Local Anesthesia and Euthanasia

Of the two local anesthetics what do we use most?

Amides

What different physiological properties do Esters have?

Shorter duration of action

Increased systemic toxicity

Differences in ___ can have an affect on potency and clinical properties?

Stereochemistry

A local anesthetic needs to be ___ to cross a cell membrane?

Non-ionized

What form of a local anesthetic will bind to a Na+ channel?

Ionized

Why don't local anesthetics work as well in regions of inflammation?

They are more acidic which makes the Local anesthetic more charged and ionized meaning it cannot cross the membrane and wont bind as well

What are the Pharmacodynamics of local anesthetics?

Block Na+ channel and inhibit neuronal channels

-Decreases Na+ influx and slows impulse conduction (longer time to produce signal)

Local anesthetics will usually have a higher affinity for what?

Activated/ inactivated channels

(not as much for resting/closed channels)

The duration of action of a local anesthetic is dependent on what?

Time at sight of action and how fast it diffuses away

What is systemic absorption of LA affected by?

Dosage,

Site of inj / blood flow

Drug-tissue binding

Chem properties of drug

Vasoconstriction agents

What are the ways Epinephrine affects lidocaine administration?

Decrease diffusion

Prolongs duration

Decrease systemic absorption

Decrease toxicity risk

What are pharmacokinetics of Amides?

Metabolized by P450

-Can be toxic if hepatic dz

What are pharmacokinetics of Esters?

Metabolized in plasma w/ butyrylcholinesterase

What are local AE of LA?

Tissue damage from inj of local anesthetic - increased w/ epi

Neurotoxicity and Myotoxicity

What are systemic AE of LA?

Skeletal muscle twitches

Tonic clonic seizures

Prolonged PR and QRS intervals - slowed impulse conduction

hypotension and decreased myocardial strength

We will see what cardiac effects w/ LA?

Negative inotropic effects

What are CI of Benzocaine?

Cats and rabbits - methemoglobinemia

What are Indications for Lidocaine?

Infiltration

Nerve block

Epidural

systemic - Ventricular fiburlation and tachycardia

pro kinetic effects good for ileus in horses

All LA used peri-operatively will have what effect

Lower MAC effect (less inhaled anesthesia needed)

We will see worse AE of lidocaine in what animal?

Cats - more near and cardio depression

What are indications of Bupivacaine?

Spinal anesthesia

Influtration blocks

Epidural

Post op pain

Bupivacaine-liposome is labeled for what?

CCL sx

What are pharmacodynamics of Bupivacaine?

Longer duration of action

Binds to resting Na+ channels as well

Mor potent SENSORY block

What are important AE of Bupivacaine?

Greater cardio toxicity

Why do we use mepivacaine in limb blocks?

Less post inj edema (dont need to combine w/ epi)

Why do we used Ropivacane less than other local anesthetics?

Slower onset, longer duration of lidocaine

What are indications of Benzocaine?

Fish anesthesia / euthanasia

What is important pharmacokinetic of Benzocaine?

Lowest pKa and EASILY absorbed!!!! (Gloves)

What is the indication of proparacaine?

Ophthalmic dx procedures - short duration

What are indications for Tetracaine?

Opthalmological procedures p deeper plane/ longer duration of anesthesia

What are AE of Tetracaine?

Burning sensation and itching

Defused epithelial keratitis

iritis

Descemetitis

Defused stromal edema

Suppressed blink reflex

Corneal opacification

Keratits

What are the guidelines for euthanasia?

1. Rapid loss of consciousness

2. Loss of motor function

3. Cardiac and resp arrest

4. Permanent loss of brain function

What drugs would not be indicated for euthanasia?

Paralytic agents - cause fear and dont have loss of consciousness first

Rabbist and chickens have ____?

Fear induced tonic immobility - careful

What is the DOC for Euthanasia?

Barbiturates

What are the pharmacodynamics of Barbiturates?

Depress CNS at cortex w/ loss consciousness, deep anesthesia, repress resp center and lead to cardiac arrest

Why do we combine medications w/ Pentobarbital?

It will cause excitation and can cause unpleasant visuals

What are contraindications for Barbiturates?

NEVER give to animal entering food chain

What must we ensure in the disposal of animals?

Carcass will not enter food chain

No burial - scavenging