Paper: Chauvin A et al. Reducing Pain by Using Venous Blood Gas Instead of Arterial Blood Gas (VEINART): A Multicentre Randomised Controlled Trial. EMJ 2020. [Epub Ahead of Print]
Clinical Question: In non-hypoxemic patients (pulse oximetry >95% on room air), is the maximal pain during sampling less with VBG or ABG?
What They Did:
- Multicenter, open-label, randomized, prospective clinical trial in 4 French EDs over a 4-week period
- Non-hypoxemic adults, whose clinicians desired blood gas analysis to help guide care
- Randomized to arterial vs venous sampling
Outcomes:
- Primary: Maximal pain during sampling using a visual analog scale (VAS) on a 0 to 100 scale
- Secondary:
- Ease of sampling as rated by the nurse drawing the blood
- Easy
- Moderately easy
- Difficult
- Very difficult
- Physician satisfaction regarding usefulness of biochemical data
- Not at all
- Partly satisfied
- Satisfied
- Very satisfied
- Ease of sampling as rated by the nurse drawing the blood
Inclusion:
- Blood gas analysis needed based on physician decision
- Percutaneous O2 saturation >95% on room air
- Age ≥18 years
- GCS of 15
Exclusion:
- Patients under legal protection
- Unable to receive information
- No social security insurance
- Refused to participate
Results:
- 113 patients included
- Suspicion of metabolic acidosis was the main reason for blood gas analysis
- 75% of patients did not receive analgesics before the sampling (none had application of an anesthetic cream)
- None of the providers used ultrasound for sampling
- Mean Maximal Pain (Primary Outcome):
- ABG: 40.5mm +/- 24.9mm
- VBG: 22.6mm +/- 20.2mm
- Absolute Difference: 17.9mm (95% CI 9.6 to 26.3; p<0.0001)
- Ease of blood sampling greater with VBG vs ABG (p = 0.02)
- 1st attempt success: VBG 91% vs ABG 80%
- Blood sampling assessed as easy: VBG 69% vs ABG 44%
- Blood sampling assessed as difficult: VBG 3% vs ABG 15%
- Usefulness of results did not differ (p = 0.25)
- Physician satisfaction with usefulness of information satisfying or very satisfying: VBG 95% vs ABG 97%
Strengths:
- Asks a clinically important question
- 1st randomized clinical trial assessing pain experienced by patients for ABG vs VBG in the ED setting
- Multicenter, randomized clinical trial
- Patients were asked their VAS pain score within 3 minutes of the blood draw to reduce recall bias
- Almost all patients received their allocated intervention (1 patient did not in the ABG group)
- No patients were lost to follow up
- Performed two post-hoc sensitivity analyses to account for the corresponding group in which actual blood sampling technique was used and for baseline imbalance despite randomization
Limitations:
- Patients were imbalanced at baseline in regard to age, medical history, and diagnosis hypotheses motivating blood sampling.
- Diameter of the arterial puncture needle was 22G for ABG and varied for VBGs between 20 and 25G. Smaller gauge needles will cause less pain than larger gauge needles
- Outcome assessments were not blinded which could bias the results of the physician (This should not bias the results of the patients)
- 64 patients were not consented out of 177 eligible patients. This is more of a convenience sample than a consecutive sample.
- Years of professional experience and comfort with the procedures was not recorded in this study
- Patients were not treated equally. 25% had analgesia prior to sampling but this wasn’t standard practice
- VAS pain scales are a subjective scale of pain and may differ between patients
Discussion:
- A clinically relevant difference was set at a VAS of at least 20mm and a SD of the difference of 28mm. However the authors only found an 18% difference between groups. As the study was not truly powered to detect this small a difference, this could be statistical noise and a much larger study would be needed to delineate this
- Peripheral venous lactate determination cannot be substituted for arterial lactate determination in all cases. Agreement between VBG and ABG values can decline when venous lactate is ≥2mmol/L. This can result in a greater difference in agreement between samples. A normal lactate level on venous lactate does however rule out increased arterial lactate concentrations
Author Conclusion: “Venous blood gas is less painful for patients than ABG in non-hypoxaemic patients. Venous blood gas should replace ABG in this setting.”
Clinical Take Home Point: In non-hypoxemic patients requiring acid-base evaluation:
- VBG is less painful for patients compared to ABG
- VBG is easier for the healthcare team compared to ABG
- VBG provides useful information similar to ABG for physicians in regard to treatment decisions
References:
- Chauvin A et al. Reducing Pain by Using Venous Blood Gas Instead of Arterial Blood Gas (VEINART): A Multicentre Randomised Controlled Trial. EMJ 2020. [Epub Ahead of Print]
- Kelly AM et al. Review Article – Can Venous Blood Gas Analysis Replace Arterial in Emergency Medical Care. Emerg Med Australas 2010. PMID: 21143397
- Razi E et al. Correlation of Arterial Blood Gas Measurements with Venous Blood Gas Values in Mechanically Ventilated Patients. Tanaffos 2012. PMID: 25191435
- McCanny P et al. Venous vs Arterial Blood Gases in the Assessment of Patients Presenting with an Exacerbation of Chronic Obstructive Pulmonary Disease. AJEM 2012. PMID: 21908141
- Zeserson E et al. Correlation of Venous Blood Gas and Pulse Oximetry with Arterial Blood Gas in the Undifferentiated Critically Ill Patient. J Intensive Care Med 2018. PMID: 27283009
Post Peer Reviewed By: Anand Swaminathan, MD (Twitter: @EMSwami)
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