TITLE:
Addition of Capsaicin to Local Anesthetics for Spinal Anesthesia in Rats Shortens Motor Deficits and Prolongs Anti-Nociception
AUTHORS:
Charles H. Wang, Jeffrey C. Wang, Mieke A. Soens, Peter Gerner, Gary Strichartz
KEYWORDS:
Spinal Anesthesia, Differential Blockade, Analgesia, TRPV-1
JOURNAL NAME:
Open Journal of Anesthesiology,
Vol.4 No.6,
June
12,
2014
ABSTRACT: Background and
Objectives: Sensory-selective anesthesia, greater or longer-lasting
anti-nociception than motor or autonomic deficits, is often clinically desirable
but traditional local anesthetics rarely have such selective actions. Addition
of capsaicin to tertiary amine local anesthetics has recently been reported to affect
a preferential prolongation of nociceptive over motor block in rat sciatic
nerve. We hypothesized that this combination when used intrathecally will also
prolong nociceptive block. Methods: Under sevoflurane inhalation anesthesia,
rats were injected intrathecally either with local anesthetics (bupivacaine,
lidocaine, and articaine) alone or simultaneously with capsaicin. Motor block
was evaluated by the contractile function of foot muscles, from proximal to
distal. Anti-nociception was assessed by reductions in nocifensive withdrawal
and vocalization induced by pinching the skin fold over the lateral metatarsus.
Durations and degrees of deficits were assessed, along with complete recovery
times and compared between local anesthetics alone and in combination with
capsaicin. Results: Addition of capsaicin to any of the local anesthetics shortened
motor deficits. Bupivacaine, lidocaine and articaine motor blocks were reduced
upon combination with capsaicin to 0.32, 0.32 ans 0.43 of the duration from the
respective local anesthetic alone. Duration of anti-nociceptive action was
increased by capsaicin only for articaine. The ratios of block nociceptive to
sensory block durations were 3.5, 5.1 and 3.3 for the respective local
anesthetics. Conclusions: Intrathecal injection of capsaicin combined with
local anesthetics produced a preferentially longer anti-nociceptive deficit.
These combinations have potential clinical applications, including
peri-operative spinal anesthesia and pain management.