Overview
The PaCO₂ is the arterial partial pressure of carbon dioxide, as measured on an arterial blood gas.
An increase or decrease in the PaCO₂ level suggests the presence of a respiratory process causing an acid-base imbalance. This can either be primary (the derangement is due to a respiratory issue) or secondary (there is respiratory compensation for a metabolic issue).
Normal Range
- 36 - 44 mmHg
Hypercapnia
An increased PaCO₂ of greater than 44 mmHg on an arterial blood gas suggests the presence of a respiratory process - either primary (respiratory acidosis) or secondary (respiratory compensation of metabolic alkalosis).
Interpretation
- Reduced pH with elevated PCO₂ - suggests respiratory acidosis
- Elevated pH with elevated PCO₂ and elevated HCO₃ - suggests respiratory compensation for metabolic alkalosis
- Normal pH with elevated PCO₂ and elevated HCO₃ - suggests mixed respiratory acidosis-metabolic alkalosis
Hypocapnia
A reduced PaCO₂ of less than 36 mmHg on an arterial blood gas suggests the presence of a respiratory process - either primary (respiratory alkalosis) or secondary (respiratory compensation of metabolic acidosis).
Interpretation
- Elevated pH with reduced PCO₂ - suggests respiratory alkalosis
- Reduced pH with reduced PCO₂ and reduced HCO₃ - suggests respiratory compensation for metabolic acidosis
- Normal pH with reduced PCO₂ and reduced HCO₃ - suggests mixed respiratory alkalosis-metabolic acidosis
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