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Test%20Review:%20Anesthesia

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Title: Test%20Review:%20Anesthesia


1
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
2
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

3
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

4
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

5
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
  • 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

6
Stages of Anesthesia
  • 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

7
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

8
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

9
Effects of Disease
  • Hepatic disease
  • Acepromazine, thiobarbiturates and a-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

10
Pre-anesthetic Agents and Adjuncts
  • Anticholinergics
  • Tranquilizers
  • Opioids
  • Alpha2adrenergic agonists
  • Alpha2adrenergic antagonists
  • Tranquilizer-opioid combinations
  • Paralytic agents

11
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

12
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

13
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

14
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

15
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

16
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

17
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

18
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

19
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

20
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

21
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

22
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

23
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

24
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

25
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

26
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

27
Paralytic Reversal Agents
  • Anticholinerases
  • Bradycardia, arrhythmias, secretions
  • CNS stimulation
  • Edrophonium, neostigmine, pyridostigmine
  • 4 Aminopyridine and Guanidine
  • Calcium
  • Only partially effective

28
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

29
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

30
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

31
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

32
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
  • Dont 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

33
Non-Barbiturate Anesthetics
  • 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

34
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

35
Inhalation Anesthesia
  • Administration and elimination through lungs
  • Dependent upon
  • Vapor pressure
  • Boyles law
  • Daltons law
  • Temperature
  • Charles law
  • Solubility
  • Partition coefficients
  • Pharmacokinetics
  • Biotransformation
  • MAC
  • Much more control

36
Inhalation Anesthetics
  • Historical Inhalant Agents
  • Chloroform
  • Cyclopropane
  • Diethyl ether
  • Fluroxene
  • Trichlorethylene

37
Inhalation Anesthetics
  • 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

38
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

39
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

40
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
  • lt28C 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

41
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

42
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

43
Good Luck!
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