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1、药物诱导的麻醉第1页，本讲稿共22页PRINCIPLESOFTHEADMINISTRATIONOFGENERALANAESTHETICSnUptake and Distribution of inhalational general anestheticsnDepth of Anesthesia-Tension of anaesthetic agent in brain-controls-rates of induction and recovery nTension and partial pressure are interchangeable terms第2页，本讲稿共22页Tensio

2、ninthearterialbloodandbrainaresameandaredeterminedby:nConcentrationoftheanaestheticintheinspiredairdependsonrateofventilationnTransferofthegasfromthealveolitothebloodnDecreasedindisease(ex.emphysema)nRateoftransferisdeterminedby:nSolubility(Bloodgaspartitioncoefficient.)nRateofbloodflow(directlyprop

3、ortionaltotheC.O.nPartialpressuresoftheagentinarterialandmixedvenousblood.nLossoftheagentfromthearterialbloodtoallthetissueofthebody第3页，本讲稿共22页ANAESTHESIAMACHINESnAre devices by which the anesthesiologist is able to delivernMeasured quantities of anaesthetic gases and oxygen through accurate flowmet

4、ers and with the use of special vaporizers it is possible to add the vapor of volatile anesthetic liquid to the gas stream.The mixture of oxygen and anaesthetic agent is then delivered to a breathing circuit for administration by Inhalation.第4页，本讲稿共22页GeneralAnestheticsarethemostdangerousdrugsTherap

5、euticindexrangesbetween2-42-3timesdosecausescirculatoryfailure第5页，本讲稿共22页OraldosedeliversthetotaldoseWhen gas or vapor is inhaled only a small amount is absorbedWhereas the rest is exhaled out in next 1-2 secondsThe drug reaches the brain by leaving the bloodAnaesthetic blood levels of these cannot

6、be measures accuratelyConcentrations in the lungs can be easily frequently and accurately be measuredThe partials pressures of the anaesthetic in the lung and the brain are almost equal at equilibrium第6页，本讲稿共22页Minimum Alveolar ConcentrationMAC is the measure of potency of general anestheticsIt is t

7、he minimum alveolar concentration(MAC)at one atmospheric pressure that produces immobility in 50%patients or animals exposed to noxious stimuli第7页，本讲稿共22页ELIMINATIONOFGENERALANAESTHETICSFreegasesandvaporswashoutofthelungs:Thearterialbloodtensiondeclinesfirst.Followedbythatinthetissueswheretheanaesth

8、eticagentpersistsforalongertime.Tissuehavinglowbloodflow(muscle)relievetheagentmuchslowly.OTHERROUTES:Theseagentsarealsoeliminatedinsmallerquantitiesfromskin,mucousmembraneandthekidneys第8页，本讲稿共22页第9页，本讲稿共22页DEPTHOFGENERALANAESTHESIAOCCURSINSTAGESSTAGE-1ANALGESIASTAGE-2DELERIUMSTAGE-3SURGICALANESTHES

9、IASTAGE-4MEDULLARYPARALYSES第10页，本讲稿共22页APPROACHESFORTESTINGDEPTHOFANAESTHESIA-Blinking of eyelids on striking the eyelashes.-Swallowing-Regularity and depth of respiration.-Increase in respiratory rate and B.P.on incision-Tightness of jaw muscles.Above responses fade on deepening of the anesthesia.D

10、eepanesthesiaLeedsto:RespiratorydepressionApneaLoweringofB.P.Asystole第11页，本讲稿共22页PREANAESTHETICMEDICATIONDecreaseanxietywithoutdrowsinessAmnesiaRelievepreoperativepainDecreaserequirementforaninhalationalagent.Minimisingundesirableeffectsofanesthetics.(salivation,decreaseinheartrate,coughing,vomiting

11、)Decreasevolumeandacidityofthegastriccontents.Decreasestressresponseinpreoperativeperiod第12页，本讲稿共22页PREANAESTHETICMEDICATION2-3drugsareusedconcomitantly:SedativesHypnoticsAntianxietydrugsOpoidsAntiemeticsH-2antagonistsGastrokineticagentsAnticholinergics第13页，本讲稿共22页DRUGSUSEDINPREANAESTHETICMEDICATION

12、SBenzodiazepines:Diazepam,Lorazepam,Midazolam.Barbibiturates:Pentobarbitone,secobarbitone.Antihistamines:Hydroxyzine,Diphenhydramine.Phenothiazines:Promethazine.Butyrophenones:Droperidol.Opoids:Morphine,fentanyl,meperidine.Anticholinergics:atropine,scopolamine,glycopyrrolate.Antiemetics:OndansetronD

13、rugsdecreasinggastricacidity:H-2antagonists.Antacids.Gastrokineticagents.第14页，本讲稿共22页MECHANISMOFACTIONSOFGENERALANAESTHETICSAlldrugsbelongtodiversegroupsInertgasesasxenonInorganic/OrganiccompdsasNitrousoxideandChloroform.ComplexOrganicMoleculesHalogenatedAlkanesandethersTheModeofactioniswithoutanysa

14、tisfactoryexplanation.POSTULATIONS:-Influencesynaptictransmission.-Axonalconductionisunaffected.-Potentiatereleaseofinhibitoryneurotransmitters.-Inhibitexcitatorysynapses.第15页，本讲稿共22页MECHANISMOFACTIONSOFGENERALANAESTHETICSActionoftheseagentsisonLipidbilayerand/orproteinlipidinterfaceORIONCHANNELS(Na

15、/K/Ca)ORLigandgatedChannelsl-Glutamate.NMDANAChRGABA-A第16页，本讲稿共22页Atthemolecularlevel,anestheticsprobablyexerttheireffectsbydirectinteractionswithproteinsratherthanbydisturbingthematrixofthelipidbilayerasearlierpostulated.AnestheticsMaybindtohydrophobicpocketsorclefts,producingsmallchangesinproteinC

16、onformationalertingreceptorofchannelfunction.ItisalsopossiblethatspecializedareasOfthemembranesuchastheboundarylipidssurroundingmembraneProteinsareimportantsitesofanaestheticbindingandaction.MECHANISMOFACTIONSOFGENERALANAESTHETICS第17页，本讲稿共22页MECHANISMOFACTION:Theexactmechanismbywhichinhalationalanes

17、theticsfunctionisnotknown.Thereappearstobeacorrelationbetweenanestheticpotencyandlipidsolubility(Meyer-Overtontheory),suggestingthattheseanestheticslikelyaffectthelipidmatrixofnervecellmembranesinthebrain.Furthermore,NMRandelectronspinresonancestudiesindicatethatanestheticscausealocaldisorderingofth

18、elipidmembranematrix,possiblydecreasingthenumberofmoleculesthatalternatesimultaneouslybetweenthegelandcrystallinestates,andtherebyalteringmembranefunction.第18页，本讲稿共22页NEUROLEPT ANALGESIA-State of quiescence-Reduced motor activity-Reduced anxiety-Indifference to the surroundings without loss of consc

19、iousnessThe patient responds to commands.Drugs:a neurolept compd(Droperidol)plus an opoid analgesic(fentanyl)Neurolept analgesia may be converted into neurolept anaesthesia by concominant administration of 65%nitrous oxide 第19页，本讲稿共22页DISSOCIATIVE ANAESTHESIAastateofsedation,immobility,amnesiaandmar

20、kedanalgesia(feelingofdissociation)asingledrugsuchasketaminecanresultinthisstate.第20页，本讲稿共22页Inhalationagents:NEWERAGENTSOLDERDRUGSHalothaneChloroformEnfluraneEtherVolatileliquids:IsofluraneEthylchlorideDesfluraneTrichlorethyleneSevofluraneGases:NitrousoxideCyclopropaneEthyleneIntravenousagents:ThiopentoneBenzodiazepinesEtomidateKetaminePropofolGENERALANAESTHETICSCLASSIFICATION第21页，本讲稿共22页CHARACTERSITICS OF ANIDEAL ANAESTHETIC1.Rapidandpleasantinduction2.Rapidchangesinthedepthofanesthesia3.AdequateMuscleRelaxation4.Widemarginofsafety5.Absenceoftoxic/adverseeffects第22页，本讲稿共22页