1、ABG INTERPRETATIONDebbie Sander PAS-IIObjectives Whats an ABG? Understanding Acid/Base Relationship General approach to ABG Interpretation Clinical causes Abnormal ABGs Case studies Take homeWhat is an ABGArterial Blood GasDrawn from artery- radial, brachial, femoralIt is an invasive procedure.Cauti
2、on must be taken with patient on anticoagulants.Helps differentiate oxygen deficiencies from primary ventilatory deficiencies from primary metabolic acid-baseabnormalities What Is An ABG?pH H+PCO2 Partial pressure CO2PO2 Partial pressure O2HCO3 BicarbonateBE Base excessSaO2 Oxygen SaturationAcid/Bas
3、e Relationship This relationship is critical for homeostasis Significant deviations from normal pH ranges are poorly tolerated and may be life threatening Achieved by Respiratory and Renal systems Case Study No. 160 y/o male comes ER c/o SOB.Tachypneic, tachycardic, diaphoretic andCyanotic. Dx acute
4、 resp. failure and ABGsShow PaCO2 well below nl, pH above nl, PaO2 is very low. The blood gas documentResp. failure due to primary O2 problem. Case Study No. 260 y/o male comes ER c/o SOB.Tachypneic, tachycardic, diaphoretic andCyanotic. Dx acute resp. failure and ABGsShow PaCO2 very high, low pH an
5、d PaO2is moderately low. The blood gas documentResp. failure due to primarily ventilatoryinsufficiency.There are two buffers that work in pairsH2CO3 NaHCO3Carbonic acid base bicarbonateThese buffers are linked to the respiratory and renal compensatory system BuffersRespiratory Component function of
6、the lungs Carbonic acid H2CO3 Approximately 98% normal metabolites are in the formof CO2CO2 + H2O H2CO3 excess CO2 exhaled by the lungs Metabolic Component Function of the kidneys base bicarbonate Na HCO3 Process of kidneys excreting H+ into the urine and reabsorbingHCO3- into the blood from the ren
7、al tubules1) active exchange Na+ for H+ between the tubularcells and glomerular filtrate2) carbonic anhydrase is an enzyme that accelerateshydration/dehydration CO2 in renal epithelial cells H2O + CO2 H2CO3 HCO3 + H+Acid/Base RelationshipNormal ABG valuespH 7.35 7.45PCO2 35 45 mmHgPO2 80 100 mmHgHCO
8、3 22 26 mmol/LBE -2 - +2SaO2 95% Acidosis AlkalosispH 45HCO3 7.45PCO2 26Respiratory Acidosis Think of CO2 as an acid failure of the lungs to exhale adequate CO2 pH 45 CO2 + H2CO3 pHCauses of Respiratory Acidosis emphysema drug overdose narcosis respiratory arrest airway obstructionMetabolic Acidosis
9、 failure of kidney function blood HCO3 which results in availability of renaltubular HCO3 for H+ excretion pH 7.45 PCO2 7.45 HCO3 26Causes of Metabolic Alkalosis loss acid from stomach or kidney hypokalemia excessive alkali intakeHow to Analyze an ABG1. PO2 NL = 80 100 mmHg2. pH NL = 7.35 7.45Acidot
10、ic 7.453. PCO2 NL = 35 45 mmHgAcidotic 45Alkalotic 26Four-step ABG InterpretationStep 1: Examine PaO2 & SaO2 Determine oxygen status Low PaO2 (7.45Four-step ABG InterpretationStep 3: study PaCO2 & HCO 3 respiratory irregularity if PaCO2 abnl & HCO3 NL metabolic irregularity if HCO3 abnl & PaCO2 NLFo
11、ur-step ABG InterpretationStep 4:Determine if there is a compensatory mechanism workingto try to correct the pH.ie: if have primary respiratory acidosis will have increasedPaCO2 and decreased pH. Compensation occurs whenthe kidneys retain HCO3. Four-step ABG Interpretation PaCO2 pH Relationship80 7.
12、2060 7.3040 7.4030 7.5020 7.60CompensatedRespiratoryAcidosisCO2More AbnormalRespiratoryAcidosisCO2ExpectedMixedRespiratoryMetabolicAcidosisCO2Less AbnormalCO2 Changec/wAbnormalityMetabolicMetabolic AcidosisCO2NormalCompensatedMetabolicAcidosisCO2 ChangeopposesAbnormalityAcidosisABG InterpretationCom
13、pensatedRespiratoryAlkalosisCO2More AbnormalRespiratoryAlkalosisCO2ExpectedMixedRespiratoryMetabolicAlkalosisCO2Less AbnormalCO2 Changec/wAbnormalityMetabolicAlkalosisCO2NormalCompensatedMetabolicAlkalosisCO2 ChangeopposesAbnormalityAlkalosisABG InterpretationRespiratory AcidosispH 7.30 PaCO2 60 HCO3 26
