may be merely an additional 2 mL of anesthetic. When in doubt, err on the high side of the recommended dosage. When blocking large nerves, many clinicians also opt for 2% lidocaine rather than the 1% solution.

With most blocks, the onset of anesthesia occurs in 2 to 15 minutes, depending on the distance that the anesthetic must diffuse to the nerve and the type of anesthetic used. Wait 30 minutes before deciding that a block is unsuccessful.

Complications and Precautions

Complications may result from peripheral nerve blocks but are rare in clinical practice. Most cannot be prevented by even perfect technique. General precautions include measures to minimize nerve injury, intravascular injection, and systemic toxicity. No actual statistics exist on the complication rate from nerve blocks performed by emergency clinicians, but they are extremely rare in clinical practice. Theoretically, infrequently performed blocks, blocks that require high doses of anesthetic, and blocks close to major vascular structures are more likely to have complications.

Nerve Injury

Nerve injury is rare but can occur secondary to (1) chemical irritation from the anesthetic, (2) direct trauma from the needle, or (3) ischemia as a result of intraneural injection. Overall, the incidence of serious neuronal injury is rare and occurs in 1.9 per 10,000 blocks. Given that placement of a nerve block is a blind procedure, nerve injuries do not necessarily represent an error in technique.

Chemical neuritis from the anesthetic is the most common nerve injury. The patient may complain of pain and varying degrees of nerve dysfunction, including paresthesia or motor or sensory deficit. Most cases are transient and resolve completely. Supportive care and close follow-up are the mainstays of treatment. Emergency clinicians should not exceed the recommended doses and concentrations of anesthetic ( Table 31.1 ). In general, buffered lidocaine 1% or 2% or buffered bupivacaine 0.25% or 0.5% is safe for nerve blocks performed in the ED.

TABLE 31.1

Recommended Volumes of Anesthetic for Various Nerve Blocks

NERVE	VOLUME (mL)
Axillary	20–30 ^a
Elbow
Ulnar	5–10 ^a
Radial	5–15 ^a
Median	5–15 ^a
Wrist
Ulnar	5–15 ^a
Radial	5–15 ^a
Median	3–5 ^a
Hip
Femoral	10–20 ^a
Three-in-one	25–30 ^a
Knee
Tibial	5–15 ^a
Peroneal	5–10 ^a
Saphenous	5–10 ^a
Ankle
Posterior tibial	5–10 ^a
Deep peroneal	3–5 ^a
Saphenous, sural, and superficial peroneal	4–10 ^a
Intercostal	5–15 ^a
Hand
Metacarpal and web space	2–4 ^b
Finger	1–2 ^b
Foot
Metatarsal	10–15 ^b
Web space	3–5 ^b
Toe	2–5 ^b

a Anesthetic: 1% lidocaine or 0.25% bupivacaine (both with epinephrine).

b Anesthetic: 1% lidocaine or 0.25% bupivacaine (both without epinephrine).

Direct nerve damage can be minimized by proper needle style, positioning, and manipulation. Use a short, beveled needle and keep the bevel parallel to the longitudinal axis of the nerve. Sharp pain or paresthesia indicates that the needle is close to or in the nerve. Avoid excessive needle movement when the tip of the needle is in contact with the nerve. If a 25-gauge needle is used, physical damage to a nerve should be minimal, even when directly touched by the tip of the needle. A 27-gauge needle is theoretically attractive, but its small size may limit aspiration testing and it may bend or break when attempting to block deep nerves.

Intraneural injection may rarely cause nerve ischemia and injury. Elicitation of a paresthesia or severe pain suggests that the needle has made contact with the nerve. When a paresthesia is elicited, withdraw the needle 1 to 2 mm before injecting the anesthetic. If the paresthesia occurs during injection, stop the injection and reposition the needle. Most neurons are surrounded by a strong perineural sheath through which the nutrient arteries run lengthwise. Injection directly into a nerve sheath may increase pressure within the nerve and compress the nutrient artery. Impaired blood flow results in nerve ischemia and subsequent paralysis. Intraneural injection is often heralded by severe pain, which worsens with further injection and may radiate along the course of innervation. The operator may notice difficulty depressing the plunger of the syringe. If the tip of the needle is in proper position, slow injection of the anesthetic should be minimally painful, and the anesthetic should go in without resistance.

Intravascular Injection

Intravascular injection may rarely result in both systemic and limb toxicity. Inadvertent intravascular injection produces high blood levels of the anesthetic. Exercise care when administering large amounts of anesthetic in close proximity to large blood vessels.

Intraarterial injection of anesthetics with epinephrine may cause peripheral vasospasm and further compromise injured tissue. Intravascular anesthetic is not toxic to the limb itself, although it may produce transient blanching of the skin by displacing blood from the vascular tree. Epinephrine, however, can cause prolonged vasospasm and subsequent ischemia if it is injected into an artery. This is especially worrisome when anesthetizing areas with little collateral circulation, such as the toes, fingers, penis, and tip of the nose. Severe epinephrine-induced tissue blanching or vasospasm may be reversed with local or intravascular injection of phentolamine (see extensive discussion in Chapter 29 ).

Vasospasm associated with the epinephrine in anesthetic solutions is rare, but experience in related clinical situations can help guide therapy. Roberts and Krisanda used a total of 5 mg of phentolamine infused intraarterially to reverse arm ischemia following 3 mg of epinephrine inadvertently administered into the brachial artery during cardiac resuscitation. Accidental injection of epinephrine from an Epi-Pen (Mylan, Canonsburg, PA) will produce an area of vasoconstriction. This is usually self limited and requires no intervention, but it may take a few hours to be complete. However, digital ischemia from inadvertent epinephrine autoinjection (Epi-Pen) has been successfully treated both by proximal “digital block” with 2 mg of phentolamine and by local infiltration at the ischemic site with 1.5 mg of phentolamine.

The route of phentolamine administration should be guided by the clinical situation. Phentolamine must reach the site of vasospasm. Local infiltration may be effective for ischemia in a single toe or finger, whereas arterial injection has the advantage of delivering the medication directly to the arteries exhibiting spasm. For larger areas of involvement or in instances in which local infiltration is ineffective, use intraarterial injection. A dose of 1.5 to 5 mg appears to be effective in most cases, although a total of 10 mg may be used for local infiltration. Phentolamine, 5 mg, can be mixed with 5 mL of either normal saline or lidocaine. The small volume of the distal pulp space may limit the volume of the infiltration dose to 0.5 to 1.5 mL in the fingertip. Larger volumes and dosages can be used with proximal infiltrations. For intraarterial infusion of the radial artery at the wrist or the dorsalis pedis at the ankle, dosages of 1.5 to 5 mg of phentolamine are suitable. Slow infusion or graded dosages of 1 mg may provide enough phentolamine to reverse the ischemia without excessive systemic effects such as hypotension.

Hematoma

Hematoma formation may result from arterial puncture, particularly during blocks in which a major blood vessel is being used as a landmark to locate the nerve (e.g., axillary or femoral artery). Direct pressure for 5 to 10 minutes usually controls further bleeding. Use of small-gauge needles (e.g., 25- to 27-gauge) also helps minimize bleeding from a punctured artery. A minor coagulopathy is not a contraindication to a nerve block.

Infection

Infection is rare and can be minimized by following aseptic technique and using the lowest possible concentration of epinephrine. Injection should be made through noninfected skin that has been antiseptically prepared. Injection through a site of infection may spread the infection to adjacent tissues, fascial planes, and joints.

Systemic Toxicity

The incidence of systemic toxicity with local anesthetics has diminished significantly in the past 30 years. Interestingly, peripheral nerve blocks have been reported to have the highest incidence of systemic toxicity. Allergic reactions account for only 1% of untoward reactions (see Chapter 29 ).

Limb Injury

Injury to the anesthetized limb can result if the patient is permitted to use the limb, is advised to use heat or cold application, or performs wound care before the anesthesia has worn off. With major nerve blocks, do not release the patient from the ED until sensation and function have returned.

With minor blocks, the patient may be sent home but should be properly cautioned. Advise the patient to avoid ischemia-producing compression dressings (e.g., elastic bandages) because the anesthetized area may not sense impending problems.

Specific Nerve Blocks

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