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”
Stage II: “The stage of delirium
or involuntary movement”
 Initial administration of anesthetic
to the loss of consciousness
 CNS depression
 Tachycardia and hypertension
 Exaggerated reflexes
 Irregular / increased respiration
 Struggling, breath holding,
tachypnea, hyperventilation
 Breath holding
 Pupils dilate
 Struggling as animal becomes
ataxic
 Some analgesic effects
 Loss of voluntary control
 Cardiac arrhythmias may occur
 Eyelash and palpebral reflexes
present
 Vocalization
 Salivation
 Laryngeal spasm
Stages of Anesthesia
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
Plane II:
Surgical Anesthesia
Bradycardia
Hypotension
Capillary refill slows
Normal BP with strong pulse
Palpebral reflex diminishes
and disappears
Decrease of respiratory rate and depth
Eyeball rotates ventrally
Pupils less dilated
Abdominal muscle tone lost
Eyeball may rotate
Minimal jaw tone
Palpebral reflex present
Pedal reflex absent
Slight reaction to surgical manipulation
Dysrhythmia possibility low
Loses jaw tone
Stages of Anesthesia
Stage III (cont): “Stage of Surgical Anesthesia”
Plane III:
Plane IV:
 Deep surgical anesthesia
 Deep/ Overdose
 Intercostal and abdominal muscle tone minimum
 Dysrhythmia probability
 Weak corneal reflexes
 Respirations slow and irregular
 Diaphragmatic breathing
 Lowered HR
 Profound muscle relaxation
 Cyanosis
 Centered and dilated pupils
 Widely dilated pupil and
unresponsive to light
 Bradycardia intensifies
 Flaccid muscle tone
 Hypotension increases
 Jaw tone lost
 Respiratory rate and depth decrease
 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
Diazepam
 Phenothiazine
 Benzodiazepine
 May reduce or prevent malignant
hypothermia in swine
 Prevents seizures
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
 Rapidly passes blood-brain and
placental barriers
 Should be injected slowly to
prevent venous thrombosis and
should not be injected IA
 IM injection not recommendedpainful
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
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
Methadone hydrochloride
(Methadone, Dolophine)
 Synthetic opioid unrelated to
morphine
 2-6 hours of analgesia
 Decreases barbiturate dose by
50%
Oxymorphone hydrochloride
(Numorphan)
 Rapidly excreted
 Semi synthetic
 Does not cause vomiting
 10 times more potent than
morphine
 Slow administration recommended
 Provided effective epidural
analgesia
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
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
Pentazocine lactate (Talwin)
 1/3rd as effective as morphine
 Minimal CV effects
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)
Detomidine
 Most common sedative/analgesic in
horses and cattle
 Sedative with analgesic properties
 Short term surgical anesthetic when
combined with ketamine
 Primarily used in horses
 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
 Cardiac, respiratory and antidiuretic effects
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
Vecuronium
 More potent and shorter acting than
pancuronium
 rapid recovery
 Muscle pain and stiffness associated
 no effect on HR
 Rise in intraocular pressure
 Widely used
 Cats, swine and ponies resistant
 do not use with renal or hepatic failure
 May not be reversible
Pancuronium
 Lasts 20 to 30 minutes
 Causes increased HR
 Metabolized in liver, excreted via kidneys
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
Atracurium
 20% as potent as vecuronium
 Unstable- refrigerate
 Rapid recovery
 Intermediate muscle relaxant
Curare (dTubocurarine)
 Long acting
 Increases HR
Metocurine
 Safer than curare
Gallamine
 Widely used
Doxacurium
 Long acting
 No autonomic side effects
Mivacurium
 Long acting
 Lasts slightly longer than
succinylcholine and ½ the duration of
vecuronium
 Produces tachycardia
 No autonomic side effects
 The only non-depolarizing agent to
cross the placenta
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
Methohexital Sodium (Brevital)
 Long acting
 Ultra short acting (redistribution)
 Effective anticonvulsant
 Respiratory failure with overdose
 Excreted slowly and cumulative
 Good for induction
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
Thiobarbiturates
Thiopental sodium
Thiamylal sodium
 Ultra short acting
 Ultra short acting
 Most secreted in urine within 4
days
 IV bolus lasts approx. 15 minutes
 Initial respiratory depression
 Less CV effects than thiopental
 Increase in HR, BP and vascular
resistance
 Less cumulative than thiopental
Non-Barbiturate Anesthetics
Althesin
Chloralose
 Don’t use with barbiturates
 Minimal CV depression
 Good muscle relaxation
 Less depression of neuronal
function
 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
 Long duration, acute procedures
Urethane, N.F.
 Carcinogenic
Magnesium sulfate
 Globally depresses CNS
 Means of euthanasia after
unconsciousness
Non-Barbiturate Anesthetics
Metomidate (Hypnodil)
Propofol
 Hypnotic w/ relaxant properties
 Supports microbial growth
 Sleep without anesthesia
 Rapid uptake into CNS
Etomidate
 No depression of CV or respiratory
centers
 Does not trigger MH in swine
 Anticonvulsant properties
 Venous pain during injection
 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
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



Temperature





Charles’ law
Solubility
Partition coefficients
Pharmacokinetics
Biotransformation


Boyle’s law
Dalton’s law
MAC
Much more control
Inhalation Anesthetics
Historical Inhalant Agents
Chloroform
Cyclopropane
Diethyl ether
Fluroxene
Trichlorethylene
Inhalation Anesthetics
Nitrous oxide
Ether
 Rapid onset
 Explosive
 Minimal cardiovascular, liver and
kidney effects
 Highly irritating
 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
Methoxyflurane
 Low volatility
 High solubility
 Extensively metabolized
 Respiratory depressant
Isoflurane
 Potent and low solubility
 Rapid induction and recovery
 “Safer” than halothane
 Coronary vasodilator
Inhalation Anesthetics
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
 Lidocaine

Topical

Solution in gel or aerosol

Injectable local

Ring block

Brachial plexus block

Epidural

IV regional block

Intercostal nerve
blocks
•

Examples
Affects 2 adjacent
intercostal spaces
Muscle nerve blocks
•
For extensive surgical
manipulation
•
Interpleural admin
 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
Good Luck!