Basics In Arterial Blood Gas Interpretation

1. Basics in Arterial
Blood Gas
Interpretation
Crisbert I. Cualteros, M.D.

2. Obtaining Blood GasObtaining Blood Gas
SamplesSamples
Radial artery- best siteRadial artery- best site
 located superficially, easy to palpatelocated superficially, easy to palpate
& stabilize& stabilize
 excellent collateral circulation viaexcellent collateral circulation via
ulnar arteryulnar artery
 not adjacent to large veinsnot adjacent to large veins
 probing needle relatively pain-free ifprobing needle relatively pain-free if
periosteum is avoidedperiosteum is avoided

3. TechniqueTechnique for Radial Arteryfor Radial Artery
PuncturePuncture
 Explain process to patient. Examine skin,Explain process to patient. Examine skin,
palpate radial & ulnar arteries. Performpalpate radial & ulnar arteries. Perform
modified Allen Test.modified Allen Test.

4. The Allen TestThe Allen Test
 have the patienthave the patient
clench his/her fistclench his/her fist
 press on bothpress on both
radial and ulnarradial and ulnar
arteriesarteries
 have the patienthave the patient
unclench fistunclench fist
 test for goodtest for good
collateral flow.collateral flow.

5. Technique for Radial ArteryTechnique for Radial Artery
PuncturePuncture
 Position patient- hyperextend wrist. CleanPosition patient- hyperextend wrist. Clean
site with 70% isopropyl alcohol.site with 70% isopropyl alcohol.
 Use latex gloves while doing procedure.Use latex gloves while doing procedure.
 Local anesthesia may be used.Local anesthesia may be used.
 Use G20 or G21 needle. Flush syringe withUse G20 or G21 needle. Flush syringe with
sodium heparin (10 mg/ml or 1,000sodium heparin (10 mg/ml or 1,000
units/ml) & empty.units/ml) & empty. 0.15-0.25 ml of heparin will0.15-0.25 ml of heparin will
anticoagulate 2-4 ml of blood.anticoagulate 2-4 ml of blood.

6. Technique for Radial ArteryTechnique for Radial Artery
PuncturePuncture
 Palpate artery with one hand while holdingPalpate artery with one hand while holding
properly prepared syringe & needle with otherproperly prepared syringe & needle with other
hand. Hold syringe like a pencil & enter skinhand. Hold syringe like a pencil & enter skin
at 45at 45
o
. Advance needle slowly.
 Never redirect needle without first withdrawing toNever redirect needle without first withdrawing to
subcutaneous tissue.subcutaneous tissue.
 Obtain 2-4 ml blood. If possible don’t aspirate.Obtain 2-4 ml blood. If possible don’t aspirate.
 Remove air bubbles from syringe. ImmediatelyRemove air bubbles from syringe. Immediately
seal syringe with cap.seal syringe with cap.
 Place sample in ice slush. Analyze blood samplePlace sample in ice slush. Analyze blood sample
within 10 minutes.within 10 minutes.
 Apply pressure to site until bleeding has stopped.Apply pressure to site until bleeding has stopped.

7. Potential ComplicationsPotential Complications
 PainPain
 Hematoma, hemorrhageHematoma, hemorrhage
 Trauma to vesselTrauma to vessel
 ArteriospasmArteriospasm
 Air or clotted-bloodAir or clotted-blood
emboliemboli
 Vasovagal responseVasovagal response
 Arterial occlusionArterial occlusion
 InfectionInfection

8. Indications for ABGIndications for ABG
 Assess ventilation & acid-baseAssess ventilation & acid-base
balancebalance
 Assess oxygenation statusAssess oxygenation status

9. Ventilatory/Ventilatory/
Acid-Base StatusAcid-Base Status

10. Henderson-Hasselbach Parameters & theirHenderson-Hasselbach Parameters & their
normal laboratory rangesnormal laboratory ranges
pH=pH= [HCO[HCO33]p]p
PPC02C02
pHpH PCO2PCO2
(mmHg)(mmHg)
[HCO3]p[HCO3]p
(mmol/L)(mmol/L)
NormalNormal 7.35-7.457.35-7.45 35-4535-45 22-2622-26
AcidoticAcidotic < 7.35< 7.35 > 45> 45 < 22< 22
AlkaloticAlkalotic > 7.45> 7.45 < 35< 35 > 26> 26

11. Traditional Metabolic Acid-Base NomenclatureTraditional Metabolic Acid-Base Nomenclature
NomenclatureNomenclature pHpH PCOPCO22
[HCO3][HCO3]
pp
BEBE
Metabolic acidosisMetabolic acidosis
Uncompensated (acute)Uncompensated (acute)  NN  (-)(-)
Partly compensatedPartly compensated
(subacute)(subacute)
   (-)(-)
Compensated (chronic)Compensated (chronic) NN   (-)(-)
Metabolic alkalosisMetabolic alkalosis
Uncompensated (acute)Uncompensated (acute)  NN  (+)(+)
Partly compensatedPartly compensated
(subacute)(subacute)
   (+)(+)
Compensated (chronic)Compensated (chronic) NN   (+)(+)

12. Traditional Respiratory Acid-Base NomenclatureTraditional Respiratory Acid-Base Nomenclature
NomenclatureNomenclature pHpH PCOPCO
22
[HCO3][HCO3]
pp
BEBE
RespiratoryRespiratory
acidosisacidosis
Uncompensated (acute)Uncompensated (acute)   NN NN
Partly compensatedPartly compensated
(subacute)(subacute)
   
Compensated (chronic)Compensated (chronic)
NN   
RespiratoryRespiratory
alkalosisalkalosis
Uncompensated (acute)Uncompensated (acute)   NN NN
Partly compensatedPartly compensated
(subacute)(subacute)
   
Compensated (chronic)Compensated (chronic) NN   

13. Base Excess/ DeficitBase Excess/ Deficit
 Blood with large buffering capacity:Blood with large buffering capacity:
significant changes in acid content with little change in freesignificant changes in acid content with little change in free
HH++
concentrations (pH)concentrations (pH)
 Acidemia or alkalemia:Acidemia or alkalemia:  buffering capacity, > potential forbuffering capacity, > potential for
pH change from any given change in HpH change from any given change in H++
contentcontent
 Buffering capacity depends on:Buffering capacity depends on:
[HCO[HCO33
--
]]
RBC massRBC mass
other factorsother factors
 Base excess/deficit= (measured pH – predicted pH) x 100 xBase excess/deficit= (measured pH – predicted pH) x 100 x
2/32/3
Normal metabolic acid-base status:Normal metabolic acid-base status: ++ 3 mmol/L3 mmol/L
Relatively balanced metabolic acid-base status:Relatively balanced metabolic acid-base status: ++ 55
mmol/Lmmol/L
Clinically significant imbalance:Clinically significant imbalance: ++ 1010
mmol/Lmmol/L

14. Nomenclature & Criteria for Clinical InterpretationNomenclature & Criteria for Clinical Interpretation
Clinical TerminologyClinical Terminology CriteriaCriteria
Ventilatory failureVentilatory failure (respiratory acidosis)(respiratory acidosis) PPaaCOCO22 > 45> 45
mm Hgmm Hg
Acute ventilatory failureAcute ventilatory failure (respiratory acidosis)(respiratory acidosis) PPaaCOCO22 > 45> 45
mmHgmmHg pH < 7.35pH < 7.35
Chronic ventilatory failureChronic ventilatory failure (respiratory acidosis)(respiratory acidosis) PPaaCOCO22 > 45> 45
mmHgmmHg
pH 7.36- 7.44pH 7.36- 7.44
Alveolar hyperventilationAlveolar hyperventilation (respiratory alkalosis)(respiratory alkalosis) PPaaCOCO22 < 35< 35
mmHgmmHg
Acute alveolar hyperventilationAcute alveolar hyperventilation (respiratory(respiratory PPaaCOCO22 < 35< 35
mmHgmmHg
alkalosis)alkalosis) pH > 7.45pH > 7.45
Chronic alveolar hyperventilationChronic alveolar hyperventilation (respiratory(respiratory PPaaCOCO22 < 35< 35
mmHgmmHg alkalosis)alkalosis) pH 7.36-pH 7.36-
7.447.44

15. Nomenclature & Criteria for Clinical InterpretationNomenclature & Criteria for Clinical Interpretation
Clinical TerminologyClinical Terminology CriteriaCriteria
AcidemiaAcidemia pH < 7.35pH < 7.35
AlkalemiaAlkalemia pH > 7.45pH > 7.45
AcidosisAcidosis HCOHCO33
--
< 22 mmol/L< 22 mmol/L
BD > 5 mmol/LBD > 5 mmol/L
AlkalosisAlkalosis HCOHCO33
--
> 26 mmol/L> 26 mmol/L
BE > 5 mmol/LBE > 5 mmol/L
CombinedCombined Respiratory Acidosis & Metabolic AcidosisRespiratory Acidosis & Metabolic Acidosis
Respiratory Alkalosis & Metabolic AlkalosisRespiratory Alkalosis & Metabolic Alkalosis
MixedMixed Respiratory Acidosis & Metabolic AlkalosisRespiratory Acidosis & Metabolic Alkalosis
Respiratory Alkalosis & Metabolic AcidosisRespiratory Alkalosis & Metabolic Acidosis

16. RespiratoryRespiratory
AcidosisAcidosis
AcuteAcute
pH =pH = 0.08 x (PCO0.08 x (PCO22 – 40)– 40)
1010
ex. PCOex. PCO22 = 60= 60
 pH =pH = 0.08 x (60 - 40)0.08 x (60 - 40) = 0.16= 0.16
1010
expected pH = 7.40 – 0.16 = 7.24expected pH = 7.40 – 0.16 = 7.24
HCOHCO33
--
increases 0.1 – 1 meq/L per 10 mmHg PCOincreases 0.1 – 1 meq/L per 10 mmHg PCO22
increaseincrease
Compensation: cellular buffering: HCO3
renal adaptation: H+
secretion, Cl-
reabsorption,
net acid excretion

17. Respiratory acidosisRespiratory acidosis
ChronicChronic
pH =pH = 0.03 x (PCO0.03 x (PCO22 – 40)– 40)
1010
ex. PCOex. PCO22 = 60= 60
 pH =pH = 0.03 x (60 – 40)0.03 x (60 – 40) = 0.06= 0.06
1010
expected pH = 7.40 – 0.06 = 7.34expected pH = 7.40 – 0.06 = 7.34
HCOHCO33
--
increases 1-3.5 meq/L per 10 mmHg PCOincreases 1-3.5 meq/L per 10 mmHg PCO22
increaseincrease

18. Respiratory AcidosisRespiratory Acidosis
 COPDCOPD
 OO22 excess in COPDexcess in COPD
 DrugsDrugs
• BarbituratesBarbiturates
• AnestheticsAnesthetics
• NarcoticsNarcotics
• SedativesSedatives
 Extreme ventilation-Extreme ventilation-
perfusion mismatchperfusion mismatch
 ExhaustionExhaustion
 Inadequate MVInadequate MV
 Neurologic disordersNeurologic disorders
 NeuromuscularNeuromuscular
diseasedisease
• PoliomyelitisPoliomyelitis
• ALLALL
• G-B syndromeG-B syndrome
• Electrolyte deficienciesElectrolyte deficiencies
(K(K++
, PO, PO44
--
))
• Myasthenia gravisMyasthenia gravis
 Excessive COExcessive CO22
productionproduction
• TPNTPN
• SepsisSepsis
• Severe burnsSevere burns
• NaHCONaHCO33 administrationadministration

19. RespiratoryRespiratory
AlkalosisAlkalosis
AcuteAcute
pH =pH = 0.08 x (40 – PCO0.08 x (40 – PCO22))
1010
ex. PCOex. PCO22 = 20= 20
pH =pH = 0.08 x (40 – 20)0.08 x (40 – 20) = 0.16= 0.16
1010
expected pH = 7.40 + 0.16 = 7.56expected pH = 7.40 + 0.16 = 7.56
HCOHCO33
--
decreases 0-2 meq/L per 10 mmHg PCOdecreases 0-2 meq/L per 10 mmHg PCO22
decreasedecrease
Compensation: cellular buffering
renal response: retention of endogenous acids,
excretion of HCO3

20. Respiratory AlkalosisRespiratory Alkalosis
ChronicChronic
pH =pH = 0.03 x (40 – PCO0.03 x (40 – PCO22))
1010
ex. PCOex. PCO22 = 20= 20
 pH =pH = 0.03 x (40 – 20)0.03 x (40 – 20) = 0.06= 0.06
1010
expected pH = 7.40 + 0.06 = 7.46expected pH = 7.40 + 0.06 = 7.46
HCOHCO33
--
decreases 2-5 meq/L per 10 mmHg PCOdecreases 2-5 meq/L per 10 mmHg PCO22
decreasedecrease

21. Respiratory AlkalosisRespiratory Alkalosis
Primary centralPrimary central
disordersdisorders
 HyperventilationHyperventilation
syndrome, anxietysyndrome, anxiety
 Cerebrovascular diseaseCerebrovascular disease
 Meningitis, encephalitisMeningitis, encephalitis
Pulmonary diseasePulmonary disease
 Interstitial fibrosisInterstitial fibrosis
 PneumoniaPneumonia
 Pulmonary embolismPulmonary embolism
 Pulmonary edemaPulmonary edema
(some patients)(some patients)
HypoxiaHypoxia
Septicemia,Septicemia,
hypotensionhypotension
Hepatic failureHepatic failure
DrugsDrugs
 SalicylatesSalicylates
 NicotineNicotine
 XanthinesXanthines
 ProgestationalProgestational
hormoneshormones
High altitudeHigh altitude
Mechanical ventilatorsMechanical ventilators

22. Metabolic AcidosisMetabolic Acidosis
Anion GapAnion Gap
 artificial disparity between major plasma cationsartificial disparity between major plasma cations
& anions that are routinely measured& anions that are routinely measured
 major plasma cationsmajor plasma cations –– major plasma anionsmajor plasma anions
 [Na[Na++
]] –– ([Cl([Cl--
] + [HCO3] + [HCO3--
])])
 1212 ++ 2 (normal)2 (normal)
 Minor cations: KMinor cations: K++
, Ca, Ca++++
 Minor anions: phosphates, sulfates, organicMinor anions: phosphates, sulfates, organic
anionsanions

23. Metabolic AcidosisMetabolic Acidosis
 Anion gap acidosisAnion gap acidosis
~ process increases “minor anions”~ process increases “minor anions”
~ ex. lactatemia, ketonemia, renal failure,~ ex. lactatemia, ketonemia, renal failure,
excessiveexcessive
organic salt treatment, dehydration,organic salt treatment, dehydration,
ingestioningestion
(salicylates, methanol, ethylene glycol,(salicylates, methanol, ethylene glycol,
paraldehyde)paraldehyde)
~ process which decreases “minor cations” rare!~ process which decreases “minor cations” rare!
 Non-anion gap acidosisNon-anion gap acidosis
~ associated with increased plasma Cl~ associated with increased plasma Cl--
that hasthat has
replacedreplaced
HCOHCO3
--

24. Metabolic AcidosisMetabolic Acidosis
Abnormalities:Abnormalities:
 Overproduction of acidsOverproduction of acids
 Loss of buffer storesLoss of buffer stores
 Underexcretion of acidsUnderexcretion of acids

25. Metabolic AcidosisMetabolic Acidosis
Expected PCOExpected PCO22 = ( [HCO= ( [HCO33
--
] x 1.5) + 8] x 1.5) + 8 ++ 22
ex. [HCOex. [HCO33
--
] = 11] = 11
expected PCOexpected PCO22 = (11 x 1.5) + 8= (11 x 1.5) + 8 ++ 2 = 22.5-2 = 22.5-
26.526.5
PCOPCO22 decreases 1- 1.5 mmHg per 1 meq/L HCOdecreases 1- 1.5 mmHg per 1 meq/L HCO33
--
decreasedecrease

26. MetabolicMetabolic
AcidosisAcidosis
CompensationCompensation
 ↓↓ pCOpCO22 (hyperventilation)(hyperventilation)
 Pathway:Pathway:
↑ pCO2
HCO3
ratio ↑ H+
conc
Acidification of ECF ↓ ECF ↓ pH
Stimulation of brainstem ↑ RR ↓ pCO2
Normalization of pH
↓ HCO3

27. MetabolicMetabolic
AcidosisAcidosis
CompensationCompensation
 Ionic shiftIonic shift
• KK++
moves extracellularly for Hmoves extracellularly for H++
• HCOHCO33
--
generation, Hgeneration, H++
excretionexcretion

28. Corrected [HCOCorrected [HCO33
--
] for Anion Gap] for Anion Gap
Metabolic AcidosisMetabolic Acidosis
Measured serum [HCOMeasured serum [HCO33
--
] + (anion gap] + (anion gap
– 12)– 12)

29. Metabolic AlkalosisMetabolic Alkalosis
Expected PCOExpected PCO22 = ( [HCO= ( [HCO33
--
] x 0.75 ) + 20] x 0.75 ) + 20 ++ 55
ex. [HCOex. [HCO33
--
] = 34] = 34
expected PCOexpected PCO22 = (34 x 0.75) + 20= (34 x 0.75) + 20 ++ 5 = 40.5-5 = 40.5-
50.550.5
PCOPCO22 increases 0.5- 1 mmHg per 1 meq/L HCOincreases 0.5- 1 mmHg per 1 meq/L HCO33
--
increaseincrease

30. MetabolicMetabolic
AlkalosisAlkalosis
 PathwayPathway
HCO3
↓PaCO2
HCO3
ratio ↓ H+
conc
Alkalinization of ECF ↑ PaCO2 with mild hypoxemia
Normalization of pH

31. Causes of Metabolic Alkalosis
Hypokalemia*
Ingestion of large amounts of alkali or licorice
Gastric fluid loss: Vomiting, NG suctioning*
Hyperaldosteronism 20
to nonadrenal factors
Bartter’s syndrome
Inadequate renal perfusion
diuretics (inhibiting NaCl reabsorption)*
Bicarbonate administration
Sodium bicarbonate overcorrection
Blood transfusion
Adrenocortical hypersecretion (e.g tumor)
Steroids*
Eucapnic ventilation posthypercapnia
* Common in the ICU

32. Limits of CompensationLimits of Compensation
Imbalance [HCO3
-
] meq/L PCO2 mmHg
Respiratory AcidosisRespiratory Acidosis
AcuteAcute 0.1- 1/ 10 mmHg0.1- 1/ 10 mmHg
PCOPCO22
ChronicChronic 1- 3.5/ 10 mmHg1- 3.5/ 10 mmHg
PCOPCO22
Respiratory AlkalosisRespiratory Alkalosis
AcuteAcute 0- 2/ 10 mmHg PCO0- 2/ 10 mmHg PCO22
ChronicChronic 2- 5/ 10 mmHg PCO2- 5/ 10 mmHg PCO22
Metabolic AcidosisMetabolic Acidosis 1- 1.5/ 1 meq/L1- 1.5/ 1 meq/L
[HCO[HCO33
--
]] 
Metabolic AlkalosisMetabolic Alkalosis 0.5- 1/ 1 meq/L0.5- 1/ 1 meq/L
[HCO[HCO33
--
]] 

33. Steps for Analyzing Acid- Base DisturbancesSteps for Analyzing Acid- Base Disturbances
 Is patient acidemic or alkalotic?Is patient acidemic or alkalotic? pHpH
 Is disturbance primarily respiratory or metabolic?Is disturbance primarily respiratory or metabolic?
PCOPCO22, [HCO, [HCO33
--
]]
 If disturbance respiratory, is it acute or chronic?If disturbance respiratory, is it acute or chronic?
 If disturbance metabolic, is anion gap normal orIf disturbance metabolic, is anion gap normal or
abnormal?abnormal?
 If disturbance metabolic, is the respiratoryIf disturbance metabolic, is the respiratory
system compensating adequately?system compensating adequately?
 If disturbance is anion gap metabolic acidosis, areIf disturbance is anion gap metabolic acidosis, are
there any other metabolic disturbances present?there any other metabolic disturbances present?

34. Oxygenation StatusOxygenation Status

35. Normal ValuesNormal Values
 Seated PO2 = 104.2 – 0.27 (age in years)Seated PO2 = 104.2 – 0.27 (age in years)
Supine PO2 = 103.5 – 0.42 (age in years)Supine PO2 = 103.5 – 0.42 (age in years)
 PatientsPatients << 60 y. o.60 y. o.
PO2 = 100PO2 = 100 ++ 2020
 Patients > 60 y. o.Patients > 60 y. o.
PO2 = 80 – (# years > 60)PO2 = 80 – (# years > 60)

36. Steps for AnalyzingSteps for Analyzing
Oxygenation StatusOxygenation Status

37. 1. Is the patient hypoxemic or normoxemic?1. Is the patient hypoxemic or normoxemic?
Indices of Oxygenation:Indices of Oxygenation:
a. AaDOa. AaDO22 = PAO= PAO22 – PaO– PaO22
PAOPAO22 = FiO= FiO22 (713) –(713) – PaCOPaCO22
0.80.8
PaOPaO22 = obtained from blood gas determination= obtained from blood gas determination
b. aAOb. aAO22 == PaOPaO22
PAOPAO22
c. P/F ratio =c. P/F ratio = POPO22
FiOFiO22
Normal Value:Normal Value: patientspatients << 60 y. o. > 40060 y. o. > 400
patients > 60 y. o. expected P/F =patients > 60 y. o. expected P/F =
400400
–– [(age in years – 60) x 5][(age in years – 60) x 5]
Actual P/F Ratio < expected =Actual P/F Ratio < expected = hypoxemichypoxemic
Actual P/F RatioActual P/F Ratio >> expected =expected = normoxemicnormoxemic

38. 2. If hypoxemic, is it uncorrected,2. If hypoxemic, is it uncorrected,
corrected, or overcorrected?corrected, or overcorrected?
With OWith O22 supplementationsupplementation
PaOPaO22 (mmHg)(mmHg)
Uncorrected hypoxemiaUncorrected hypoxemia < 80< 80
Corrected hypoxemiaCorrected hypoxemia 80 – 12080 – 120
OvercorrectedOvercorrected > 120> 120
FiOFiO22 to PaOto PaO22 Relationship in Normal LungsRelationship in Normal Lungs
FiOFiO22 PaOPaO22 (mmHg)(mmHg)
0.300.30 > 150> 150
0.400.40 > 200> 200
0.500.50 > 250> 250
0.800.80 > 400> 400
1.001.00 > 500> 500

39. Room Air (patientRoom Air (patient << 60 y. o.)60 y. o.)
PaOPaO22 (mmHg)(mmHg)
Mild hypoxemiaMild hypoxemia 60 to < 8060 to < 80
Moderate hypoxemiaModerate hypoxemia 40 to < 6040 to < 60
Severe hypoxemiaSevere hypoxemia < 40< 40
For each year > 60 subtract 1 mmHg for limits ofFor each year > 60 subtract 1 mmHg for limits of
mild &mild &
moderate hypoxemia.moderate hypoxemia.
At any age, PaOAt any age, PaO22 < 40 mmHg indicates severe< 40 mmHg indicates severe
hypoxemia.hypoxemia.

40. 3. If normoxemic, is oxygenation3. If normoxemic, is oxygenation
adequate or more thanadequate or more than
adequate?adequate?

41. Thank you !Thank you !