title: Evaluation of an oxygen mask-based capnometry device in subjects extubated after abdominal surgery.
abstract: BACKGROUND
  For early detection of respiratory and hemodynamic changes during anesthesia, continuous end-tidal carbon dioxide concentration (PETCO2) is monitored by capnometry. However, the accuracy of CO2 monitoring during spontaneous breathing in extubated patients remains undetermined. Therefore, we aimed to compare P(ETCO2) measured by capnometry using an oxygen mask with a carbon dioxide sampling port (capnometry-type oxygen mask) and P(CO2) in extubated subjects who had undergone abdominal surgery. Furthermore, we investigated whether spontaneous deep breathing affected dissociation between P(aCO2) and P(ETCO2).
  
  
  METHODS
  Adult post-abdominal surgery subjects admitted to the ICU were enrolled in this study. After extubation, oxygen was supplied at 6 L/min using the capnometry-type oxygen mask. After 30 min of oxygen supply, P(aCO2) blood gas analysis was performed, and P(ETCO2) was measured under resting and deep-breathing conditions. For both resting and deep-breathing conditions, the correlation between P(aCO2) and P(ETCO2) was analyzed. Furthermore, bias, precision, and limits of agreement were calculated using the Bland-Altman method.
  
  
  RESULTS
  Twenty-five subjects (15 men, 10 women) with a mean age of 62 y (interquartile range of 57-76 y) and body mass index of 20-24 kg/m(2) were studied. The correlation (r) between P(aCO2) and P(ETCO2) under resting and deep-breathing conditions was 0.50 and 0.56, respectively. Compared with P(aCO2), the bias and limits of agreement were -12.6 (-20.6 to -4.6) for resting P(ETCO2) and -9.1 (-16.0 to -2.1) for deep-breathing P(ETCO2). The association between P(aCO2) and deep-breathing P(ETCO2) was significantly smaller compared with resting P(ETCO2) (P = .002).
  
  
  CONCLUSIONS
  It is possible to measure the P(ETCO2) under varying breathing conditions with the capnometry-type oxygen mask in subjects receiving oxygen supplementation after extubation following upper abdominal surgery to determine whether they are properly ventilating. (ClinicalTrials.gov registration UMIN000011925.).
authors.affiliation: Department of Anesthesiology and Intensive Care Unit, Yokohama City University Hospital, Kanagawa, Japan. shunty5323@gmail.com.
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Takaki
authors.affiliation: Department of Anesthesiology, Kanagawa Children's Medical Center, Kanagawa, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Mihara
authors.affiliation: Department of Anesthesiology and Intensive Care Unit, Yokohama City University Hospital, Kanagawa, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Mizutani
authors.affiliation: Department of Anesthesiology and Intensive Care Unit, Yokohama City University Hospital, Kanagawa, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Yamaguchi
authors.affiliation: Department of Anesthesiology and Intensive Care Unit, Yokohama City University Hospital, Kanagawa, Japan.
authors.forename: Takahisa
authors.initials: T
authors.lastname: Goto
mesh_terms: D000005:Abdomen / Q000601:surgery*; D000368:Aged; D060666:Airway Extubation; D001784:Blood Gas Analysis; D019296:Capnography / Q000295:instrumentation* / Q000379:methods; D002245:Carbon Dioxide / Q000032:analysis; D005260:Female; D006801:Humans; D008297:Male; D008397:Masks; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000295:instrumentation / Q000379:methods; D010100:Oxygen / Q000008:administration & dosage; D010102:Oxygen Inhalation Therapy / Q000295:instrumentation* / Q000379:methods; D011182:Postoperative Care / Q000295:instrumentation* / Q000379:methods; D011446:Prospective Studies
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen
keywords: capnometry; end-tidal carbon dioxide; postoperative monitoring; ventilation/perfusion mismatch