Correct Nomenclature for VBG CO2 Documentation
The correct nomenclature for documenting a venous blood gas carbon dioxide level is PvCO2 (partial pressure of carbon dioxide in venous blood), with specification of whether the sample is from a central or peripheral vein.
Standard Nomenclature Based on Guidelines
According to the ATS/ACCP standardized nomenclature 1:
- PaCO2 = arterial partial pressure of CO2
- PvCO2 = venous partial pressure of CO2 (when referring to mixed venous blood from pulmonary artery)
- PetCO2 = end-tidal CO2
For clinical documentation, you should specify:
- Central venous PCO2 (from central venous catheter)
- Peripheral venous PCO2 (from peripheral vein)
Critical Documentation Requirements
When documenting VBG CO2 values, always include:
- Source location: Central vs. peripheral venous sample
- Units: mmHg (standard) or kPa
- Method: Spectrophotometry via blood gas analyzer
- Timing: Simultaneous with any arterial sample if comparing
Common Pitfalls to Avoid
Do NOT use these terms interchangeably:
- PaCO2 and PvCO2 are fundamentally different values
- Central venous PCO2 typically exceeds arterial by ~4 mmHg in normal cardiac output 2
- Peripheral venous PCO2 is highly variable and should not be used to estimate PaCO2 2, 3
Never document as:
- "CO2" alone (ambiguous - could mean content, output, or partial pressure)
- "VCO2" (this specifically means CO2 output/production per minute) 1
- "Venous CO2" without specifying partial pressure vs. content
Clinical Context Matters
The reliability of venous CO2 measurements depends critically on:
- Cardiac output status: Central venous values are only reliable predictors when cardiac output is relatively normal 2
- Peripheral circulation: Peripheral venous values show poor correlation with arterial values (95% prediction interval -10.7 to +2.4 mmHg) 3
- Metabolic state: In shock states, the venous-arterial CO2 difference (ΔPCO2) >6 mmHg suggests inadequate tissue perfusion 4
For accurate documentation: State "Central venous PCO2 = X mmHg" or "Peripheral venous PCO2 = X mmHg" rather than generic "VBG CO2."