Point-of-care bedside gas analyzer: Limited use of venous pCO2in emergency patients

Abstract

Background: Because arterial punctures are more painful, venous blood gas analysis has been proposed as an alternative. Objectives: To determine if venous pCO2 can replace arterial pCO2 in emergency patients using a bedside blood gas analyzer. Methods: This is a cross-sectional study. We recruited patients who were deemed by the attending Emergency Physicians to require arterial blood gas analysis to determine their ventilation or acid-base status. A venous and an arterial blood gas sample were drawn from the patient, temporally as close to each other as possible. Both samples were then analyzed using the same bedside blood gas analyzer immediately after collection. Results: There were 122 paired samples obtained. The strength of the association between arterial and venous pCO2 is r = 0.838 (p = 0.001). The Bland-Altman bias plot methods for agreement show a mean difference of 3.3 mm Hg with two standard deviation limits of agreement being -17.4 to 23.9; 93.4% of the pCO2 values fell within two standard deviation limits. Venous pCO2 below 30 mm Hg had a 100% (95% confidence interval [CI] 90.5-100) sensitivity and 100% (95% CI 80.7-100) Negative predictive value to rule out hypercarbia, defined as arterial pCO2 > 45 mm Hg. Conclusions: There is significant variability in the arteriovenous difference of pCO2 readings, hence, arterial punctures are still needed to specifically determine the arterial pCO2. © 2008.