REGIONAL ANESTHESIA FOR TRAUMA
JOHN BRAMHALL PhD MD
UNIVERSITY OF WASHINGTON
SEATTLE
Not all trauma victims need surgery, and of those that do, the planned procedures may be urgent or may be elective. Purely elective surgery was not commonly practiced until the advent of effective, reliable and safe anesthetic techniques. Except under the most compelling motivating circumstances patients were unlikely to submit to excruciatingly painful life-enhancing (in contrast to life-sustaining) surgical procedures.
Even as recently as the early 1940s mortality attributable to the effects of general anesthesia could be as high as 1:1000 and few rational physicians would expose patients to such risks unless the perceived gains were large enough to balance the equation. As a consequence, in part because of the insecurities surrounding general anesthesia, throughout the first half of this century there was considerable emphasis placed on, and expertise developed in, alternative strategies for painless elective surgery; in particular techniques for selectively anesthetizing specific, isolated anatomic regions; i.e. regional anesthesia. The risk of mortality and major morbidity associated with these approaches was considered to be vastly lower than that associated with general anesthesia, and there was a great deal of enthusiasm among surgeons for the development of specific sensory nerve blocks of every conceivable anatomic structure.
REGIONAL ANESTHESIA
The term was first introduced by Harvey Cushing in 1901 when describing
pain relief by the use of nerve block.1 Modern techniques of local
anesthesia derive from the use of cocaine for nerve blocks by
Halstead and Hall (New York) in 1884.2 Regional anesthesia performed
by surgeons at that time obviated the need for an individual dedicated
to administering inhalational anesthesia and eliminated the consequences
of toxic effects of agents such as ether, cyclopropane, chloroform
and methoxyflurane. In early practice the skin was anesthetized
with cocaine, the trunks of the brachial plexus were dissected
out and then individually anesthetized.
As the clinical risks and subjective unpleasantness of general anesthesia declined over the latter half of the twentieth century general anesthesia increasingly became the bench-standard technique and one hard to match for safety (with mortality attributable to anesthesia alone now approaching 1:250,000) and patient acceptance (with the very widespread incorporation of general anesthetic agents such as propofol and sevoflurane which have dramatically reduced anesthetic co-morbidities such as nausea and dysphoria). So much so that in many reputable and well-managed North American anesthetic practices it became common for regional techniques hardly to be used at all. In fact, there are still lively debates in the anesthesiology literature regarding the relative merits of regional versus general anesthetic techniques for a wide variety of surgical interventions, and although it sometimes seems as though there is less than compelling scientific or clinical evidence favoring one over the other, the lines of discussion are sometimes quite sharply drawn.
BENEFITS OF REGIONAL TECHNIQUES
There are relatively few types of surgery where regional anesthesia
is absolutely indicated (as opposed to merely being an option)
but certain surgeries lend themselves particular to regional techniques,
and there are compelling reasons, sometimes, for either avoiding
general anesthesia or, more commonly, for supplementing general
anesthesia with some form of regional block. In general terms,
the types of advantages to be expected from regional techniques
are a reduction in overall stress of surgery
REDUCED SURGICAL STRESS
Stress can sometimes be monitored by looking at changes in heart
rate or blood pressure, or, more sophisticatedly by monitoring
cerebral blood flow or the release into the blood of specific
markers of stress reactions such as cortisol. TCD studies show
VMCA increases significantly for several minutes after skin incision
in patients under 1-2 MAC isoflurane anesthesia3 and there is
evidence, in children at least, that this effect is abolished
or attenuated when there is effective concomitant epidural regional
anesthesia.
REDUCED POSTOPERATIVE PAIN
Some injuries are particularly painful, for example crush injuries
of the foot or knee. Patients who have surgery to correct this
type of injury will need a high level of analgesia post-operatively,
and, although this can be provided by simple techniques such as
morphine injections, these tend to produce nausea, constipation,
sleep disturbances and, sometimes, mood changes and dysphoria.
By incorporating a regional technique such as sciatic or femoral
nerve block into the anesthesia all these complications can be
reduced or eliminated; in addition, the period of awakening from
general anesthesia (emergence) is typically much smoother, less
stressful and more comfortable when all pain from the surgical
site has been eliminated by a regional nerve block, rather than
simply masked by systemic opioids.
REDUCED POSTOPERATIVE INFECTION
Inactive post-surgical patients lying in hospital beds are at
significant risk for acquiring pneumonia. In general, opioids
such as morphine cause respiratory depression and patients tend
to breath less energetically than they should, exacerbating this
risk. This is the reason why many post-trauma patients need routine
respiratory therapy or incentive spirometry during convalescence.
Reducing the amount of morphine needed generally reduces the incidence
of respiratory depression and consequent pulmonary complications,
and patients with good pain control provided by peripheral nerve
blocks or epidural infusions require dramatically less morphine
than they would otherwise.
The specific group of patients who have suffered painful rib fractures during their accident or during resuscitation, who have had chest drainage tubes placed, or who have had thoracic surgery represents a group at even greater risk of postoperative pneumonia. Painful chest injuries make it very difficult to cough breath deeply, and patients will often sit up in bed panting shallowly because it hurts to take proper breaths. This is a set-up for atalectasis, pulmonary infection and reduced oxygen supply; in many cases the appropriate use of regional techniques such as rib blocks or thoracic epidural infusions can make a significant positive difference, and can even make the difference between a successful recovery or death in elderly or frail injury victims.
IMPROVED HEALING
Traumatic amputation of finger, hand or even arm can often be
repaired surgically if the victim can be transported to an appropriate
hospital quickly enough. The surgery is delicate and quite time-consuming,
and the goal is to restore blood circulation to the amputated
tissues as quickly as possible. The body has a natural defense
against blood loss after amputation and that is vasospasm, intense
vasoconstriction causing arteries to clamp down in response to
the stress of injury to reduce the amount of blood loss. Although
this is beneficial acutely at the time of injury, it does not
help in recovery and vasospasm or vasoconstriction is a feared
complication of the surgical repair, starving the surgical wound
of the blood needed for healing. One of the effects of regional
nerve blocks using local anesthetics is sympathectomy, the elimination
of vasoconstriction provoked by sympathetic responses to stress.
For this reason, many surgeons request that regional blocks be
used in patients undergoing re-implantation or reconstructive
procedures in order to improve wound healing and to increase the
chances of a successful graft.
POTENTIAL HAZARDS OF REGIONAL ANESTHESIA
FAILED BLOCK
Although not strictly a hazard this can, nevertheless, be a significant
complication to the use of regional techniques. Unlike general
anesthesia, the execution of a nerve block does not guarantee
a successful result; this can sometimes be because the patient
has unrealistic expectations (and really wants to be completely
oblivious to the surgery or injury) or may be because analgesia
is not complete (resulting in pain to the patient) or motor block
is not complete (resulting in an irritated surgeon). Remember
that in cases of traumatic injury being treated acutely the stomach
is full and unconscious sedation cannot be provided without adequate
airway protection (i.e. endotracheal intubation using the appropriate
precautions against pulmonary aspiration); the risk for inexperienced
practitioners is that they may be rushed to induce general anesthesia
without careful airway assessment and optimization of intubation
conditions if a failed block is suddenly revealed as surgery develops.
ALLERGIC REACTIONS
As noted above, allergic reactions to amide local anesthetics
are rare; careful history elicited from those with a history of
an allergic reaction to amides invariably reveals symptoms of
tachycardia, chest tightness and lightheadedness, the consequence
of intravascular injection of epinephrine, a common additive to
a local anesthetic mixture. True allergies to ester local anesthetics
are not common, but do occur; ester local anesthetics should certainly
be avoided in individuals with allergies to PABA. If signs or
symptoms of allergic response occur then standard medical interventions
need to be implemented immediately, get assistance, support the
airway, administer fluids and don’t delay giving epinephrine
in the event of hypovolemic shock and/or severe bronchospasm.
LOCAL TOXICITY
Local anesthetics are potentially neurotoxic; and in clinical
practice injected doses are frequently much greater than those
thought capable of producing neurotoxicity. It is the presence
of the perineurium acting as a diffusion barrier which prevents
excessively high concentrations of local anesthetic from reaching
the intraneural structures. Neurotoxicity is likely to occur only
with intraneural injection, and is accompanied by intense pain.
Pain may be the only initial indication of trouble to come and
many conservative practitioners will avoid performing nerve blocks
on patients who are excessively sedated, or otherwise uncommunicative
and who may not be able to give warning of the intraneural injection.
For similar reasons, care is exercised when supplementing pre-existing
nerve blocks.
SYSTEMIC TOXICITY
The danger sites are the brain and the heart. Most systemic reactions
occur as a result of inadvertent intravascular injection or injection
into a highly vascular tissue bed with resultant rapid local anesthetic
uptake into the circulating system. Incorporation of epinephrine
5 mg/mL into the local anesthetic dose (1:200,000 dilution) both
delays systemic absorption and, more significantly, when used
as a test-dose, can warn of intravascular injection by eliciting
tachycardia.
Central nervous and cardiovascular system toxicity are dose and time dependent. The faster plasma levels of local anesthetic rise, the more likely that an adverse reaction will occur. Prevent high blood levels by always using the lowest dose/weakest concentration compatible with desired effect, and by injecting slowly or in divided doses. Minimize redistribution by incorporating epinephrine or phenylephrine in the mix.
CENTRAL NERVOUS SYSTEM TOXICITY
Initial symptoms of CNS toxicity are tinnitus, metallic taste,
difficulty focusing, lightheadedness, numbness around the lips
and intellectual confusion. If brain tissue levels continue to
rise the patient will experience muscle twitching, tremors and
then generalized tonic-clonic convulsions resulting in loss of
consciousness, generalized CNS depression and respiratory arrest.
Benzodiazapines raise the threshold for CNS toxicity. Small doses
of midazolam or valium may conceivably prevent the symptoms of
CNS toxicity and larger doses may terminate a seizure. If seizures
occur, the airway should be protected and the patient mask ventilated
with oxygen until the seizure abates. If necessary, the seizure
can be aborted with sodium pentothal and the patient intubated
and ventilated.
CARDIOVASCULAR TOXICITY
Local anesthetics affect the cardiac electrical conducting system,
depress the myocardium and peripheral vascular smooth muscle.
As in nerve, local anesthetics reduce the action potential in
the heart by limiting the inward flow of sodium current. Lidocaine
is a "fast-in, fast-out" sodium channel blocker that
reaches steady-state block in one or two beats. Bupivacaine, conversely
is a "fast-in, slow-out" local anesthetic whose blocking
action increases with successive beats and with faster heart rates.
The reason for this is that several local anesthetics, bupivacaine
included, will only penetrate the ion channel when it is in the
"open" conformation.
Local anesthetics prolong conduction time in the heart (prolonged PR and QRS intervals). Increasing plasma levels will suppress the sino-atrial and atrio-ventricular nodes causing sinus bradycardia, conduction block, electrical inexcitability and cardiac arrest. Bupivacaine’s "fast-in, slow-out" action makes the heart vulnerable to malignant re-entry cardiac arrhythmias. The ratio of the dosage required for irreversible cardiovascular collapse and the dosage that will produce CNS toxicity, CC/CNS ratio, is approximately 7:1 for lidocaine and 3.7:1 for bupivacaine indicating that bupivacaine has greater cardiovascular toxicity that lidocaine; (the heart is further sensitized to bupivacaine during pregnancy).
Commercially available bupivacaine is the racemic mixture of its r and s enantiomers. A newer local anesthetic ropivacaine, is analogous to the pure s enantiomer of bupivacaine. Ropivacaine was initially believed to be less cardiotoxic than bupivacaine; however, adjusting for ropivacaine’s lesser potency, equipotent doses confer the same degree of cardiotoxicity as bupivacaine. Little is known about the most appropriate anti-arrhythmic to use during local anesthetic induced cardiac arrest. High doses of epinephrine and atropine may be appropriate, bretylium may be of benefit in cases of bupivacaine toxicity. In the cardiac arrest situation one must pay particular attention to oxygenation and ventilation and be prepared to perform cardiopulmonary resuscitation for an indefinite period of time. In extreme situations, cardiopulmonary bypass may have to be implemented until the effects of the local anesthetic have dissipated. Understand that if organ oxygenation and perfusion can be maintained effectively until local anesthetic levels diminish the patient will recover fully.
GENERAL TECHNIQUES OF REGIONAL ANESTHESIA
LOCAL INFILTRATION
Anesthetic solutions such as bupivacaine or lidocaine are injected
into the soft tissues surrounding a wound or surgical site; the
technique is effective, for example, for the excision of small
superficial cysts or lipomas, or for painless suturing of lacerations.
It is not useful for large wounds.
INTRAVENOUS ANESTHESIA
The anesthetic solution is injected into a major vain draining
an extremity. Commonly used for short surgical procedures on the
arm; the limb is first squeezed free of blood (elastic bandage,
then isolated (tourniquet) and the anesthetic (almost always lidocaine
0.5%) is injected into a distal vein. Excellent technique for
surgeries such as carpal tunnel release or for joint mobilizations.
PERIPHERAL NERVE BLOCK
A major nerve supplying a limb or specific area of the body is
identified (anatomy, paresthesias, nerve stimulator) and a solution
of local anesthetic is injected very close to, but not inside,
the nerve yielding a sensory (and often motor) block dense enough
for painless surgery. The Block may last up to 24 hours depending
on the amount and type of anesthetic agent used; or may be prolonged
indefinitely by use of a continuous infusion of agent directed
through a fine plastic catheter.
NEURAXIAL BLOCK
A term used to describe epidural and spinal analgesia in which
small amounts of local anesthetic are injected or infused into
the epidural space (yielding a segmental blockade of the nerves
supplying a large territory) or into the subarachnoid space (yielding
a spinal blockade of the lower half of the body.
Although it is quite acceptable for local, intravenous and peripheral blocks to be administered by non-anesthesiologists, neuraxial blocks must only be placed by specialists who have undergone intensive training both in the techniques of block placement and also in resuscitation and airway management.
AGENTS USED
All local anesthetics used clinically consist of a benzene ring
connected to a hydrocarbon chain. The lipid solubility is usually
quite high, but is pH-dependent, with high pH favoring increased
lipid solubility, anesthetic potency (Table
1) and speed of onset(Table
2). The linkage between ring and chain can be an ester or
an amide, substitutions on the ring or tertiary amine group (usually
on the chain) alter its pka, lipid solubility and protein binding,
determining respectively the speed of onset, potency and duration
of action.; examples of both classes (esters and amides) are listed
below:
ESTERS
TETRACAINE, BENZOCAINE
Useful for topical anesthesia, quite long duration of action.
PROCAINE
First synthetic local anesthetic, low potency, low toxicity, short
duration.
2-CHLOROPROCAINE
Commonly used in Europe for intravenous regional anesthesia; not
widely used for this purpose in the US
COCAINE
Naturally-occurring, produces vasoconstriction as well as anesthesia,
potential for abuse and addiction.
AMIDES
BUPIVACAINE
Long duration of action, delayed onset; sensory block better than
motor block; high potential for cardiotoxicity.
MEPIVACAINE, ROPIVACAINE
Similar to bupivacaine; less potential for toxicity; widely used
for peripheral nerve blocks of the upper extremity.
ETIDOCAINE
Very rapid onset, long duration of action; profound motor block.
PRILOCAINE
Similar to lidocaine, possibly less CNS toxicity when released
into vascular system.
Lidocaine: Most versatile local anesthetic.
EMLA: Eutectic Mixture of Local Anesthetic
(lidocaine and prilocaine); provides useful topical anesthesia
of applied under occlusive dressings for 30 minutes prior to incision.
The distinction between ester and amide is useful, clinically, because allergic reactions can occur, quite frequently, with esters (in particular benzocaine and procaine) because they break down to structures similar to PABA (p-amino benzoic acid) a common component of cosmetics and sun-screens; allergic reactions to amides are extremely rare.
BASIC SCIENCE
When applied to peripheral nerves, local anesthetics reversibly
inhibit signal transmission by blocking sodium influx via membrane
sodium channels. The agents used are marketed as water soluble
hydrochloride salts. In an aqueous solution the local anesthetic’s
fixed dissociation constant (pka) determines the equilibrium between
the charged local anesthetic cation and the uncharged base. It
is the uncharged base that freely diffuses through the lipid bilayer
of neurons. After crossing a neuron’s lipid bilayer the local
anesthetic molecule again dissociates into its basic and cationic
forms with the uncharged cation entering the protein based sodium
channel. It is the presence of the local anesthetic molecule within
the sodium channel that renders the channel impermeable to sodium
thus preventing the propagation of action potentials and impulse
conduction. With time, the local anesthetic diffuses out of neurons
rendering the neurons once again susceptible to depolarization.
ADDITIVES COMMONLY MIXED WITH LOCAL ANESTHETICS
SODIUM BICARBONATE
Because the free base form of most local anesthetics is poorly
soluble in water, they are prepared as hydrochloride salts with
commercial solutions having a pH in the range of 4-6. Addition
of bicarbonate can increase the rate of onset of some local anesthetics
by shifting the equilibrium to the uncharged base form which readily
penetrates into nerve tissue. Neutralizing the pH of a local anesthetic
solution may also decrease the associated pain on injection. Using
an 8.4% sodium bicarbonate solution, one ml can be added to a
lidocaine 30 ml vial or 0.2 ml can be added to a bupivacaine 30
ml vial. Attempts to add further bicarbonate will result in precipitation
of the local anesthetic from its solution.
PRESERVATIVES
Antimicrobial preservatives are added to multi-dose vials of local
anesthetics. Preservative-containing local anesthetic solutions
must not be used in spinal, epidural anesthesia because of their
potentially cytotoxic effects. The most frequently used antimicrobials
are methyl- ethyl- and propyl-parabenzoates
.
Antioxidants or ion chelating agents such as sodium ethylenediaminetetraacetic
acid (EDTA) are added to commercially available local anesthetics
to prevent oxidation, or to scavenge divalent cations and thus
retard their degradation. Preservative free preparations are available
for patients suspected of having allergies to any of these preservatives.
EPINEPHRINE
Low concentrations of epinephrine can be added to local anesthetics
in order to retard their systemic absorption. This has the effect
of decreasing blood levels thus minimizing toxic reactions and
prolonging the duration of anesthesia they produce. Addition of
epinephrine 5 mg to each ml of local anesthetic produces the commonly
used 1:200,000 concentration. Caution is exercised with patients
known to suffer from coronary vascular disease; and epinephrine
containing solutions should never be injected into areas with
no collateral circulation such as fingers, toes, ears, penis and
nose.
TYPES OF TRAUMATIC INJURY
HEAD/NECK/SPINE
Generally not well suited to regional techniques. It is seldom
wise to attempt neuraxial blocks in victims of neck or spine injury
(optimal positioning is usually impossible, neurologic deficits
may later be blamed on spinal or epidural placement and profound
sensory/motor blockade can mask evolving neurologic deficits and
delay appropriate therapy). Although many types of brain surgery
can, in fact, be performed with patients awake, using regional
blocks, this approach is seldom useful in cases of traumatic brain
injury. A singular exception might be craniectomy for evacuation
of a sub-dural hematoma under suboccipital nerve blockade.
ORTHOPAEDIC
The surgical repair of a wide variety of fractures can be very
effectively accomplished using regional anesthesia. Fractures
of the digits, wrist, ankle, long bones, hip, pelvis can all be
treated painlessly with the use of appropriate blocks, which may
be supplemented in many instances with general anesthesia or unconscious
sedation at patient request. Cases likely to involve massive blood
loss or other fluid shifts; or likely to be associated with significant
coagulopathies or other associated co-morbidities may be better
treated by general anesthesia incorporating airway protection.
THORACIC/ABDOMINAL
Thoracic injuries often result in rib fractures which subsequently
make for painful ventilation; in some circumstances it may be
useful to employ rib blocks or thoracic epidural anesthesia in
order to minimize this pain and promote vigorous breathing, thus
reducing the incidence of pneumonia. Abdominal crush injuries
are seldom, in the early stages of treatment, candidates for neuraxial
blocks.
BURNS
If the burns are to an extremity, then peripheral nerve blocks
can help with painful dressing change regimens and also with excision
and grafting, however, there is often an increased risk for infection
with manipulation, and it seems that most victims of this type
of injury have a preference for being "asleep" during
painful procedures so regional blocks are not commonly performed
with this type of injury.
PENETRATING TRAUMA
Gunshot and stab wounds, penetrating injuries from motor vehicle
accidents and workplace incidents, injuries resulting from falls
from significant height and major lacerations from glass shards
or metal spikes are usually better treated under general anesthesia.
CRUSH INJURIES
.Pelvic crush injuries, leading to painful acetabular fractures
or open-book pelvic ring fractures are often treated surgically
at Harborview under lumbar epidural anesthesia. Block placement
can sometimes be challenging because it is difficult for victims
of this sort of injury to assume the optimal positioning for block
placement. On occasions the lumbar epidural may be placed while
the patient is under general anesthesia; because there are potential
risks to this approach the perceived benefits of the epidural
have to be more valuable.
Crush injuries to the heel (calcaneus), ankle, knee (tibial plateau) and also to the hand or wrist are all extremely painful. Although surgical repair of the injury is often accomplished under general anesthesia, at Harborview a significant proportion of these injuries are also treated with regional blocks to accomplish four specific goals: a) to "smooth" the anesthetic by reducing the responses to intermittent surgical stimulation such as bone drilling etc.; b) to provide a comfortable emergence and early stage of recovery from general anesthesia (partially because of reduced pain on wake-up and partly because of the decreased need for general anesthetics at high doses); c) to reduce postoperative pain and dependence on opioid therapy (with its attendant nausea, dysphoria and respiratory depression); d) and to accelerate mobilization and physical therapy (leading to faster discharge from the hospital).
AVULSIONS
When extremities are wrenched violently there is a risk of stretch
damage, and even tearing, of nerves which can lead to exceptionally
troublesome pain syndromes lasting long after the acute phase
of treatment. The shoulder joint is particularly vulnerable; avulsion
injuries of the brachial plexus are quite common, and much to
be feared. The precise mechanisms leading to severe postoperative
pain are not clear, but intuitively it seems to be rational that
tearing and stretching of major nerve trunks is going to lead
to trouble. One way of minimizing (but not eliminating) subsequent
pain is by the prompt administration of peripheral nerve blocks
proximal to the site(s) of injury. Again, the precise reason why
this is helpful is not yet clear, but such blocks are effective
in eliminating nociceptive afferents (pain signals to the CNS)
and this seems to inhibit the formation of circuit responses,
or reflex arcs, that lead to complex pain syndromes that become
very hard to treat at a later stage.
AMPUTATIONS
As mentioned earlier, nerve blocks are very useful in cases where
amputated extremities are being re-implanted; the value lies not
particularly in pain control, but rather in the increased blood
flow to the wound site and re-attached tissues promoted by sympathectomy.
USEFUL REGIONAL TECHNIQUES
The list of injury types and sites, above, suggests a parallel
list of regional nerve blocks likely to be of most use in the
treatment of traumatic injuries; such a list follows and each
block will be described in general terms in the accompanying slide
presentation. Detailed descriptions of each block can also be
found by reference to standard texts and atlases; I particularly
recommend those by Brown4 and Scott.5
HAND/ARM/SHOULDER BLOCKS
INTERSCALENE
SUPRACLAVICULAR
INFRACLAVICULAR
AXILLARY
WRIST
DIGIT
FOOT/LEG/HIP BLOCKS
EPIDURAL
SCIATIC
FEMORAL
POPLITEAL
ANKLE
THORACIC BLOCKS
EPIDURAL
RIB (INTERCOSTAL)
PELVIC BLOCKS
EPIDURAL
REFERENCES
1. Cushing HW: Ann Surg 36: 321, 1902
2. Halsted WS: NY med J 42: 294, 1885
3. von Knobelsdorff G, Kusagaya H, Werner C, Kochs E, Schulte
m Esch J:
The effects of surgical stimulation on intracranial hemodynamics.
J Neurosurg Anesthesiol 8(1): 9-14, 1996
4. Brown DL: Atlas of Regional Anesthesia. W.B. Saunders, Philadelphia,
1999
5. Scott DB: Techniques of Regional Anesthesia. Appleton &
Lange, East Norwalk, 1989
