Abstract

Blood gas analysis is an integral part of the assessment of emergency department (ED) patients with acute respiratory or metabolic disease. Traditionally ABG analyses have been used, but increasingly, emergency clinicians are using venous blood gas (VBG) analyses. This has been challenged, especially by respiratory physicians, as being too inaccurate. This clinical review, using case examples, summarises the evidence supporting use of VBG to guide management decisions. Arteriovenous agreement for pH is such that values are clinically interchangeable and agreement for bicarbonate is also close. Agreement for pCO₂ is poor with 95% limits of agreement of the order of 20 mm Hg (2.67 kPa); however, there is solid evidence that a venous pCO₂ ≤45 mm Hg (6 kPa) reliably excludes clinically significant hypercarbia. Evidence regarding arteriovenous agreement for base excess is unclear. Given knowledge of the performance characteristics of VBG analyses, integration of the clinical findings with VBG results is often sufficient to safely guide treatment decision making.