title: Equal increases in respiratory system elastance reflect similar lung damage in experimental ventilator-induced lung injury.
abstract: OBJECTIVE
  We hypothesized that a 50% increase in respiratory system elastance (Ers) would indicate similar degree of lung damage (equi-damage, ED), independently of ventilation strategy.
  
  
  METHODS
  A prospective, randomized animal laboratory investigation at a university hospital laboratory.
  
  
  METHODS
  35 anesthetized, paralyzed, mechanically ventilated male Sprague-Dawley rats.
  
  
  METHODS
  Each rat was ventilated with a different combination of tidal volume, positive end-expiratory pressure, and inspired fraction of oxygen. Ers was determined throughout the experiment; the studies were interrupted when Ers reached 150% (ED) of its baseline value, or after 5 h.
  
  
  RESULTS
  Lung wet to dry weight ratio (W/D) was assessed. Morphological damage of the lung was scored on a grading of perivascular edema, hemorrhage, and breaks in the alveolar septa to obtain a total injury score. Twenty-four rats achieved an Ers of 150%: nine within 1 h (class 1), nine in 1-2 h (class 2), and six in 2-5 h (class 3). Eleven rats did not reach the target 50% increase in Ers (class 4). W/D was higher in rats that reached the target than in those that did not. W/D did not differ among rats that reached ED. Similarly, the total injury score did not differ among classes 1-3 but was higher than class 4.
  
  
  CONCLUSIONS
  In the setting of VILI a 50% increase in Ers corresponds to an equal level of lung damage, irrespective of ventilatory setting and time of ventilation.
authors.affiliation: Istituto di Anestesia e Rianimazione, Ospedale Maggiore di Milano, IRCCS, Via F. Sforza n. 35, 20122 Milan, Italy.
authors.forename: Silvio
authors.initials: S
authors.lastname: Sibilla
authors.forename: Stefano
authors.initials: S
authors.lastname: Tredici
authors.forename: Anna
authors.initials: A
authors.lastname: Porro
authors.forename: Manuela
authors.initials: M
authors.lastname: Irace
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Guglielmi
authors.forename: Gabriella
authors.initials: G
authors.lastname: Nicolini
authors.forename: Giovanni
authors.initials: G
authors.lastname: Tredici
authors.forename: Franco
authors.initials: F
authors.lastname: Valenza
authors.forename: Luciano
authors.initials: L
authors.lastname: Gattinoni
mesh_terms: D000818:Animals; D004548:Elasticity; D055370:Lung Injury; D008297:Male; D011446:Prospective Studies; D051381:Rats; D017207:Rats, Sprague-Dawley; D012121:Respiration, Artificial / Q000009:adverse effects*; D012143:Respiratory Physiological Phenomena