Airway pressure-time curve profile (stress index) detects tidal recruitment/hyperinflation in experimental acute lung injury.
OBJECTIVE
To evaluate whether the shape of the airway pressure-time (Paw-t) curve during constant flow inflation corresponds to radiologic evidence of tidal recruitment or tidal hyperinflation in an experimental model of acute lung injury.


METHODS
Prospective randomized laboratory animal investigation.


METHODS
Department of Clinical Physiology, University of Uppsala, Sweden.


METHODS
Anesthetized, paralyzed, and mechanically ventilated pigs.


METHODS
Acute lung injury was induced by lung lavage. During constant inspiratory flow, the Paw-t curve was fitted to a power equation: airway pressure =a x time + c, where coefficient b (stress index) describes the shape of the curve:b = 1, straight curve; b < 1, progressive increase in slope; and b > 1, progressive decrease in slope. Tidal volume (Vt) was 6 mL/kg, and positive end-expiratory pressure was set to obtain a b value between 0.9 and 1.1 before (b = 1) and after (b = 1 after recruiting maneuver) application of a recruiting maneuver. Positive end-expiratory pressure was decreased and Vt increased to obtain 0.9 >b > 0.8 and 0.8 >b > 0.6, whereas positive end-expiratory pressure and Vt were both increased to obtain 1.3 >b > 1.1 and 1.5 >b > 1.3. Experimental conditions sequence was random.


RESULTS
Pulmonary computed tomography was obtained during end-expiratory and end-inspiratory occlusions. Tidal recruitment was quantified as nonaerated (between -100 and +100 Hounsfield units) lung area at end-expiration minus end-inspiration. Tidal hyperinflation was quantified as hyperinflated (between -900 and -1000 Hounsfield units) lung area at end-inspiration minus end-expiration. Computed tomography images showed that tidal recruitment and tidal hyperinflation corresponded to b < 1 and b > 1, respectively. Stress index values and tidal recruitment and tidal hyperinflation values were significantly correlated (R =.917 and R =.911, p <.0001, respectively).


CONCLUSIONS
Shape of the Paw-t curve detects tidal recruitment and tidal hyperinflation.
Grasso
Salvatore
S
Servizio di Anestesia e Rianimazione, Ospedale Di Venere, Bari, Italy.
Terragni
Pierpaolo
P
Mascia
Luciana
L
Fanelli
Vito
V
Quintel
Michel
M
Herrmann
Peter
P
Hedenstierna
Goran
G
Slutsky
Arthur S
AS
Ranieri
V Marco
VM
D000818:Animals; D045422:Continuous Positive Airway Pressure / Q000379:methods*; D008176:Lung Volume Measurements; D008297:Male; D011175:Positive-Pressure Respiration / Q000379:methods*; D011650:Pulmonary Alveoli / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D001261:Pulmonary Atelectasis / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D012128:Respiratory Distress Syndrome / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D013552:Swine; D013990:Tidal Volume / Q000502:physiology*; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome