title: Use of maximum end-tidal CO(2) values to improve end-tidal CO(2) monitoring accuracy.
abstract: BACKGROUND
  The arterial partial pressure of CO(2) (P(aCO(2))) can be grossly estimated by the end-tidal partial pressure of CO(2) (P(ETCO(2))). This principle is used in SmartCare (Dräger, Lübeck, Germany), which is an automated closed-loop system that uses P(ETCO(2)) to estimate alveolar ventilation during mechanical ventilation.
  
  
  OBJECTIVE
  To assess whether the maximum P(ETCO(2)) value (instead of the averaged P(ETCO(2)) value) over 2-min or 5-min periods improves P(aCO(2)) estimation, and determine the consequences for the SmartCare system.
  
  
  METHODS
  We continuously monitored breath-by-breath P(ETCO(2)) during ventilation with SmartCare in 36 patients mechanically ventilated for various disorders, including 14 patients with COPD. Data were collected simultaneously from SmartCare recordings, every 2 min or 5 min, and through a dedicated software that recorded ventilation data every 10 s. We compared the maximum and averaged P(ETCO(2)) values over 2-min and 5-min periods to the P(aCO(2)) measured from 80 arterial blood samples clinically indicated in 26 patients. We also compared SmartCare's classifications of patient ventilatory status based on averaged P(ETCO(2)) values to what the classifications would have been with the maximum P(ETCO(2)) values.
  
  
  RESULTS
  Mean P(aCO(2)) was 44 ± 11 mm Hg. P(aCO(2)) was higher than averaged P(ETCO(2)) by 10 ± 6 mm Hg, and this difference was reduced to 6 ± 6 mm Hg with maximum P(ETCO(2)). The results were similar whether patients had COPD or not. Very few aberrant values (< 0.01%) needed to be discarded. Among the 3,137 classifications made by the SmartCare system, 1.6% were changed by using the maximum P(ETCO(2)) value instead of the averaged P(ETCO(2)) value.
  
  
  CONCLUSIONS
  Use of maximum P(ETCO(2)) reduces the difference between P(aCO(2)) and P(ETCO(2)) and improves SmartCare's classification of patient ventilatory status.
authors.affiliation: Réanimation Médicale, l'Assistance Publique-Hôpitaux de Paris, Hôpital Henri Mondor, France.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Galia
authors.forename: Serge
authors.initials: S
authors.lastname: Brimioulle
authors.forename: Frederic
authors.initials: F
authors.lastname: Bonnier
authors.forename: Nicolas
authors.initials: N
authors.lastname: Vandenbergen
authors.forename: Michel
authors.initials: M
authors.lastname: Dojat
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Vincent
authors.forename: Laurent J
authors.initials: LJ
authors.lastname: Brochard
mesh_terms: D000368:Aged; D019296:Capnography; D015331:Cohort Studies; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000175:diagnosis*; D016857:Hypocapnia / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D015203:Reproducibility of Results; D012121:Respiration, Artificial; D012131:Respiratory Insufficiency / Q000175:diagnosis / Q000209:etiology / Q000628:therapy*; D013990:Tidal Volume / Q000502:physiology*