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Define local anesthesia
Use of a chemical agent which disrupts the nerve impulse transmission in sensory neurons, leading to a temp loss of sensation
Advantages of local an
1. min equip
2. min systemic side effects
3.low cost
4. X pain contril
5. min recovery time
6. good for skin & where can place an. in area to effect the nerve
Disadmantages of local
1. small patient risk of OD
2. Needs cooperation or restraint
3. may need sedation w/ resultant systemic effects
4. need to know your anatomy for precise placement of drug
5. Ineffective in fat, bone, cartilage, fascis, tendon, & other connective
Mechanism of action of local
pweipheral nervous system & spinal cord
NO SEDATING EFFECT unless in combo
What 2 types of neurons can be effected
1. sensory
2. motor (for voluntary & involuntary
What is the order of loss of sensation (specifically w/ epidural)
Joint sensation
Deep pressure in caudal adbomen & pelvic limbs
Local affect on ANS
sympathetic blockage - ANS neurons lose their function.
Why may a sympathetic blockage occur after an epidural?
sympathetic ganglia adj to spinal cord become affected by the local.
What are the signs of ANS sympathetic blockage
1.Flushing & increased skin temp.
2. If severe - hypotension
3. If in thoracic spinal canal - innnervation of heart causing bradycardia & arrhythmias
Mechanism of action
loss of transmission of electrical imppulses along nerve fiber blocking membrane channels thru which Na flows into neuron which blocks depolarization
When is the mechanism of action of a local an reversed
when drug is absorbed into local circulation & metaboliaed in liver
Where are esters metabolized?

1 Esters- by enzyme -=aminobenzoic acid

2. amides - liver - caution w/ hepatic patients
How do you classify local an?
Duration of action:
1. Short: 30-60 mmin - procaine
2.Intermediate: 60-90 min - lidocaine
Mepivicivsinr 2-3 hours
3.long acting: Bupivicaine 4-6 hours
3. Long
What effects the rate of absorption?
vascularity of injection site & specific drug used
Which locals have the greatest risk of toxicity
those w/ fastest absorption rate,& shorter duration of action
How doe epinephrine added to local lidocaine effect the drug
blood vessels constrict, decreasing drug absorption prolonging the effect & reducing the toxicity potential
What local should be used in animals with known cardiac dz?
Lidocaine w/o epinephrine on extermities & IV
Routes of Administration for local
1. Topical:
2. Infiltration ID or SQ
3. Intraarticulatr = in joint
4. Regional nerve blocl - major nerve plexus
5. Intravenous infusion - distal limb w/ tourniquet
When are splash block used
Examples of topical local
1. INtact skin - lidocaine + prilocaine
2. MM - proparacaine or tetracaine - eyes
3. MM - lidocaine - larynx & urethra
4. Wound catheters w/ pin pricks like a lawn sprinkler. - large site bupivacaine or lidocaine directly into sx site
5. splash block for declaw
Ex of infiltration Local?
1. Inject ID or SQ
2. Esp sx for superficial tissues - skin biopsy
3. Nerve block - in close proximity to anatomically specific nerve - dentistry
4. Line block
5. field block
What can you add to take the sting out of lidocaine
sodium bicarbonate
What is a line block
a line of anesthetic infused proximal to lesaions -

EX. ring block for declaw or teat sx
What is a field block
line block that goes deeper into tissue - Multi injections to get wider & deeper
How long do you wait for infiltration block to take effect
3-5 minutes
Problems caused by infiltration blocks
1. scar, fibrous tissue, fat, edema, hemmorrhage can impede diffusion of local agent
2. Inflammed areas have acidic pH wwhich rapidly inactivates the local
What is an intraarticular injection & when would it be used
Bupivacaine in joint capsule - before closing & used as a tx modality
What is regional nerve block & an example
1. inejction into major nerve plexus or close to spinal cord

EX: Epidural, intrathecal (spinal) & brachial plexus ( orthopedic on front limb
When might regional nerve block be used
1. Debilitated patient in conjunction w/ neroletanalgesic

2. post-op pain relief (morphine)

3. In reqar protion of animal - tail amputation, anal sac removal, perianal sx, urethrostomies, obgyn, rear limb sx
When would use IV infusion
1. Rarely
2. Distal limb procedures
3. tourniquet
4. inject lidocaine w/o epi
5. 25-30 min of analgesia
6. remove tourniquet w/in 2 hrs or ischemic necrosis of limb
7. remove slowly to min. toxicity
Toxicity when using local an?
1. Loss of function if injected into nerve fiber
2. tissue irritation
3. Paresthesia (tngling, pain, irritation) on recovery
4. allergic reaction
5. CNS toxicity
6. cardiovascular toxicity
Which drug is least likely to cause tissue irritation
What could cause paresthesia
too loarge a volume of SQ drug
What could cause CNS toxicity
1. inadvertent IV injection or
2. use in highly vascular areas (epidural)
3. Large volumes SQ
What are the clinical signs of CNS toxicity
1. sedation
2. nausea
3. restlessness
4. Musc. twitching
5. hyperexcitibility
6. seizures ending w/ resp depression & coma
Adverse effects of using local an?
1/ Trauma to spinal cord after epidural or spinal
2. myelitis
3. meningitis
4. paralysis of thoracic musc, intercostals or phrenic nerve (cervical region)
How to tx CNS toxicity
1. diazepam
2. ultra-short acting barbiturates
3. propofol
4. O2
Cause of cardiovascular toxicity
1. directly affect conduction of electrical impulses w/in myocardium causing arrhythmias
2. Profound vasodilaton leading to hypotension
3. cardia arrest from decreased ventricular contrctility, > conduction in myocardium & loss of peripheral vasomotor tone
ow to tx cardiovascular toxicity
1. Fluids
2. CPR
3. O2
until drug is metabolized
Which is mor dardiotoxic Buprivacaine or lidocaine
How to minimize toxicity
Lidocaine: 10mg/kg - D
4mg/kg - C
Buprivacaine: 2mg/kg - D
0.5 - 1 - C

2. IV only:
Lidocaine: 4mg/kg - d
0.5mg/kg - C

3. Small undamaged needles (23-25 gauge)

4. Sx prep of injection site b/f block

5. Aspirate so no accidental IV

6. Elevate head during epidural so does NOT flow mid-thoracic

7. Prepare for intubation & ventilation if epidural
Injection site for epidural
lumbosacral vertebral junction
Species for epidural
D, C, small ruminants, cattle
Species NOT for epidural
Epidural side for D& C
L-7 & S-1 lumbo-sacral junction
What is the causa equine
termination of spinal cord in a group of neurons
Where does D spinal cord end?

D- L-6

C- S-1 to S-3
Who is at most risk during epidurals - D or C
Cats b'x the end of the spinal cord varies
What protects, supports & stabilizes the spinal cord
1. vertebral column
2. ligaments
3. meninges
Where is the epidural space located
immediately below the ligamentum flavum separating the dura mater from the vertebral periosteum
What is the placement of the epidural needle
1. ventral direction thru the skin, SQ fat, spraspinous ligmament, intraspinous ligament & ligamentum flavum.
What is beyond the ligamentum flavum & the epidural space
1. dura mater
2. arachnoid membrane
3. pia mater
4. spinal cord
What are the meningial membrane layers that protect the spinal cord
1. dura mater - tough outer layer
2. arachnoid membrane - thin, avascular lining surface of dura matter
3. pia mater - closely approximates spinal cord - highly vascular where all blood vessels enter & leave the CNS
Where is the CSF located
subarachnoid space separating the arachnoid membrane & pia mater
What will you see if you inadvertantly perforate the dura mater or sub-arachnoid1
CNF in the hub
What to do if you get into the dura mater or sub arachnoid memebrane
Give 1/2 dose intended for epidutal
Another name for spinal injection
intrathecal injection
Epidural technique:
1. Sternal recumbency with hind limbs pulled forward

2. clip, prep, surgical gloves
3. inject
Duration of effect of epidural
Lidocaine: 1-2 hr
Bupivacaine: up to 6 hours
Main reason for epidural
post-op pain control
3 classes of patient fo repidural
1. Large animals - esp cattle
2. debilitated small animals
3. patients needing major pain control post-op.
Vet use for neuromuscular blocking agents
1.Paralyze muscles of respiration during mechanical or controlled ventilation
2. orthopedic sx
3. c-section
4. facilitate difficult intubation

ESP : tortoise intubations

Mechanism of action of neuromuscular blocking agents
interrupt transmission of impulse from motro nerve to muscel synapse
How do depolarizing agents work
1. Cause SINGLE SURGE of activity at neuromusc. junction ff by paralysis period (called refractory period)
What do yo see with depolarizing agents
spontaneous musc movement ff y paralysis
Example of depolarizing agent
How do nondepolarizing agents work
Block receptors at the end place

Can be reversed w/ anticholinesterase
Ex of nondepolarizing agent
atracurium besylate
Reversing agents for nondepolarizing agents
anticholinesterase agent like neostigmine or endrophonium
Why would you pre-tx a patient when using nondepolarizing agents? & what drug would you use
counteract bradycardia with

Predicatble order of skeletal muscle paralysis when using neuromuscular blocking agents
1.Facial & neck paralysis
2. limb
3. tail
4. abd muscles.
5.intercostals & diaphragm last
Risks of using neuromuscular blocking agents
1.Hypothermia b/c skeletal muscle is paralysed & can't generate heat
2. Difficult to determine an. depth
3. Contraindicated in animals w/ glaucoma, hepatic or renal Dz
Concurrent use of which drugs increases the potency of neuromuscular blocking agents

What to do?
1. iso
2. halothan
3, organophosphates

Use lesser volumes
Healthy awake, main stimulus to breathe is the result of ?
xcess CO2 concentration in blood
In healthy awake animal, exhalation lasts - times as long as inhalation
Inital tidal volume in awake animal is __ mg/kg
What to see in anesthetized animal breathing ROOM AIR
< PaCO2, > Pao2
Line block local will directly effect _
Local an. may effect:
2. motor
3. autonomic neurons
Local an. work b/c
interfer w/ movement of Na ions
Local an injected around a major nerve is called
infiltration nerve block
T/F Epinephrine may be mixed w/ local an. to prolong the effects of the drug
How far caudal can the spinal cord extend in teh cat
Max SQ dose of lidocaine in a dog is
IV an., use lidocaine _____ epineprhine
without epinephrine
atelectasis means
collapse of alveoli
Most common acid-base abnormality in anesthetized patient
respiratory acidosis
When lungs of patient connected to circle system w/ precision vaporizer are continuously ventilated manually, ___
decrease vapor setting
How to monitor anesthetic depth in patient under Nueromuscular block
heart rate
T/F NMBA will paralyse the skeletal muscle & give some analgesia
When given a_____drug, an initial sure of muscle activity may be seen b/f paralysis
Muscle type most affected by NMBA is
Problems resulting form excess controlled ventilation may include
1. > cardiac ooutput
2. resp alkalosis
3. ruptured alveoli
Lidocaine or proparacaine work well when applied
1. Topically MM
2. Topically cornea
3. Injection
Factors interfering w/ action of local an. include
1. Fat
2. Scar
Clinical signs of systemic toxicity from local an
1. sedation
2. convulsions
3. muscle twitching
4. respiratoroy depression
Effects of epidural if drug reaches thoracic & cervical spinal cord
1.sympathetic blockage
2. paralysis of intercostals
3. paralysis of diaphragm
Which is NOT a toxic effect of local an:
neurologic damage if injected into a nerve
T/F Neostigmine reverses effects of succinyl choline
false sucinyl choline is a NON-reversible type of muscle paralysing agent
T/F succinyl choline is an example of a depolarizing agent
T/F Muscles are polarized at rest
Muscle= paralyzing agents should Not bre used if the animal has been given aminoglycoside antibiotic

In cattle the epidural block is performed by placing the needle btwn ____ & ____
Cy1 & Cy2

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