Arterial Blood Gas Analysis

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Arterial Blood Gas Analysis ..1
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Dr Satish Deopujari Pediatrician Hon. Prof. (
Pediatrics) JNMC Chairman National Intensive care
chapter Indian academy of pediatrics deopujari_at_red
iffmail.com Visit us at. http//rdsoxy.org
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The Goal
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To provide Bedside approach to
ABG analysis
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H ION CONC. N.MOLS / L.
OH ION
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pH
20 7.70 30
7.52 40
7.40 50
7.30 60
7.22
pH stand for "power of hydrogen"
H 80 - last two digits of pH
H ION
Dont click wait ..till Last message .. H
80-last two digits of pH
0
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Bicarbonate
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Standard Bicarbonate Plasma HCO3 after
equilibration to a PaCO2 of 40 mm Hg Reflects
non-respiratory acid base change No
quantification of the extent of the buffer
base abnormality
Base Excess D base to normalise HCO3 (to 24)
with PaCO2 at 40 mm Hg (Sigaard-Andersen)
Reflects metabolic part of acid base D 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 (Dont 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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Normal arterio/venous difference
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0 10 20 30 40 50 60 70 80 90 100 PaO2
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Rt. Shift
Oxygen delivered to tissues with normally
placed curve
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60
Delivered oxygen with Rt. Shift curve
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Normal
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Shift of the curve changes saturation for a
given PaO2
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Alveolar-arterial Difference
Inspired O2 21 piO2 (760-45) x . 21
150 mmHg
palvO2 piO2 pCO2 / RQ 150 40 / 0.8
150 50 100 mm Hg
O2 CO2
PaO2 90 mmHg
palvO2 partO2 10 mmHg
One click and wait
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Alveolar- arterial Difference
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Oxygenation Failure WIDE GAP piO2
150 pCO2 40 palvO2 150 40/.8 150-50
100 PaO2 45 D 100 - 45 55
Ventilation Failure NORMAL GAP piO2 150 pCO2
80 palvO2 150-80/.8 150-100 50 PaO2
45 D 50 - 45 5
O2 CO2

PAO2 (partial pres. of O2. in
the alveolus.)
150
- ( PaCO2 / .8 )
760 45 715 21 of 715 150
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Expected PaO2
FiO2 5 PaO2
Normal situation
20 5 100
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The essentials
The Blood Gas Report normals pH 7.40
0.05 PaCO2 40 5 mm Hg PaO2 80 - 100 mm
Hg HCO3 24 4 mmol/L O2 Sat gt95 Always
mention and see FIO2
HCO3
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The
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Steps for Successful Blood Gas Analysis
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Step 1 Look at the pH Is the patient acidemic
pH lt 7.35 or alkalemic pH gt 7.45

• 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 lt 20 mmol/L metabolic
• With PCO2 gt45 mm hg respiratory
• Alkalemia With HCO3 gt28 mmol/L metabolic
• With PCO2 lt35 mm Hg respiratory

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Step 3 If there is a primary respiratory
disturbance, is it acute ?
10 mm Change PaCO2
.08 change in pH ( Acute ) .03 change in pH (
Chronic )

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• Step 4
• If the disturbance is metabolic is the
  respiratory
• compensation appropriate?
• For metabolic acidosisExpected 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 lt12 If gt12, Anion Gap
Acidosis
M ethanol U remia D iabetic Ketoacidosis P
araldehyde I nfection (lactic acid) E thylene
Glycol S alicylate

• Common pediatric causes
• Lactic acidosis
• 2) Metabolic disorders
• 3) Renal failure

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5
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th step
Clinical correlation
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Same direction
HCO3
pH
META.
Same direction
PaCO2
RESP.
pH
Opposite direction
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Remember the format pH PaCO2 PaO2
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HYPER VENTILATION
pH
PaCO2
BICARB CHANGES pH in same direction
Compensation
Bicarbonate
Primary lesion
Low Alkali
Primary lesion
METABOLIC ACIDOSIS
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Three clicks
HYPO VENTILATION
pH
PaCO2
BICARB CHANGES pH in same direction
Compensation
Bicarbonate
High Alkali
Primary lesion
METABOLIC ALKALOSIS
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Three clicks Wait for red circle
pH
CO 2 CHANGES pH in opposite direction
BICARB
compensation
PaCO 2
High CO2
Respiratory acidosis
Primary lesion
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ALKALOSIS META.
RESP. ACIDOSIS
PCO2
pH

CO2H20H2CO3 H HCO3
HIGH H HIGH HCO3

HCO3
HCO3
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Three clicks Wait for red circle
pH
PaCO 2 CHANGES pH in opposite direction
BICARB
compensation
PaCO 2
Primary lesion
Low PaCO2
Primary lesion
Respiratory alkalosis
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RESP. ALK.
ACID. META.
pH

CO2 H20 H2CO3 H HCO3
CO2
SERUM HCO3

LOW H IONS LOW HCO3
Bicarbonate
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pH
PaCO2 of 10
Acute change .08 Chronic change .03
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INTERPRETATION OF A.B.G.

• FOUR STEP METHOD OF DEOSAT
• LOOK FOR pH
• WHO IS THE CULPRIT ?
• IF RESPIRATORY ACUTE / CHRONIC ?
• IF METABOLIC / COMP. / ANION GAP
• CLINICAL CORRELATION

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considered complete when the pH returns to
normal range
compensation
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Clinical blood gases by Malley
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METABLIC ACIDOSIS PaCO2 Up to 10 ? METABOLIC
ALKALOSIS PaCO2 Maximum 6O RESPIRATORY
ACIDOSIS BICARB Maximum 40 RESPIRATORY
ALKALOSIS BICARB Up to 10
COMPENSION LIMITS
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One click for answer
Case 1 16 year old female with sudden onset of
dyspnea. No Cough or Chest Pain Vitals normal
but RR 56, anxious.
Blood Gas Report Measured 37.0o
C pH 7.523 PaCO2 30.1 mm Hg PaO2 105.3 mm
Hg Calculated Data HCO3 act 22 mmol / L O2
Sat 98.3 PO2 (A - a) 8 mm Hg D PO2 (a /
A) 0.93 Entered Data FiO2 21.0
Acute respiratory alkalosis And why acute ?
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Case 2 6 year old male with progressive
respiratory distress
Muscular dystrophy .
Blood Gas Report Measured 37.0o
C pH 7.301 PaCO2 76.2 mm Hg PaO2 45.5 mm
Hg Calculated Data HCO3 act 35.1 mmol / L O2
Sat 78 PO2 (A - a) 9.5 mm Hg D PO2 (a /
A) 0.83 Entered Data FiO2 21
D CO2 76-4036 Expected D pH for ( Acute ) .08
for 10 Expected ( Acute ) pH 7.40 -
0.297.11 Chronic resp. acidosis
Chronic respiratory acidosis With hypoxia due to
hypoventilation
Hypoventilation
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Last two digits pH
80 PaCO2
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pH
PaCO2
7.10
70
7.20
60
7.30
50
7.40
40
7.50
30
7.60
20
Acute respiratory change
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8-year-old male asthmatic with resp. distress
Case 3 8-year-old male asthmatic 3 days of
cough, dyspnea and orthopnea not responding to
usual bronchodilators. O/E Respiratory
distress suprasternal and intercostal
retraction tired looking on 4 L NC.
D CO2 49 - 40 9 Expected D pH ( Acute )
9/10 x 0.08 0.072 Expected pH ( Acute ) 7.40
- 0.072 7.328 Acute resp. acidosis
piO2 715x.3214.5 / palvO2 214-49/.8153
Wide A / a gradient
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Case 4 8 year old diabetic with respi. distress
fatigue and loss of appetite.
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Blood Gas Report Measured 37.0o
C pH 7.23 PaCO2 23 mm Hg PaO2 110.5 mm
Hg Calculated Data HCO3 act 14 mmol / L O2
Sat PO2 (A - a) mm Hg D PO2 (a /
A) Entered Data FiO2 21.0
If Na 130, Cl 90 Anion Gap 130 - (90
14) 130 104 26
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Case 5 10 year old child with encephalitis
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Blood Gas Report Measured 37.0o
C pH 7.46 PaCO2 28.1 mm Hg PaO2 55.3 mm
Hg Calculated Data HCO3 act 19.2 mmol / L O2
Sat PO2 (A - a) mm Hg D PO2 (a /
A) Entered Data FiO2 24.0
BICARBINATURIA
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Case 6.
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pH 7.39 PCO2 l5mmHg HCO3 8mmol/L PaO2 90 mmHg
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.
For metabolic acidosis FULL COMPENSATION Expected
PaCO2 (1.5 x HCO3) 8 ) 2 (Winters
equation) PCO 2 SHOULD BE 20
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Case 7.
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 mmHg HCO3 8mmol/L
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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.
What is the probable cause for the above findings
? Are they OK as far as oxygenation is concerned
?
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Patient was hypo volumic , received Normal Saline
bolus... Corrected acidosis He was operated
.but post-op became drowsy His
ABG.. FiO2.30
pH 7.38 PaCO2 38 PaO2 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 surgery Pure and
simple hypoventilation ? sedation
PRE OP .ABG on room air pH 7.39 PaCO2 l5mmHg
PaO2 90 mmHg HCO3 8mmol/L
Oxygenation status good ..?
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
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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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Learning point
Correlate PaO2 with FiO2 But please also
correlate with PaCO2
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Case 8,,,,,,,,,,,,,,,,,,
pH 7.583 PCO2 19.8 HCO3 18.7
Respiratory Alkalosis Is it acute ?
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Bicarb.
pH
CO2
THANKS