Pressure-time curve predicts minimally injurious ventilatory strategy in an isolated rat lung model.
BACKGROUND
We tested the hypothesis that the pressure-time (P-t) curve during constant flow ventilation can be used to set a noninjurious ventilatory strategy.


METHODS
In an isolated, nonperfused, lavaged model of acute lung injury, tidal volume and positive end-expiratory pressure were set to obtain: (1) a straight P-t curve (constant compliance, minimal stress); (2) a downward concavity in the P-t curve (increasing compliance, low volume stress); and (3) an upward concavity in the P-t curve (decreasing compliance, high volume stress). The P-t curve was fitted to: P = a. tb +c, where b describes the shape of the curve, b = 1 describes a straight P-t curve, b < 1 describes a downward concavity, and b > 1 describes an upward concavity. After 3 h, lungs were analyzed for histologic evidence of pulmonary damage and lavage concentration of inflammatory mediators. Ventilator-induced lung injury occurred when injury score and cytokine concentrations in the ventilated lungs were higher than those in 10 isolated lavaged rats kept statically inflated for 3 h with an airway pressure of 4 cm H2O.


RESULTS
The threshold value for coefficient b that discriminated best between lungs with and without histologic and inflammatory evidence of ventilator-induced lung injury (receiver-operating characteristic curve) ranged between 0.90-1.10. For such threshold values, the sensitivity of coefficient b to identify noninjurious ventilatory strategy was 1.00. A significant relation (P < 0.001) between values of coefficient b and injury score, interleukin-6, and macrophage inflammatory protein-2 was found.


CONCLUSIONS
The predictive power of coefficient b to predict noninjurious ventilatory strategy in a model of acute lung injury is high.
Ranieri
V M
VM
Division of Respiratory Medicine, Samuel Lunenfeld Research Institute, and Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, University of Toronto, Toronto, Ontario, Canada. mranieri@teseo.it
Zhang
H
H
Mascia
L
L
Aubin
M
M
Lin
C Y
CY
Mullen
J B
JB
Grasso
S
S
Binnie
M
M
Volgyesi
G A
GA
Eng
P
P
Slutsky
A S
AS
D000818:Animals; D016207:Cytokines / Q000378:metabolism; D004195:Disease Models, Animal; D008168:Lung / Q000378:metabolism; D008297:Male; D011175:Positive-Pressure Respiration / Q000009:adverse effects / Q000379:methods*; D011237:Predictive Value of Tests; D012372:ROC Curve; D051381:Rats; D017207:Rats, Sprague-Dawley; D012128:Respiratory Distress Syndrome / Q000209:etiology* / Q000378:metabolism / Q000517:prevention & control*; D013990:Tidal Volume; D012122:Ventilators, Mechanical / Q000009:adverse effects
D016207:Cytokines