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1、ABG INTERPRETATION,Debbie Sander PAS-II,Objectives,Whats an ABG? Understanding Acid/Base Relationship General approach to ABG Interpretation Clinical causes Abnormal ABGs Case studies Take home,What is an ABG,Arterial Blood GasDrawn from artery- radial, brachial, femoralIt is an invasive procedure.C
2、aution must be taken with patient on anticoagulants.Helps differentiate oxygen deficiencies from primary ventilatory deficiencies from primary metabolic acid-base abnormalities,What Is An ABG?,pH H+PCO2 Partial pressure CO2PO2 Partial pressure O2HCO3 BicarbonateBE Base excessSaO2 Oxygen Saturation,A
3、cid/Base 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. 1,60 y/o male comes ER c/o SOB. Tachypneic, tachycardic, diaphoretic and Cyanotic
4、. Dx acute resp. failure and ABGs Show PaCO2 well below nl, pH above nl, PaO2 is very low. The blood gas document Resp. failure due to primary O2 problem.,Case Study No. 2,60 y/o male comes ER c/o SOB. Tachypneic, tachycardic, diaphoretic and Cyanotic. Dx acute resp. failure and ABGs Show PaCO2 very
5、 high, low pH and PaO2 is moderately low. The blood gas document Resp. failure due to primarily ventilatory insufficiency.,There are two buffers that work in pairsH2CO3 NaHCO3 Carbonic acid base bicarbonateThese buffers are linked to the respiratory and renal compensatory system,Buffers,Respiratory
6、Component,function of the lungsCarbonic acid H2CO3Approximately 98% normal metabolites are in the form of CO2CO2 + H2O H2CO3excess CO2 exhaled by the lungs,Metabolic Component,Function of the kidneysbase bicarbonate Na HCO3Process of kidneys excreting H+ into the urine and reabsorbing HCO3- into the
7、 blood from the renal tubules 1) active exchange Na+ for H+ between the tubular cells and glomerular filtrate 2) carbonic anhydrase is an enzyme that accelerates hydration/dehydration CO2 in renal epithelial cells,H2O + CO2 H2CO3 HCO3 + H+,Acid/Base Relationship,Normal ABG values,pH 7.35 7.45PCO2 35
8、 45 mmHgPO2 80 100 mmHgHCO3 22 26 mmol/LBE -2 - +2SaO2 95%,Acidosis Alkalosis,pH 45HCO3 7.45PCO2 26,Respiratory Acidosis,Think of CO2 as an acidfailure of the lungs to exhale adequate CO2pH 45CO2 + H2CO3 pH,Causes of Respiratory Acidosis,emphysemadrug overdosenarcosisrespiratory arrestairway obstruc
9、tion,Metabolic Acidosis,failure of kidney function blood HCO3 which results in availability of renal tubular HCO3 for H+ excretionpH 7.35HCO3 7.45PCO2 7.45HCO3 26,Causes of Metabolic Alkalosis, loss acid from stomach or kidneyhypokalemiaexcessive alkali intake,How to Analyze an ABG,PO2 NL = 80 100 m
10、mHg2. pH NL = 7.35 7.45Acidotic 7.45PCO2 NL = 35 45 mmHgAcidotic 45Alkalotic 26,Four-step ABG Interpretation,Step 1: Examine PaO2 & SaO2Determine oxygen statusLow PaO2 (80 mmHg) & SaO2 means hypoxiaNL/elevated oxygen means adequate oxygenation,Step 2:pH acidosis 7.45,Four-step ABG Interpretation,Ste
11、p 3:study PaCO2 & HCO 3respiratory irregularity if PaCO2 abnl & HCO3 NLmetabolic irregularity if HCO3 abnl & PaCO2 NL,Four-step ABG Interpretation,Step 4:Determine if there is a compensatory mechanism working to try to correct the pH.ie: if have primary respiratory acidosis will have increased PaCO2
12、 and decreased pH. Compensation occurs when the kidneys retain HCO3.,Four-step ABG Interpretation, PaCO2 pH Relationship,80 7.20 60 7.30 40 7.40 30 7.50 20 7.60,Compensated,Respiratory,Acidosis,CO2,More Abnormal,Respiratory,Acidosis,CO2,Expected,Mixed,Respiratory,Metabolic,Acidosis,CO2,Less Abnormal
13、,CO2 Change,c/w,Abnormality,Metabolic,Metabolic Acidosis,CO2,Normal,Compensated,Metabolic,Acidosis,CO2 Change,opposes,Abnormality,Acidosis,ABG Interpretation,Compensated,Respiratory,Alkalosis,CO2,More Abnormal,Respiratory,Alkalosis,CO2,Expected,Mixed,Respiratory,Metabolic,Alkalosis,CO2,Less Abnormal
14、,CO2 Change,c/w,Abnormality,Metabolic,Alkalosis,CO2,Normal,Compensated,Metabolic,Alkalosis,CO2 Change,opposes,Abnormality,Alkalosis,ABG Interpretation,Respiratory Acidosis,pH 7.30 PaCO2 60 HCO3 26,Respiratory Alkalosis,pH 7.50 PaCO2 30 HCO3 22,Metabolic Acidosis,pH 7.30 PaCO2 40 HCO3 15,Metabolic Al
15、kalosis,pH 7.50 PCO2 40 HCO3 30,What are the compensations?,Respiratory acidosis metabolic alkalosisRespiratory alkalosis metabolic acidosisIn respiratory conditions, therefore, the kidneys will attempt to compensate and visa versa.In chronic respiratory acidosis (COPD) the kidneys increase the elimination of H+ and absorb more HCO3. The ABG will Show NL pH, CO2 and HCO3.Buffers kick in within minutes. Respiratory compensation is rapid and starts within minutes and complete within 24 hours. Kidney compensation takes hours and up to 5 days.,
