arterial blood gas analysis
DESCRIPTION
ARTERIAL BLOOD GAS ANALYSIS. Arnel Gerald Q. Jiao, MD, FPPS, FPAPP Pediatric Pulmonologist Philippine Children’s Medical Center. Guidelines for Interpreting ABG’S. The body always tries to maintain a normal ph The lungs compensate rapidly; the kidneys compensate slowly - PowerPoint PPT PresentationTRANSCRIPT
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ARTERIAL BLOOD GASANALYSIS
Arnel Gerald Q. Jiao, MD, FPPS, FPAPPPediatric Pulmonologist
Philippine Children’s Medical Center
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Guidelines for Interpreting ABG’S
• The body always tries to maintain a normal ph
• The lungs compensate rapidly; the kidneys compensate slowly
• There is no overcompensation.
• Consider the underlying disease
• Maintain an adequate level of hemoglobin
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Bicarbonate-Carbonic AcidBuffer System:
CO2 + H2O H2CO3 H+ + HCO3-
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Normal Arterial Blood Gas Values
pH: 7.35 – 7.45
paCO2: 35 – 45 mm Hg
paO2: 80 – 100 mm Hg
HCO3: 22 – 26 mEq/LBE/BD: - 2 to + 2
O2 Sat: > 95 %
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Clinically Acceptable LevelspH: 7.30 – 7.50paCO2: 30 – 50 mm HgpaO2
Neonates: 60 – 80 mm Hg2 months above: 80 – 100 mmHgDecreases with age: Subtract
1 mm Hg from 80 mm Hg for every year past the age of 60
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Nomenclature for Clinical interpretation
• Acidosis: patho- physiologic state where a significant base deficit is present
(HCO3 < 22mEq/L)
• Alkalosis: patho-physiologic state where a significant base excess is present
(HCO3 > 26mEq/L)
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• Mathematical interrelationship among pH, pCO2 and HCO3
• Basis for all Acid-Base interpretation:
pH= HCO3/pCO2
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Clinical Approach to Interpretation:
Steps
1. Assessment of the pCO2 and pH:ventilatory status and acid-base balance
2. Assessment of Arterial Oxygenation
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Step 1
• Classify carbon dioxide tension
• Consider pH and determine classification
• Consider BE/BD or HCO3 levels and determine classification
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Step 1Classification of PaCO2
< 35 mmHg: alveolar hyperventilation
(respiratory alkalosis)
35 – 45 mmHg: Normal alveolar ventilation
> 45 mmHg: ventilatory failure (respiratory acidosis)
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Step 1Three questions to ask:
• Is the PaCO2 abnormal?• Is the pH explained by the level of PaCO2?
Yes: respiratoryNo: metabolic
• Is the pH:Abnormal: acute/uncompensatedNormal: chronic/ compensated
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Step 1PaCO2 < 35 mmHg
pH < 7.35 7.35 – 7.39 7.41 - 7.45 pH > 7.45
Partially Compensated
Metabolic
Acidosis
Compensated
Metabolic
Acidosis
Chronic
Respiratory
Alkalosis
Acute
Respiratory
Alkalosis
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PCO2 < 35 mm Hg
pH < 7.35
HCO3 decreased
partly compensated metabolic acidosis
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PCO2 < 35 mm Hg
pH 7.35 – 7.45
HCO3 decreased
chronic respiratory alkalosis
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PCO2 < 35 mm Hg
pH > 7.45
HCO3 normal
acute respiratory alkalosis
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PCO2 < 35 mm Hg
pH > 7.45
HCO3 decreased
partly compensated respiratory alkalosis
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PCO2 < 35 mm Hg
pH > 7.45
HCO3 increased
combined respiratory and metabolic alkalosis
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Step 1PaCO2 35 – 45 mmHg
pH < 7.35 7.35 – 7.45 pH > 7.45
Acute
Metabolic
Acidosis
Normal
Acid- Base
Balance
Acute
Metabolic
Alkalosis
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PCO2 35 – 45 mm Hg
pH < 7.35
HCO3 decreased
acute metabolic acidosis
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PCO2 35 – 45 mm Hg
pH 7.35 – 7.45
HCO3 normal
normal acid-base balance
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PCO2 35 – 45 mm Hg
pH > 7.45
HCO3 increased
acute metabolic alkalosis
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Step 1PaCO2 > 45 mmHg
pH < 7.35 7.35-7.39 7.41-7.45 pH > 7.45
Acute Resp.
Acidosis
Chronic Resp.
Acidosis
Compens Metabolic
Alkalosis
Partially CompensMetabolic
Alkalosis
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PCO2 > 45 mm Hg
pH < 7.35
HCO3 normal
acute respiratory acidosis
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PCO2 > 45 mm Hg
pH < 7.35
HCO3 decreased
combined respiratory and metabolic acidosis
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PCO2 > 45 mm Hg
pH < 7.35
HCO3 increased
partly compensated respiratory acidosis
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PCO2 > 45 mm Hg
pH 7.35 – 7.45
HCO3 increased
chronic respiratory acidosis
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PCO2 > 45 mm Hg
pH > 7.45
HCO3 increased
partly compensated metabolic alkalosis
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Approximate PaCO2-pH Relationship
PaCO2 ( mm Hg) pH
80 7.2
60 7.3
40 7.4
30 7.5
20 7.6
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Determining Base Excess/ Deficit
1. Determine pCO2 variance: difference between measured pCO2 & 40, move decimal
point two places to the left2. Determine the predicted pH:
pCO2 > 40, subtract half pCO2 variance from 7.40
pCO2 < 40, add pCO2 variance to 7.403. Estimate BE/BD:
Difference between measured and predicted pH
Move decimal point two places to right.Multiply by 2/3
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Base Excess: measured pH > predicted pHBase Deficit: measured pH < predicted pH
pH 7.04 pCO2 76 predicted pH 7.227.22 – 7.04 = 0.1818 x 2/3 = 12 mEq/L (BD)
pH 7.21 pCO2 90 predicted pH 7.157.21 – 7.15 = 0.066 x 2/3 = 4 mEq/L (BE)
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Causes of AcidosisMetabolic
Diabetes (ketoacidosis)
Renal failure (impaired H+ secretion)
Diarrhea (loss of base)
Tissue hypoxia (lactic acidosis)
Respiratory
Respiratory insufficiency
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Causes of AlkalosisMetabolic
Excessive loss of HCl (e.g. pyloric stenosis)
Excessive citrate/bicarbonate load
Respiratory
Hyperventilation (fever, psychogenic)
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TreatmentMetabolic Acidosis
HCO3 administration
Empiric: 1-2 meq/kg
Calculated:
(Desired – actual) x k x KBW =
meqs required
k = 0.5 - 0.6 (represents fraction of body wt. where material is apparently distributed)
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TreatmentMetabolic Alkalosis
Volume expansion; Cl and K replacement
Respiratory Acidosis
Inc. RR, PIP, or both
Respiratory Alkalosis
Dec. RR
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Step 2: Assessment of Arterial Oxygenation
Evaluation of Hypoxemia
Room Air (Patient < 60 y/o):Mild: PaO2 < 80 mmHgModerate: PaO2 < 60 mmHgSevere: PaO2 < 40 mm Hg
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Step 2On Oxygen Therapy:
• Uncorrected hypoxemia:
PaO2 < 80 mm Hg• Corrected hypoxemia:
PaO2 = 80 – 100 mm Hg• Overcorrected hypoxemia:
PaO2 > 100 mm Hg
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FiO2 (Fractional InspiredOxygen Concentration)
the measurable amount of oxygen received by the patient
21% - room air > 21% - supplemental oxygen
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Inspired Oxygen to PaO2 Relationship
FiO2 Predicted Minimal PaO2
30 % 150
40 % 200
50 % 250
80 % 400
If PaO2 < minimal predicted (FiO2 x 5), the patient can be assumed to be hypoxemic at room air.
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Treatment of Hypoxemia
For ventilated patients
Increase:
FiO2
RR
PIP
PEEP
Inspiratory time
Flow rate
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Exercises
pH 7.44
PCO2 40
PO2 99
HCO3 22
BE +2
SaO2 95
FiO2 21%
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normal
acid-base
balance
with adequate
oxygenation
Exercises
pH 7.44
PCO2 40
PO2 99
HCO3 22
BE +2
SaO2 95
FiO2 21%
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pH 7.36
PCO2 25
PO2 78
HCO3 15
BE -10
SaO2 95
FiO2 35%
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pH 7.36
PCO2 25
PO2 78
HCO3 15
BE -10
SaO2 95
FiO2 35%
chronic
metabolic
acidosis
with
uncorrected
hypoxemia
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pH 7.24
PCO2 60
PO2 80
HCO3 26
BE -2
SaO2 95
FiO2 60%
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pH 7.24
PCO2 60
PO2 80
HCO3 26
BE -2
SaO2 95
FiO2 60%
acute
respiratory
acidosis
with corrected
hypoxemia
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pH 7.55
PCO2 52
PO2 70
HCO3 44
BE +17
SaO2 97
FiO2 90%
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pH 7.55
PCO2 52
PO2 70
HCO3 44
BE +17
SaO2 97
FiO2 90%
partly
compensated
metabolic
alkalosis
with uncorrected
hypoxemia
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pH 7.19
PCO2 56
PO2 120
HCO3 17
BE -30
SaO2 94
FiO2 45%
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pH 7.19
PCO2 56
PO2 120
HCO3 17
BE -30
SaO2 94
FiO2 45%
combined
metabolic and
respiratory
acidosis with
overcorrected
hypoxemia
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