5. For intravenous regional anaesthesia
Perpheral Nerve Block
Upper Extremity
The most common LA's employed are 1% to 1.25% lidocaine or mepivacaine epinephrine for 2- to 4-hour duration of surgical block. Longer blockade (but slower onset) is achieved with 0.5% bupivacaine, levobupivacaine, or ropivacaine with epinephrine, which provide 4 to 12 hours of surgical block.
The technique of IVRA.
An intravenous catheter is placed in the hand, a tourniquet (usually a double cuff) is applied to the arm, the limb is exsanguinated by elevation and wrapping with an elastic bandage, and the proximal tourniquet is inflated well above arterial pressure. The bandage is removed and a dilute LA solution, usually 40 to 50ml of 0.5% lidocaine, is injected into the catheter. The LA gains access to nerves through the blood vessels supplying those nerves, and anesthesia occurs in 10 to 15 minutes and remains as long as the tourniquet is inflated.
Substances used are for local anesthesia:
a) Cocaine is used essentially for topical anaesthesia and thus
for operations in the nasal cavity in a concentration ranging
from 4-20%.
b) Procaine (Novocaine) the substance was introduced in 1905 and
is not effective topically but is much less toxic than
cocaine.
It can be used for subcutaneous infiltration in a 0.5%
solution; 2% solution is required for nerve blocks.
c) Lignocaine (Xylocaine) 0.5% solution is used for local
infiltration. 1-2% for nerve block. The relative advantages
and disadvantages of procaine and lignocaine can be
appreciated.
Lignocaine it is apparent, provides longer duration of
anaesthesia, however, has a lower maximum dose.
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