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Arterial Blood Gas (ABG)

PaCO₂ (Arterial CO₂)

Normal range 35–45 mm Hg (4.7–6 kPa SI). Specimen: Arterial blood.

Also known as: partial pressure of carbon dioxide, pCO2.

35–45 mm HgCritical: read below

Reference range

Conventionalmm Hg
3545
SIkPa
4.76
SpecimenArterial blood
Conventional range35–45 mm Hg
SI range4.7–6 kPa
Conversion factor×0.133 (conventional → SI)
Critical value< 20 or > 60 mm Hg
PanelArterial Blood Gas (ABG)

Convert any PaCO₂ (Arterial CO₂) result between units on the unit converter.

What is the normal range for PaCO₂ (Arterial CO₂)?

The standard teaching reference range for PaCO₂ (Arterial CO₂) is 35–45 mm Hg in conventional units, or 4.7–6 kPa in SI units. This value is measured in arterial blood.

A commonly taught critical (panic) value is < 20 or > 60 mm Hg. Critical results are reported to the provider immediately under your facility's policy.

Source: Adult reference values compiled from Pagana & Pagana, Mosby's Diagnostic and Laboratory Test Reference, and Fischbach & Dunning, A Manual of Laboratory and Diagnostic Tests. Reference ranges vary by laboratory, method, age, sex, and population — always use the range printed on the actual result.

Above the range

Common causes of a high PaCO₂ (Arterial CO₂)

  • Hypoventilation (respiratory acidosis)
  • COPD
  • Sedation / respiratory depression

Below the range

Common causes of a low PaCO₂ (Arterial CO₂)

  • Hyperventilation (respiratory alkalosis)
  • Anxiety
  • Compensation for metabolic acidosis

At the bedside

Nursing considerations

  • The respiratory component of acid–base balance.
  • Rising PaCO₂ with a falling pH signals ventilatory failure.

Study aid

Your notes on PaCO₂ (Arterial CO₂)

Same panel

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