The role of venous blood gas in the Emergency Department

Abstract

The aim of this study is to provide a systematic review of the literature reporting agreement between arterial and venous pH, partial pressure of carbon dioxide (PCO2), bicarbonate (HCO3⁻), base excess and lactate; and to perform a meta-analysis of the differences. Medline and Embase searches using Eduserv Athens from 1950 to present were conducted using the terms 'VBG', 'ABG', 'arterial', 'venous', 'blood', 'gas', 'lactate', 'emergency' and 'department'. References of the published papers were hand searched and full-text versions of those deemed helpful to the question were obtained. Mean difference (MD) and 95% limits of agreement (LOA) were either reported or calculated from the published data. Pooled MDs with 95% confidence intervals (CIs) were calculated for differences between arterial and venous pH, PCO2, bicarbonate and lactate. Thirteen articles relevant to pH, 12 relevant to PCO2, 10 relevant to bicarbonate and three relevant to lactate were found. The pooled MD (venous-arterial) for pH was -0.033 pH units (95% CI -0.039 to 0.027) with narrow 95% LOA, the pooled MD for PCO2 was 4.41 mmHg (95% CI 2.55-6.27) with 95% LOA ranging from -20.4 to 25.8 mmHg, the pooled MD for bicarbonate was 1.03 mmol/l (95% CI 0.56-1.50) with 95% LOA ranging from -7.1 to 10.0 mmol/l and the pooled MD for lactate was 0.25 mmol/l (95% CI 0.15-0.35) with 95% LOA ranging from -2.0 to 2.3 mmol/l. Venous and arterial pH and bicarbonate agree reasonably at all values, but the agreement is highest at normal values. Arteriovenous agreement for PCO2 is poor and PvCO2 cannot be relied upon as an absolute representation of PaCO2. However, normal peripheral PvCO2 has a good negative predictive value for normal arterial PCO2, and a normal PvCO2 can be used as a screen to exclude hypercapnic respiratory disease. There may be a poor agreement between arterial and venous lactate at abnormal values; however, if the venous lactate is normal, it is likely the arterial values of this parameter will also be normal.