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高中英语Unit5 First aid文章 BLEEDING人教版必修五.doc

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用心爱心专心BLEEDINGBleedingiswhenoneormorebloodvesselsaredamagedandcanbefromarteriesveinsorcapillaries.Theseriousnessofthehaemorrhagedependsonthedepthofthecutamountofbleedingtimetakentocontrolthebleedingandtypeofbloodvesselsdamaged.Seeingyourownbloodcanbeashockandonlookerswatchingthescenemayexperienceshock.Thecaregiverisalsoinpotentialdangerofbecominginfectedbyatransmissibledisease—forexampleHIVorhepatitis.Externalbleedingisalmostalwayseasytoidentifybutinternalbleedingisoftenmoredifficulttodetectandtreat.Anaverageadulthasabout5lofbloodandcansafelylosehalfalitre.Rapidlossoflargervolumesofbloodhoweverleadstohypovolaemicshockanddeath.Hypovolaemicshockisaclinicalstateinwhichtissueperfusionisinadequateduetoalossofbloodorplasma.Areductioninbloodvolumecausesafallinsystolicbloodpressurewhichtriggersasympatheticcatecholamineresponse.Bloodflowtotheperipheriesisreduced.Anaerobicmetabolismwithlactateproductionoccursintissuesthatareinadequatelyperfusedandthiscangoontoimpairthefunctionofvitalorganssuchasthebrainheartandkidneys.