Anesthesia_Test_Review-Jenifer_Sweet.ppt

Test Review:
Anesthesia
Jenifer Sweet, B.A., S.R.S., L.A.T.
MPI Research
in coordination with
The Academy of Surgical Research
Testing Committee

Overview
General Anesthesia
Definition
Stages of Anesthesia
Considerations
Pharmacokinetics
Method of action
Modifying factors
Types of Anesthesia
Pre-anesthetic Agents and Adjuncts
Injectable Anesthetic Agents and
Adjuncts
Inhalation Anesthesia
Local and Regional Anesthesia
Physical Methods of Anesthesia
Equipment
Review

General Anesthesia
What is general anesthesia?
Doses based on “average”
animal
Biological variations
Metabolic rate
% fat
General health
Sex
Genetics
Time of day
Species
Individualized sensitivity
The perfect anesthetic agent
does not exist

Stages of Anesthesia
4 Stages of Anesthesia
Stage I: “The stage of
voluntary movement”
Initial administration of anesthetic
to the loss of consciousness
Tachycardia and hypertension
Irregular / increased respiration
Breath holding
Pupils dilate
Struggling as animal becomes
ataxic
Some analgesic effects
Stage II: “The stage of delirium
or involuntary movement”
CNS depression
Loss of voluntary control
Exaggerated reflexes
Struggling, breath holding,
tachypnea, hyperventilation
Cardiac arrhythmias may occur
Eyelash and palpebral reflexes
present
Vocalization
Salivation
Laryngeal spasm

Stage III: “Stage of Surgical Anesthesia”
Pulse rate returns to normal
Muscles relax
Swallowing and vomiting reflexes lost
3-4 planes
Plane I:
Eyeball movement ceases
Normal BP with strong pulse
Decrease of respiratory rate and depth
Pupils less dilated
Eyeball may rotate
Palpebral reflex present
Slight reaction to surgical manipulation
Loses jaw tone
Plane II:
Surgical Anesthesia
Bradycardia
Hypotension
Capillary refill slows
Palpebral reflex diminishes
and disappears
Eyeball rotates ventrally
Abdominal muscle tone lost
Minimal jaw tone
Pedal reflex absent
Dysrhythmia possibility low

Stage III (cont): “Stage of Surgical Anesthesia”
Plane III:
Deep surgical anesthesia
Intercostal and abdominal muscle tone minimum
Weak corneal reflexes
Diaphragmatic breathing
Profound muscle relaxation
Centered and dilated pupils
Bradycardia intensifies
Hypotension increases
Respiratory rate and depth decrease
Plane IV:
Deep/ Overdose
Dysrhythmia probability
Respirations slow and irregular
Lowered HR
Cyanosis
Widely dilated pupil and
unresponsive to light
Flaccid muscle tone
Jaw tone lost
Sphincter control lost

Pharmacokinetics
 Action of anesthetic on CNS
 Partial pressure gradients
 Inhalants vs. Injectables
 Distribution and clearance
 Modifying factors
Concentration
Plasma pH
Protein binding
Hydration
Multiple drugs present

Effects of Disease
Cardiovascular dysfunction
Most anesthetics cause CV
depression
Animals prone to fluid overload &
arrhythmias
Pulmonary dysfunction
Most anesthetics cause
pulmonary depression
Balancing between lowering
doses and preventing anxiety
Intubation and ventilation are key
Nitrous oxide contraindicated
Neurologic disease
Loss of ICF and CBF regulation
Watch for respiratory depression
Nitrous oxide contraindicated
Renal disease
Stress and anesthetic agents
decrease rate of filtration
Reduction in elimination = increase
in acidity and plasma
concentrations
Lingering effects
K+ increases in serum

Effects of Disease
 Hepatic disease
Acepromazine, thiobarbiturates and α-2-adrenergic agents
contraindicated
Propofol, ketamine and inhalation the safest
Lowered elimination rate and coagulation
 Gastrointestinal disease
Damaged GI can release toxins
Decrease in cardiac function and ventilation
 Endocrine disorders
Select anesthesia for easiest reversibility

Pre-anesthetic Agents and Adjuncts
 Anticholinergics
 Tranquilizers
 Opioids
 Alpha2adrenergic agonists
 Alpha2adrenergic antagonists
 Tranquilizer-opioid combinations
 Paralytic agents

Anticholinergics
Block acetylcholine receptors
Reduce secretions
Prevent vagal inhibition and GI stimulation
Reduce vagus nerve response (vomiting and laryngospasm)
Promote bronchodilation
Dilate the pupil
Treatment of choice for opioid, xylazine and vagal reflex activity induced
bradycardia

Anticholinergics
Atropine Sulfate
Contraindicated with tachycardia,
constipation and obstruction
May cause thick mucus secretions
in cats
Atropine esterase occurs in cats,
rats, and rabbits
Minimally effective in sheep and
goats
Increased incidence of bloat
Prolongs thiopental anesthesia
Overdose: dry mucous
membranes, thirst, dilated pupils
and tachycardia (dogs most
susceptible)
Can be treated with physostigmine
IV over several minutes
Glycopyrrolate
Reduces diffusion over blood brain
or placental membranes
Lasts longer than atropine
Prevents ketamine/xylazine
associated bradycardia in rabbits
Longer onset of action in ruminants

Tranquilizers
NO ANALGESIC EFFECTS
Relieve anxiety
Decrease anesthetic dosages
Reduce histamine release and vomiting
Make anesthetic recovery smoother
Promote skeletal muscle relaxation and vasodilatation
May lead to hypotension and excessive heat loss
May raise seizure thresholds/ act as anticonvulsants

Tranquilizers
Acepromazine Maleate
Phenothiazine
May reduce or prevent malignant
hypothermia in swine
Droperidol
Butyrophenone
Alpha-adrenergic antagonist
May prevent epinephrine induced
dysrhythmias
Decreases barbiturate doses
Primarily used as a component of
InnovarVt in a mixture with fentanyl
Diazepam
Benzodiazepine
Prevents seizures
Rapidly passes blood-brain and
placental barriers
Should be injected slowly to
prevent venous thrombosis and
should not be injected IA
IM injection not recommended-
painful

Tranquilizers
Midazolam
Benzodiazepine
Shorter duration of action and
clearance than diazepam
May cause behavioral changes in
dogs and cats
Suitable for IM injection
Can be mixed with other
preanesthetic agents
Flumazenil
Reverses CNS action of
benzodiazepine without anxiety,
tachycardia, or hypertension
Rapid action (24 minutes)
Replaced aminophylline and
physostigmine

Opioids
Depress CNS
Lower the amount of anesthetic agents
needed
Do not cause unconsciousness at
therapeutic levels
Addictive
Most are controlled substances
Best for continuous dull pain

Opioids
Methadone hydrochloride
(Methadone, Dolophine)
Synthetic opioid unrelated to
morphine
2-6 hours of analgesia
Decreases barbiturate dose by
50%
Oxymorphone hydrochloride
(Numorphan)
Semi synthetic
10 times more potent than
morphine
Provided effective epidural
analgesia
Morphine sulfate
Stimulates vomiting
Decreases BMR and body temp
Variable effects
Poor effects on neuropathic pain
Meperidine hydrochloride
(Demerol, Pethidine)
Analgesic effect 1/10 of morphine
Rapidly excreted
Does not cause vomiting
Slow administration recommended

Opioids
Fentanyl citrate
250 times more potent than
morphine
Rapid onset of action
Short duration; peak at 30 minutes
Depressed respiration
Exaggerated response to loud
noise
Little cardiac output or BP effects
Carfentanil citrate
10,000 times more potent than
morphine
Used primarily for capture of wild
animals
Sufentanil
5 to 10 times as potent as fentanyl
Provided unpredictable anesthesia
in dogs
Provides neuroleptanalgesia when
combined with tranquilizers and
glycopyrrolate
Alfentanil
1/5th
to 1/10th
as potent as fentanyl
80-1000 times more potent than
morphine SC
More rapid onset than fentanyl or
sufentanyl
Used primarily for the capture of
wild animals

Opioids
Pentazocine lactate (Talwin)
1/3rd
as effective as morphine
Minimal CV effects
Buprenorphine (Buprenex)
25 to 30 times as potent as
morphine
Max analgesic effect less than
morphine
Slow onset of action (20-30
minutes)
Excreted in feces

Alpha 2 Adrenergic Agonists
Produce sedation, muscle relaxation and analgesia
Not potent respiratory depressant
Non-addictive
Anticonvulsants
Wide range of drug interactions
Barbiturate, inhalant and dissociative anesthetic doses should be lowered
used in combination with alpha 2 adrenergic agonists

Alpha 2 Adrenergic Agonists
Xylazine hydrochloride (Rompun)
 Most common sedative/analgesic in
horses and cattle
 Short term surgical anesthetic when
combined with ketamine
 Effects within 10-15 minutes IM or 3-5
minutes IV
 IV bolus causes bradycardia, hypotension
followed by decreased CO and BP
 Poor efficacy in swine
 Wide margin of safety
 May cause emesis in cats and dogs
 Reduces insulin secretion, effecting blood
glucose levels
Medetomidine
 More potent than xylazine
 BP and RR decreases dose dependent
Detomidine
 Sedative with analgesic properties
 Cardiac, respiratory and antidiuretic
effects
 Primarily used in horses
Dexmedetomidine (Precedex)
 More potent than medetomidine
 Sedative, analgesic, sympatholytic and
anxiolytic effects
 Sedation without respiratory depression
 Shortens time to extubation
 Reduces anesthetic dosages
Clonidine
Alpha-methyldopa

Alpha 2 Adrenergic Antagonists
 Used as reversal agents for injectable anesthetics
Yohimbine
Reverses xylazine
Also reverses ketamine and pentobarbital combinations when combined with
4-aminopyridine.
Tolazoline
Reverses xylazine and some anesthetic drug combinations with xylazine
Atipamezole
Selectivity ration 200 to 300 times higher than yohimbine
Rapid IV doses may cause death or severe hypotension and tachycardia

Tranquilizer-Opioid Combinations
 Provide neuroleptanalgesia
 Intense analgesic action with short duration
Fentanyl citrate Droperidol (Innovarvet)
Wide margin of safety with easy recovery
Partially reversed with opioid antagonists

Paralytics
 Provide superior muscle relaxation as an adjunct to general anesthesia
 DO NOT PROVIDE ANALGESIA OR UNCONSCIOUSNESS
 Prohibited as a sole anesthetic by the Guide
 Mechanical ventilation required
 More difficult anesthesia management

Paralytics
Succinylcholine
 Depolarizing neuromuscular paralytic
 Marked twitching for 30 minutes before
muscle relaxation
 Muscle pain and stiffness associated
 Rise in intraocular pressure
 Cats, swine and ponies resistant
 May not be reversible
Pancuronium
 Lasts 20 to 30 minutes
 Causes increased HR
 Metabolized in liver, excreted via
kidneys
Vecuronium
 More potent and shorter acting than
pancuronium
 rapid recovery
 no effect on HR
 Widely used
 do not use with renal or hepatic failure
Pipecuronium
 Long acting- twice duration of
pancuronium
 2 to 4 times as potent as pancuronium
 Rapid onset
 Retained in kidneys for days
 no effect on HR

Paralytics (continued)
Rocuronium
 20% as potent as vecuronium
 Rapid recovery
Curare (dTubocurarine)
 Long acting
 Increases HR
Metocurine
 Safer than curare
Gallamine
 Long acting
 Produces tachycardia
 The only non-depolarizing agent to
cross the placenta
Atracurium
 Unstable- refrigerate
 Intermediate muscle relaxant
 Widely used
Doxacurium
 Long acting
 No autonomic side effects
Mivacurium
 Lasts slightly longer than
succinylcholine and ½ the duration of
vecuronium
 No autonomic side effects

Paralytic Reversal Agents
Anticholinerases
 Bradycardia, arrhythmias, secretions
 CNS stimulation
 Edrophonium, neostigmine, pyridostigmine
 4 Aminopyridine and Guanidine
Calcium
 Only partially effective

Injectable Anesthetic Agents and Adjuncts
 Enter blood stream for transport to target tissues
 Require redistribution
 Generally detoxified in liver and excreted via kidneys
 Metabolism based on first order kinetics
 Constant fraction metabolized in a given period
 Less control of elimination process
 Barbiturates

Barbiturates
Divided into Ultra short, Short, Intermediate and Long acting
Depress CNS neurons
May lead to respiratory depression, central and peripheral CV depression,
decreased BP and BMR, reduced stroke volume and increased HR
Hypnotic sedatives
Cross cell walls and placental membrane
Glucose effect in some animals
Should not be administered to animals less than 3 months old
IV administration preferred
Barbiturate slough may occur
Oxybarbiturates
Thiobarbiturates

Oxybarbiturates
Phenobarbital Sodium
Long acting
Effective anticonvulsant
Excreted slowly and cumulative
Pentobarbital Sodium
 Short acting
 Initial spike in HR followed by a
decrease in HR and BP
 Prolonged use leads to decreased
systolic BP, stroke volume, pulse
pressure, CO, pH, and BT (shock-like)
 Crosses placenta
 Tranquilizers advised for smooth
recovery
Methohexital Sodium (Brevital)
Ultra short acting (redistribution)
Respiratory failure with overdose
Good for induction

Thiobarbiturates
Thiopental sodium
Ultra short acting
Most secreted in urine within 4
days
Initial respiratory depression
Increase in HR, BP and vascular
resistance
Thiamylal sodium
Ultra short acting
IV bolus lasts approx. 15 minutes
Less cumulative than thiopental
Less CV effects than thiopental

Non-Barbiturate Anesthetics
Chloralose
Minimal CV depression
Less depression of neuronal
function
Long duration, acute procedures
Urethane, N.F.
Carcinogenic
Magnesium sulfate
Globally depresses CNS
Means of euthanasia after
unconsciousness
Althesin
Don’t use with barbiturates
Good muscle relaxation
May cause allergic reaction
Chloral Hydrate, U.S.P.
Oral admin may cause vomiting
Depresses cerebrum
Good hypnotic/poor anesthetic
Amount needed for anesthesia
close to lethal dose

Propofol
Supports microbial growth
Rapid uptake into CNS
Quick and smooth recovery
Minimal analgesic effects
Propanidid
Extremely short duration of action
Difficult to administer fast enough
Severe respiratory depression and
hypotension in dogs
Tricaine Methanesulfonate (MS222)
Anesthesia of fish and amphibians
Metomidate (Hypnodil)
Hypnotic w/ relaxant properties
Sleep without anesthesia
Etomidate
No depression of CV or respiratory
centers
Does not trigger MH in swine
Anticonvulsant properties
Venous pain during injection
Non-Barbiturate Anesthetics

Dissociative Anesthetics
 Interrupts transmission from the unconscious to the conscious brain
 Characterized by a cataleptic state in which eyes remain open and
nystagmus present
Ketamine
Least potent
Rapid onset of action
Rapid redistribution
Tissue irritation due to low pH (3.5)
Analgesic effects greater for
somatic pain than visceral pain
Transient decrease in respiratory
rate
Hallucinatory behavior
Telazol
Tiletamine hydrochloride and
Zolazepam
Wide safety margin
Rapid and smooth
induction/recovery
Good muscle relaxant
Lingering analgesic effects
May cause increased HR and
respirations
Decrease in MAP

Inhalation Anesthesia
 Administration and elimination through lungs
 Dependent upon:
 Vapor pressure
 Boyle’s law
 Dalton’s law
 Temperature
 Charles’ law
 Solubility
 Partition coefficients
 Pharmacokinetics
 Biotransformation
 MAC
 Much more control

Inhalation Anesthetics
Historical Inhalant Agents
Chloroform
Cyclopropane
Diethyl ether
Fluroxene
Trichlorethylene

Nitrous oxide
Rapid onset
Minimal cardiovascular, liver and
kidney effects
May cause pneumothorax, blood
embolus, increase in middle ear
pressure
Must be combined with another
agent
Beware of diffusion hypoxia
Halothane
Potent and rapid onset
High volatility
Respiratory depression
Mixed with thymol for stability
Ether
Explosive
Highly irritating
Methoxyflurane
Low volatility
High solubility
Extensively metabolized
Respiratory depressant
Isoflurane
Potent and low solubility
Rapid induction and recovery
“Safer” than halothane
Coronary vasodilator

Desflurane
Very rapid induction and recovery
Lower solubility than isoflurane
Respiratory irritant
Requires heated vaporizer
Sevoflurane
Very rapid induction and recovery
Lower solubility than isoflurane,
halothane or methoxyflurane

Local and Regional Anesthesia
 Administration
 Topical
 Solution in gel or aerosol
 Injectable local
 Ring block
 Brachial plexus block
 Epidural
 IV regional block
 Intercostal nerve
blocks
• Affects 2 adjacent
intercostal spaces
 Muscle nerve blocks
• For extensive surgical
manipulation
• Interpleural admin
Examples
 Lidocaine
 Proparacaine
 Benzocaine
 Tetracaine
 Butacaine

Physical Methods of Anesthesia
Hypothermia
 Some vital organs can survive for longer
periods at low temps with reduced blood
supply
 Risks profound CNS and vital organ
depression
 <28°C may cause VF
 Prolonged clotting time
 3 methods of hypothermia
 Surface
 Body cavity
 extracorporeal
Electronarcosis
 Delivered via electrodes applied to head
 Convulsions during induction
 Difficult to monitor and questionably
humane
Acupuncture
 Useful for chronic pain

Equipment
 Anesthesia machine
 Components
 Vaporizer in circuit or out of circuit?
 Rebreathing, non-rebreathing, semi-closed
circuits
 CO2 absorber/ Scavenging
 Medical gas cylinders
 Color codes
 Airway maintenance
 Endotracheal tubes
 Laryngoscope blades

Review:
What do you need to know?
 Know your drugs- what group they belong to and what
they do
 Know the stages of anesthesia
 Have a basic understanding of the pharmacokinetics
behind anesthesia
 Know your patient and how biological variations can
effect anesthesia
 Be familiar with anesthetic equipment
 Areas not covered in depth: fasting, thermoregulation,
fluids and acid/base balance

Anesthesia_Test_Review-Jenifer_Sweet.ppt

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