Presentation on theme: "Test Review: Anesthesia"— Presentation transcript:
1 Test Review: Anesthesia Jenifer Sweet, B.A., S.R.S., L.A.T.MPI Researchin coordination withThe Academy of Surgical Research Testing CommitteeToday 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.
2 Overview General Anesthesia Pharmacokinetics Types of Anesthesia DefinitionStages of AnesthesiaConsiderationsPharmacokineticsMethod of actionModifying factorsTypes of AnesthesiaPre-anesthetic Agents and AdjunctsInjectable Anesthetic Agents and AdjunctsInhalation AnesthesiaLocal and Regional AnesthesiaPhysical Methods of AnesthesiaEquipmentReviewToday 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 factorsWe’ll go over the types of anesthesia, which is a good deal of what you will be studyingWe’ll talk about equipment and then quickly review
3 General Anesthesia What is general anesthesia? Doses based on “average” animalBiological variationsMetabolic rate% fatGeneral healthSexGeneticsTime of daySpeciesIndividualized sensitivityThe perfect anesthetic agent does not existGeneral anesthesia is defined as … a state of unconsciousness, muscle relaxation, and loss of sensation throughout the bodyDoses 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 neededLess anesthetic is needed for animals with a high % of fatAnimals in poor health may need less or special anesthetic considerationsThe sex and species of animal has been linked to how much anesthetic is neededAnimals 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.
4 Stages of Anesthesia 4 Stages of Anesthesia Stage I: “The stage of voluntary movement”Initial administration of anesthetic to the loss of consciousnessTachycardia and hypertensionIrregular / increased respirationBreath holdingPupils dilateStruggling as animal becomes ataxicSome analgesic effectsStage II: “The stage of delirium or involuntary movement”CNS depressionLoss of voluntary controlExaggerated reflexesStruggling, breath holding, tachypnea, hyperventilationCardiac arrhythmias may occurEyelash and palpebral reflexes presentVocalizationSalivationLaryngeal spasmThere 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……..
5 Stages of Anesthesia Stage III: “Stage of Surgical Anesthesia” Pulse rate returns to normalMuscles relaxSwallowing and vomiting reflexes lost3-4 planesPlane I:Eyeball movement ceasesNormal BP with strong pulseDecrease of respiratory rate and depthPupils less dilatedEyeball may rotatePalpebral reflex presentSlight reaction to surgical manipulationLoses jaw tonePlane II:Surgical AnesthesiaBradycardiaHypotensionCapillary refill slowsPalpebral reflex diminishes and disappearsEyeball rotates ventrallyAbdominal muscle tone lostMinimal jaw tonePedal reflex absentDysrhythmia possibility lowIf 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…….
6 Stages of Anesthesia Stage III (cont): “Stage of Surgical Anesthesia” Plane III:Deep surgical anesthesiaIntercostal and abdominal muscle tone minimumWeak corneal reflexesDiaphragmatic breathingProfound muscle relaxationCentered and dilated pupilsBradycardia intensifiesHypotension increasesRespiratory rate and depth decreasePlane IV:Deep/ OverdoseDysrhythmia probabilityRespirations slow and irregularLowered HRCyanosisWidely dilated pupil and unresponsive to lightFlaccid muscle toneJaw tone lostSphincter control lostWhen 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……
7 Pharmacokinetics Action of anesthetic on CNS Inhalants vs. Injectables Partial pressure gradientsInhalants vs. InjectablesDistribution and clearanceModifying factorsConcentrationPlasma pHProtein bindingHydrationMultiple drugs presentPharmacokinetics- What are the methods behind anesthesia?Anesthetic drugs reach equilibrium by passive mechanisms.
8 Effects of Disease Cardiovascular dysfunction Pulmonary dysfunction Most anesthetics cause CV depressionAnimals prone to fluid overload & arrhythmiasPulmonary dysfunctionMost anesthetics cause pulmonary depressionBalancing between lowering doses and preventing anxietyIntubation and ventilation are keyNitrous oxide contraindicatedNeurologic diseaseLoss of ICF and CBF regulationWatch for respiratory depressionNitrous oxide contraindicatedRenal diseaseStress and anesthetic agents decrease rate of filtrationReduction in elimination = increase in acidity and plasma concentrationsLingering effectsK+ increases in serumDifferent 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 regulationNitrous 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.*
9 Effects of Disease Hepatic disease Gastrointestinal disease Acepromazine, thiobarbiturates and α-2-adrenergic agents contraindicatedPropofol, ketamine and inhalation the safestLowered elimination rate and coagulationGastrointestinal diseaseDamaged GI can release toxinsDecrease in cardiac function and ventilationEndocrine disordersSelect anesthesia for easiest reversibilityWith 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.
10 Pre-anesthetic Agents and Adjuncts AnticholinergicsTranquilizersOpioidsAlpha2adrenergic agonistsAlpha2adrenergic antagonistsTranquilizer-opioid combinationsParalytic agentsTypes 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…….
11 Anticholinergics Block acetylcholine receptors Reduce secretions Prevent vagal inhibition and GI stimulationReduce vagus nerve response (vomiting and laryngospasm)Promote bronchodilationDilate the pupilTreatment of choice for opioid, xylazine and vagal reflex activity induced bradycardiaREAD SLIDE
12 Anticholinergics Atropine Sulfate Glycopyrrolate Contraindicated with tachycardia, constipation and obstructionMay cause thick mucus secretions in catsAtropine esterase occurs in cats, rats, and rabbitsMinimally effective in sheep and goatsIncreased incidence of bloatProlongs thiopental anesthesiaOverdose: dry mucous membranes, thirst, dilated pupils and tachycardia (dogs most susceptible)Can be treated with physostigmine IV over several minutesGlycopyrrolateReduces diffusion over blood brain or placental membranesLasts longer than atropinePrevents ketamine/xylazine associated bradycardia in rabbitsLonger onset of action in ruminantsThe 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.
13 Tranquilizers NO ANALGESIC EFFECTS Relieve anxiety Decrease anesthetic dosagesReduce histamine release and vomitingMake anesthetic recovery smootherPromote skeletal muscle relaxation and vasodilatationMay lead to hypotension and excessive heat lossMay raise seizure thresholds/ act as anticonvulsantsREAD SLIDE
14 Tranquilizers Acepromazine Maleate Droperidol Diazepam Phenothiazine May reduce or prevent malignant hypothermia in swineDroperidolButyrophenoneAlpha-adrenergic antagonistMay prevent epinephrine induced dysrhythmiasDecreases barbiturate dosesPrimarily used as a component of InnovarVt in a mixture with fentanylDiazepamBenzodiazepinePrevents seizuresRapidly passes blood-brain and placental barriersShould be injected slowly to prevent venous thrombosis and should not be injected IAIM injection not recommended- painfulThe 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
15 Tranquilizers Midazolam Flumazenil Benzodiazepine Shorter duration of action and clearance than diazepamMay cause behavioral changes in dogs and catsSuitable for IM injectionCan be mixed with other preanesthetic agentsFlumazenilReverses CNS action of benzodiazepine without anxiety, tachycardia, or hypertensionRapid action (24 minutes)Replaced aminophylline and physostigmineWhile 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 catsFlumazenil rapidly reverses the CNS action of benzodiazepine without anxiety tachycardia or hypertension.
16 Opioids Depress CNS Lower the amount of anesthetic agents needed Do not cause unconsciousness at therapeutic levelsAddictiveMost are controlled substancesBest for continuous dull painREAD SLIDE
17 Opioids Morphine sulfate Meperidine hydrochloride (Demerol, Pethidine) Stimulates vomitingDecreases BMR and body tempVariable effectsPoor effects on neuropathic painMeperidine hydrochloride(Demerol, Pethidine)Analgesic effect 1/10 of morphineRapidly excretedDoes not cause vomitingSlow administration recommendedMethadone hydrochloride (Methadone, Dolophine)Synthetic opioid unrelated to morphine2-6 hours of analgesiaDecreases barbiturate dose by 50%Oxymorphone hydrochloride(Numorphan)Semi synthetic10 times more potent than morphineProvided effective epidural analgesiaThere 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,…
18 Opioids Fentanyl citrate Carfentanil citrate Sufentanil Alfentanil 250 times more potent than morphineRapid onset of actionShort duration; peak at 30 minutesDepressed respirationExaggerated response to loud noiseLittle cardiac output or BP effectsCarfentanil citrate10,000 times more potent than morphineUsed primarily for capture of wild animalsSufentanil5 to 10 times as potent as fentanylProvided unpredictable anesthesia in dogsProvides neuroleptanalgesia when combined with tranquilizers and glycopyrrolateAlfentanil1/5th to 1/10th as potent as fentanyltimes more potent than morphine SCMore rapid onset than fentanyl or sufentanylUsed primarily for the capture of wild animalsFentanyl 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 captureSufentanyl is 5-10x as potent as fentanyl and unpredictable in dogs. It provides neuroleptanalgesia when combined with tranquilizers and glycoAlfentanil, up to 1,000 x as potent as morphine and also used in wild animal capture.
19 Opioids Pentazocine lactate (Talwin) Buprenorphine (Buprenex) 1/3rd as effective as morphineMinimal CV effectsBuprenorphine (Buprenex)25 to 30 times as potent as morphineMax analgesic effect less than morphineSlow onset of action ( minutes)Excreted in fecesThe commonly used buprenorphine, x as potent as morphine but with less of an analgesic effect andLast but not least pentazocine lactate, less effective than morphine but demonstrating minimal CV effects.
20 Alpha 2 Adrenergic Agonists Produce sedation, muscle relaxation and analgesiaNot potent respiratory depressantNon-addictiveAnticonvulsantsWide range of drug interactionsBarbiturate, inhalant and dissociative anesthetic doses should be lowered used in combination with alpha 2 adrenergic agonistsREAD SLIDE*half way through!!
21 Alpha 2 Adrenergic Agonists Xylazine hydrochloride (Rompun)Most common sedative/analgesic in horses and cattleShort term surgical anesthetic when combined with ketamineEffects within minutes IM or minutes IVIV bolus causes bradycardia, hypotension followed by decreased CO and BPPoor efficacy in swineWide margin of safetyMay cause emesis in cats and dogsReduces insulin secretion, effecting blood glucose levelsMedetomidineMore potent than xylazineBP and RR decreases dose dependentDetomidineSedative with analgesic propertiesCardiac, respiratory and antidiuretic effectsPrimarily used in horsesDexmedetomidine (Precedex)More potent than medetomidineSedative, analgesic, sympatholytic and anxiolytic effectsSedation without respiratory depressionShortens time to extubationReduces anesthetic dosagesClonidineAlpha-methyldopaAlpha 2 Adrenergic Agonists include Xylazine hydrochloride, commonly known as Rompun, and MedetomidineXylazine 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 levelsMedetomidine is the more potent Alpha 2 Adrenergic Agonist, effecting Blood pressure and respiration rate dose dependently
22 Alpha 2 Adrenergic Antagonists Used as reversal agents for injectable anestheticsYohimbineReverses xylazineAlso reverses ketamine and pentobarbital combinations when combined with 4-aminopyridine.TolazolineReverses xylazine and some anesthetic drug combinations with xylazineAtipamezoleSelectivity ration 200 to 300 times higher than yohimbineRapid IV doses may cause death or severe hypotension and tachycardiaHere we have the Alpha 2 Adrenergic Antagonists or the reversal agentsYohimbine reverses xylazine and ketamine/pentobarb combinations when combined with 4-aminopyridineTolazoline reverses xylazine and Xylazine drug combinationsAtipamezole has a greater selectivity ratio than Yohimbine and should be delivered slowly IV.
23 Tranquilizer-Opioid Combinations Provide neuroleptanalgesiaIntense analgesic action with short durationFentanyl citrate Droperidol (Innovarvet)Wide margin of safety with easy recoveryPartially reversed with opioid antagonistsTranquilizer-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.
24 ParalyticsProvide superior muscle relaxation as an adjunct to general anesthesiaDO NOT PROVIDE ANALGESIA OR UNCONSCIOUSNESSProhibited as a sole anesthetic by the GuideMechanical ventilation requiredMore difficult anesthesia managementREAD SLIDE
25 Paralytics Succinylcholine Pancuronium Vecuronium Pipecuronium Depolarizing neuromuscular paralyticMarked twitching for 30 minutes before muscle relaxationMuscle pain and stiffness associatedRise in intraocular pressureCats, swine and ponies resistantMay not be reversiblePancuroniumLasts 20 to 30 minutesCauses increased HRMetabolized in liver, excreted via kidneysVecuroniumMore potent and shorter acting than pancuroniumrapid recoveryno effect on HRWidely useddo not use with renal or hepatic failurePipecuroniumLong acting- twice duration of pancuronium2 to 4 times as potent as pancuroniumRapid onsetRetained in kidneys for daysThe 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?
26 Paralytics (continued) Rocuronium20% as potent as vecuroniumRapid recoveryCurare (dTubocurarine)Long actingIncreases HRMetocurineSafer than curareGallamineProduces tachycardiaThe only non-depolarizing agent to cross the placentaAtracuriumUnstable- refrigerateIntermediate muscle relaxantWidely usedDoxacuriumLong actingNo autonomic side effectsMivacuriumLasts slightly longer than succinylcholine and ½ the duration of vecuronium
28 Injectable Anesthetic Agents and Adjuncts Enter blood stream for transport to target tissuesRequire redistributionGenerally detoxified in liver and excreted via kidneysMetabolism based on first order kineticsConstant fraction metabolized in a given periodLess control of elimination processBarbituratesO.K. on to Injectable Anesthesia.READ SLIDE
29 BarbituratesDivided into Ultra short, Short, Intermediate and Long actingDepress CNS neuronsMay lead to respiratory depression, central and peripheral CV depression, decreased BP and BMR, reduced stroke volume and increased HRHypnotic sedativesCross cell walls and placental membraneGlucose effect in some animalsShould not be administered to animals less than 3 months oldIV administration preferredBarbiturate slough may occurOxybarbituratesThiobarbituratesBarbiturates 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 placentaThe glucose effect is a unique re-anesthetizing action seen with some barbituratesThe 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.
30 Oxybarbiturates Phenobarbital Sodium Pentobarbital Sodium Long actingEffective anticonvulsantExcreted slowly and cumulativePentobarbital SodiumShort actingInitial spike in HR followed by a decrease in HR and BPProlonged use leads to decreased systolic BP, stroke volume, pulse pressure, CO, pH, and BT (shock-like)Crosses placentaTranquilizers advised for smooth recoveryMethohexital Sodium (Brevital)Ultra short acting (redistribution)Respiratory failure with overdoseGood for inductionOxybarbiturates 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.
31 Thiobarbiturates Thiopental sodium Thiamylal sodium Ultra short acting Most secreted in urine within 4 daysInitial respiratory depressionIncrease in HR, BP and vascular resistanceThiamylal sodiumUltra short actingIV bolus lasts approx. 15 minutesLess cumulative than thiopentalLess CV effects than thiopentalThiopental 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 daysThiamylal lasts for approximately 15 minutes. It is less cumulative than thiopental with less effect on the cardiovascular system.
32 Non-Barbiturate Anesthetics AlthesinDon’t use with barbituratesGood muscle relaxationMay cause allergic reactionChloral Hydrate, U.S.P.Oral admin may cause vomitingDepresses cerebrumGood hypnotic/poor anestheticAmount needed for anesthesia close to lethal doseChloraloseMinimal CV depressionLess depression of neuronal functionLong duration, acute proceduresUrethane, N.F.CarcinogenicMagnesium sulfateGlobally depresses CNSMeans of euthanasia after unconsciousnessThere 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 barbituratesChloral 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 carcinogenicMagnesium sulfate globally depresses the central nervous system. It is a documented means of euthanasia after unconsciousness in the panel
33 Non-Barbiturate Anesthetics Metomidate (Hypnodil)Hypnotic w/ relaxant propertiesSleep without anesthesiaEtomidateNo depression of CV or respiratory centersDoes not trigger MH in swineAnticonvulsant propertiesVenous pain during injectionPropofolSupports microbial growthRapid uptake into CNSQuick and smooth recoveryMinimal analgesic effectsPropanididExtremely short duration of actionDifficult to administer fast enoughSevere respiratory depression and hypotension in dogsTricaine Methanesulfonate (MS222)Anesthesia of fish and amphibiansMetomidate 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.
34 Dissociative Anesthetics Interrupts transmission from the unconscious to the conscious brainCharacterized by a cataleptic state in which eyes remain open and nystagmus presentKetamineLeast potentRapid onset of actionRapid redistributionTissue irritation due to low pH (3.5)Analgesic effects greater for somatic pain than visceral painTransient decrease in respiratory rateHallucinatory behaviorTelazolTiletamine hydrochloride and ZolazepamWide safety marginRapid and smooth induction/recoveryGood muscle relaxantLingering analgesic effectsMay cause increased HR and respirationsDecrease in MAPDissociative 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 presentKetamine 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.
35 Inhalation Anesthesia Administration and elimination through lungsDependent upon:Vapor pressureBoyle’s lawDalton’s lawTemperatureCharles’ lawSolubilityPartition coefficientsPharmacokineticsBiotransformationMACMuch more controlInhalation 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.
36 Inhalation Anesthetics Historical Inhalant AgentsChloroformCyclopropaneDiethyl etherFluroxeneTrichlorethyleneHistorical 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.
37 Inhalation Anesthetics Nitrous oxideRapid onsetMinimal cardiovascular, liver and kidney effectsMay cause pneumothorax, blood embolus, increase in middle ear pressureMust be combined with another agentBeware of diffusion hypoxiaHalothanePotent and rapid onsetHigh volatilityRespiratory depressionMixed with thymol for stabilityEtherExplosiveHighly irritatingMethoxyfluraneLow volatilityHigh solubilityExtensively metabolizedRespiratory depressantIsofluranePotent and low solubilityRapid induction and recovery“Safer” than halothaneCoronary vasodilatorThere 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.
38 Inhalation Anesthetics DesfluraneVery rapid induction and recoveryLower solubility than isofluraneRespiratory irritantRequires heated vaporizerSevofluraneLower solubility than isoflurane, halothane or methoxyfluraneDesflurane 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?!
39 Local and Regional Anesthesia AdministrationTopicalSolution in gel or aerosolInjectable localRing blockBrachial plexus blockEpiduralIV regional blockIntercostal nerve blocksAffects 2 adjacent intercostal spacesMuscle nerve blocksFor extensive surgical manipulationInterpleural adminExamplesLidocaineProparacaineBenzocaineTetracaineButacaineLocal 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.
40 Physical Methods of Anesthesia HypothermiaSome vital organs can survive for longer periods at low temps with reduced blood supplyRisks profound CNS and vital organ depression<28°C may cause VFProlonged clotting time3 methods of hypothermiaSurfaceBody cavityextracorporealElectronarcosisDelivered via electrodes applied to headConvulsions during inductionDifficult to monitor and questionably humaneAcupunctureUseful for chronic painPhysical 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 monitorAcupuncture is another physical method of anesthesia, useful mainly for chronic pain.
41 Equipment Anesthesia machine Medical gas cylinders Airway maintenance ComponentsVaporizer in circuit or out of circuit?Rebreathing, non-rebreathing, semi-closed circuitsCO2 absorber/ ScavengingMedical gas cylindersColor codesAirway maintenanceEndotracheal tubesLaryngoscope bladesWhen 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 isAlso 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?
42 Review: What do you need to know? Know your drugs- what group they belong to and what they doKnow the stages of anesthesiaHave a basic understanding of the pharmacokinetics behind anesthesiaKnow your patient and how biological variations can effect anesthesiaBe familiar with anesthetic equipmentAreas not covered in depth: fasting, thermoregulation, fluids and acid/base balanceSo 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.
43 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.
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