What local anesthetics are
used for blocks of the brachial plexus and in what doses?
Local anesthetics are sodium channel blockers
that inhibit the progression of the action potential across the membrane.
Therefore, nerve impulses are interrupted. There are two main groups of local
anesthetics: esters and amides. Both consist of a hydrophilic hydrocarbon chain
and a lipophilic aromatic ring. The ester anesthetics have an ester bond
(-CO-), whereas the amides have an amide bond (-NHC-) linking the two groups.
The amide local anesthetics used for brachial
plexus anesthesia are lidocaine, mepivacaine, bupivacaine, levo-bupivacaine,
and ropivacaine. Each differs in its duration of onset, action, and toxicity
(Table 57.3). The surgical procedure and need for postoperative analgesia must be
considered when choosing an appropriate drug. Lidocaine and/or mepivacaine can
be used for surgical procedures of short duration, such as carpal tunnel repair
or bone manipulations. Surgeries of much longer duration, such as joint
replacements, benefit from bupivacaine, ropivacaine, or levobupivacaine. When
postoperative pain control is needed, a mixture of a short- and a long-acting
anesthetic is optimal. The newer local anesthetics, levobupivacaine and
ropivacaine, are less cardiotoxic than bupivacaine, and therefore may be safer