Arterial Blood Gases

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Arterial Blood Gases
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Why measure Blood Gases?

• Evaluation of
• Adequacy of Ventillation
• Oxygenation
• Acid Base Levels

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Normal Values

• PaO2 11 - 13kPa
• PaCO2 4.7 5.9kPa
• pH 7.36 7.44
• HCO3- 21 28mmol/L
• BE /- 2
• H 35 45nmol/L

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Bicarbonate Buffering System

• CO2 H20 ? H2CO3 ? H HCO3-
• Henderson-Hasselbalch Equation
• pH 6.1 logHCO3-
• PaCO2 x 0.03

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Which is more different from Normal, PaCO2 or
HCO3- ?
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(A-a)pO2 (Alveolar-arterial gradient. is the
difference in the oxygen partial pressures
between the alveolar and arterial sides
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The Anion Gap

• AG (Na K) (Cl- HCO3-)
• Normal Values 8 16mmol/L

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Acid-Base Disorder pH PaCO2 HCO3-
Respiratory Acidosis ? ? N
Metabolic Acidosis ? N ?
Respiratory Alkalosis ? ? N
Metabolic Alkalosis ? N ?
Resp Acidosis with renal compensation ? ? ?
Met Acidosis with respiratory compensation ? ? ?
Resp Alkalosis with renal compensation ? ? ?
Met alkalosis with respiratory compensation ? ? ?
Mixed resp and met acidosis ? ? ?
Mixed resp and met alkalosis ? ? ?
May be normal depending on level of compensation