title: Venous pH can safely replace arterial pH in the initial evaluation of patients in the emergency department.
abstract: OBJECTIVE
  This study aims to determine the extent of correlation of arterial and venous pH with a view to identifying whether venous samples can be used as an alternative to arterial values in the clinical management of selected patients in the emergency department.
  
  
  METHODS
  This prospective study of patients who were deemed by their treating doctor to require an arterial blood gas analysis to determine their ventilatory or acid-base status, compared pH on an arterial and a venous sample taken as close to simultaneously as possible. Data were analysed using Pearson correlation and bias (Bland-Altman) methods.
  
  
  RESULTS
  Two hundred and forty six patients were entered into the study; 196 with acute respiratory disease and 50 with suspected metabolic derangement. The values of pH on arterial and venous samples were highly correlated (r=0.92) with an average difference between the samples of -0.4 units. There was also a high level of agreement between the methods with the 95% limits of agreement being -0.11 to +0.04 units.
  
  
  CONCLUSIONS
  Venous pH estimation shows a high degree of correlation and agreement with the arterial value, with acceptably narrow 95% limits of agreement. Venous pH estimation is an acceptable substitute for arterial measurement and may reduce risks of complications both for patients and health care workers.
authors.affiliation: Department of Emergency Medicine, Western Hospital, Private Bag, Footscray 3011, Melbourne, Australia. Anne-Maree.Kelly@wh.org.au
authors.forename: A M
authors.initials: AM
authors.lastname: Kelly
authors.forename: R
authors.initials: R
authors.lastname: McAlpine
authors.forename: E
authors.initials: E
authors.lastname: Kyle
mesh_terms: D000137:Acid-Base Imbalance / Q000175:diagnosis; D001158:Arteries; D001784:Blood Gas Analysis / Q000379:methods*; D004630:Emergencies; D004636:Emergency Service, Hospital; D006801:Humans; D006863:Hydrogen-Ion Concentration; D011446:Prospective Studies; D014680:Veins