Prone position delays the progression of ventilator-induced lung injury in rats: does lung strain distribution play a role?
OBJECTIVE
To investigate if prone position delays the progression of experimental ventilator-induced lung injury, possibly due to a more homogeneous distribution of strain within lung parenchyma.


METHODS
Prospective, randomized, controlled trial.


METHODS
Animal laboratory of a university hospital.


METHODS
Thirty-five Sprague Dawley male rats (weight 257 +/- 45 g).


METHODS
Mechanical ventilation in either supine or prone position and computed tomography scan analysis.


METHODS
: Animals were ventilated in supine (n = 15) or prone (n = 15) position until a similar ventilator-induced lung injury was reached. To do so, experiments were interrupted when respiratory system elastance was 150% of baseline. Ventilator-induced lung injury was assessed as lung wet-to-dry ratio and histology. Time to reach lung injury was considered as a main outcome measure. In five additional animals, computed tomography scans (GE Light Speed QX/I, thickness 1.25 mm, interval 0.6 mm, 100 MA, 100 Kv) were randomly taken at end-expiration and end-inspiration in both positions, and quantitative analysis was performed. Data are shown as mean +/- sd.


RESULTS
Similar ventilator-induced lung injury was reached (respiratory system elastance, wet-to-dry ratio, and histology). The time taken to achieve the target ventilator-induced lung injury was longer with prone position (73 +/- 37 mins vs. 112 +/- 42, supine vs. prone, p = .011). Computed tomography scan analysis performed before lung injury revealed that at end-expiration, the lung was wider in prone position (p = .004) and somewhat shorter (p = .09), despite similar lung volumes (p = .455). Lung density along the vertical axis increased significantly only in supine position (p = .002). Lung strain was greater in supine as opposed to prone position (width strain, 7.8 +/- 1.8% vs. 5.6 +/- 0.9, supine vs. prone, p = .029).


CONCLUSIONS
Prone position delays the progression of ventilator-induced lung injury. Computed tomography scan analysis suggests that a more homogeneous distribution of strain may be implicated in the protective role of prone position against ventilator-induced lung injury.
Valenza
Franco
F
Università degli Studi di Milano, Istituto di Anestesia e Rianimazione, Ospedale Maggiore di Milano-IRCCS, Via F. Sforza 35, 20122 Milano, Italy. franco.valenza@unimi.it
Guglielmi
Massimiliano
M
Maffioletti
Micol
M
Tedesco
Cecilia
C
Maccagni
Patrizia
P
Fossali
Tommaso
T
Aletti
Gabriele
G
Porro
Giuliana Anna
GA
Irace
Manuela
M
Carlesso
Eleonora
E
Carboni
Nadia
N
Lazzerini
Marco
M
Gattinoni
Luciano
L
D000818:Animals; D018450:Disease Progression; D008168:Lung / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008297:Male; D016684:Prone Position; D051381:Rats; D017207:Rats, Sprague-Dawley; D012121:Respiration, Artificial / Q000009:adverse effects / Q000379:methods*; D012128:Respiratory Distress Syndrome / Q000000981:diagnostic imaging / Q000209:etiology / Q000503:physiopathology* / Q000628:therapy; D013314:Stress, Mechanical; D014057:Tomography, X-Ray Computed