title: Agreement between mathematically arterialised venous versus arterial blood gas values in patients undergoing non-invasive ventilation: a cohort study.
abstract: BACKGROUND
  Blood gas analysis is important for assessment of ventilatory function. Traditionally, arterial analysis has been used. A method for mathematically arterialising venous blood gas values has been developed. Our aim was to validate this method in patients undergoing non-invasive ventilation (NIV) in an emergency department (ED).
  
  
  METHODS
  This post hoc substudy of a prospective cohort study included adult patients undergoing NIV for acute respiratory compromise. When arterial blood gas analysis was required for clinical purposes, a venous sample was also drawn. Mathematically arterialised values were calculated independent of arterial values. Primary outcome of interest was agreement between mathematically arterialised venous and arterial values for pH and pCO2. Bland-Altman agreement plot analysis was used.
  
  
  RESULTS
  Eighty sample-pairs (58 patients) were studied. Mean difference for arterial pH (actual-calculated) was 0.01 pH units (95% limits of agreement: -0.04, 0.06). Mean difference for pCO2 (actual-calculated) was -0.06 kPa (95% limits of agreement: -1.34, 1.22).
  
  
  CONCLUSIONS
  For patients undergoing NIV in an ED, agreement between mathematically arterialised venous values and arterial values was close for pH but only moderate for pCO2. Depending on clinician tolerance for agreement, this method may be a clinically useful alternative to arterial blood gas analysis in the ED.
authors.affiliation: Joseph Epstein Centre for Emergency Medicine Research at Western Health, Melbourne, Australia The University of Melbourne, Melbourne, Australia.
authors.forename: Anne-Maree
authors.identifier: http://orcid.org/0000-0002-4655-5023
authors.initials: AM
authors.lastname: Kelly
authors.affiliation: Joseph Epstein Centre for Emergency Medicine Research at Western Health, Melbourne, Australia.
authors.forename: Sharon
authors.initials: S
authors.lastname: Klim
authors.affiliation: Respiratory and Critical Care Group (RCARE), Center for Model-Based Medical Decision Support, Institute for Health Science and Technology, Aalborg University, Aalborg, Denmark.
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Rees
mesh_terms: D000368:Aged; D001784:Blood Gas Analysis / Q000379:methods*; D002245:Carbon Dioxide / Q000097:blood; D015331:Cohort Studies; D004636:Emergency Service, Hospital; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D063087:Noninvasive Ventilation; D011237:Predictive Value of Tests; D012131:Respiratory Insufficiency / Q000097:blood* / Q000628:therapy*; D014680:Veins
chemical_list: D002245:Carbon Dioxide
keywords: Emergency Department; Respiratory; Ventilation, Non invasive