title: Assessment of Bohr and Enghoff Dead Space Equations in Mechanically Ventilated Children.
abstract: BACKGROUND
  Recent findings suggest that using alveolar PCO2(PACO2) estimated by volumetric capnography in the Bohr equation instead of PaCO2(Enghoff modification) could be appropriate for the calculation of physiological dead space to tidal volume ratio (VD/VT Bohrand VD/VT Enghoff, respectively). We aimed to describe the relationship between these 2 measurements in mechanically ventilated children and their significance in cases of ARDS.
  
  
  METHODS
  From June 2013 to December 2013, mechanically ventilated children with various respiratory conditions were included in this study. Demographic data, medical history, and ventilatory parameters were recorded. Volumetric capnography indices (NM3 monitor) were obtained over a period of 5 min preceding a blood sample. Bohr's and Enghoff's dead space, S2 and S3 slopes, and the S2/S3 ratio were calculated breath-by-breath using dedicated software (FlowTool). This study was approved by Ste-Justine research ethics review board.
  
  
  RESULTS
  Thirty-four subjects were analyzed. Mean VD/VT Bohrwas 0.39 ± 0.12, and VD/VT Enghoffwas 0.47 ± 0.13 (P= .02). The difference between VD/VT Bohrand VD/VT Enghoffwas correlated with PaO2/FIO2and with S2/S3. In subjects without lung disease (PaO2/FIO2≥ 300), mean VD/VT Bohrwas 0.36 ± 0.11, and VD/VT Enghoffwas 0.39 ± 0.11 (P= .056). Two children with status asthmaticus had a major difference between VD/VT Bohrand VD/VT Enghoffin the absence of a low PaO2/FIO2.
  
  
  CONCLUSIONS
  This study suggests that VD/VT Bohrand VD/VT Enghoffare not different when there is no hypoxemia (PaO2/FIO2> 300) except in the case of status asthmaticus. In subjects with a low PaO2/FIO2, the method to measure VD/VTmust be reported, and results cannot be easily compared if the measurement methods are not the same.
authors.affiliation: Pediatric Intensive Care Unit, Hopital Femme-Enfant-Adolescent, Centre Hospitalier Universitaire de Nantes, Nantes, France. pierre.bourgoin@chu-nantes.fr.
authors.forename: Pierre
authors.initials: P
authors.lastname: Bourgoin
authors.affiliation: Centre Hospitalier Universitaire de Lyon, Lyon, France.
authors.forename: Florent
authors.initials: F
authors.lastname: Baudin
authors.affiliation: Pediatric Intensive Care Unit, Centre Hospitalier Universitaire Sainte-Justine, Montreal, Quebec, Canada.
authors.forename: David
authors.initials: D
authors.lastname: Brossier
authors.affiliation: Centre Hospitalier Universitaire Sainte-Justine and Pediatrics, Université de Montréal, Montréal, Quebec, Canada.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Emeriaud
authors.affiliation: Centre de Recherche du Centre Hospitalier Universitaire Sainte-Justine, Université de Montreal, Quebec, Canada, and GE Healthcare, France.
authors.forename: Marc
authors.initials: M
authors.lastname: Wysocki
authors.affiliation: Centre Hospitalier Universitaire Sainte-Justine and the Division of Pediatric Critical Care Medicine, Department of Pediatrics, Université de Montréal, Montréal, Quebec, Canada.
authors.forename: Philippe
authors.initials: P
authors.lastname: Jouvet
mesh_terms: D019296:Capnography / Q000379:methods / Q000706:statistics & numerical data*; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D008297:Male; D008962:Models, Theoretical; D008991:Monitoring, Physiologic / Q000379:methods / Q000706:statistics & numerical data; D012121:Respiration, Artificial / Q000706:statistics & numerical data*; D012126:Respiratory Dead Space; D012128:Respiratory Distress Syndrome / Q000503:physiopathology* / Q000628:therapy; D013990:Tidal Volume
keywords: ARDS; capnography; mechanical ventilation; pediatric ICU; respiratory physiological concepts; ventilation-perfusion ratio