Download - Arterial Blood Gass - Analysis 01
Arterial Blood Gas Analysis …..1
Dr DeopujariPediatrician Nagpur
The Goal :
To provide simple and bedside approach to ABG report
Not to:To teach physiology .
To teach theories on acid-base regulation
To look for alternative approaches to interpretation
In details
A Systematic and pointed ………approach
Use of pH for Hydrogen Ion Activity ……..
The credit (or Blame) for introducing the term pH, the negative log of hydrogen ion (H+) concentration, goes to S. P. L. Sørensen (1868-1939), who apparently was tired of writing seven zeros in a paper on enzyme activity and wanted a simpler designation…..?.
H ION CONC.N.MOLS / L. pH
20 7.70
30 7.52
40 7.40
50 7.30
60 7.22H ION
OH ION
0
14
pH stand for "power of hydrogen"
H+ = 80 - last two digits of pH
The Anatomy of a Blood Gas Report
----- XXXX Diagnostics ------
Blood Gas Report248 05:36 Jul 22 2000Pt ID 2570 / 00
Measured 37.0o
CpH 7.463pCO2 44.4 mm HgpO2 113.2 mm Hg
Corrected 38.6o
CpH 7.439pCO2 47.6 mm HgpO2 123.5 mm Hg
Calculated DataHCO3 act 31.1 mmol / LHCO3 std 30.5 mmol / LBE 6.6 mmol / LO2 CT 14.7 mL / dlO2 Sat 98.3 %ct CO2 32.4 mmol / LpO2 (A - a) 32.2 mm HgpO2 (a / A) 0.79
Entered DataTemp 38.6 oCct Hb 10.5 g/dlFiO2 30.0 %
Measured Values the most important
Temperature Correction:Is there any value to it?
Calculated Data:Which are the useful ones?
Entered Data:As important
Bicarbonate:----- XXXX Diagnostics ------
Blood Gas Report
Measured 37.0o
CpH 7.463pCO2 44.4 mm HgpO2 113.2 mm Hg
Corrected 38.6o
C
Calculated DataHCO3 act 31.1 mmol / LHCO3 std 30.5 mmol / LBE 6.6 mmol / LO2 CT 14.7 mL / dlO2 Sat 98.3 %t CO2 32.4 mmol / LpO2 (A - a) 32.2 mm HgpO2 (a / A) 0.79
Entered DataTemp 38.6 oCct Hb 10.5 g/dlFiO2 30.0 %
Henderson - Hasselbach equation:
pH = pK + Log HCO3
Dissolved CO2
----- XXXX Diagnostics ------
Blood Gas Report
Measured 37.0o
CpH 7.463pCO2 44.4 mm HgpO2 113.2 mm Hg
Corrected 38.6o
C
Calculated DataHCO3 act 31.1 mmol / LHCO3 std 30.5 mmol / LBE 6.6 mmol / LO2 CT 14.7 mL / dlO2 Sat 98.3 %t CO2 32.4 mmol / LpO2 (A - a) 32.2 mm HgpO2 (a / A) 0.79
Entered DataTemp 38.6 oCct Hb 10.5 g/dlFiO2 30.0 %
Standard Bicarbonate:Plasma HCO3 after equilibrationto a PCO2 of 40 mm Hg
: reflects non-respiratory acid base change: does not quantify the extent of the buffer base abnormality : does not consider actual buffering capacity of blood
Base Excess: base to normalise HCO3 (to 24) with PCO2 at 40 mm Hg(Sigaard-Andersen)
: reflects metabolic part of acid base : no info. over that derived from pH, pCO2 and HCO3
: Misinterpreted in chronic or mixed disorders
----- XXXX Diagnostics ------
Blood Gas Report
Measured 37.0o
CpH 7.463pCO2 44.4 mm HgpO2 113.2 mm Hg
Corrected 38.6o
C
Calculated DataHCO3 act 31.1 mmol / LHCO3 std 30.5 mmol / LBE 6.6 mmol / LO2 CT 14.7 mL / dlO2 Sat 98.3 %t CO2 32.4 mmol / LpO2 (A - a) 32.2 mm HgpO2 (a / A) 0.79
Entered DataTemp 38.6 oCct Hb 10.5 g/dlFiO2 30.0 %
Oxygenation Parameters:O2 Content of blood:Hb x O2 Sat + Dissolved O2
Oxygen Saturation:( remember this is calculated )
Alveolar / arterial gradient:
Arterial / alveolar ratio:
Rt. Shift
Lt.Shift
Alveolar-arterial DifferenceInspired O2 = 21 % piO2 = (760-45) x . 21 = 150 mmHg
O2
CO2
palvO2 = piO2 – pCO2 / RQ
= 150 – 40 / 0.8= 150 – 50 = 100 mm Hg
partO2 = 90 mmHg
palvO2 – partO2 = 10 mmHg
Alveolar- arterial Difference
O2
CO2
Oxygenation FailurepiO2 = 150
pCO2 = 40
palvO2= 150 – 40/.8=150-50 =100
pO2 = 45
= 100 - 45 = 55
Ventilation FailurepiO2 = 150
pCO2 = 80
palvO2= 150-80/.8 =150-100
= 50
pO2 = 45
= 50 - 45 = 5 PAO2 (partial pres. of O2. in the alveolus.)
= 150 - ( PaCO2 / .8 )760 – 45 = 715 : 21 % of 715 = 150
----- XXXX Diagnostics ------
Blood Gas Report
Measured 37.0o
CpH 7.463pCO2 44.4 mm HgpO2 113.2 mm Hg
Corrected 38.6o
C
Calculated DataHCO3 act 31.1 mmol / L
O2 CT 14.7 mL / dlO2 Sat 98.3 %t CO2 32.4 mmol / LpO2 (A - a) 32.2 mm HgpO2 (a / A) 0.79
Entered DataTemp 38.6 oCct Hb 10.5 g/dlFiO2 30.0 %
Oxygenation: Limitations of parameters:
O2 Content of blood:Useful in oxygen transport calculationsDerived from calculated saturation
Oxygen Saturation:Ideally measured by co-oximetryCalculated values may be error-prone
Alveolar / arterial gradient:Reflects O2 exchange with fixed FiO2 ImpracticalDifferentiates hypoventilation as cause
Arterial / alveolar ratio:Proposed to be less variableSame limitations as A-a gradient
20 × 5 = 100
----- XXXX Diagnostics ------
Blood Gas Report
Measured 37.0o
CpH 7.463pCO2 44.4 mm HgpO2 113.2 mm Hg
Calculated DataHCO3 act 31.1 mmol / L
O2 Sat 98.3 %pO2 (A - a) 32.2 mm Hg
Entered DataFiO2 30.0 %
The Blood Gas Report:
pH 7.40 + 0.05PCO2 40 + 5 mm HgPO2 80 - 100 mm Hg
HCO3 24 + 4 mmol/L
O2 Sat >95Always mention and see FIO2
----- XXXX Diagnostics ------
Blood Gas Report
Measured 37.0o
CpH 7.463pCO2 44.4 mm HgpO2 113.2 mm Hg
Corrected 38.6o
CpH 7.439pCO2 47.6 mm HgpO2 123.5 mm Hg
Calculated DataHCO3 act 31.1 mmol / LHCO3 std 30.5 mmol / LBE 6.6 mmol / LO2 CT 14.7 mL / dlO2 Sat 98.3 %t CO2 32.4 mmol / LpO2 (A - a) 32.2 mm HgpO2 (a / A) 0.79
Entered DataTemp 38.6 oCct Hb 10.5 g/dlFiO2 30.0 %
The essentials
A ) low PAO2 ( Low Alveolar Pressure )
1) low barometric pressure,2) low fraction of inspired oxygen (FiO2) 3) Hypercarbia – elevated (PaCO2).
B ) Wide A / a gradient ( Normal Alveolar pressure )
1) Shunt ( cardiac or non cardiac )2) Diffusion abnormality
Low PaO2 can be the result of
Technical Errors Glass vs. plastic syringe: Changes in pO2 are not clinically importantNo effect on pH or pCO2
Heparin (1000 u / ml):Need <0.1 ml / ml of bloodpH of heparin is 7.0; pCO2 trends downAvoided by heparin flushing & drawing 2-4 cc blood
Delay in measurement:Rate of changes in pH, pCO2 and pO2 can be
reduced to 1/10 by cooling in ice slush(4o C)No major drifts up to 1 hour
5The
Steps forSuccessfulBlood Gas
Analysis
Step 1Look at the pH
Is the patient acidemic pH < 7.35or alkalemic pH > 7.45
Step 2Who is responsible for this change ( culprit )?
Acidemia: With HCO3 < 20 mmol/L = metabolicWith PCO2 >45 mm hg = respiratory
Alkalemia: With HCO3 >28 mmol/L = metabolicWith PCO2 <35 mm Hg = respiratory
The culprit
BICARB pH
CO2 pH
BICARB pH
CO2 pH
Step 3If there is a primary respiratory disturbance, is it acute?
(Acute)change in pH = 0.08 for 10 mm change in PCO2(Chronic)change in pH = 0.03 for 10 mm change in PCO2
Step 4If the disturbance is metabolic is the respiratorycompensation appropriate?
For metabolic acidosis:Expected PCO2 = (1.5 x [HCO3]) + 8 ) + 2(Winter’s equation)( Last two digits of pH )
For metabolic alkalosis:Expected PCO2 = 6 mm for 10 mEq. rise in Bicarb.
If : actual PCO2 more than expected : additional respiratory acidosisactual PCO2 less than expected : additional respiratory alkalosis
The last two digits
Step 4 cont.If there is metabolic acidosis, is there a wide anion gap ?
Na - (Cl-+ HCO3-) = Anion Gap usually <12
If >12, Anion Gap Acidosis : MethanolUremiaDiabetic KetoacidosisParaldehydeInfection (lactic acid)Ethylene GlycolSalicylate
Common pediatric causes1) Lactic acidosis2) Metabolic disorders3) Renal failure
th step
Clinical correlation5
HCO3 META.pH
PCO2 pH RESP.
Same direction
Opposite direction
Same direction
24 CO2
BICARBONATE = H ION CONC.
24 40 = 960
BICARBONATE = H ION CONC.
960 24
= H ION CONC. = 40 N.MOLS / L.
H+ N.MOLS / L. = 80 - last two digits of pH
N.MOLS / L.
N.MOLS / L.
Primary lesionPrimary lesion
compensation
pH
HCO3
CO2
METABOLIC ACIDOSIS
HYPER VENTILATION
BICARB CHANGES pH in same direction
Primary lesion
compensation
pH
HCO3
CO2
METABOLIC ALKALOSIS
HYPO VENTILATION
BICARB CHANGES pH in same direction
Primary lesion
compensation
pH
CO 2
BICARB
Respiratory acidosis
CO 2 CHANGES pH in opposite direction
pHCO2+H20=H2CO3 = H + HCO3+
HCO3HCO3
RESP. ACIDOSIS ALKALOSIS META.
ACUTE RISE : PCO2 10 : pH .08CHRONIC RISE : PCO2 10 : pH .03
PCO2
HIGH H HIGH HCO3
+
Primary lesionPrimary lesion
compensation
pH
CO 2
BICARB
Respiratory alkalosis
CO 2 CHANGES pH in opposite direction
CO2 + H20 = H2CO3 = H + HCO3+pH
HCO3LOW H IONS …LOW HCO3
RESP. ALK. ACID. META.
ACUTE FALL : PCO2 10 : pH .08CHRONIC FALL: PCO2 10 : pH .03
CO2
+
Pco2 of 10 pH
Acute change .08
Chronic change .03
INTERPRETATION OF A.B.G.
FOUR STEP METHOD OF DEOSAT
1) LOOK FOR pH
2) WHO IS THE CULPRIT ?
3) IF RESPIRATORY ACUTE / CHRONIC ?
4) IF METABOLIC / COMP. / ANION GAP
CLINICAL CORRELATION
compensatio
n
considered complete when the pH returns to normal range
Clinical blood gases by Malley
CO
MP
EN
SIO
N
LIMIT
S
METABLIC ACIDOSISCO2 = Up to 10 ?
METABOLIC ALKALOSISCO2 = Maximum 6O
RESPIRATORY ACIDOSISBICARB = Maximum 40
RESPIRATORY ALKALOSISBICARB = Up to 10
----- XXXX Diagnostics ------
Blood Gas Report
Measured 37.0o
CpH 7.523pCO2 30.1 mm HgpO2 105.3 mm Hg
Calculated DataHCO3 act 22 mmol / L
O2 Sat 98.3 %pO2 (A - a) 8 mm Hg pO2 (a / A) 0.93
Entered DataFiO2 21.0 %
----- XXXX Diagnostics ------
Blood Gas Report
Measured 37.0o
CpH 7.523pCO2 30.1 mm HgpO2 105.3 mm Hg
Calculated DataHCO3 act 22 mmol / L
O2 Sat 98.3 %pO2 (A - a) 8 mm Hg pO2 (a / A) 0.93
Entered DataFiO2 21.0 %
Case 1
16 year old female withsudden onset of dyspnea.
No Cough or Chest Pain
Vitals normal but RR 56,anxious.
Case 2 6 year old male with progressive respiratory distress
Muscular dystrophy .----- XXXX Diagnostics ------
Blood Gas Report
Measured 37.0o
CpH 7.301pCO2 76.2 mm HgpO2 45.5 mm Hg
Calculated DataHCO3 act 35.1 mmol / L
O2 Sat 78 %pO2 (A - a) 9.5 mm Hg pO2 (a / A) 0.83
Entered DataFiO2 21 %
----- XXXX Diagnostics ------
Blood Gas Report
Measured 37.0o
CpH 7.301pCO2 76.2 mm HgpO2 45.5 mm Hg
Calculated DataHCO3 act 35.1 mmol / L
O2 Sat 78 %pO2 (A - a) 9.5 mm Hg pO2 (a / A) 0.83
Entered DataFiO2 21 %
CO2 =76-40=36Expected pH ( Acute ) = .08 for 10Expected ( Acute ) pH = 7.40 - 0.29=7.11Chronic resp. acidosis
pH <7.35 :acidemia
respiratory acidemia : co2 and pH
HypoxiaNormal A-a gradientDue to hypoventilation
Case 38-year-old male asthmatic;3 days of cough, dyspneaand orthopnea notresponding to usualbronchodilators.
O/E: Respiratory distress;suprasternal and intercostal retraction;tired looking; on 4 L NC.
----- XXXX Diagnostics ------
Blood Gas Report
Measured 37.0o
CpH 7. 24pCO2 49.1 mm HgpO2 66.3 mm Hg
Calculated DataHCO3 act 18.0 mmol / L
O2 Sat 92 %pO2 (A - a) mm Hg pO2 (a / A)
Entered DataFiO2 30 %
----- XXXX Diagnostics ------
Blood Gas Report
Measured 37.0o
CpH 7. 24pCO2 49.1 mm HgpO2 66.3 mm Hg
Calculated DataHCO3 act 18.0 mmol / L
O2 Sat 92 %pO2 (A - a) mm Hg pO2 (a / A)
Entered DataFiO2 30 %
153-66= 87
pH <7.35 ; acidemia
pCO2 >45; respiratory acidemia
piO2 = 715x.3=214.5 / palvO2 = 214-49/.8=153 Wide A / a gradient
Hypoxia
WITH INCREASE IN CO2 BICARB MUST RISE ? Metabolic acidosis + respiratory acidosis
30 × 5 = 150
CO2 = 49 - 40 = 9Expected pH ( Acute ) = 9/10 x 0.08 = 0.072Expected pH ( Acute ) = 7.40 - 0.072 = 7.328Acute resp. acidosis
Case 4 8 year old diabetic with respi. distress fatigue and loss of appetite.
----- XXXX Diagnostics ------
Blood Gas Report
Measured 37.0o
CpH 7.23pCO2 23 mm HgpO2 110.5 mm Hg
Calculated DataHCO3 act 14 mmol / L
O2 Sat %pO2 (A - a) mm Hg pO2 (a / A)
Entered DataFiO2 21.0 %
----- XXXX Diagnostics ------
Blood Gas Report
Measured 37.0o
CpH 7.23pCO2 23 mm HgpO2 110.5 mm Hg
Calculated DataHCO3 act 14 mmol / L
O2 Sat %pO2 (A - a) mm Hg pO2 (a / A)
Entered DataFiO2 21.0 %
pH <7.35 ; acidemia
HCO3 <22; metabolic acidemia
Last two digits of pHCorrespond with co2
If Na = 130, Cl = 90Anion Gap = 130 - (90 + 14)
= 130 – 104 = 26
----- XXXX Diagnostics ------
Blood Gas Report
Measured 37.0o
CpH 7.46pCO2 28.1 mm HgpO2 55.3 mm Hg
Calculated DataHCO3 act 19.2 mmol / L
O2 Sat %pO2 (A - a) mm Hg pO2 (a / A)
Entered DataFiO2 24.0 %
----- XXXX Diagnostics ------
Blood Gas Report
Measured 37.0o
CpH 7.46pCO2 28.1 mm HgpO2 55.3 mm Hg
Calculated DataHCO3 act 19.2 mmol / L
O2 Sat %pO2 (A - a) mm Hg pO2 (a / A)
Entered DataFiO2 24.0 %
Case 5 : 10 year old child with encephalitis
pH almost within normal rangeMild alkalosis
Co2 is low , respiratoryCo2 low by around 10 ( Acute ) by .08 (Chronic ) by .03
Bicarb looks low ?Is it expected ?
More cases
ABG OF THE DAY
The arterial blood gas report : Room air pH 7.39 PCO2 l5mniHg HCO3 8mmol/L PaO2 90 mmHg
PCO2 24
BICARBONATEH ION CONCENTRATION =
= 45 nmol/lit
1) These findings are most consistent with…. a) Metabolic acidosis with compensatory Hypocapnia. b) Primary metabolic acidosis with
respiratory alkalosis. c) Acute respiratory alkalosis fully compensated. d) Chronic respiratory alkalosis fully compensated.
pH 7.39 PCO2 l5mniHg HCO3 8mmol/L PaO2 90 mmHg
For metabolic acidosis: FULL COMPENSATIONExpected PCO2 = (1.5 x [HCO3]) + 8 ) + 2(Winter’s equation)PCO 2 ……SHOULD BE 20
2) What is the oxygenation status a) Normal oxygenation status b) Hypoxemia c) None of the above
palvO2 = piO2 – pCO2 / RQ
= 150 – 15 / 0.8= 150 – 18 = 132 mm Hg
132 – 90 = 42 WIDE A / a gradient
pH 7.39 PCO2 l5mniHg HCO3 8mmol/L PaO2 90 mmHg
pCO2 pH
70 7.10
60 7.20
50 7.30
40 7.40
30 7.50
20 7.60
When pH is normal and: Bicarbonate is high ( Metabolic alkalosis + respiratory acidosis ) Bicarbonate is low ( Metabolic acidosis + resp. alkalosis) Bicarbonate is normal and: anion gap is high ( Metabolic Acidosis + Metabolic alkalosis) When bicarbonate is normal and: pH is in acidic range ( Chronic resp. acidosis + resp alk.) pH is in alkalemic range ( Metab.alk. + resp alk.) Anion gap is elevated and: clinical and laboratory data suggest a diagnosis other than metabolic acidosis PCO2 level and bicarbonates are shifted from normal in opposing directions.
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