title: Lung stress and strain during mechanical ventilation: any safe threshold?
abstract: BACKGROUND
  Unphysiologic strain (the ratio between tidal volume and functional residual capacity) and stress (the transpulmonary pressure) can cause ventilator-induced lung damage.
  
  
  OBJECTIVE
  To identify a strain-stress threshold (if any) above which ventilator-induced lung damage can occur.
  
  
  METHODS
  Twenty-nine healthy pigs were mechanically ventilated for 54 hours with a tidal volume producing a strain between 0.45 and 3.30. Ventilator-induced lung damage was defined as net increase in lung weight.
  
  
  RESULTS
  Initial lung weight and functional residual capacity were measured with computed tomography. Final lung weight was measured using a balance. After setting tidal volume, data collection included respiratory system mechanics, gas exchange and hemodynamics (every 6 h); cytokine levels in serum (every 12 h) and bronchoalveolar lavage fluid (end of the experiment); and blood laboratory examination (start and end of the experiment). Two clusters of animals could be clearly identified: animals that increased their lung weight (n = 14) and those that did not (n = 15). Tidal volume was 38 ± 9 ml/kg in the former and 22 ± 8 ml/kg in the latter group, corresponding to a strain of 2.16 ± 0.58 and 1.29 ± 0.57 and a stress of 13 ± 5 and 8 ± 3 cm H(2)O, respectively. Lung weight gain was associated with deterioration in respiratory system mechanics, gas exchange, and hemodynamics, pulmonary and systemic inflammation and multiple organ dysfunction.
  
  
  CONCLUSIONS
  In healthy pigs, ventilator-induced lung damage develops only when a strain greater than 1.5-2 is reached or overcome. Because of differences in intrinsic lung properties, caution is warranted in translating these findings to humans.
authors.affiliation: Dipartimento di Anestesiologia, Terapia Intensiva e Scienze Dermatologiche, Università degli Studi di Milano, Milan, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Protti
authors.forename: Massimo
authors.initials: M
authors.lastname: Cressoni
authors.forename: Alessandro
authors.initials: A
authors.lastname: Santini
authors.forename: Thomas
authors.initials: T
authors.lastname: Langer
authors.forename: Cristina
authors.initials: C
authors.lastname: Mietto
authors.forename: Daniela
authors.initials: D
authors.lastname: Febres
authors.forename: Monica
authors.initials: M
authors.lastname: Chierichetti
authors.forename: Silvia
authors.initials: S
authors.lastname: Coppola
authors.forename: Grazia
authors.initials: G
authors.lastname: Conte
authors.forename: Stefano
authors.initials: S
authors.lastname: Gatti
authors.forename: Orazio
authors.initials: O
authors.lastname: Leopardi
authors.forename: Serge
authors.initials: S
authors.lastname: Masson
authors.forename: Luciano
authors.initials: L
authors.lastname: Lombardi
authors.forename: Marco
authors.initials: M
authors.lastname: Lazzerini
authors.forename: Erica
authors.initials: E
authors.lastname: Rampoldi
authors.forename: Paolo
authors.initials: P
authors.lastname: Cadringher
authors.forename: Luciano
authors.initials: L
authors.lastname: Gattinoni
mesh_terms: D000818:Animals; D001992:Bronchoalveolar Lavage Fluid; D016207:Cytokines / Q000097:blood / Q000378:metabolism; D004195:Disease Models, Animal; D008168:Lung / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D009929:Organ Size; D012121:Respiration, Artificial / Q000009:adverse effects*; D012129:Respiratory Function Tests; D013312:Stress, Physiological; D013552:Swine; D013990:Tidal Volume; D014057:Tomography, X-Ray Computed; D055397:Ventilator-Induced Lung Injury / Q000473:pathology / Q000503:physiopathology*
chemical_list: D016207:Cytokines