• Daniel Hynes, Samantha Bates, Ashley Loughman, Sharon Klim, Craig French, and Anne-Maree Kelly.
• Joseph Epstein Centre For Emergency Medicine Research, Western Health, Melbourne, VIC, Australia.
• Crit Care Resusc. 2015 Dec 1;17(4):253-6.

ObjectiveVenous blood gas (VBG) analysis is suggested as an alternative to arterial blood gas (ABG) analysis. In haemodynamically stable patients, there is clinically acceptable arteriovenous (AV) agreement for pH and bicarbonate (HCO3-) concentration, but in haemodynamically unstable patients, evidence is conflicting. We aimed to evaluate the level of AV agreement for the values of pH, PCO2, base excess, HCO3- and lactate between ABGs and VBGs in critically ill patients with varying degrees of hypotension.Design And SettingA prospective cohort study of a convenience sample of patients in an intensive care unit of a metropolitan teaching hospital.InterventionPaired ABG and central VBG samples were drawn within 5 minutes of each other from existing arterial lines and central venous lines, and analysed for AV agreement of pH, PCO2, base excess, HCO3- and lactate. The outcome of interest was AV agreement with varying levels of blood pressure (BP). Analysis was by descriptive statistics, box whisker plot and Bland-Altman bias plot analysis.ResultsWe studied 50 patients with 117 paired ABG and VBG samples. The AV differences (venous-arterial) were: pH, -0.04; HCO3-, -0.37 mmmol/L; base excess, 0.08 mEq/ L; and lactate, 0.16 mmol/L. There was not a clinically relevant deterioration in agreement for these parameters with falling BP.ConclusionIn critically ill patients with varying degrees of hypotension in the ICU, there is clinically acceptable AV agreement for the values of pH, HCO3-, base excess and lactate, an agreement that does not deteriorate significantly with falling blood pressure.

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