title: Disparity between mainstream and sidestream end-tidal carbon dioxide values and arterial carbon dioxide levels.
abstract: BACKGROUND
  Measuring and monitoring end-tidal carbon dioxide (PETCO2) is an important aspect of caring for critically ill patients. The 2 methods used for PETCO2 measurement are the mainstream and sidestream methods.
  
  
  OBJECTIVE
  To assess the agreement between PETCO2 measurements performed by mainstream and sidestream methods with the PaCO2 values.
  
  
  METHODS
  This was a prospective observational study. A total of 114 subjects were enrolled in the study. PETCO2 measurements using mainstream and sidestream methods were performed simultaneously with the arterial blood sampling in subjects who were observed in the emergency department and required arterial blood gas analysis. Agreement between the PETCO2 measurements and the PaCO2 values obtained from arterial blood gas analysis were evaluated using the Bland-Altman method.
  
  
  RESULTS
  Sixty subjects (52.6%) were female, and the mean age was 60.9 years (95% CI 58.3-63.6). The mean PaCO2 was 35.16 mm Hg (95% CI 33.81-36.51), the mainstream PETCO2 was 22.11 (95% CI 21.05-23.18), and the sidestream PETCO2 was 25.48 (95% CI 24.22-26.75). Bland-Altman analysis showed an average difference between mainstream PETCO2 and PaCO2 values of 13 mm Hg (95% limits of agreement -0.6 to 25.5) and moderate correlation (r = 0.55, P < .001). The average difference between the sidestream PETCO2 and PaCO2 values was 9.7 mm Hg (95% limits of agreement -5.4 to 24.7) and poor correlation (r = 0.41, P < .001).
  
  
  CONCLUSIONS
  PETCO2 values obtained by mainstream and sidestream methods were found to be significantly lower than the PaCO2 values. There was essentially no agreement between the measurements obtained by 2 different methods and the PaCO2 values.
authors: Department of Emergency Medicine, Faculty of Medicine, Kocaeli University, Kocaeli, Turkey. mpekdemir@yahoo.com
authors: Murat
authors: M
authors: Pekdemir
authors: Orhan
authors: O
authors: Cinar
authors: Serkan
authors: S
authors: Yilmaz
authors: Elif
authors: E
authors: Yaka
authors: Melih
authors: M
authors: Yuksel
mesh_terms: D001784:Blood Gas Analysis / Q000379:methods / Q000592:standards; D019296:Capnography / Q000379:methods / Q000592:standards; D002245:Carbon Dioxide / Q000032:analysis*; D057186:Comparative Effectiveness Research; D003422:Critical Care / Q000379:methods / Q000592:standards; D016638:Critical Illness / Q000628:therapy; D061827:Dimensional Measurement Accuracy; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data; D015588:Observer Variation; D011446:Prospective Studies; D011659:Pulmonary Gas Exchange; D013223:Statistics as Topic; D013990:Tidal Volume
chemical_list: D002245:Carbon Dioxide
keywords: arterial carbon dioxide; end-tidal carbon dioxide; mainstream; noninvasive; sidestream