Download - Arterial Blood Gas Analysis …..1
Arterial Blood Gas Analysis …..1
Dr Satish DeopujariPediatricianHon. Prof. ( Pediatrics) JNMCChairman NationalIntensive care chapterIndian academy of [email protected]
Visit us at…. http://rdsoxy.org
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The Goal :
To provide Bedside approach to ABG analysis
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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
Don’t click wait …..till Last message …….. “H = 80-last two digits of pH”
Bicarbonate:
Henderson - Hasselbach equation:
pH = pK + Log HCO3
Dissolved CO2
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Standard Bicarbonate:Plasma HCO3 after equilibrationto a PaCO2 of 40 mm Hg
: Reflects non-respiratory acid base change: No quantification of the extent of the buffer base abnormality
Base Excess: base to normalise HCO3 (to 24) with PaCO2 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
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Oxygenation Indices:O2 Content of blood:Hb. x O2 Sat + Dissolved O2
(Don’t forget hemoglobin)
Oxygen Saturation: reported as ABG report( Derived from oxygen dis. curve not a measured value )
Alveolar / arterial gradient:( Useful … to classify respiratory failure )
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0 10 20 30 40 50 60 70 80 90 100 PaO2
20
40
60
80
100
Rt. Shift
Normal arterio/venous difference
Shift of the curve ……changes saturation for a given PaO2
Normal
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Oxygen delivered to tissues
with normally placed curve
Delivered oxygen with Rt. Shift curve
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
PaO2 = 90 mmHg
palvO2 – partO2 = 10 mmHg One click and wait
Alveolar- arterial Difference
O2
CO2
Oxygenation Failure WIDE GAPpiO2 = 150pCO2 = 40
palvO2= 150 – 40/.8=150-50 =100
PaO2 = 45
= 100 - 45 = 55
Ventilation Failure NORMAL GAPpiO2 = 150
pCO2 = 80
palvO2= 150-80/.8 =150-100= 50PaO2 = 45 = 50 - 45 = 5
PAO2 (partial pres. of O2. in the alveolus.) = 150 - ( PaCO2 / .8 )760 – 45 = 715 : 21 % of 715 = 150
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20 × 5 = 100
Expected PaO2 =
FiO2 × 5 = PaO2
Normal situation
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The Blood Gas Report: normals…
pH 7.40 + 0.05PaCO2 40 + 5 mm HgPaO2 80 - 100 mm Hg
HCO3 24 + 4 mmol/L
O2 Sat >95Always mention and see FIO2
The essentials
HCO3
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5The
Steps forSuccessfulBlood Gas
Analysis
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Step 2 Who is responsible for this change in pH ( culprit )? CO2 will change pH in opposite direction Bicarb. will change pH in same direction
Acidemia: With HCO3 < 20 mmol/L = metabolicWith PCO2 >45 mm hg = respiratory
Alkalemia:With HCO3 >28 mmol/L = metabolicWith PCO2 <35 mm Hg = respiratory
Step 1Look at the pH
Is the patient acidemic pH < 7.35or alkalemic pH > 7.45
Step 3If there is a primary respiratory disturbance, is it acute ?
.08 change in pH ( Acute )
.03 change in pH ( Chronic )
10 mm Change PaCO2
=
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Step 4If the disturbance is metabolic is the respiratorycompensation appropriate?For metabolic acidosis:Expected PaCO2 = (1.5 x [HCO3]) + 8 ) + 2 or simply…expected PaCO2 = last two digits of pH
For metabolic alkalosis:Expected PaCO2 = 6 mm for 10 mEq. rise in Bicarb.
Suspect if ............. actual PaCO2 is more than expected :
additional …respiratory acidosis actual PaCO2 is less than expected :
additional …respiratory alkalosis
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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 : M ethanolU remiaD iabetic KetoacidosisP araldehydeI nfection (lactic acid)E thylene GlycolS alicylate
Common pediatric causes1) Lactic acidosis2) Metabolic disorders3) Renal failure
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th step
Clinical correlation5
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HCO3 META.pH
PaCO2 pH RESP.
Same direction
Opposite direction
Same direction
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Remember the format
pHPaCO2
PaO2
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Primary lesionPrimary lesion
Compensation
pH
Bicarbonate
PaCO2
METABOLIC ACIDOSIS
HYPER VENTILATION
BICARB CHANGES pH in same direction
Low Alkali
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Primary lesion
Compensation
pH
Bicarbonate
PaCO2
METABOLIC ALKALOSIS
HYPO VENTILATION
BICARB CHANGES pH in same direction
High Alkali
Three clicks
Primary lesion
compensation
pH
PaCO 2
BICARB
Respiratory acidosis
CO 2 CHANGES pH in opposite direction
HighCO2
Three clicksWait for red circle
Primary lesionPrimary lesion
compensation
pH
PaCO 2
BICARB
Respiratory alkalosis
PaCO 2 CHANGES pH in opposite direction
LowPaCO2
Three clicksWait for red circle
PaCO2 of 10 pH
Acute change .08
Chronic change .03
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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
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compensatio
n
considered complete when the pH returns to normal range
Clinical blood gases by Malley
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CO
MP
EN
SIO
N
LIMIT
S
METABLIC ACIDOSISPaCO2 = Up to 10 ?
METABOLIC ALKALOSISPaCO2 = Maximum 6O
RESPIRATORY ACIDOSISBICARB = Maximum 40
RESPIRATORY ALKALOSISBICARB = Up to 10
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Blood Gas Report
Measured 37.0o
CpH 7.523PaCO2 30.1 mm HgPaO2 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.
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Acute respiratory alkalosis And why acute ?
Case 2 6 year old male with progressive respiratory distress
Muscular dystrophy .
Blood Gas Report
Measured 37.0o
CpH 7.301PaCO2 76.2 mm HgPaO2 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 %
pH <7.35 :acidemia
Res. Acidemia : High PaCO2 and low pH
HypoxemiaNormal A-a gradient
CO2 =76-40=36Expected pH for ( Acute ) = .08 for 10Expected ( Acute ) pH = 7.40 - 0.29=7.11Chronic resp. acidosis
Hypoventilation
Chronic respiratory acidosisWith hypoxia due to hypoventilation
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7.60 20 7.50 30 7.4040
7.3050
7.2060
7.1070
pHPaCO2
Acute respiratory change
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Last two digits
pH80 – PaCO2
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.
Blood Gas Report
Measured 37.0o
CpH 7. 24PaCO2 49.1 mm HgPaO2 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
PaCO2 >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 ?Bicarbonate is low……… 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
8-year-old male asthmatic with resp. distress Six clicks
Case 4 8 year old diabetic with respi. distress fatigue and loss of appetite.
Blood Gas Report
Measured 37.0o
CpH 7.23PaCO2 23 mm HgPaO2 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
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Blood Gas Report
Measured 37.0o
CpH 7.46PaCO2 28.1 mm HgPaO2 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
PaCO2 is low , respiratorylow by around 10 ( Acute ) by .08 (Chronic ) by .03
BICARBINATURIA
Bicarb looks low ?Is it expected ?
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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 l5mmHg HCO3 8mmol/L PaO2 90 mmHg
For metabolic acidosis: FULL COMPENSATIONExpected PaCO2 = (1.5 x [HCO3]) + 8 ) + 2(Winter’s equation)PCO 2 ……SHOULD BE 20
Case 6………….
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Adolescent boy with appendicitis , posted for surgery , he is a known case of SLE.His pre-op ABG shows: Room air pH 7.39 pCO2 l5mmHg paO2 90 mmHgHCO3 8mmol/L
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.
What is the probable cause for the above findings ? Are they OK as far as oxygenation is concerned ?
Case 7……….
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Patient was hypo volumic , received Normal Saline bolus... Corrected acidosisHe was operated ….but post-op became drowsy His ABG……..FiO2….30%
pH 7.38PaCO2 38PaO2 60
1) Why hypoxemia ?2) Were the lungs bad to begin with ? ( Pre OP PaO2 90 mmHg )
3) Micro atelectesis during surgery ? Anesthetist goofed up the case 4) Pure and simple hypoventilation …..Sedation ?
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Why hypoxemia ?Lungs were bad to begin with ?Micro atelectesis during surgeryPure and simple hypoventilation ? sedation
PRE OP ….ABG on room airpH 7.39 PaCO2 l5mmHg PaO2 90 mmHgHCO3 8mmol/L
Pre OP .....A/a gradient palvO2 = PiO2 – PaCO2 / RQ
= 150 – 15 / 0.8= 150 – 18 = 132 mm Hg
132 – 90= 42 WIDE A / a gradient
Oxygenation status good …..?
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Apparently the lungs looked good with PaO2 of 90…….But have a good look at the ABG again With wash out of CO 2 ……….The expected PaO2 should have been more than 90 .
This coupled with correction of acidosis( normalizing PaCO2 )Lowered the PaO2 …post operatively.Conclusion …….. Lungs were not normal to begin with ( SLE )……..
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Correlate PaO2 with FiO2
But please also correlate with PaCO2
Learning point
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Respiratory Alkalosis
Is it acute ?
What is the Diagnosis
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Case 8,,,,,,,,,,,,,,,,,,
pH 7.583PCO2 19.8HCO3 18.7
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