TopicoftheDayI(forInternsandCA-2’s)Oct26-Discussunilateralepiduralblock-explainthisresult形成单侧硬膜外阻滞的原因Discussionpoint.Aunilateralanestheticblockmayresultfromtheadministrationoflocalanestheticintheepiduralspacesecondarytotheplicamedianadorsalis,aconnectivetissuebandintheepiduralspacethatextendsinaverticaldirectionbetweentheligamentumflavumandduramaterdividingtheepiduralspaceinhalf.由于背正中皱襞的存在，在硬膜外腔注入局部麻醉药后可造成单侧阻滞。背正中皱襞作为连接黄韧带和硬膜的带状结缔组织在硬膜外腔垂直延伸，并把其一分为二。Oct27-Comparesympathetic,motor&sensoryblockofepiduralsvsspinals比较硬膜外麻醉和脊髓麻醉的交感、运动和感觉神经阻滞Discussionpoints.Epiduralanesthesiaresultsinsympatheticnerveblockade,sensorynerveblockade,andmotornerveblockadejustasinspinalanesthesia.Inepiduralanesthesia,however,thelevelsofeacharedifferentthantheyareinspinalanesthesia.First,sympatheticnerveblockadeisatalevelequaltosensorynerveblockade,ratherthanthetwotosixsegmentshigherthatisseeninspinalanesthesia.Second,motornerveblockademayaveragefoursegmentslowerthansensorynerveblockade,ratherthanthetwosegmentsseeninspinalanesthesia.Themajorsiteofactionoflocalanestheticsadministeredintheepiduralspaceisatthespinalnerveroots.Atthespinalnerverootstheduramaterisrelativelythin,allowingfortheeasiestdiffusionoflocalanestheticthroughtheduramatertothenerves.ThereisoftenadelayedonsetinanesthesiaattheSl-S2nerverootregionduringanepiduralanesthetic.Thismaybeduetothecoveringofthesenerverootswithconnectivetissue,slowingthediffusionoflocalanesthetictothesenerveroots.Thediffusionoflocalanestheticfromtheepiduralspacetothesubarachnoidspaceisaminorcontributortotheanestheticeffectsoflocalanestheticsolutionsintheepiduralspace.正如脊髓麻醉一样，硬膜外麻醉亦可阻滞交感、感觉和运动神经。但是，各神经被阻滞的平面在硬膜外麻醉与脊髓麻醉中有所不同。首先，硬膜外麻醉中交感阻滞与感觉阻滞的平面相同，而脊髓麻醉中前者要比后者高2~6个节段。其次，硬膜外麻醉中运动阻滞平面平均比感觉阻滞平面低4个节段，而脊髓麻醉中前者比后者低2个节段。脊神经根是硬膜外腔注入的局部麻醉药的主要作用部位。脊神经根附近的硬膜相对较薄，使局部麻醉药容易经此扩散至神经而发挥作用。在硬膜外麻醉过程中，骶1~2神经根支配区域的麻醉起效常有延迟。这可能是因为包裹这些神经根的结缔组织减慢了局部麻醉药向神经根的扩散。在硬膜外麻醉中，局麻药液从硬膜外腔扩散至蛛网膜下腔而产生的麻醉效果所占比例很小。Oct28-Discusspotentialsideeffectsofepiduralanesthesia硬膜外麻醉的潜在并发症Discussionpoints.Thepotentialsideeffectsofspinalanesthesiaalsoapplytoepiduralanesthesia.Additionalsideeffectsofanepiduralanestheticthatdonotapplytospinalanesthesiaincludetherisksofaccidentalduralpuncture,localanesthetictoxicity,subduralinjection,andepiduralhematomaformation.Theriskofepiduralhematomaformationresultingfromanepiduralanestheticisextremelylow.Patientsonanticoagulantsareconsideredtobeatthegreatestrisk,althoughtheincidenceisextremelyloweveninpatientswithbleedingabnormalities.Therearemultiplereviewsintheliteratureofpatientswhoreceivedanticoagulationintraoperativelyandpostoperativelywithoutanyneurologicsequelae.Nevertheless,theAmericanSocietyofRegionalAnesthesiapublishedtheirconsensusstatementtitledNeuraxialAnesthesiaandAnticoagulationinMay1998withtheirrecommendationsonhowepiduralcathetersshouldbemanagedintheperioperativeperiodinthepresenceofanticoagulation.Accidentalpunctureoftheduramaterduringattemp...
