VBG in ICU

 Q: Which venous blood gas (VBG) is preferable? (select one)

A) Central venous 

 B) Peripheral venous

Answer: A

In ICUs arterial blood gas (ABG) is preferred. During hemodynamic instability the discrepancy between ABG and VBG becomes significantly high and VBG cannot be relied upon. In shock state, the difference between mixed venous (SvO2) and arterial PCO2 increased by three times. 

Said that, in otherwise hemodynamically stable patients, VBG can be utilized. If a central venous catheter (CVC) (central line) is present VBG should be obtained from it. This is due to the fact that during normal hemodynamics HCO3 tends to be the same in ABG and CVC-VBG. In peripheral VBG, HCO3 is about 2-3 meq/L higher. Moreover, inappropriate use of a tourniquet during peripheral blood draw can make VBG unreliable due to transient local ischemia.

#acid-base

References:

1. Malinoski DJ, Todd SR, Slone S, et al. Correlation of central venous and arterial blood gas measurements in mechanically ventilated trauma patients. Arch Surg 2005; 140:1122. 

2. Walkey AJ, Farber HW, O'Donnell C, et al. The accuracy of the central venous blood gas for acid-base monitoring. J Intensive Care Med 2010; 25:104.