title: Effects of lung recruitment maneuver and positive end-expiratory pressure on lung volume, respiratory mechanics and alveolar gas mixing in patients ventilated after cardiac surgery.
abstract: BACKGROUND
  It is unclear whether positive end-expiratory pressure (PEEP) is needed to maintain the improved oxygenation and lung volume achieved after a lung recruitment maneuver in patients ventilated after cardiac surgery performed in the cardiopulmonary bypass (CPB).
  
  
  METHODS
  A prospective, randomized, controlled study in a university hospital intensive care unit. Sixteen patients who had undergone cardiac surgery in CPB were studied during the recovery phase while still being mechanically ventilated with an inspired fraction of oxygen (FiO2) 1.0. Eight patients were randomized to lung recruitment (two 20-s inflations to 45 cmH2O), after which PEEP was set and kept for 2.5 h at 1 cmH2O above the pressure at the lower inflexion point (14+/-3 cmH2O, mean +/-SD) obtained from a static pressure-volume (PV) curve (PEEP group). The remaining eight patients were randomized to a recruitment maneuver only (ZEEP group). End-expiratory lung volume (EELV), series dead space, ventilation homogeneity, hemodynamics and PaO2 (oxygenation) were measured every 30 min during a 3-h period. PV curves were obtained at baseline, after 2.5 h, and in the PEEP group at 3 h.
  
  
  RESULTS
  In the ZEEP group all measures were unchanged. In the PEEP group the EELV increased with 1220+/-254 ml (P<0.001) and PaO2 with 16+/-16 kPa (P<0.05) after lung recruitment. When PEEP was discontinued EELV decreased but PaO2 was maintained. The PV curve at 2.5 h coincided with the curve obtained at 3 h, and both curves were both steeper than and located above the baseline curve.
  
  
  CONCLUSIONS
  Positive end-expiratory pressure is required after a lung recruitment maneuver in patients ventilated with high FiO2 after cardiac surgery to maintain lung volumes and the improved oxygenation.
authors.affiliation: Department of Anesthesiology, Gentofte University Hospital, Denmark. thdy@gentoftehosp.kbhamt.dk
authors.forename: Thomas
authors.initials: T
authors.lastname: Dyhr
authors.forename: N
authors.initials: N
authors.lastname: Laursen
authors.forename: A
authors.initials: A
authors.lastname: Larsson
mesh_terms: D000368:Aged; D001784:Blood Gas Analysis; D002315:Cardiopulmonary Bypass; D005260:Female; D006331:Heart Diseases / Q000503:physiopathology* / Q000601:surgery; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D008170:Lung Compliance / Q000502:physiology; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration; D011446:Prospective Studies; D011650:Pulmonary Alveoli / Q000502:physiology*; D012123:Pulmonary Ventilation / Q000502:physiology*; D012121:Respiration, Artificial; D015656:Respiratory Mechanics / Q000502:physiology*; D013990:Tidal Volume / Q000502:physiology; D014109:Total Lung Capacity / Q000502:physiology*