PV card: VBG versus ABG

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]
Go to ALiEM (PV) Cards for more resources.

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.

References

1. McCanny P, Bennett K, Staunton P, McMahon G. Venous vs arterial blood gases in the assessment of patients presenting with an exacerbation of chronic obstructive pulmonary disease. Am J Emerg Med. 2012;30(6):896-900. [PubMed]
2. Kelly A, McAlpine R, Kyle E. Venous pH can safely replace arterial pH in the initial evaluation of patients in the emergency department. Emerg Med J. 2001;18(5):340-342. [PubMed]
3. Ma O, Rush M, Godfrey M, Gaddis G. Arterial blood gas results rarely influence emergency physician management of patients with suspected diabetic ketoacidosis. Acad Emerg Med. 2003;10(8):836-841. [PubMed]
4. Middleton P, Kelly A, Brown J, Robertson M. Agreement between arterial and central venous values for pH, bicarbonate, base excess, and lactate. Emerg Med J. 2006;23(8):622-624. [PubMed]
5. Koul P, Khan U, Wani A, et al. Comparison and agreement between venous and arterial gas analysis in cardiopulmonary patients in Kashmir valley of the Indian subcontinent. Ann Thorac Med. 2011;6(1):33-37. [PubMed]

Author information

Michelle Lin, MD

ALiEM Founder and CEO
Professor and Digital Innovation Lab Director
Department of Emergency Medicine
University of California, San Francisco

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