II. Approach
- Draw venipuncture without a Tourniquet
- Send to lab on ice and run immediately
- VBG Oxygen Saturation <75% decreases accuracy (and may be unreliable <50%)
- VBG pH will be less than ABG pH
- VBG pCO2 will be greater than ABG pCO2
III. Efficacy: Best data points that correlate well between VBG and ABG
- Venous pH correlates well with arterial pH
- Correlation
- Average weighted difference: 0.03 pH units
- Variation range: +/- 0.1 pH Units
- Conditions where ABG and VBG are well correlated
- Diabetic Ketoacidosis (DKA)
- COPD Exacerbation
- Conditions where ABG and VBG are less correlated
- Mixed acid base disorders
- Hypotension (e.g. systolic Blood Pressure 60 mmHg)
- Correlation
- Venous bicarbonate has fair correlation with arterial bicarbonate
- Serum bicarbonate may also be obtained from serum chemistry panel
- Correlation
- Average weighted difference: 1.3 mmol
- Variation range: +/- 4-5 mmol
IV. Efficacy: Results or conditions in which VBG correlates well with ABG in some studies
- Carbon dioxide (pCO2)
- Correlation
- Some studies (see Zeserson study) have shown close correlation: 4.8 mmHg
- Other studies have shown 6 mmHg up to 20 mmHg variation from ABG
- Normal pCO2 is reassuring
- pCO2 <40 has 100% Negative Predictive Value for significant hypercarbia
- Correlation
V. Efficacy: Results or conditions in which VBG correlates poorly with ABG
-
Serum Potassium
- Varies by as much as 0.5 mEq/L
- Cardiac Arrest
VI. Resources
- Internet Book of Critical Care (EMCRIT.org)
VII. References
- Kelly and Herbert in Majoewsky (2012) EM:Rap 12(12): 8
- Zeserson (2016) CJ Intensive Care Med +PMID: 27283009 [PubMed]