You obtain a venous blood gas (VBG) on a patient with a COPD exacerbation because you are concerned about hypercarbia. You get a value of 55 mmHg. How correlative is that compared to an arterial blood gas (ABG).
There has been a lot of literature on how well the pH correlates between the ABG and VBG but what about pCO2?
A small study (n=89) from 20121 found that with a cutoff of pCO2 < 45 mmHg, the venous pCO2 is 100% sensitive in ruling out arterial hypercarbia. When the pCO2 was ≥ 45 mmHg, the VBG was less correlative.
Below is a review by Dr. Michelle Reina (EM resident at Univ of Utah) and Dr. Rob Bryant (Intermountain Medical Center in Utah) of the VBG vs ABG correlative data, along with a proposed algorithm on what to do with patients with COPD exacerbation.
What is your practice with an elevated pCO2 value on VBG?
Adapted from 1–5
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Updated 1/31/13 at 2 pm PST:
- Changed range of pH correlation between VBG and ABG = 0.03-0.04
- Was typo in abstract of Kelly et al article.2 Stated difference between pHs was 0.4, rather than 0.04 as described in main results text.