LEC 8,9 - General + Local Anesthetics Flashcards
General anesthetic effects (5)
Analgesia
Loss of conciousness
Amnesia
Inhibition of snesory + ANS reflexes
Muscle relaxation
Drugs for analgesia (2)
N2O
Opiods
Drugs for loss of conciousness (2)
IV anesthetics
N2O
Drugs for amensia (3)
Midazolam
Droperidol
Ketamine
Drugs for ANS inhibition (3)
Atropine
Opiates
Scopolamine
Drugs for muscle relaxation
Depolarizing + Nondepolarizing muscle relaxants
What is the purpose of pre-medications?
Facilitate anesthesia + surgery
improves rapidity + smoothness of:
Iduction
Anxiety
Analgesia/Amnesia
What are the four major drug groups used for pre-meds?
Opiods
tranquilizers
Anticholinergics
Central muscle relaxants
What is the purpose of opioids in pre-meds?
Analgesia
What is the purpose of tranquilizers in pre-meds?
Pre-operative sedation + amnesia
Prevent/counteract CNS stimulation
What is the purpose of anticholinergics in pre-meds?
Prevent salivation + bradycardia
Propofol - Mechanism
Activates GABAa receptors
Propofol - admin
IV
Propofol - Distribution
Rapid redistribution + metaboolism
Propofol - Effects on cerebral pressure
Decreases blood flow + oxygen consumption
Safe for animals with head trauma
Propofol - Duration of anesthesia
2 to 10 min
Propofol - Distribution/breeds to watch out for
Distributes to fat
Sighthounds
Propofol - Metabolism
Glucoronidation
Propofol - 1/2 life
1 to 2 hours
Propofol - Adverse effects
Myoclonic twitching
Myocardial depression
Transient apnea
Etomidate - Mechanism
Sedative hypnotic nonbarbiturate
Facilitates GABA transmission
Etomidate - Effects
Decrease cerebral blood flow
Metabolic rate
oxygen consumption
Etomidate - Uses
Good for patients with:
Cardiac dysfuncton
Head trauma
Critically ill
Etomidate - Metabolism
Heptaic hydrolysis
No accumulation
Etomidate - 1/2 life
3 hours
Etomidate - Adverse effects
Very hypertonic
Pain + Hemolyssi upon IV injection
Alfaxalone - Mechanism
Synthetic neuroactive steroid
Interacts with GABA receptors
Anesthesia + Muscle relaxtion
Alfaxalone - 1/2 life
< 1 hour
Alfaxalone - Pharmacokinetic curce
non-linear aka zero order
Alfaxalone - Use
General anesthesia
Bolus or CRI
Alfaxalone - Adverse effects
CNS depression
Hypotension
Ketamine - Use
FDA approval in cats
Induction
CRI for general anestehsia
Sedation for chemical restraint
Ketamine - Mechanism
Inhibits excitaory NT ACh + L-glutamate in spinal cord
Non-competitive antagonist of NNMDA receptor
Dissociative anesthesia
Analgesia
Ketamine - Admin
IM/IV - Cats + Dogs + Small Ruminants + Swine
IV - Adult horses
Ketamine - Metabolism
CYP450
Congugated with glucuronide
Ketamine - Excretion
Kidneys -
Unchanged in cats
Ketamine - 1/2 life
Cat
Calf
Horse
= 1 to 1.5 hours
Ketamine - Adverse side effects
Seizures (Horses + Dogs )
Profuse salivation (Cats)
SNS stimulation = Inc CO + HR
Rougher induction/recovery
Increase muscle tone
Apneustic breathing pattern
CSF pressure increased
What muscle relaxers are given with ketamine?
Alpha2 agonists - to horses for muscle relaxation
Diazepam/Midazolam/etx. - to cats/dogs for seizure prevention + skeletal muscle relaxation
Midazolam - Mechanism
Benzodiazapine
Increases effects of GABA
Increases frequency of open Cl- channel
Midazolam - Use
Induction
Neonatal seizures
Status epilepticus
Midazolam - Neuroleptanalgesic combo
+ Opioid
Midazolam - Muscle relaxation combo
Ketamine
Midazolam - Protein bidning
94 to 97% bound
Unbound crosses BBB to enter CSF
Midazolam - Admin
SC + IM + IV
Midazolam - metabolism
Glucuronidation in liver
Midazolam - Affinity vs. Potency
2x’s affinity for GABA
3x’s potency
Midazolam - Adverse effects
Cardiorespiratory depression
Paradoxical excitement
Dysphoria
w/ drugs that have protein binding will increase CSF concentration
Midazolam - reversal
Flumazenil
Flumazenil - Mechanism
Competitive antagonist for BZD receptors
Tiletamine/Zolazepam - Use
Chemical resitrant in fracitous cats
Short term anesthesia in dogs/cats
Tiletamine/Zolazepam - Admin
Deep IM
Tiletamine/Zolazepam - Adverse effects
Excessive salivation
Erratic recovery
Muscle twitching
How do you treat excessive salivation with Tiletamine/Zolazepam administration?
Atropine
Barbiturates - Mechanism
Bind to GABA Cl- channels
Increase duration of opening
= hyperpolarization of neurons
Barbiturates - effects
Transient hypotension + increased HR
Depress respiratory centers (Cats > Dogs)
General anesthesia
Barbiturates - overdose
Apnea
Cardiovascular depression
Death
Barbiturates - Distribution factors
Lipid solubility
Protein binding
Ionization
What type of drugs cross the BBB?
Non-protein bound
– and –
Non-ionized
Why are thiobarbiturates rapid in onset?
High lipid solubiltiy
Characteristics of ultrashort acting barbiturates
very lipid soluble
Onset rapid
Duration short (10 to 30min)
Methohexital - use
Dogs/Cats
Ultra short procesures
Methohexital - Duration of action
5 to 15 minutes
Methohexital - Time of onset
15 to 60 seconds
Methohexital - Distribution
No effect on fetus so safer for C-section
Can reduce O2 in pups so move fast
Does not move to fat - good in greyhounds
Methohexital - Adverse effects
More likely to cause period of excitement during induction
Profound respiratory depression
Pentobarbital - Four main uses
Sedation
General anesthesia
Seizure control
Euth
Pentobarbital - Sedation uses
Mechanical ventilation
Ruminants + Horses
Pentobarbital - General Anesthetic uses
Cats/Dogs
Pentobarbital - Seizure uses
Refractory to phenobarbital or diazepam
Pentobarbital - duration of action
30 to 60 min
Pentobarbital - 1/2 life
Ruminants - 0.9 hours
Dogs - 8 hours
Pentobarbital - Adverse effects
Low doses - ecitement phase
Phenobarbital - mechanism
Long-acting
Phenobarbital - uses
Anticonvulsant in status epilepticus treatment
Excess, chronic drooling in dogs
Chlorinated hydrocarbon detox in cattle
Phenobarbital - ADmin
PO
IV loading in horses
Phenobarbital - Duration of action
6 to 12 hours
Phenobarbital - Metabolism
Liver 75 %
Urine, unchanged 25%
Phenobarbital - Adverse effects
Ataxia + Lethargy + depression
PU/PD/PP
Coagulopathies + Adrenal insufficency in cats
Increased liver enzymes in dogs
Define: MAC
1 mac = [] at 1 atm that prevents skeletal muscle movemnet in painful stim in 50% of the population
Oil : Gas ppartition coefficients
Measure of potency
MAC-awake
Inhibits voluntary movements
MAC-BAR
Blunting autonomic reflexs
MIR
Eliminates reflexes used to judge depth of anestehisa
Blood : Gas Partition Coeffcient
Rate of increase of Pa towards Pi
Inversely related to solubility of anesthetic to blood
Partition coefficient =
Solubility of inhaled anesthetic in different body components
Nitrous Oxide - Effects
Direct myocradial function depression
SNS stimulation
No sensitization of myocardium to epi
Nitrous Oxide - Use
Not very potant
Combine with other inhaled anesthetics to make more stable anesthesia
Analgesic
Nitrous Oxide - Secondary effects
Second gas effect
Diffusional hypozia
Describe second gas effect
Nitrous + Other inhalant anesthetic
NO highly diffusible, quick to leave alveoli
[] of other compoundss increase in alveoli
[] effect increases theri absorption into the blood
= decrease concentration needed
Nitrous Oxide - Distribution
Accumulations in gas filled spaces
Rumen of cattle
Cecum of horses
Describe diffusion hypoxia
NO is turned off
NO quickly diffuses out of blood into alveoli
Intra-alveolar oxygen [] is decreased
Treatment for diffusion hypoxia
100% oxygen
Preventing diffusion hypoxia
Wean patients off of NO
Isoflurane - Effects
Decrease arterial BP
Depresses CV function
Catecholamine sensitization = Cardiac arrhythmias
RR + TV decreased
Increases effect of non-depolarizing muscle relaxers
Isoflurane - MAC that effects cerebral blood floow
1.2
Isoflurane - Use
Dog + Cats + Birds + Horses
Anesthetic
Status epilepticus in Dogs (refractory to benzodiazepines)
Isoflurane - kinetics
Low blood : gas partition coeffiecent
Rapid induction/recovery
Exhaled unmetabolized
Isoflurane - Adverse effects
Malignant hyperthermia
Higher risk of causing vasodilation
(Responsive to fluid bolus)
Sevoflurane - Effects
Decrease SV
Depresses myocardial contractility
Decreases arterial BP
Sevoflurane - Kinetics
Low blood : Gas partition coefficient
Fast induction/recovery
Sevoflurane - Elimination
Liver - 2 to 5%
The rest is exhaled
Sevoflurane - Adverse effects
Malignant hyperthermia
What is the order in which euthanasia should take place?
Rapid loss of conciousness
Loss of motor function
Arrest of respiratory + cardiac functions
Permanent loss of brain function
Barbiturates for Euth - mechanism
Depress CNS in descending order
Cerebral cortex w/ loss of conciousness to anesthesia
Repsiratory center depression
Cardiac arrest
Barbiturates for Euth - Food animals
NEVER TO BE USED IN ANIMALS IN THE FOOD CHAIN
Dissociative agents + Alpha2 antagonist - use in euth
Can be given prior to the admin of euthanasia solutions to minimize animal distress + help with restraint + easier euthanasia for O
Acceptable euthanasia methods - Cats
IV barbiturates
Anesthetic OD
Acceptable euthanasia methods - Cattle
IV Barbiturates
Acceptable euthanasia methods - Dogs
IV barbiturates
Anesthetic OD
Acceptable euthanasia methods - Horse
IV barbiturates
Acceptable euthanasia methods - Poultry
Injected barbiturates
Anesthetic OD
Acceptable euthanasia methods - Swine
Injected barbiturates
What are the two types of local anesthetics?
Esters
– and –
Amides
Characteristics of esters
Shorter duration
Increased toxicity
How does sterochemistry effect local anesthetics?
Potency
Clinical properties
What is the purpose of salts in local anesthetics?
Increase stability + solubility
pKa of local anesthetics
7.5 to 9
Predominant form of Local anesthetic in body
Ionized form LAH+
Where is the binding site for the local anesthetics?
Inner membrane
What is steps in which local anesthetics enter the cell?
Non-ionized cross membrane
Become ionized within the cell and become stuck
Ionized form binds within the cell
aka Hydrophobic pathway
Target of local anesthetics
Block Na+ channel = inhibit neuronal firing
effect of local anesthetics on the neuron
Increased t-hold for excitation
Slowed impulse conduction
What is the amount by which the local anesthetic blocks the area dependent on?
Voltage
Firing time
What channel type are local anesthetics have the highest affinity for?
Acitvated + inactivated
What neuronal activity level do local anesthetics have the highest affinity for?
Rapidly firing
Where are the adverse effects targeted with local anesthetics?
CNS + Cardiac
Duration of action dependent on =
Time at site
Toxic effects dependent on =
1/2 life
What effect does epi have on local anesthetics?
Decreased diffusion of the drug
Prolongs duration of action
Decreases systemic absorption
Decreases risk of systemic toxicity
Amides - Elimination
Metabolized by liver CYP450s
Amides - Toxicity
seen with -
Hepatic disease
Reduced hepatic blood flow
Local anesthetics - Secretion
Renal
Esters - Metabolism
Rapid metabolism by butyrylcholinesterase in plasma
What are the four major adverse effects with local anesthetics?
CNS
CV system
Methemoglobinemia
Tissue damage
Local Anesthetics - CNS adverse effects
Skeletal muscle twitching first sign
Tonic-clonic seizures normally first clinical sign
Local Anesthetics - MetHg adverse effect
Use of prilocaine + benzocaine in cats and rabbits
Local Anesthetics - Tissue damage
Neurotoxicity
Myotoxicity
Local Anesthetics - CV system adverse effects
Prolonged PR + QRS interval due to slowed impulse conduction
Hypotension
Decreased myocardial strength
Tetracaine - Use
Opthalmological
Tetracaine - Mechanism
Ester
Tetracaine - Onset of action
> 10 mintues
Tetracaine - Duration of action
2 to 3 hours
Tetracaine - Adverse effects
Burning + Chemosis
Allergic reaction
Chornic use = keratitis
Supressed blink reflex
Lidocaine - use
Correct Vtach + SVT + PVT in dogs
Analgesia (Dogs +Horses)
Prokinetic effects (Horses)
Lidocaine - Mechanism
Amide
Lidocaine - Duration
Rapid absorption
Intermediate duration of action
Bupivacaine - Mechanism
Amide
Bupivacaine - use
Post-op pain control
Bupivacaine - Adverse affect
Greater cardiotoxicity
Binds more Na channels
Dissociates slower from the channels
Proparacaine - Mechanism
Amide
Proparacaine - Action
Fast onset
Short duration
Cats = 15 min
Dogs = 45 min
Mepivacaine - Mechanism
Amide
Mepivacaine - Use
Equine limb block
Diffuses through surrounding tissue
Les postinjection edema
Benzocaine - Mechanism
Ester
Benzocaine - Use
Topically absobed -
Lozenges
Fish anesthesia