病理生理课件血气

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.Caution must be taken with patient on anticoagulants.Helps differentiate oxygen deficiencies from primary ventilatory deficiencies from primary metabolic acid-baseabnormalities What Is An ABG?pHH+PCO2 Partial pressure CO2PO2 Partial pressure O2HCO3 BicarbonateBE Base excessSaO2 Oxygen SaturationAcid/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.160 y/o male comes ER c/o SOB.Tachypneic,tachycardic,diaphoretic andCyanotic.Dx acute 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 and PaO2is moderately low.The blood gas documentResp.failure due to primarily ventilatoryinsufficiency.There are two buffers that work in pairsH2CO3NaHCO3Carbonic acid base bicarbonate These buffers are linked to the respiratory and renal compensatory system BuffersRespiratory Component function of the lungs Carbonic acid H2CO3 Approximately 98%normal metabolites are in the form of CO2 CO2 +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 reabsorbing HCO3-into the blood from the renal tubules1)active exchange Na+for H+between the tubular cells and glomerular filtrate2)carbonic anhydrase is an enzyme that accelerates hydration/dehydration CO2 in renal epithelial cells H2O +CO2 H2CO3 HCO3 +H+Acid/Base RelationshipNormal ABG valuespH7.35 7.45PCO235 45 mmHgPO280 100 mmHgHCO322 26 mmol/LBE-2-+2SaO295%AcidosisAlkalosispH 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 failure of kidney function blood HCO3 which results in availability of renal tubular HCO3 for H+excretion pH 7.35 HCO3 7.45 PCO2 7.45 HCO3 26Causes of Metabolic Alkalosis loss acid from stomach or kidney hypokalemia excessive alkali intakeHow to Analyze an ABG1.PO2NL=80 100 mmHg2.pHNL =7.35 7.45Acidotic7.453.PCO2NL=35 45 mmHgAcidotic45Alkalotic354.HCO3NL=22 26 mmol/LAcidotic 26Four-step ABG InterpretationStep 1:Examine PaO2&SaO2 Determine oxygen status Low PaO2(80 mmHg)&SaO2 means hypoxia NL/elevated oxygen means adequate oxygenationStep 2:pHacidosis7.45Four-step ABG InterpretationStep 3:study PaCO2&HCO 3 respiratory irregularity if PaCO2 abnl&HCO3 NL metabolic irregularity if HCO3 abnl&PaCO2 NLFour-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 Relationship807.20607.30407.40307.50207.60CompensatedRespiratoryAcidosisCO2More AbnormalRespiratoryAcidosisCO2ExpectedMixedRespiratoryMetabolicAcidosisCO2Less AbnormalCO2 Changec/wAbnormalityMetabolicMetabolic AcidosisCO2NormalCompensatedMetabolicAcidosisCO2 ChangeopposesAbnormalityAcidosisABG InterpretationCompensatedRespiratoryAlkalosisCO2More AbnormalRespiratoryAlkalosisCO2ExpectedMixedRespiratoryMetabolicAlkalosisCO2Less AbnormalCO2 Changec/wAbnormalityMetabolicAlkalosisCO2NormalCompensatedMetabolicAlkalosisCO2 ChangeopposesAbnormalityAlkalosisABG InterpretationRespiratory AcidosispH7.30 PaCO2 60 HCO3 26 Respiratory AlkalosispH7.50 PaCO2 30 HCO3 22 Metabolic AcidosispH7.30 PaCO2 40 HCO3 15 Metabolic AlkalosispH7.50 PCO2 40 HCO3 30 What are the compensations?Respiratory acidosismetabolic alkalosisRespiratory alkalosis metabolic acidosisIn respiratory conditions,therefore,the kidneys willattempt to compensate and visa versa.In chronic respiratory acidosis(COPD)the kidneys increasethe elimination of H+and absorb more HCO3.The ABG willShow NL pH,CO2 and HCO3.Buffers kick in within minutes.Respiratory compensationis rapid and starts within minutes and complete within 24 hours.Kidney compensation takes hours and up to 5 days.Mixed Acid-Base AbnormalitiesCase Study No.3:56 yo neurologic dz required ventilator support for severalweeks.She seemed most comfortable when hyperventilatedto PaCO2 28-30 mmHg.She required daily doses of lasix toassure adequate urine output and received 40 mmol/L IV K+each day.On 10th day of ICU her ABG on 24%oxygen&VS:ABG ResultspH7.62BP115/80 mmHgPCO230 mmHgPulse88/minPO285 mmHgRR10/minHCO330 mmol/LVT1000mlBE10 mmol/LMV10LK+2.5 mmol/L Interpretation:Acute alveolar hyperventilation(resp.alkalosis)and metabolic alkalosis with corrected hypoxemia.Case study No.427 yo retarded with insulin-dependent DM arrived at ERfrom the institution where he lived.On room air ABG&VS:pH7.15BP180/110 mmHgPCO222 mmHgPulse130/minPO292 mmHgRR40/minHCO3 9 mmol/LVT800mlBE-30 mmol/LMV32LInterpretation:Partly compensated metabolic acidosis.Case study No.574 yo with hx chronic renal failure and chronic diuretic therapywas admitted to ICU comatose and severely dehydrated.On40%oxygen her ABG&VS:pH7.52BP130/90 mmHgPCO255 mmHgPulse120/minPO292 mmHgRR25/minHCO342 mmol/LVT150mlBE17 mmol/LMV 3.75LInterpretation:Partly compensated metabolic alkalosis with corrected hypoxemia.Case study No.643 yo arrives in ER 20 minutes after a MVA in which heinjured his face on the dashboard.He is agitated,has mottled,cold and clammy skin and has obvious partial airway obstruction.An oxygen mask at 10 L is placed on his face.ABG&VS:pH7.10BP150/110 mmHgPCO260 mmHgPulse150/minPO2125 mmHgRR45/minHCO318 mmol/LVT?mlBE-15 mmol/LMV?L.Interpretation:Acute ventilatory failure(resp.acidosis)andacute metabolic acidosis with corrected hypoxemiaCase study No.717 yo,48 kg with known insulin-dependent DM came to ERwith Kussmaul breathing and irregular pulse.Room airABG&VS:pH7.05BP140/90 mmHgPCO212 mmHgPulse118/minPO2108 mmHgRR40/minHCO35 mmol/LVT1200mlBE-30 mmol/LMV48LInterpretation:Severe partly compensated metabolicacidosis without hypoxemia.Case No.7 contdThis patient is in diabetic ketoacidosis.IV glucose and insulin were immediately administered.Ajudgement was made that severe acidemia was adverselyaffecting CV function and bicarb was elected to restore pH to 7.20.Bicarb administration calculation:Base deficit X weight(kg)430 X 48 =360 mmol/LAdmin 1/2 over 15 min&4 repeat ABGCase No.7 contdABG result after bicarb:pH7.27BP130/80 mmHgPCO225 mmHgPulse100/minPO292 mmHgRR22/minHCO311 mmol/LVT600mlBE-14 mmol/LMV13.2LCase study No.847 yo was in PACU for 3 hours s/p cholecystectomy.Shehad been on 40%oxygen and ABG&VS:pH7.44BP130/90 mmHgPCO232 mmHgPulse95/min,regularPO2121 mmHgRR20/minHCO322 mmol/LVT350mlBE-2 mmol/LMV7LSaO298%Hb13 g/dLCase No.8 contdOxygen was changed to 2L N/C.1/2 hour pt.ready to be D/Cto floor and ABG&VS:pH7.41BP130/90 mmHgPCO210 mmHgPulse95/min,regularPO2148 mmHgRR20/minHCO36 mmol/LVT350mlBE-17 mmol/LMV7LSaO299%Hb7 g/dLCase No.8 contd What is going on?Case No.8 contdIf the picture doesnt fit,repeat ABG!pH7.45BP130/90 mmHgPCO231 mmHgPulse95/minPO287 mmHgRR20/minHCO322 mmol/LVT350mlBE-2 mmol/LMV7LSaO2 96%Hb13 g/dLTechnical error was presumed.Case study No.967 yo who had closed reduction of leg fx without incident.Four days later she experienced a sudden onset of severe chestpain and SOB.Room air ABG&VS:pH7.36BP130/90 mmHgPCO233 mmHgPulse100/minPO255 mmHgRR25/minHCO318 mmol/LBE-5 mmol/LMV18LSaO288%Interpretation:Compensated metabolic acidosis withmoderate hypoxemia.Dx:PECase study No.1076 yo with documented chronic hypercapnia secondary tosevere COPD has been in ICU for 3 days while being tx forpneumonia.She had been stable for past 24 hours and wastransferred to general floor.Pt was on 2L oxygen&ABG&VS:pH7.44BP135/95 mmHgPCO263 mmHgPulse110/minPO252 mmHgRR22/minHCO342 mmol/LBE+16 mmol/LMV10LSaO286%.Interpretation:Chronic ventilatory failure(resp.acidosis)with uncorrected hypoxemiaCase No.10 contdShe was placed on 3L and monitored for next hour.She remained alert,oriented and comfortable.ABG wasrepeated:pH7.36BP140/100 mmHgPCO275 mmHgPulse105/minPO265 mmHgRR24/minHCO342 mmol/LBE+16 mmol/LMV4.8LSaO292%.Pts ventilatory pattern has changed to more rapid andshallow breathing.Although still acceptable the pH andCO2 are trending in the wrong direction.High-flow oxygen may be better for this pt to prevent intubationTake Home Message:Valuable information can be gained from an ABG as to the patients physiologic condition Remember that ABG analysis if only part of the patient assessment.Be systematic with your analysis,start with ABCs as always and look for hypoxia(which you can usually treat quickly),then follow the four steps.A quick assessment of patient oxygenation can be achieved with a pulse oximeter which measures SaO2.Its not magic understanding ABGs,it just takes a little practice!Any Questions?References1.Shapiro,Barry A.,et al;Clinical Application of BloodGases;19942.2.American Journal of Nursing1999;Aug99(8):34-63.3.Journal Post Anesthesia Nursing1990;Aug;5(4)264-724.4.Irvine,David;ABG Interpretation,A Rough and DirtyProductionPractice ABGs1.PaO2 90SaO295 pH 7.48 PaCO2 32 HCO3 242.PaO2 60SaO290 pH 7.32 PaCO2 48 HCO3 253.PaO2 95SaO2100 pH 7.30 PaCO2 40 HCO3 184.PaO2 87SaO2 94 pH 7.38 PaCO2 48 HCO3 285.PaO2 94SaO2 99 pH 7.49 PaCO2 40 HCO3 306.PaO2 62SaO2 91 pH 7.35 PaCO2 48 HCO3 277.PaO2 93SaO2 97 pH 7.45 PaCO2 47 HCO3 298.PaO2 95SaO2 99 pH 7.31 PaCO2 38 HCO3 159.PaO2 65SaO2 89 pH 7.30 PaCO2 50 HCO3 2410.PaO2 110 SaO2 100 pH 7.48 PaCO2 40 HCO3 30Answers to Practice ABGs1.Respiratory alkalosis2.Respiratory acidosis3.Metabolic acidosis4.Compensated Respiratory acidosis5.Metabolic alkalosis6.Compensated Respiratory acidosis7.Compensated Metabolic alkalosis8.Metabolic acidosis9.Respiratory acidosis10.Metabolic alkalosis