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Are CNS or cardiovascular signs seen first w/toxicity? Does general anesthesia enhance or mask the signs of toxicity?
- CNS (trembling, convulsions)
- GA masks signs (so assess arrhythmias, hypotension, and respiratory effects)
What are cardiovascular effects with LA overdose?
- depressed cardiac tissue automaticity
- direct myocardial depression so bradycardia, decr. CO
Which LA has highest affinity for cardiomyocytes, thus making it the most difficult toxicity to treat?
What 2 LA's can cause methemoglobinemia, thus impairing O2 carrying capacity?
benzocaine and prilocaine
What is LipidRescue?
lipid emulsion given IV to sequester LA and prevent them crossing cell membranes (treats overdose)
What are four considerations to prevent risk of LA toxicity?
- dose according to LEAN body mass (adjust in obese)
- very careful w/small animals
- dilute to safe working volumes
- always aspirate before injecting to prevent accidental IV admin.
What is max dose of Lidocaine in dogs? cats?
- dog: 6mg/kg (lidocaine has highest max dose)
- cat: 4mg/kg
What is max dose of Mepivacaine in dog? cat?
- dog: 5mg/kg
- cat: 2.5 mg/kg
What is max dose of Bupivacaine in dog? cat?
- dog: 2 mg/kg (bupivacaine has lowest max dose)
- cat: 1.5 mg/kg
In combination, are LA's considered additive?
yes, so reduce doses accordingly
what are localized toxicity effects?
- allergic reaction
- local tissue irritation
- neurotoxic (after spinal anesthesia)
Which LA is less hist-toxic than Lidocaine?
When should special attention be paid to NOT use formulations with preservatives?
for intra-articular or spinal/epidural use
What drug is added to alkalinize the LA, thus increasing efficacy and decreasing pain of injection?
What drug is added to increase efficacy, extend duration of action, and has anti-inflammatory effects?
- (mu and kappy agonists are anti-inflammatory)
What is a commonly combined LA and opioid used for epidural block?
bupivicaine + morphine
What drug is added to increase efficacy, duration of action but has rapid systemic uptake so care should be taken in compromised patients?
alpha-2 agonists (medetomidine, dexmedetomidine, xylazine)
Which federal agency regulates food animal withdrawal times?
Which LA lasts longest (4-6 hours) and is most cardiotoxic with hi potency/low max dose (mg/kg)?
Which LA has similar properties as lidocaine but is less of a tissue irritant? commonly used in equine blocks and in joints.
Which formulation of bupivicaine is less cardiotoxic and believed to cause less intense motor block?
What is onset time and DOA for lidocaine?
- onset: 5-15min.
- duration: 1-2 hours
- (very similar to mepivicaine)
What is onset time and DOA for bupivicaine?
- onset: 15-30 min
- duration: 4-6 hours
What are the 2 LA's in EMLA cream used for minor skin lacerations or to desensitize for IV catheter? Can you use this on mucous membranes?
- 2.5% prilocaine and 2.5% lidocaine
Does systemic absorption occur with topical application of LAs to skin or mucous membranes?
What is a "splash block"?
- direct application of injectable local to site of interest
- (ex: body wall before closing abdomen, peritoneum intra-op, ovarian ligament)
Is splash block an effective technique on wounds?
- not very effective and systemic absorption significant
- not effective at all if infected tissue
What are 3 options for topical analgesia used in ocular surgery? Can you use injectable formulations?
- lidocaine, tetracaine, proxymetacaine
- injectable not suitable for cornea
What are 4 characteristics of good LA for ocular surgery?
- rapid onset
- non irritant
- good analgesia
- no pupillary dilation
What is main theoretical risk associated with interpleural and intraperitoneal analgesia?
phrenic nerve runs through thoracic cavity --> bilateral desensitization results in diaphragm dysfunction
what local technique is used for excising small masses or near incision/laceration repair?
infiltration/incisional block (deposit into SC)
What LAs are commonly used for conintuous local anesthesia with diffusion catheter? What type of procedure calls for these "soaker" type catheters?
- lidocaine + mepivicaine
- limb amputation, large tumor resection
Can intratesticular LA injection be performed in cats?
yes, but more sensitive to overdose so careful dosing
What 2 drugs are commonly combined to be injected in articular surgery? what is another option that may be less irritating to tissue?
- bupivicaine + morphine
- mepivicaine = less irritating