title: Spontaneous breathing during lung-protective ventilation in an experimental acute lung injury model: high transpulmonary pressure associated with strong spontaneous breathing effort may worsen lung injury.
abstract: OBJECTIVE
  We investigated whether potentially injurious transpulmonary pressure could be generated by strong spontaneous breathing and exacerbate lung injury even when plateau pressure is limited to <30 cm H2O.
  
  
  METHODS
  Prospective, randomized, animal study.
  
  
  METHODS
  University animal research laboratory.
  
  
  METHODS
  Thirty-two New Zealand White rabbits.
  
  
  METHODS
  Lavage-injured rabbits were randomly allocated to four groups to receive low or moderate tidal volume ventilation, each combined with weak or strong spontaneous breathing effort. Inspiratory pressure for low tidal volume ventilation was set at 10 cm H2O and tidal volume at 6 mL/kg. For moderate tidal volume ventilation, the values were 20 cm H2O and 7-9 mL/kg. The groups were: low tidal volume ventilation+spontaneous breathingweak, low tidal volume ventilation+spontaneous breathingstrong, moderate tidal volume ventilation+spontaneous breathingweak, and moderate tidal volume ventilation+spontaneous breathingstrong. Each group had the same settings for positive end-expiratory pressure of 8 cm H2O.
  
  
  RESULTS
  Respiratory variables were measured every 60 mins. Distribution of lung aeration and alveolar collapse were histologically evaluated. Low tidal volume ventilation+spontaneous breathingstrong showed the most favorable oxygenation and compliance of respiratory system, and the best lung aeration. By contrast, in moderate tidal volume ventilation+spontaneous breathingstrong, the greatest atelectasis with numerous neutrophils was observed. While we applied settings to maintain plateau pressure at <30 cm H2O in all groups, in moderate tidal volume ventilation+spontaneous breathingstrong, transpulmonary pressure rose >33 cm H2O. Both minute ventilation and respiratory rate were higher in the strong spontaneous breathing groups.
  
  
  CONCLUSIONS
  Even when plateau pressure is limited to <30 cm H2O, combined with increased respiratory rate and tidal volume, high transpulmonary pressure generated by strong spontaneous breathing effort can worsen lung injury. When spontaneous breathing is preserved during mechanical ventilation, transpulmonary pressure and tidal volume should be strictly controlled to prevent further lung injury.
authors.affiliation: Department of Anesthesiology, Osaka University Graduate School of Medicine and Pathology, Suita, Japan. doctor@mvj.biglobe.ne.jp
authors.forename: Takeshi
authors.initials: T
authors.lastname: Yoshida
authors.forename: Akinori
authors.initials: A
authors.lastname: Uchiyama
authors.forename: Nariaki
authors.initials: N
authors.lastname: Matsuura
authors.forename: Takashi
authors.initials: T
authors.lastname: Mashimo
authors.forename: Yuji
authors.initials: Y
authors.lastname: Fujino
mesh_terms: D055371:Acute Lung Injury / Q000473:pathology / Q000503:physiopathology / Q000628:therapy*; D000818:Animals; D004195:Disease Models, Animal; D008168:Lung / Q000473:pathology / Q000503:physiopathology; D008297:Male; D011659:Pulmonary Gas Exchange / Q000502:physiology; D011817:Rabbits; D012121:Respiration, Artificial / Q000009:adverse effects; D015656:Respiratory Mechanics / Q000502:physiology; D012143:Respiratory Physiological Phenomena; D056152:Respiratory Rate / Q000502:physiology; D013990:Tidal Volume / Q000502:physiology; D055397:Ventilator-Induced Lung Injury / Q000209:etiology / Q000503:physiopathology