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The
nerves of the upper extremity (i.e., the arm and hand) originate in
the neck where they exit from the spinal cord. These nerves form a
complicated web of nerves known as the brachial plexus. This network
of nerves gives rise to the three main nerves that travel down the
arm, carrying both messages of sensation (from arm and hand back to
brain) as well as messages of movement (from brain to muscles). When
a solution of a
local anaesthetic drug is injected
in the proximity of the brachial plexus, it anesthetizes the nerves
and interrupts the transmission of these messages. This results in
numbness of the arm and hand as well as inability to cause the
muscles in that area to move.
This form of anaesthesia can thus provide good operating conditions
for surgery on the arm or hand. As with all anaesthetic techniques,
there is a possibility of certain
complications.
There are several methods that have been developed to anesthetize
the brachial plexus. Some of the methods make use of a
nerve stimulator
to help the anaesthesiologist precisely locate
the site of injection. The more widely used approaches are:
This approach is very similar to the supraclavicular block but
differs in that the site of injection is closer to the base of the
neck. It is also sometimes used for
post-op pain management
following surgery on the shoulder.
Brachial plexus blocks may be used when regional anaesthesia is
desired for surgery on the upper extremity. They have an advantage
over Bier Block anaesthesia in that with proper choice of anaesthetic
agent they can be made to last several hours and achieve enough
numbness in the arm for tourniquets to be well tolerated (surgeons
often desire the use of tourniquets to interrupt the circulation and
provide bloodless operating conditions; unlike Bier Block, however,
a tourniquet is not a requirement for brachial plexus block).
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Complications of Brachial Plexus Block |
Possible complications differ in their likelihood with the different
approaches, but include:
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Collapse of the lung on the same side. The tip of the lung is
very near to the brachial plexus, and there have been cases
where the needle punctured the membrane lining the lung,
resulting in collapse. If the lung collapses far enough,
re-expansion by means of a surgically placed chest tube may be
required. This is not a frequent complication of brachial plexus
block.
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Inadequate or "patchy" block. When anaesthetic solutions are
injected near the brachial plexus, they normally spread
uniformly to anesthetize the entire plexus. On occasion,
however, the spread is not uniform and incomplete numbness is
achieved. If the surgeon cannot compensate for this by adding a
small amount of local anaesthesia, a general anaesthetic is
usually required to complete the operation.
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Phrenic nerve block. More often seen with interscalene and to a
lesser degree with supraclavicular block, this happens when
enough anaesthetic solution spreads upwards from the plexus to
anesthetize the phrenic nerve, which controls the half diaphragm
on the side of the block. Blockade of this nerve causes weakness
of this important breathing muscle until the anaesthetic wears
off. However, in normal persons with adequate lung reserves, it
is usually well tolerated. Patients with advanced lung disease
might tolerate it poorly enough to require assistance with the
breathing, and possibly
endotracheal intubation
with breathing assistance, until the effects have dissipated.
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Axillary hematoma. Some approaches to axillary block involve
finding the plexus by first locating, with the needle, an artery
that lies immediately next to the plexus. Small amounts of blood
that escape from the needle hole in the artery can form a blood
clot, or hematoma, beneath the skin. This can show up as a
discoloration similar to a bruise in the armpit and can cause a
little soreness for a few days. This is usually no more than a
temporary nuisance, and resolves spontaneously.
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