Test Review: Anesthesia

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 Today I will be covering the very broad topic of anesthesia.  Some of my slides today cover quite a bit of information and can seem a bit busy. I may read off of some slides or I may skim over information here and there to keep within my time constraints, but I wanted this presentation to be something one might go back and refer to when studying for a test. Hopefully it helps.

Overview General Anesthesia Pharmacokinetics Types of 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 Today we’ll go over general anesthesia- what is it? What are these stages of anesthesia everyone talks about? And special considerations. We’ll talk a little about pharmacokinetics- What method of action drugs take and modifying factors We’ll go over the types of anesthesia, which is a good deal of what you will be studying We’ll talk about equipment and then quickly 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 General anesthesia is defined as … a state of unconsciousness, muscle relaxation, and loss of sensation throughout the body Doses are based on the average animal, but what defines the average animal? What is average weight? Average health? There are numerous biological variations that play a role in anesthetic decisions. the higher the metabolic rate, the more anesthetic needed Less anesthetic is needed for animals with a high % of fat Animals in poor health may need less or special anesthetic considerations The sex and species of animal has been linked to how much anesthetic is needed Animals may be genetically predispositioned to certain anesthetic complications or respond differently to anesthetics due to genetics. Malignant hyperthermia is a good example of this. Above all, it is important to remember that 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 There are 4 stages of anesthesia. The stage from the initial administration of anesthetic to the loss of conciousness is known as “The stage of voluntary movement”. In this stage we see………. Stage II is “The stage if delirium or involuntary movement” We now see CNS depressoin……..

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 If you choose to remember just one of the stages, which is not necessarily recommended, make sure it’s stage III. This is the stage of surgical anesthesia. In stage III we see normal pulse rate, relaxation of muscles and a loss of swallowing/vomiting reflexes. Stage III is separated into 3 or 4 planes depending on which textbook you read. In plane I, we see the following……. Stage III, Plane II is surgical anesthesia. In this plane we see…….

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 When an animal starts exhibiting minimal muscle tone, ……….. They are crossing over into deep surgical plane of anesthesia, also known as Stage III, Plane III. Plane IV walks the line between deep anesthesia and overdose. You are likely to see……

Pharmacokinetics Action of anesthetic on CNS Inhalants vs. Injectables
Partial pressure gradients Inhalants vs. Injectables Distribution and clearance Modifying factors Concentration Plasma pH Protein binding Hydration Multiple drugs present Pharmacokinetics- What are the methods behind anesthesia? Anesthetic drugs reach equilibrium by passive mechanisms.

Effects of Disease Cardiovascular dysfunction Pulmonary 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 Different diseases effect anesthesia in different ways. With cardiovascular dysfuncion, animals are prone to fluid overload and arrhythmias.* Most anesthetics cause pulmonary depression. Intubation and ventilation are key. Anesthesia for a patient with pulmonary depression is a balancing act between lowering doses and preventing anxiety.* With neurologic disease, you want to watch for respiratory depression and loss of intracellular fluid and Cerebral blood flow regulation Nitrous oxide is contraindicated for both pulmonary and neurologic diseases.* Most injectable anesthetics are eliminated through the kidneys. With renal disease we see an increase in acidity, a decrease in rate of filtration and a rise in potassium levels.*

Effects of Disease Hepatic disease Gastrointestinal 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 With liver disease we must watch for lowered elimination rate and coagulation. Propofol, ketamine and inhalation anesthesia are the safest. Ace, thiobarbiturates, and alpha 2 adrenergic agents are contraindicated. A damaged GI can release toxins. You may note a decrease in cardiac function and ventilation. And finally, we must look at anesthesia with easy reversal when dealing with endocrine disorders.

Pre-anesthetic Agents and Adjuncts
Anticholinergics Tranquilizers Opioids Alpha2adrenergic agonists Alpha2adrenergic antagonists Tranquilizer-opioid combinations Paralytic agents Types of anesthesia: Not the most exciting of topics, but probably the meat and potatoes of what most of you will be studying. Pre-anesthetic agents and adjuncts include…….

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 READ SLIDE

Anticholinergics Atropine Sulfate Glycopyrrolate
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 The two main drugs in this category are Atropine Sulfate and Glycopyrrolate. Note that atropine esterase occurs in cats, rats and rabbits and is minimally effective in sheep and goats. Glyco takes longer to kick in for ruminants, but is in general a longer lasting anticholinergic.

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 READ SLIDE

Tranquilizers Acepromazine Maleate Droperidol Diazepam 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 The 5 tranquilizers include Acepromazine, Droperidol, Diazepam, Midazolam and Flumazanil. They can prevent MH, like Ace, or decrease barbiturate dosages like Droperidol. Diazepam is widely used to prevent seizures as it rapidly passes the blood brain barrier, and should be injected slowly IV, not IM

Tranquilizers Midazolam Flumazenil 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 While midazolam is suitable for IM injection, it has a shorter duration of action and clearance than diazepam and may cause behavioral changes in dogs and cats Flumazenil rapidly reverses the CNS action of benzodiazepine without anxiety tachycardia or hypertension.

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 READ SLIDE

Opioids Morphine sulfate Meperidine hydrochloride (Demerol, Pethidine)
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 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 There are 10 different opioids you should know. These include: morphine, meperidine (with an analgesic effect 1/10 of morphine), the synthetic opioid methadone, which lasts 2-6 hours and decreases barbiturate doses by 50%, the semisynthetic oxymorphone, 10 X as potent as morphine and used successfully in epidural analgesia, …

Opioids Fentanyl citrate Carfentanil citrate Sufentanil Alfentanil
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 times more potent than morphine SC More rapid onset than fentanyl or sufentanyl Used primarily for the capture of wild animals Fentanyl citrate which is 250 x as potent as morphine with a rapid onset and a short duration is also known for little cardiac output or blood pressure effects. Carfentanyl citrate is 10,000 x more potent than morphine and used in wild animal capture Sufentanyl is 5-10x as potent as fentanyl and unpredictable in dogs. It provides neuroleptanalgesia when combined with tranquilizers and glyco Alfentanil, up to 1,000 x as potent as morphine and also used in wild animal capture.

Opioids Pentazocine lactate (Talwin) Buprenorphine (Buprenex)
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 ( minutes) Excreted in feces The commonly used buprenorphine, x as potent as morphine but with less of an analgesic effect and Last but not least pentazocine lactate, less effective than morphine but demonstrating 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 READ SLIDE *half way through!!

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 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 Agonists include Xylazine hydrochloride, commonly known as Rompun, and Medetomidine Xylazine is most commonly used in horses and cattle. It can be combined with ketamine to produce short term anesthesia, it has poor efficacy in swine and may cause emesis in cats and dogs. It also effects blood glucose levels Medetomidine is the more potent Alpha 2 Adrenergic Agonist, effecting Blood pressure and respiration rate dose dependently

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 Here we have the Alpha 2 Adrenergic Antagonists or the reversal agents Yohimbine reverses xylazine and ketamine/pentobarb combinations when combined with 4-aminopyridine Tolazoline reverses xylazine and Xylazine drug combinations Atipamezole has a greater selectivity ratio than Yohimbine and should be delivered slowly IV.

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 Tranquilizer-Opioid Combinations provide neuroleptanalgesia and intense analgesic action with short duration. Fentanyl citrate Droperidol is known as Innovarvet. It has a wide margin of safety and can be 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 READ SLIDE

Paralytics Succinylcholine Pancuronium Vecuronium Pipecuronium
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 The 7 types of paralytics include Rocuronium, Curare, Metocurine, Gallamine, Atracurium, Doxacurium, and Mivacurium. Each have their pluses and minuses. To reverse these paralytics, one should use Anticholinerases such as edrophonium, neostigmine or pyridostigmine. Calcium may also be used, but is only partially effective. Is everyone still with me? It’s almost as if I’m performing actual anesthesia on the audience today and not just giving a lecture about anesthesia, right?  I was trying to think of a good anesthesia joke to tell half way through the presentation, but they were either too dry or too racy for me to get through without a red face. Anyone have one? No?

Paralytics (continued)
Rocuronium 20% as potent as vecuronium Rapid recovery Curare (dTubocurarine) Long acting Increases HR Metocurine Safer than curare Gallamine 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

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 O.K. on to Injectable Anesthesia. READ SLIDE

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 Barbiturates are divided into the categories of ultra short, short, intermediate and long acting. Barbiturates depress the central nervous system so we see respiratory depression, Cardiovascular depression, decreased blood pressure and BMR and reduced stroke volume. They are metabolized in the liver and should be avoided in animals less than 3 months old due to the inability of their livers to metabolize barbiturates appropriately. They are in fact hypnotic sedatives crossing cell walls and the placenta The glucose effect is a unique re-anesthetizing action seen with some barbiturates The preferred method of administration is IV, but you should watch out for barbiturate slough as they are strongly alkaline. If you accidentally inject perivascularly, the area may be treated with SC fluids and lidocaine. Barbiturates can be oxybarbiturates or thiobarbiturates.

Oxybarbiturates Phenobarbital Sodium Pentobarbital 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 Oxybarbiturates include phenobarbital sodium, pentobarbital sodium and methohexital sodium also known as brevital. Phenobarbital is a long acting anticonvulsant. Pentobarbital is a short acting barbiturate. You may see a spike in Heart rate after initial administration followed closely by a decrease in heart rate and blood pressure. Prolonged use of pentobarb leads to shock-like tendencies such as decreased systolic blood pressure, stroke volume, pulse pressure, cardiac output, pH and body temp. Tranquilizers are advised when using pentobarb for a smooth recovery. Methohexital is ultra short acting due to rapid redistribution. It is a good drug for induction.

Thiobarbiturates Thiopental sodium Thiamylal 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 Thiopental sodium and Thiamylal are both ultra short acting Thiobarbiturates. With thiopental we see an initial respiratory depression followed by an increase in heart rate, blood pressure and vascular resistance. It is metabolized and excreted within 4 days Thiamylal lasts for approximately 15 minutes. It is less cumulative than thiopental with less effect on the cardiovascular system.

Non-Barbiturate Anesthetics
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 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 There are 10 non-barbiturate anesthetics. With Althesin you get good muscle relaxation, but it may cause allergic reactions and is not to be used with other barbiturates Chloral Hydrate is a good hypnotic but a poor anesthetic. The amount needed for true anesthesia is close to the lethal dose. Chloralose may be used for long duration, acute procedures. It is a chosen drug for certain cardiovascular monitoring studies as it causes minimal cardiovascular depression. Urethane is not used much as it is carcinogenic Magnesium sulfate globally depresses the central nervous system. It is a documented means of euthanasia after unconsciousness in the panel

Non-Barbiturate Anesthetics
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 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 is a hypnotic, producing sleep without anesthesia. Etomidate has anticonvulsant properties and causes no cardiovascular or respiratory depression. Keep in mind that it is painful upon injection. Propofol has a rapid uptake into the CNS, provides minimal analgesia, and promotes a quick, smooth recovery. It is widely used for induction purposes. Note that it does support microbial growth. Propanidid has an extremely short duration of action and is thus difficult to administer fast enough to have any effect. It may also cause severe respiratory depression and hypotension in dogs. MS222 is our final non-barbiturate anesthetic and is used mainly in 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 Dissociative Anesthetics are named such because they interrupt transmission from the unconscious to the conscious brain. They are characterized by a cataleptic state in which the eyes remain open and nystagmus is present Ketamine is the least potent dissociative. It has rapid onset and redistribution. There may be some tissue irritation due to it’s pH of Ketamine’s analgesic effects are greater for somatic pain than visceral pain. You will see a decrease in respiratory rate with Ketamine administration and it may cause hallucinatory behavior. Those of you familiar with non-human primates on Ketamine should be able to relate. Telazol is a combination of tiletamine hydrochloride and zolazepam. It has a wide safety margin with rapid and smooth induction/recovery. Telazol is a good muscle relaxant with analgesic effects, sometimes causing increased heart rate and respirations. You may also see a decrease in pressure with after Telazol administration.

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 anesthesia is administration and elimination of an anesthetic through the lungs or respiration. It is dependent upon many things. MAC is the concentration at which 50% of subjects respond to a painful stimulus.

Inhalation Anesthetics
Historical Inhalant Agents Chloroform Cyclopropane Diethyl ether Fluroxene Trichlorethylene Historical Inhalant Agents: Chloroform, Cyclopropane, Diethyl ether, fluroxene and trichlorethylene. I’m not going to dwell much on them other than to say that there are reasons we don’t use them anymore….. High volatility being one of them.

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 There are 7 inhalation anesthetics that we do still use- Nitrous oxide, halothane, ether, methoxyflurane, isoflurane, desflurane and sevoflurane. Nitrous oxide is known for rapid onset, used a great deal with induction. It has minimal cardiovascular, liver and kidney effects, but one should be cautious of pneumothorax, blood embolus, increased middle ear pressure and diffusion hypoxia above all, which is……………………… Remember to always use Nitrous oxide in a 2:1 ratio. Halothane is a highly volatile inhalant with a potent and rapid onset. It causes respiratory depression and may be mixed with thymol for stability. Ether is an explosive and highly irritating inhalant anesthetic. Methoxyflurane has a low volatility, but is highly soluble and extensively metabolized. Isoflurane is potent and has a low solubility. People use it because of the rapid induction and recovery. It is safer to use than halothane, but is a coronary vasodilator, which one must remember when looking at different animal models. Though inhalation anesthetics may safe and easy to use, they’re not always the best choice.

Desflurane Very rapid induction and recovery Lower solubility than isoflurane Respiratory irritant Requires heated vaporizer Sevoflurane Lower solubility than isoflurane, halothane or methoxyflurane Desflurane and Sevoflurane provide a very rapid induction and recovery, having a lower solubility than iso. Note that desflurane is a respiratory irritant and requires a special heated vaporizer. I don’t know if you guys can see this, but this is an advertisement for a nitrous oxide exhibition. It reads “gallons of gas will be prepared and administered to all in the audience who desire to inhale it. Men will be invited from the audience to protect those under the influence of the gas from injuring themselves or others”. Can you imagine!? The good old days of anesthesia, right?!

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 Local and regional anesthesia may be used in topical form, in solution as a gel or aerosol, or may be injected locally. Different types of local injectable anesthesia include ring block, brachial plexus block, epidurals, IV regional block, intercostal nerve block and muscle nerve block, used for extensive surgical manipulation. Local injectable drugs include lidocaine, proparacaine, benzocaine, tetracaine and butacaine, among others.

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 Physical methods of anesthesia as demonstrated by little bunny foo foo. Hypothermia allows organs to survive with reduced blood supply for longer periods of time. There are risks associated, including profound CNS and vital organ depression and prolonged clotting time. At temperatures less than 28 degrees celcius, you run the risk of ventricular fibrillation. Electronarcosis is a questionably humane method of anesthesia in which electrical impulses are delivered via electrodes applied to the head. Not only do you see convulsions during induction but it is difficult to monitor Acupuncture is another physical method of anesthesia, useful mainly for chronic pain.

Equipment Anesthesia machine Medical gas cylinders Airway maintenance
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 When it comes to equipment you should know the components of an anesthesia machine. Vaporizers are classified by method of output, vaporization method and location within the circuit. You should know the difference between a vaporizer in circuit and out of circuit. Know that vaporizers out of circuit allow for a more precise adjustment of anesthetic dosage. Know what a rebreathing, non-rebreathing, and semi-closed circuit is and which animals each is used for. For example when oxygen consumption equals the rate of flow you have a total rebreathing circuit. Know why we have a CO2 absorber or active scavenging. You should know what color an oxygen, nitrous oxide or CO2 tank is Also under equipment, you have endotracheal tubes. What is the difference between a murphy tube and a cole tube- A murphy tube has the balloon attached, right? What is the difference between a miller, Mcintosh and potterson laryngoscope blade?

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 So here’s what you’ve been waiting for…… What you really want to know. We have been asked numerous times for direction as to what you are to study, but like I said at the beginning of the presentation, this is a very broad topic. I think the point when taking or giving the test is to make sure people have some familiararity with all of it.

Good Luck! Good Luck! And now I will turn the floor over to Angela who will be speaking about pre-, peri- and post-operative care.

Test Review: Anesthesia

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