title: Positive end-expiratory pressure improves end-expiratory lung volume but not oxygenation after induction of anaesthesia.
abstract: OBJECTIVE
  Induction of anaesthesia promotes collapse of dependent lung regions in both obese and nonobese patients. We hypothesized that end-expiratory lung volume (EELV) may be more sensitive than oxygenation to evaluate the effects of positive end-expiratory pressure (PEEP) after anaesthesia induction.
  
  
  METHODS
  Forty patients (20 nonobese patients and 20 obese patients) were prospectively studied. After anaesthesia induction, PEEP was adjusted in a stepwise fashion [zero end-expiratory pressure (ZEEP), PEEP 5 cmH2O and PEEP 10 cmH2O]. At each step, we measured EELV, static elastance, gas exchange and dead space. Other than changing PEEP, respiratory settings were kept constant throughout.
  
  
  RESULTS
  Anaesthesia induction and ZEEP both lowered EELV by 39% in nonobese patients and 59% in obese patients (both P < 0.05), as well as oxygenation (P < 0.05). Compared with ZEEP, in nonobese patients, PEEP 5 cmH2O and PEEP 10 cmH2O improved EELV (+15 and +40%, respectively, P < 0.01) and elastance but not oxygenation. In obese patients, PEEP 10 cmH2O also improved EELV (49% vs. ZEEP and 30% vs. PEEP 5 cmH2O, P < 0.01), elastance and dead-space fraction, with no effect on oxygenation. PEEP-induced changes of EELV correlated with changes of elastance (r = 0.46, P = 0.003), but not with oxygenation.
  
  
  CONCLUSIONS
  After induction of anaesthesia, mechanical ventilation with ZEEP is associated with a profound reduction in EELV. PEEP improves efficiently EELV and respiratory mechanics, with no major effect on oxygenation. EELV may be a useful indicator to guide PEEP setting in the operating room.
authors.affiliation: Department of Anaesthesiology and Critical Care, Hotel-Dieu Hospital, University Hospital of Clermont-Ferrand, Clermont-Ferrand, France. efutier@chu-clermontferrand.fr
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Futier
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Constantin
authors.forename: Antoine
authors.initials: A
authors.lastname: Petit
authors.forename: Boris
authors.initials: B
authors.lastname: Jung
authors.forename: Fabrice
authors.initials: F
authors.lastname: Kwiatkowski
authors.forename: Martine
authors.initials: M
authors.lastname: Duclos
authors.forename: Samir
authors.initials: S
authors.lastname: Jaber
authors.forename: Jean-Etienne
authors.initials: JE
authors.lastname: Bazin
mesh_terms: D000768:Anesthesia, General / Q000379:methods*; D001794:Blood Pressure / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications / Q000601:surgery*; D010100:Oxygen / Q000008:administration & dosage / Q000032:analysis; D011175:Positive-Pressure Respiration / Q000379:methods*; D011446:Prospective Studies; D012129:Respiratory Function Tests; D016896:Treatment Outcome
chemical_list: D010100:Oxygen