Not medically reviewed
Blood gases
Partial pressure of arterial carbon dioxide (PaCO2)
Not medically reviewed · Content last updated · 1 min read ·
This is the date the draft was written, not a medical review date.
The pressure of carbon dioxide in arterial blood, inversely proportional to alveolar ventilation. It is the respiratory component of acid-base balance.
Reference interval
| Conventional (mmHg) | SI (kPa) | |
|---|---|---|
| Adults | 35–45 mmHg | 4.7–6 kPa |
Specimen: Arterial whole blood (heparinised syringe) · Conventional × 0.1333 = SI
Causes of high values
Hypoventilation (respiratory acidosis): COPD, severe asthma, opioid or sedative overdose, neuromuscular disease, obesity hypoventilation, chest wall disorders. Also appears as compensation for metabolic alkalosis.
Causes of low values
Hyperventilation (respiratory alkalosis): anxiety, pain, hypoxaemia, pulmonary embolism, sepsis, salicylate poisoning, pregnancy, mechanical over-ventilation. Also appears as compensation for metabolic acidosis.
Pre-analytical and method notes
The usual interval is 35 to 45 mmHg (4.7 to 6.0 kPa). In metabolic acidosis Winter’s formula gives the expected compensatory PaCO2; a measured value outside this estimate suggests an additional respiratory disorder. Chronic CO2 retainers have a higher baseline. Reference intervals vary by laboratory, method and population; use the interval printed on the report.
Related calculators
References
- Murray and Nadel's Textbook of Respiratory Medicine. Elsevier, 7th edition (2021) — Tier 3 (textbook)
- Rifai N, Horvath AR, Wittwer CT. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Elsevier, 6th edition (2018) — Tier 3 (textbook)
- Hall JE, Hall ME. Guyton and Hall Textbook of Medical Physiology. Elsevier, 14th edition (2020) — Tier 3 (textbook)
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