++
Whereas many pain relievers work by altering the transmission,
perception or modulation of pain impulses at the spinal or brain level,
local anesthetics primarily exert their effect by blocking axonal
transmission in peripheral nerves, thereby preventing nociceptive signals
from reaching the central nervous system. By stopping the pain impulses
before they arrive at the dorsal horn of the spinal cord, regional
anesthetic techniques reduce the degree of central sensitization, or
“wind-up,” and allow for high-quality pain relief with minimal side
effects.
++
Regional and local anesthesia is particularly well suited to the ED,
where many patients present with acute, localized painful injuries that are
amenable to a short-term, selective peripheral blockade.
++
Topical anesthesia involves the application of local anesthetic
directly to a mucosal or skin surface. It has the advantage of a needle-less
technique, and many small lacerations and injuries can be effectively
anesthetized by the application of these agents. Several studies have shown
that the application of a topical local anesthetic mixture significantly
reduced the severity of pain on injection and the time to discharge in
patients with simple lacerations required suturing.54,55
++
For mucous membranes, lidocaine 1–4% provides adequate anesthesia
after topical application and can be administered several different ways.
Viscous jelly can be swished around the mouth; lidocaine can be nebulized
for anesthesia of the oropharynx and airway; pledgets can be soaked and then
applied directly to a mucosal area. Care must be taken when using local
anesthetics on mucosal surfaces because uptake is rapid, especially when
higher concentrations are used (eg, 4% lidocaine). Safe dosages should be
calculated in advance and adhered to.
++
For intact skin, the most common form of topical anesthesia is eutectic
mixture of local anesthesia (EMLA). EMLA cream is a 1:1 mixture of 2.5% lidocaine and 2.5% prilocaine and has been well established as a means to
decrease pain from venipuncture and intravenous cannulation in
children.56 It is usually applied to skin, then covered
with a barrier dressing while waiting for its anesthetic effect. Adverse
effects are minimal, although cases of methemoglobinemia have been reported
secondary to prilocaine toxicity.57 One disadvantage with
EMLA is the duration of application required for effective local anesthesia,
usually between 45 and 60 minutes. EMLA has also been used for minor
procedures such as infant penile circumcision.58
++
ELA-Max is a relatively new product that contains 4% lidocaine cream in a
liposomal matrix. It is applied to the skin in a manner similar to that of
EMLA and has been shown to be as effective as EMLA but with a faster onset
of action (30 minutes versus 60 minutes).59 Other methods
of topical anesthesia for intact skin include the delivery of lidocaine by
iontophoresis60 and the use of jet
injectors.61 Both have been used in the ED with success.
++
Nonintact skin can be effectively anesthetized by the application of a
liquid mixture of local anesthetic and vasoconstrictor. Examples include TAC
(tetracaine 0.5%, adrenaline 0.05%, and cocaine 11.8%), LET
(lidocaine 4%, epinephrine 0.1%, and tetracaine 0.5%), and MAC
(marcaine, adrenaline, and cocaine).62,63 The mixture is
applied to the wound and covered with moist gauze. Adequate anesthesia
usually results after 25–30 minutes.
++
Injecting local anesthetics subcutaneously can result in sufficient
anesthesia to allow for minor superficial procedures, such as suturing of
wounds. Because anticipation of a needle stick is often emotionally
traumatic for patients, especially children, the use of techniques to lessen
the pain on injection is always appreciated. These include the use of small
needles (ie, 27- to 30-gauge), slow administration of the anesthetic (1 mL
over 30 seconds), and the buffering of local anesthetic by sodium
bicarbonate.64,65 Bartfield and
colleagues66 studied pain on injection at wound sites and
found that local anesthesia is less painful when injected from within a
laceration than through intact skin. Vasoconstrictors such as epinephrine
added to local anesthetic increase the duration of the anesthesia (by
decreasing local uptake) and provide better hemostasis at the wound site.
Vasoconstrictors should not be used on the ear, nose, penis, fingers, or
toes because ischemia and tissue necrosis may result.
+++
Intravenous Regional Anesthesia or Bier's Block
++
Intravenous regional anesthesia (IVRA) was first performed in 1908 by
Karl August Bier, and the procedure has changed little since that
time.67 It has been shown to have an excellent safety
record, to provide effective anesthesia of the isolated limb, and to be easy
to perform.68 The method for establishing the block is
described elsewhere but essentially involves exsanguinating a limb using a
compressive device, inflating a double tourniquet on the proximal end of the
limb, then injecting local anesthetic intravenously into the isolated limb.
The local anesthetic spreads throughout the venous channels of the arm or
leg, diffusing out to act on both the free nerve endings in the tissues and
the larger peripheral nerve branches. It is a popular form of anesthesia for
reducing fractures in the ED, especially in children.69
Complications are rare with IVRA but are usually caused by inappropriate
management of the double cuff, leading to “washout” of local anesthetic
into the central circulation and subsequent toxicity. Most authors recommend
a minimum tourniquet time of 20–30 minutes before deflating, regardless of
the duration of the procedure. Some also advocate a staged tourniquet
deflation to allow for partial washout in an attempt to lower peak blood
local anesthetic concentrations.
++
The most common agent for IVRA is lidocaine, but other local anesthetics
such as prilocaine have been used. Bupivacaine has fallen out of favor owing
to the unnecessary risk of systemic toxicity. Some practitioners add
narcotics or other adjuvants to the mixture such as ketorolac, tramadol, or
clonidine. The traditional preparation is a high-volume, dilute
concentration of lidocaine (eg, 40 mL of 0.5% for an upper arm
tourniquet), but good results can be achieved with a low-volume,
high-concentration technique (eg, 12–15 mL of 2% lidocaine). Onset of
either is usually less than 5 minutes for full anesthesia.
+++
Peripheral Nerve Blocks
++
In general, blocks of peripheral nerves have several advantages over
local infiltration.70 They are often less painful to
perform and may cause less anxiety for the patient, especially when the
procedure involves sensitive areas such as the palm or sole. Tissue
distortion of the wound is usually avoided. Also, depending on the area,
less local anesthetic may be required, reducing the risk of systemic
toxicity. Compared with parenteral or oral analgesics, nerve blocks have
been shown to provide superior analgesia and greater patient satisfaction
for treatment of pain associated with femoral neck or shaft
fractures.71
++
Peripheral nerve blocks require some degree of specialized training but,
with practice, can be implemented in the ED setting to great effect. Nerve
blockade is often performed in the ED as a blind technique or one in which
paresthesias are sought as confirmation of correct needle
placement.70 Nerve stimulation as a means of locating
peripheral nerves has been slow to catch on in the ED setting, despite its
almost universal use among anesthesiologists. This may be due in part to
lack of experience with the nerve stimulators, and unfamiliarity with the
technique. However, it has been shown to be both easy to learn and effective
when performed by emergency physicians.72
++
Ultrasound-guided nerve blockade is a relatively new trend that is showing
promise as a way to improve accuracy and block success.73
This technique may be particularly attractive to emergency physicians,
because most have experience in both performing ultrasound exams and using
ultrasound for placement of intravenous lines.
++
Regardless of the technique used, there is evidence that peripheral nerve
blocks in the ED are underused as a means of acute pain
management.74 Emergency physicians should have an
armamentarium of nerve blocks that can be used for the relief of acute pain
in the ED. Finally, nerve blocks require proper patient education before the
block is performed.
++
Some blocks can be associated with some degree of discomfort (eg, ankle
block). Adequate pre-block analgesia improves patient cooperation and
ultimately satisfaction. The following is a brief overview of peripheral
nerve blocks that are commonly performed in the ED setting. For a complete
description of individual techniques, please refer to the respective
chapter.
++
Digital blocks of the fingers and toes are more comfortable and easier
to perform than local infiltration. Four nerves enter each digit—two on
the volar aspect and two on the dorsal aspect—approximately at the 2, 4,
8, and 10 o'clock positions. The most consistent method for anesthetizing
the finger or toe is to insert a fine-gauge (ie, 27-gauge) needle into the
dorsal web space, just lateral to the bone. After raising a subcutaneous
wheal with 0.5–1 mL of local anesthetic, the needle is advanced toward the
palm or sole until it is just past the bone on the volar side. After
negative aspiration, a further 1–1.5 mL is injected. Then the procedure is
repeated on the other side of the digit. In this manner, all four nerves are
blocked. Epinephrine-containing solutions should never be used in digital
blocks as ischemia and necrosis may result.
++
These blocks are appropriate for minor procedures on the palm or dorsum
of the hand, or on the fingers when more than one digit is involved. The
technique involves blocking the terminal branches of the median, ulnar, and
radial nerves or any appropriate combination of these nerves, depending on
the anatomic location of the injury. Most practitioners use a blind
technique based on the relatively consistent location of these nerves at the
wrist,75 but they can also be performed using a nerve
stimulator technique.76 Wrist blocks are safe and easy to
perform, but they require a good working knowledge of the anatomy of the
hand and wrist.
++
Ankle blocks are similar to wrist blocks to the extent that it is a
blockade of the terminal branches of several peripheral nerves just before
entering the foot. This block is suitable for relieving pain and/or
performing procedures anywhere on the foot. Like the wrist block, selective
blockade of individual peripheral nerves can be performed (eg, posterior
tibial nerve block for suturing a sole laceration). On the other hand,
blocking all five nerves (posterior tibial, sural, saphenous, and
superficial and deep peroneal) provides complete anesthesia of the foot
below the ankle. Some practitioners advocate five separate injections,
whereas others recommend a three-puncture technique. The latter approach is
carried out by first performing separate posterior tibial and sural blocks
behind the medial and lateral malleoli, respectively, then using a single
puncture site just lateral to the extensor hallucis longus tendon. With this
maneuver, the deep peroneal nerve is blocked, followed by withdrawing the
needle to just below the skin and redirecting both laterally and medially
while depositing local anesthetic in a subcutaneous wheal to block the
saphenous and superficial peroneal nerves. Ankle blocks are extremely useful
but are somewhat uncomfortable and therefore require a moderate degree of
sedation and analgesia.
++
The femoral nerve block has been used for many years in the ED for
treatment of pain associated with fractures of the femoral shaft or neck. It
is also useful for pain associated with patellar and patellar tendon
injuries as well as superficial injuries to the anterior thigh. This block
confers anesthesia to the entire anterior thigh and most of the femur and
knee joint. Because the saphenous nerve is a superficial sensory branch of
the femoral nerve that extends along the medial aspect of the lower leg,
anesthesia of this area is also achieved. The popularity of the femoral
nerve block in the ED is probably due to its reliability and ease of
performance. The femoral nerve is a superficial nerve at the level of the
inguinal crease, and its reliable position next to the femoral vessels makes
it easy to locate.77 The block is often performed using a
“double pop” technique, which corresponds to the penetration of both the
fascia lata and the fascia iliaca layers, under which the femoral nerve
resides. The clinician should feel two clicks or pops as the needle,
preferably with a noncutting tip, passes through these fascial sheets.
++
Alternatively, paresthesia may be sought in the femoral nerve
distribution. Proximity to the femoral nerve with a nerve stimulator and
stimulating needle results in quadriceps twitches and a jerking of the
patella. Usually, 15–20 mL of local anesthetic are enough to provide
quality anesthesia. Winnie and coworkers78 described the
3-in-1 block in 1973, which was designed to augment femoral nerve anesthesia
with simultaneous blockade of the lateral femoral cutaneous nerve and the
obturator nerve. The technique is performed by applying pressure to the
femoral sheath just distal to the injection point and using a relatively
high volume of local anesthetic, thereby forcing a proximal migration of the
solution. The usefulness of the 3-in-1 block has been questioned, because
the blockade of the other two components is unreliable, probably owing to
fascial septa in the femoral sheath.79 Another approach,
called a fascia iliaca block, involves a needle
insertion site several centimeters lateral to the femoral nerve, thereby
reducing concerns about vascular or nerve injury.80 The
distribution of anesthesia is similar to that of femoral nerve block.
Overall, the complication rate is low for femoral nerve block. Some
anecdotal reports of femoral nerve blockade masking the symptoms of a
compartment syndrome of the thigh have been investigated and found to be
lacking in evidence.81
+++
Intercostal Nerve Blocks
++
The intercostal nerve block is most commonly used in the ED to provide
analgesia for patients with broken or contused ribs. In this population, it
has been shown to provide excellent analgesia for most rib fractures, but
also to improve respiratory mechanics (as measured by peak expiratory flow
rate) and arterial oxygen saturation.82 It should not be
performed in patients with flail chest. Pneumothorax is the primary concern
when performing this block, and it occurs in approximately 1.4% of nerves
blocked.83 This incidence increases in patients with
obstructive lung disease. The block anesthetizes only the anterior and
lateral chest wall because it is usually performed distal to where the
posterior cutaneous diverges from the main intercostal nerve.
++
The safest location to perform the intercostal nerve block is at the
posterior axillary line, because it is here that the internal intercostal
muscle lies between the nerve and the pleura. The ribs are used as
landmarks, and a mobile needle is carefully walked off the inferior edge
where the neurovascular bundle lies in the costal groove. Proper
stabilization of the hands on the posterior chest wall is important to
prevent inadvertent slipping of the needle into the intrapleural. After
advancing 1–2 mm past the edge of the rib, the clinician aspirates to check
for blood or air, and then injects 3–5 mL of local anesthetic slowly. Care
must be taken with local anesthetic dosing because systemic uptake is high,
owing to the close presence of the intercostal vessels. After 30 minutes, if
no clinical signs of pneumothorax are present, the patient may be discharged
with advice to return if dyspnea or chest pain appears.70
+++
Axillary Brachial Plexus Blocks
++
The brachial plexus is formed by the union of spinal roots C5 to T1.
These pass under the clavicle and through the axilla to form the peripheral
branches of the nerves supplying the upper limb, namely, the
musculocutaneous, radial, ulnar, and median nerves (as well as several
smaller nerves). Although there are many approaches to the brachial plexus
used in clinical anesthesia, such as the interscalene, supraclavicular, and
infraclavicular, few emergency physicians have the level of comfort
performing these without supplemental training.
++
In contrast, the axillary approach is a favorable one for regional
anesthesia novices owing to the presence of good landmarks, the close
bundling of the nerves in a neurovascular sheath, and the low incidence of
serious complications. The axillary arterial pulse is used as the primary
landmark for all approaches, whether for seeking paresthesia, using a nerve
stimulator, or performing a transarterial technique. The latter approach may
in fact be the easiest because it requires no extra equipment apart form a
23-gauge needle and a small length of IV tubing attached to the local
anesthetic syringe. With the nondominant hand palpating the axillary pulse,
the needle is passed through the skin and into the axillary artery, which is
evidenced by the return of bright red blood through the IV tubing. The
needle is slowly advanced until the aspiration of blood ceases, which
corresponds to the passage of the needle through the back wall of the
artery. At this point, the needle tip should be within the fascial sheath
that contains the radial, ulnar, and median nerves. After negative
aspiration, the local anesthetic is injected. Some clinicians deposit local
anesthetic in front of the artery as well after withdrawing back through the
vessel. This block provides dense anesthesia of the forearm and hand and is
useful for treating pain associated with fractures and deeper wounds of
those areas. Note that the musculocutaneous nerve has already left the
sheath at this point and, if desired, requires a separate blockade by
injecting 5–10 mL of local anesthetic into the belly of the
coracobrachialis muscle.
+++
Other Peripheral Nerve Blocks
++
Often, a case arises in which a patient is a candidate for a peripheral
nerve block that falls outside the scope of the emergency physician. In
these instances, it may be appropriate to consult an anesthesiologist to
provide advice and perhaps perform the block, given the expertise in this
area. Table 68–2 outlines some blocks typically not performed by
ED personnel but may be of value in specific circumstances.
++