acid base - columbia university：酸性基-哥伦比亚大学

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1、AcidBaseApproachtoproblemsThefirstquestionistofindwhethertheplasmapHisabnormal.Totakeasimple-mindedapproach,letuscategoricallystatethatthenormalbloodpHis7.40exactly(yourealizethatthisisanoversimplification,thenormalplasmapHis7.35-7.45).NowanypHabove7.40wewillcallalkalosisandanythingbe

2、lowthatwewillcallacidosis.Ournextquestionwillbeistheproblemmetabolicorrespiratory,andthiswillrequireknowledgeofeitherthepCO2ortheHCO3,preferablybothofthem.Onceyoumakethediagnosisoftheabnormality,thenthedifferentialdiagnosisisrelativelystraightforwardandonlyrequiresmemorizationofthesec

3、auses.Case1FirstvaluespH7.32pCO228HCO315mEq/L1-3.Thepatienthasacidosis(pH<7.4).LowHCO3withacidosismeanshehasmetabolicacidosis;thebrainrespondstoacidosis(compensates)byhyperventilatinghencethepCO2islow.Inacidosisthecompensationbythebrainissofast(withinseconds,)thatthereislittledifferen

4、cebetweenacuteandchronic.1.TheaniongapisNa125-(Cl90+HCO315)=20.Itishigh2.ThetwothingstorememberareLacticAcidosisandDiabeticketoacidosis.Therestaremuchrarer;butseetable1onp.93.Thelikelycausehereislacticacidosisbecausethepatient'spO2isprettylow(56)whichstimulatesglycolysiscausingincreas

5、edproductionoflacticacid.SevereCHFcancausedecreasedoxygenation.NewValuesaftertreatmentpH7.48;pCO244HCO3356-8Thepatientnowhasalkalosis(pH>7.40)anditismetabolic,HCO3is35andthepCO2ishigh44;i.e.thepatienthaschronicmetabolicacidosiswithanincreaseinpCO2becausethealkalosisinhibitstherespirat

6、orydrive.9Non-renalHlossistypicallyseeninvomiting,orinsuctionofthegastricorupperGItract.Wearenottoldthatthepatientisvomiting,sowedon'tknow,butprobablyitdoesn'tapplyhere.10H+secretionbythekidneyoccursintheproximaltubuleandthecollectingtubule.Thetablebelowliststheconditionsthataffectthe

7、mandallarediscussedinthesyllabusProximalTubuleHighpCO2DecreasedECFVolume(HiAII,hiFiltrationFraction)Hypokalemia(makesthecellacid)ChronicAcidBasestatusCollectingTubulehighpCO2AldosteroneLumennegativepotentialproducedbystimulatedNaabsorptionHypokalemia(makesthecellacid)IncreasedNH3produ

8、ction