Carbon Dioxide



CO2 combining power, CO2, Tco2.


To assess the effect of total carbon dioxide levels on respiratory and metabolic acid-base balance.

Patient Preparation

There are no food, fluid, activity, or medication restrictions unless by medical direction.

Normal Findings

Method: Colorimetry, enzyme assay, or Pco2 electrode.

Carbon DioxideConventional and SI Units
Plasma or serum (venous)
  Infant–2 yr13–29 mEq/L or mmol/L
  2 yr–older adult23–29 mEq/L or mmol/L
Whole blood (venous)
  Infant–2 yr18–28 mEq/L or mmol/L
  2 yr–older adult22–26 mEq/L or mmol/L

Critical Findings and Potential Interventions

  • Less than 15 mEq/L or mmol/L (SI: Less than 15 mmol/L).
  • Greater than 40 mEq/L or mmol/L (SI: Greater than 40 mmol/L).

Timely notification to the requesting health-care provider (HCP) of any critical findings and related symptoms is a role expectation of the professional nurse. A listing of these findings varies among facilities.

Consideration may be given to verification of critical findings before action is taken. Policies vary among facilities and may include requesting immediate recollection and retesting by the laboratory or retesting using a rapid point-of-care testing instrument at the bedside, if available.

Observe the patient for signs and symptoms of excessive or insufficient CO2 levels, and report these findings to the HCP. If the patient has been vomiting for several days and is breathing shallowly, or if the patient has had gastric suctioning and is breathing shallowly, this may indicate elevated CO2 levels. Decreased CO2 levels are evidenced by deep, vigorous breathing and flushed skin.

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