Transcript PULMONARY EMBOLISM

Blood Gas Analysis
Dr. Prakash Mohanasundaram
Department of Emergency & Critical Care medicine
Vinayaka Missions University
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Primary & Compensatory changes
Primary
change
PaCO2
Compensation
PaCO2
[HCO3]
Metabolic
acidosis
[HCO3]
PaCO2
Metabolic
alkalosis
[HCO3]
PaCO2
Respiratory
acidosis
Respiratory
alkalosis
[HCO3]
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THE
SIX
STEP
APPROACH
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The 6 step approach
1) Acidemic or Alkalemic
2) Is the primary disturbance respiratory
or metabolic
3) If Respiratory, is it acute or chronic
4) If Metabolic, is there an anion gap?
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The 6 step approach
5) Are there any other metabolic
disturbances with the anion gap
acidosis?
6) Assess normal respiratory
compensation for a metabolic
disturbance.
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Step - 1
Acidemic or Alkalemic
Acidemic : pH < 7.35
Alkalemic : pH > 7.45
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Step - 2
Is the primary disturbance Respiratory or
Metabolic
Respiratory disorder will alter the PaCO2
High CO2 in acidosis ,Low CO2 in alkalosis
Go to Step – 3
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Step - 2
Metabolic disorder will alter the
[HCO3] HCO3 < 22, metabolic
acidosis
“Go to Step-4”
HCO3 >26 ,metabolic alkalosis
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Step - 3
RESPIRATORY
ACUTE
CHRONIC
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Step - 3
Respiratory Acidosis
Acute
pH = 0.08 x (PaCO2 – 40 ) /10
pH
Chronic
= 0.03 x (PaCO2 – 40 ) /10
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Step - 3
Respiratory Alkalosis
Acute
pH = 0.08 x (PaCO2 – 40 ) /10
Chronic
pH = 0.03 x (PaCO2 – 40 ) /10
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Respiratory Acidosis
Hypoventilation : PaCO2
CNS depression : Sedatives , CNS disease
Lung disease : Asthma , Chronic lung
disease
Musculoskeletal disorders : GBS ,
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Myasthenia
Respiratory Alkalosis
Hyperventilation : PaCO2
CNS events ( hemorrhage)
Drugs ( salicylates)
Anxiety
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Step - 4
METABOLIC ACIDOSIS
CHECK ANION GAP
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Step - 4
Anion Gap = Na- (Cl + HCO3)
Usually 12 +- 2
Anion Gap Metabolic acidosis : AG > 12
Non Anion Gap acidosis : AG < 12
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Anion Gap Metabolic Acidosis
HCO3
& AG
Methanol
Uremia
DKA
Paraldehyde
Infection
Lactic acid
Ethylene glycol
Salicylates
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Non-Anion Gap Metabolic acidosis
Loss of HCO3, or external acid infusion
Low HCO3 but AG < 12
GI loss of HCO3 (Diarrhea)
Renal losses
Renal tubular necrosis
Carbonic anhydrase inhibitors
Ureteral diversion
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Step - 5
Is there another metabolic disturbance
co-existing with an anion gap acidosis
Corrected HCO3 = HCO3 + (AG – 12)
Corrected HCO3 > 24 : Additional
metabolic alkalosis
Corrected HCO3 < 24 : Non AG acidosis
co-exists .
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Example
Anion Gap Metabolic acidosis
HCO3 10 , AG 26
Corrected HCO3 = 1O + (26-12) =24
No additional disturbance
HCO3 15 , AG 26
Corrected HCO3 = 15 + (26-12) =29
Co-existing metabolic alkalosis
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Step-6
Assess normal respiratory compensation for
a metabolic acidosis
Winter’s formula
Expected PaCO2 = (1.5 X HCO3) + (8 +- 2)
If HCO3 is 10 , PaCO2 should be 21-25
If PaCO2 < 21, additional respiratory alkalosis
If PaCO2 >25, additional respiratory acidosis
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Step - 6
Assess normal respiratory compensation
for a metabolic disturbance
In metabolic Alkalosis winters formula
not applicable
PaCO2 will rise, but not over 50-55
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Case 1
Measured
pH
7.24
PCO2 60 mm Hg
PO2 56 mm Hg
Calculated
HCO3 24mmol/L
BE
+2
SaO2
85 %
FiO2 70%
5 Month old baby with Bronchiolitis
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Case 1
pH
PCO2
PO2
7.24
60 mm Hg
56 mm Hg
HCO3
24mmol/L
Step-1
Acidemia or Alkalemia ?
Acidemia
Step-2
Primary disturbance
Respiratory
Step-3
Acute or Chronic
pH = 0.08 x (60-40) / 10 = 0.16
7.4 – 0.16 = 7.24
Acute Respiratory Acidosis
Uncompensated
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Case 2
3 year old with severe diarrhea , diminished
urine output, lethargy, Na-135 , Cl- 115
Measured
pH
7.10
PCO2 20 mm Hg
PO2 87 mm Hg
Calculated
HCO3 8 mmol/L
- 15
SaO2 96%
BE
FiO2 24%
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Case 2
Step-1
pH
7.10
PCO2 20 mm Hg
PO2
87 mm Hg
HCO3 8 mmol/L
Acidemia or Alkalemia ?
Acidemia
Na-135 , Cl- 115
Step-2
Primary disturbance
Metabolic
Step-4
What is the Anion Gap ?
Na- (Cl + HCO3) 135-(115 + 8) = 12
Step-6
What is the expected CO2 ?
Expected PaCO2 = (1.5 x HCO3) +( 8 +- 2 )
=( 1.5 x 8 ) + ( 8 +- 2 ) = 18 – 22
Compensated metabolic acidosis
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Case 3
Measured
Calculated
pH
7.1o
PCO2 60 mm Hg
PO2
60 mm Hg
HCO3 10 mmol/L
BE
- 15
SaO2 87 %
FiO2 100%
50 Year old resuscitated after a cardiac
arrest. Na-142 , Cl- 108
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Case 3
pH
7.1o
PCO2 60 mm Hg
PO2
60 mm Hg
HCO3
10 mmol/L
Na-142 , Cl- 108
Step-1
Acidemia or Alkalemia ?
Acidemia
Step-2
Primary disturbance
Metabolic
Step-4
What is the Anion Gap ?
Na- (Cl + HCO3) 142-(108 + 10) = 24
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Case 3
Step – 5 What is the corrected HCO3
Corrected HCO3 = HCO3 + (AG – 12 )
10 + ( 24 – 12 ) = 22
Step – 6 What is the expected CO2 ?
Expected PaCO2 = (1.5 x HCO3) +( 8 +- 2 )
( 1.5 x 10 ) + ( 8 +- 2 ) = 21 – 25
Mixed metabolic and respiratory acidosis
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Case 4
Measured
pH
7.52
PCO2 26 mm Hg
PO2 112mm Hg
Calculated
HCO3 22 mmol/L
BE
+2
SaO2
99%
FiO2 33%
4 year girl with lethargy, irritability,
jaundice
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Case 4
Step-1
Step-2
Step-3
pH
7.52
PCO2 26 mm Hg
PO2
112mm Hg
HCO3 22 mmol/L
Acidemia or Alkalemia ?
Alkalemia
Primary disturbance
Respiratory
Acute or Chronic
pH = 0.08 x (26-40) / 10 = 0.11
7.4 + 0.11 = 7.51
Acute Respiratory Alkalosis
Uncompensated
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THANK YOU
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