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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.

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Presentation on theme: "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."— Presentation transcript:

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 WWhat is general anesthesia? DDoses based on “average” animal BBiological variations MMetabolic rate %% fat GGeneral health SSex GGenetics TTime of day SSpecies IIndividualized sensitivity T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 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

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  1/5 th to 1/10 th as potent as fentanyl  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)  1/3 rd 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 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 PProvide superior muscle relaxation as an adjunct to general anesthesia DDO NOT PROVIDE ANALGESIA OR UNCONSCIOUSNESS PProhibited as a sole anesthetic by the Guide MMechanical ventilation required MMore difficult anesthesia management

25  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  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

33  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

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  Boyle’s law  Dalton’s 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  <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

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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