title: Intraoperative changes in arterial oxygenation during volume-controlled mechanical ventilation in modestly obese patients undergoing laparotomies with general anesthesia.
abstract: BACKGROUND
  In obese patients, arterial oxygenation can be greatly impaired during general anesthesia. Both avoidance of denitrogenation and application of positive end-expiratory pressure (PEEP) during mechanical ventilation may be effective in preventing such impairment of arterial oxygenation.
  
  
  METHODS
  We studied 28 obese/overweight and seven non-obese (BMI < 25 kg x m-2) patients who underwent laparotomies with general anesthesia (i.e. isoflurane with or without nitrous oxide). During anesthesia, their lungs were mechanically ventilated at a rate of 10 breaths x min-1 with a constant flow, inspiratory-to-expiratory ratio 1 : 2, and tidal volume approximately 10 ml x kg-1. The obese/overweight patients were allocated to four different groups in terms of denitrogenation and application of PEEP (7 cm H2O) during the ventilation (n = 7 each). In the non-obese patients, their denitrogenated lungs were ventilated without application of PEEP. Arterial gas analyses were performed before induction of anesthesia, and 30, 90, 150 and 210 min after tracheal intubation. The ratio of PaO2 to FiO2 was calculated as an index of arterial oxygenation.
  
  
  RESULTS
  No significant changes in the PaO2/FiO2 ratio were observed throughout the study in the non-obese patients and in the obese/overweight patients whose non-denitrogenated lungs were ventilated with PEEP. In the obese/overweight patients whose lungs were ventilated after denitrogenation or without application of PEEP, significant decreases in the PaO2/FiO2 ratio were observed 30 and 90 min after tracheal intubation.
  
  
  CONCLUSIONS
  In obese or overweight patients under general anesthesia, it may be advisable to avoid denitrogenation and apply PEEP during mechanical ventilation in order to minimize the impairment of arterial oxygenation.
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
authors.forename: J
authors.initials: J
authors.lastname: Yoshino
authors.forename: T
authors.initials: T
authors.lastname: Akata
authors.forename: S
authors.initials: S
authors.lastname: Takahashi
mesh_terms: D000328:Adult; D000768:Anesthesia, General; D001784:Blood Gas Analysis; D002245:Carbon Dioxide / Q000097:blood; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007813:Laparotomy; D008297:Male; D009765:Obesity / Q000503:physiopathology*; D010100:Oxygen / Q000097:blood*; D011175:Positive-Pressure Respiration; D012121:Respiration, Artificial; D012907:Smoking / Q000503:physiopathology
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen