Equal increases in respiratory system elastance reflect similar lung damage in experimental ventilator-induced lung injury.
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.
Sibilla
Silvio
S
Istituto di Anestesia e Rianimazione, Ospedale Maggiore di Milano, IRCCS, Via F. Sforza n. 35, 20122 Milan, Italy.
Tredici
Stefano
S
Porro
Anna
A
Irace
Manuela
M
Guglielmi
Massimiliano
M
Nicolini
Gabriella
G
Tredici
Giovanni
G
Valenza
Franco
F
Gattinoni
Luciano
L
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