title: Effect of pressure support on end-expiratory lung volume and lung diffusion for carbon monoxide.
abstract: OBJECTIVE
  The level of pressure-support ventilation can affect mean airway pressure and potentially lung volume, but its increase is usually associated with a reduced respiratory rate, and the net effects on the gas exchange process and its components, including end-expiratory lung volume, have not been carefully studied. We measured pulmonary conductance for gas exchange based on lung diffusion for carbon monoxide in patients receiving pressure-support ventilation.
  
  
  METHODS
  Prospective, randomized, crossover study.
  
  
  METHODS
  Medical intensive care unit of a university hospital.
  
  
  METHODS
  Sixteen patients mechanically ventilated in pressure-support ventilation mode and free from chronic obstructive pulmonary disease.
  
  
  METHODS
  Two pressure-support ventilation levels (5 cm H2O difference) at the same level of positive end-expiratory pressure.
  
  
  RESULTS
  End-expiratory lung volume, lung diffusion for carbon monoxide, and SpO2/Fio2 were evaluated. Increasing pressure-support ventilation by 5 cm H2O significantly increased the mean tidal volume from 6.8 to 8.5 mL/kg of predicted body weight and decreased the mean respiratory rate by 6.6 breaths per minute. Although SpO2/Fio2 did not change significantly, there was a slight but significant decrease in lung diffusion for carbon monoxide (average decay rate of 4.5%) at high pressure-support ventilation. The pressure-support ventilation level did not significantly affect end-expiratory lung volume (1737±629 mL at 9.6±2.5 cm H2O pressure-support ventilation level vs. 1749±657 mL at 14.9±2.1 cm H2O pressure-support ventilation level).
  
  
  CONCLUSIONS
  A 5-cm H2O increase in pressure-support ventilation neither affected end-expiratory lung volume nor increased the pulmonary volume participating in gas exchange. A target tidal volume closer to 6 mL/kg of predicted body weight than to 8 mL/kg during pressure-support ventilation was associated with better gas exchange.
authors.affiliation: Réanimation Médicale, AP-HP, Centre Hospitalier Albert Chenevier-Henri Mondor, INSERM Unité 955, Université Paris EST, Créteil, France. nathalia.pintodacosta@rdb.aphp.fr
authors.forename: Nathalina
authors.initials: N
authors.lastname: Pinto Da Costa
authors.forename: Fabiano
authors.initials: F
authors.lastname: Di Marco
authors.forename: Aissam
authors.initials: A
authors.lastname: Lyazidi
authors.forename: Guillaume
authors.initials: G
authors.lastname: Carteaux
authors.forename: Mourad
authors.initials: M
authors.lastname: Sarni
authors.forename: Laurent
authors.initials: L
authors.lastname: Brochard
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002248:Carbon Monoxide / Q000032:analysis*; D018592:Cross-Over Studies; D005260:Female; D006785:Hospitals, University; D006801:Humans; D007362:Intensive Care Units; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration / Q000379:methods*; D011446:Prospective Studies; D011659:Pulmonary Gas Exchange
chemical_list: D002248:Carbon Monoxide