title: Arteriovenous blood gas agreement in intensive care patients with varying levels of circulatory compromise: a pilot study.
abstract: OBJECTIVE
  Venous 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.
  
  
  METHODS
  A prospective cohort study of a convenience sample of patients in an intensive care unit of a metropolitan teaching hospital.
  
  
  METHODS
  Paired 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.
  
  
  RESULTS
  We 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.
  
  
  CONCLUSIONS
  In 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.
authors.affiliation: Joseph Epstein Centre For Emergency Medicine Research, Western Health, Melbourne, VIC, Australia.
authors.forename: Daniel
authors.initials: D
authors.lastname: Hynes
authors.affiliation: Intensive Care Unit, Western Health, Melbourne, VIC, Australia.
authors.forename: Samantha
authors.initials: S
authors.lastname: Bates
authors.affiliation: Department of Emergency Medicine, Western Health, Melbourne, VIC, Australia.
authors.forename: Ashley
authors.initials: A
authors.lastname: Loughman
authors.affiliation: Joseph Epstein Centre For Emergency Medicine Research, Western Health, Melbourne, VIC, Australia.
authors.forename: Sharon
authors.initials: S
authors.lastname: Klim
authors.affiliation: Intensive Care Unit, Western Health, Melbourne, VIC, Australia.
authors.forename: Craig
authors.initials: C
authors.lastname: French
authors.affiliation: Joseph Epstein Centre For Emergency Medicine Research, Western Health, Melbourne, VIC, Australia.
authors.forename: Anne-Maree
authors.initials: AM
authors.lastname: Kelly
mesh_terms: D000368:Aged; D001158:Arteries; D001639:Bicarbonates / Q000097:blood; D001784:Blood Gas Analysis / Q000379:methods*; D002245:Carbon Dioxide / Q000097:blood; D015331:Cohort Studies; D003422:Critical Care / Q000379:methods*; D016638:Critical Illness; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007022:Hypotension / Q000097:blood*; D007297:Inpatients; D019344:Lactic Acid / Q000097:blood; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D011446:Prospective Studies; D015203:Reproducibility of Results; D014680:Veins
chemical_list: D001639:Bicarbonates; D002245:Carbon Dioxide; D019344:Lactic Acid