Tidal hyperinflation during low tidal volume ventilation in acute respiratory distress syndrome.
BACKGROUND
Tidal volume and plateau pressure limitation decreases mortality in acute respiratory distress syndrome. Computed tomography demonstrated a small, normally aerated compartment on the top of poorly aerated and nonaerated compartments that may be hyperinflated by tidal inflation.


OBJECTIVE
We hypothesized that despite tidal volume and plateau pressure limitation, patients with a larger nonaerated compartment are exposed to tidal hyperinflation of the normally aerated compartment.


RESULTS
Pulmonary computed tomography at end-expiration and end-inspiration was obtained in 30 patients ventilated with a low tidal volume (6 ml/kg predicted body weight). Cluster analysis identified 20 patients in whom tidal inflation occurred largely in the normally aerated compartment (69.9 +/- 6.9%; "more protected"), and 10 patients in whom tidal inflation occurred largely within the hyperinflated compartments (63.0 +/- 12.7%; "less protected"). The nonaerated compartment was smaller and the normally aerated compartment was larger in the more protected patients than in the less protected patients (p = 0.01). Pulmonary cytokines were lower in the more protected patients than in the less protected patients (p < 0.05). Ventilator-free days were 7 +/- 8 and 1 +/- 2 d in the more protected and less protected patients, respectively (p = 0.01). Plateau pressure ranged between 25 and 26 cm H(2)O in the more protected patients and between 28 and 30 cm H(2)O in the less protected patients (p = 0.006).


CONCLUSIONS
Limiting tidal volume to 6 ml/kg predicted body weight and plateau pressure to 30 cm H(2)O may not be sufficient in patients characterized by a larger nonaerated compartment.
Terragni
Pier Paolo
PP
Università di Torino, Dipartimento di Anestesiologia e Rianimazione, Ospedale S. Giovanni Battista-Molinette, Corso Dogliotti 14, 10126 Turin, Italy.
Rosboch
Giulio
G
Tealdi
Andrea
A
Corno
Eleonora
E
Menaldo
Eleonora
E
Davini
Ottavio
O
Gandini
Giovanni
G
Herrmann
Peter
P
Mascia
Luciana
L
Quintel
Michel
M
Slutsky
Arthur S
AS
Gattinoni
Luciano
L
Ranieri
V Marco
VM
D000368:Aged; D005260:Female; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging; D008297:Male; D008875:Middle Aged; D012121:Respiration, Artificial / Q000379:methods* / Q000592:standards*; D012128:Respiratory Distress Syndrome / Q000000981:diagnostic imaging / Q000628:therapy*; D013990:Tidal Volume; D014057:Tomography, X-Ray Computed