Page 71 - BSAVA Guide to Pain Management in Small Animal Practice

BSAVA Guide to Pain Management in Small Animal Practice

VetBooks.ir response to lidocaine. Despite this no longer Currently the author [FC] is not aware of any
being a possibility, a positive response to
prospective study or even case report
supporting the e cacy of lidocaine patches in
lidocaine infusion is still an invaluable tool to
diagnose neuropathic pain, in view of utilizing providing analgesia in dogs and cats, despite
other drugs inhibiting or blocking sodium the products being available and having been
channels. In a clinical setting, lidocaine infusion used for many years (Meier et al., ; Burch et
plays a big role, at least in dogs, in the control of al., 4; eiland et al., 6; o et al., 7;
pain syndromes that are poorly responsive to eil et al., 7; o et al., 8; Saber et al.,
opioids and NSAIDs. The commonly used 9; ilhooly et al., 11; Bai et al., 1 ;
protocol suggests a loading dose of 1 mg kg, Joudrey et al., 1 .
followed by a continuous infusion of mg
kg h. Commonly observed side e ects are Toxicity
sedation and reduced appetite, but they are Cardiovascular and neurological toxicity are
generally mild and self-limiting, and rarely ma or side e ects secondary to systemic
require discontinuation of the therapy, absorption or administration of local
especially in the presence of neuropathic pain anaesthetics. At high concentrations, local
aler et al., 1996; olli e et al., 7; utson et anaesthetics also a ect potassium and calcium
al., 1 ; Papapetrou et al., 1 ; Pr eklasa channels, and this could further contribute to
us y ska et al., 16 . systemic toxicity (Nakahira et al., 16 .
The most common causes of severe
Transdermal administration systemic toxicity are accidental intravascular
Lidocaine can also be delivered transdermally administration and rapid systemic absorption
using a patch, which is licensed to treat after administration of large doses of
postherpetic neuralgia (PHN) pain in humans. anaesthetics. Neurological signs of toxicity are
The drug transferred to the skin is believed to depression and twitching, progressing to
induce local analgesia by inhibiting generalized seizures (Cox et al., ; Beecroft
spontaneous discharge of injured small and avies, 16 . oxic doses after intravenous
nociceptive bres C and Aδ), without administration have been well characterized in
signi cantly a ecting the function of large dogs, suggesting an acute neurological toxicity
sensory bres, therefore preserving sensation. occurring for doses of bupivacaine and
hile lidocaine patches are an e ective ropivacaine greater than mg kg, and
treatment for PHN pain in human patients, they greater than 1 mg kg for lidocaine eldman et
appear less e ective in treating neuropathic al., 1989 .
pain of di erent origin. he role of lidocaine Cardiovascular toxicity presents as
patches in treating postoperative pain in progressive cardiovascular depression, with
humans is still controversial, with a few studies arrhythmias, including tachycardia, ventricular
and case reports reporting some e cacy, and tachycardia and ventricular brillation. In a
meta-analyses suggesting that the overall continuous intravenous infusion model, the
e ect is negligible. cumulative dose that caused cardiovascular
Systemic absorption is minimal, and not collapse was 1 mg kg for bupivacaine, 7 mg
su cient to support a systemic e ect of the kg for levobupivacaine, 4 mg kg for
drug. Studies in dogs and cats have ropivacaine and 1 7 mg kg for lidocaine. hile
demonstrated minimal systemic absorption, as all dogs in the lidocaine group could be
in humans, and suggested that the patch may resuscitated, mortality rates were for
deliver lidocaine for up to days after bupivacaine, for levobupivacaine, and 1
application on intact skin in dogs, and up to for ropivacaine overdose. This study also neatly
days in cats. A recent study suggests that demonstrates that cardiotoxicity is a ected by
absorption may be greater if the patch is stereoselectivity, as levobupivacaine appears to
applied directly over a skin incision in dogs. be less toxic than bupivacaine roban et al.,

66

Ch05 Pain Management.indd 66 19/12/2018 10:36