Comparison of Arterial and Venous Blood Gases and the Effects of Analysis Delay and Air Contamination on Arterial Samples in Patients with Chronic Obstructive Pulmonary Disease and Healthy Controls

Background: Arterial blood gases (ABGs) are often sampled incorrectly, leading to a 'mixed' or venous sample. Delays in analysis and air contamination are common. Objectives: We measured the effects of these errors in patients with chronic obstructive pulmonary disease (COPD) exacerbations and controls. Methods: Arterial and venous samples were analyzed from 30 patients with COPD exacerbation and 30 controls. Venous samples were analysed immediately and arterial samples separated into non-air-contaminated and air-contaminated specimens and analysed at 0, 30, 60, 90 and 180 min. Results: Mean venous pH was 7.371 and arterial pH was 7.407 (p < 0.0001). There was a correlation between venous and arterial pH (r = 0.5347, p < 0.0001). The regression equation to predict arterial pH was: arterial pH = 4.2289 + 0.43113 . venous pH. There were no clinically significant differences in arterial PO(2) associated with analysis delay. A statistically significant decline in pH was detected at 30 min in patients with COPD exacerbation (p = 0.0042) and 90 min in controls (p < 0.0001). A clinically significant decline in pH emerged at 73 min in patients with COPD exacerbation and 87 min in controls. Air contamination was associated with a clinically significant increase in PO(2) in all samples, including those that were immediately analyzed. Conclusions: Arterial and venous pH differ significantly. Venous pH cannot accurately replace arterial pH. Temporal delays in ABG analysis result in a significant decline in measured pH. ABGs should be analysed within 30 min. Air contamination leads to an immediate increase in measured PO(2), indicating that air-contaminated ABGs should be discarded. Copyright (C) 2010 S. Karger AG, Basel