Original ContributionVenous vs arterial blood gases in the assessment of patients presenting with an exacerbation of chronic obstructive pulmonary disease☆
Introduction
Arterial blood gas (ABG) sampling is the gold standard test for assessing ventilatory status in patients presenting with acute exacerbations of chronic obstructive pulmonary disease (COPD). In addition to assisting the clinician to determine both ventilatory and acid-base status, it aids in the decision making regarding the need for continuing pharmacologic management and noninvasive ventilation (NIV) [1]. Several studies to date have looked at the possibility of replacing ABG sampling with venous blood gas (VBG) sampling for patients in the emergency setting [2], [3], [4], [5]. They have shown good correlation between venous and arterial values for pH but less so for Paco2. Kelly et al [6], [7] reported 100% sensitivity of Pvco2 in detecting cases of arterial hypercarbia with a specificity of 51% when a screening cutoff of greater than 45 mm Hg was applied. There is a growing body of evidence supporting the diagnostic use of VBG sampling in the assessment of patients presenting to the emergency department (ED) with acute respiratory illness.
Arterial samples are painful to acquire and carry greater risk than venous punctures. Risks include bleeding, hematoma, infection, nerve injury, and digital ischemia. The additional blood-sampling requirement carries a further opportunity of inoculation injury to staff. Venous blood gases can be drawn at the time the patient is cannulated, which is generally at an early time point in patient assessment. Furthermore, in the assessment of patients for NIV, serial blood gases are required to assess the response to optimum medical management.
Acute exacerbation of COPD can range from self-limited episodes to florid respiratory failure requiring ventilation. Exacerbations can be triggered by bacterial infection, heart disease, or other lung diseases (eg, pulmonary emboli, pneumothorax). The initial clinical focus is therefore directed by an adequate assessment of the patient and includes initiation of controlled oxygen therapy and pharmacologic management including bronchodilators, corticosteroids, rehydration, and antibiotics when indicated. Noninvasive ventilation is indicated for patients with acute exacerbations of COPD, when respiratory acidosis (pH <7.35, Paco2 >45 mm Hg) persists despite optimum medical management [1]. In this situation, noninvasive positive pressure ventilation may allow time for other therapies to work and thus avoid endotracheal intubation. The identification of patients suitable for NIV is therefore one of the treatment priorities for these patients. We were interested in evaluating the level of agreement between ABG vs VBG, using the screening cutoff of Pvco2 greater than 45 mm Hg and a threshold of 0.05 pH units or less in patients presenting with acute exacerbations of COPD [6], [7]. In this study, we undertook a comparison of paired ABG and VBG results to determine if a VBG could accurately substitute for an ABG sample in the early assessment of patients presenting to an ED with acute exacerbation of COPD.
Section snippets
Methodology
Patients aged 16 and older were eligible for the study if they had a previously documented diagnosis of COPD and were presenting with an acute exacerbation of COPD.
The study was undertaken in an urban ED from October 1, 2009, to March 1, 2010. We prospectively correlated paired ABG and VBG results from a consecutive convenience cohort of patients presenting with an exacerbation of COPD. Patients were included in the study if an arterial blood sample was clinically indicated to evaluate their
Results
A total of 94 patients were enrolled in the study. Five patients were excluded because of incomplete data sets, leaving 89 sample pairs for analysis. Of the 89 patients, 48% were male and 51% were female. The mean age of patients was 69 years. All patients included had a previously documented diagnosis of COPD. Of 89 patients, 16 (18%) were treated with NIV in addition to standard medical management for acute exacerbation of COPD. No patients required endotracheal intubation either in ED or
Discussion
Arterial blood gas sampling provides important information about the ventilatory status in patients presenting with acute respiratory illness to an emergency setting. There is a growing body of evidence to suggest that this can be safely replaced by a more convenient VBG sample. In our study, comparative analysis of paired VBG and ABG results in patients presenting with acute exacerbations of COPD revealed that VBG results accurately identified arterial hypercarbia when a previously derived Pvco
Conclusion
Correlation between venous and arterial values is excellent for both pH and HCO3. When a screening cutoff of 45 mm Hg was applied to venous CO2, VBG had 100% sensitivity in detecting arterial hypercarbia. There is insufficient agreement between venous CO2 and arterial CO2 for VBG to replace ABG in determining the degree of hypercarbia. Respiratory acidosis can be accurately identified using VBG sampling, reducing the need for arterial sampling in the early assessment of patients presenting with
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2021, American Journal of Emergency MedicineCitation Excerpt :Therefore, a blood gas may not be needed in every patient, and the focus should remain on the clinical examination. In those that fail to respond to treatment or have clinical signs suggestive of hypercarbia (i.e. somnolence) or visible respiratory muscle fatigue, a blood gas is helpful to assess for ventilation perfusion mismatch and the presence of hypercarbia in severe exacerbations [14,63-69]. The trend in pCO2, along with the trend in clinical examination may demonstrate response to therapy, or more ominously the failure to respond, particularly in those severe enough to require treatment with non-invasive ventilation.
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Competing Interests: None.