白癜风得治疗 http://m.39.net/pf/a_6983854.htmlLacticAcidosisLacticacidosisoccurswhentheproductionoflactateinthebodyisgreaterthantheliver’scapacitytoclearit.Theproblemisoverproductionorinadequateclearance.Lacticacidisproducedphysiologicallyasadegradationproductofglucosemetabolism.Itsformationfrompyruvateiscatalyzedbylactatedehydrogenase.Undernormalconditions,theratiooflactatetopyruvateislessthan20:1.Inanaerobicconditions,forexamplefollowingvigorousexercise,lactatelevelsincreasedramatically.Inaddition,lactatecanbeproducedunderaerobicconditions.Activationofβ-adrenergicreceptorsinskeletalmusclebystress(increasedcirculatingcatecholamines)orexogenousinfusion(epinephrineornorepinephrineinfusions)increaseslactate,withresultingaerobicglycolysis.LactatecanbeconvertedtoCO2andH2Obytheliver;thelactateinRingerlactatesolutionisfunctionallyHCO-3.SerumlactateandarterialpHshouldbemeasuredearlyinanycriticallyillpatient.Alactateconcentrationofmorethan2mEq/Lisclinicallysignificant,andalevelof5mEq/Linthepresenceofmetabolicacidosisissevere.Isolatedhyperlactatemiaintheabsenceofacidosisisofunclearclinicalsignificance.Twotypesoflacticacidosisarerecognized.TypeA(globalinadequateoxygendelivery)isseeninhypovolemicorhemorrhagicshock,whereastypeBoccursdespitenormalglobaloxygendeliveryandtissueperfusion.Lacticacidosismayalsodevelopinsituationsofsignificantregionalhypoperfusion.Examplesincludebowelischemia,inwhichlactateisproducedinlargequantityasaresultofglycolysisdespiteglobaloxygendeliverythatisnormal.TypeBlacticacidosisisassociatedwithanystatecharacterizedbyexcesscirculatingcatecholamines(endogenousorexogenous).Examplesincludesimpleexerciseandthehyperinflammatorystateoftraumaorsepsis.TypeBlacticacidosismayalsobeseenincyanidepoisoning(associatedwithsodiumnitroprusside),withbiguanides(metformin),andinhypercatabolicdiseases,suchaslymphoma,leukemia,acquiredimmunodeficiencysyndrome(AIDS),ordiabeticketoacidosis.Lacticacidosisisasensitivemarkerofdiseaseseverity,andfailuretocleartheacidosisisastrongpredictorofadverseout