Veterinary Medicine - January 2009 - (Page 28)

Anesthesia techniques PEER-REVIEWED added to cause vasoconstriction and slow systemic absorption, increasing the intensity and the duration of blockade and reducing the potential for toxicity. In addition, epinephrine may have some local anesthetic effects itself.1 The usual concentration of epinephrine is 5 µg/ml, or 1:200,000. This concentration can be obtained by adding 0.1 ml of 1:1,000 (0.1 local anesthetics, so reduce doses by 40% to 60%. In addition, cats should receive lower doses than dogs do since they are more likely to develop signs of toxicosis because they metabolize local anesthetics more slowly and, to a lesser extent, because of their decreased ability for glucuronidation.1-3 Relative or absolute overdosage of Never use epinephrine to block distal extremities. mg) epinephrine to 20 ml of the local anesthetic. Some commercially available local anesthetics already contain epinephrine. Epinephrine can cause tissue necrosis along wound edges and, rarely, ventricular dysrhythmias. Never use epinephrine to block distal extremities, including digits, ears, or tails, because of the potential for local tissue ischemia.1-3 Toxicity. Local anesthetics can cause severe toxic reactions after unintentional intravenous administration, vascular absorption of an excessive dose, or ingestion of topical local anesthetic preparations. Intravenous injection of bupivacaine is highly toxic to the cardiovascular system and central nervous system, resulting in agitation, muscular twitching, seizures, unconsciousness, coma, respiratory arrest, cardiac depression, dysrhythmias, hypotension, and death. Always aspirate the syringe before injecting any local anesthetic to avoid intravenous or intra-arterial injection. Base dosage calculations on lean body weight, and always calculate the maximum safe dose to avoid toxicosis (Table 2). Animals with hepatic impairment or reduced hepatic blood ow (hypotension, cardiac failure), geriatric patients, and neonates are more prone to develop toxicosis with amide-linked local anesthetics results in agitation, muscular twitching, seizures, unconsciousness, coma, respiratory arrest, cardiac depression, dysrhythmias, hypotension, and death.1,2 Some effects may be masked by general anesthesia, and dysrhythmias, hypotension, and respiratory arrest may be the only observable signs of toxicosis. Allergic reactions can occur but are uncommon. Benzocaine and prilocaine, and less commonly procaine and lidocaine, have been associated with the development of methemoglobinemia in dogs and cats.2 Cats are at increased risk for developing methemoglobinemia and Heinz-body anemia with benzocaine-containing products, including Cetacaine (a combination of benzocaine, butamben, and tetracaine), so these products should be avoided in cats.2 When given in high volumes epidurally or spinally, local anesthetics can cause excessive blockade of sympathetic neurons, resulting in hypotension, and excessive blockade of motor neurons, resulting in paralysis of intercostal muscles and the diaphragm.1,2 Opioids Opioids are sometimes added to local anesthetics to increase ef cacy and extend the duration of the block. The ef cacy of peripherally injected opioids is likely due to a combination of factors, 28 January 2009 VETERINARY MEDICINE http://www.comfortis4dogs.com

Table of Contents Feed for the Digital Edition of Veterinary Medicine - January 2009

Veterinary Medicine - January 2009 Contents Leading Off Letters Research Updates Idea Exchange A Modified Subconjunctival Enucleation Technique in Dogs and Cats Local and Regional Anesthesia Techniques Author Guidelines Product Preview CE Form/Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - January 2009

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