Lung stress and strain during mechanical ventilation: any safe threshold?

Am J Respir Crit Care Med. 2011 May 15;183(10):1354-62. doi: 10.1164/rccm.201010-1757OC. Epub 2011 Feb 4.


Rationale: Unphysiologic strain (the ratio between tidal volume and functional residual capacity) and stress (the transpulmonary pressure) can cause ventilator-induced lung damage.

Objectives: 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.

Measurements and main 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bronchoalveolar Lavage Fluid
  • Cytokines / blood
  • Cytokines / metabolism
  • Disease Models, Animal
  • Lung / diagnostic imaging
  • Lung / pathology
  • Lung / physiopathology*
  • Organ Size
  • Respiration, Artificial / adverse effects*
  • Respiratory Function Tests
  • Stress, Physiological*
  • Swine
  • Tidal Volume
  • Tomography, X-Ray Computed
  • Ventilator-Induced Lung Injury / pathology
  • Ventilator-Induced Lung Injury / physiopathology*


  • Cytokines