Lung opening and closing during ventilation of acute respiratory distress syndrome.
BACKGROUND
The effects of high positive end-expiratory pressure (PEEP) strictly depend on lung recruitability, which varies widely during acute respiratory distress syndrome (ARDS). Unfortunately, increasing PEEP may lead to opposing effects on two main factors potentially worsening the lung injury, that is, alveolar strain and intratidal opening and closing, being detrimental (increasing the former) or beneficial (decreasing the latter).


OBJECTIVE
To investigate how lung recruitability influences alveolar strain and intratidal opening and closing after the application of high PEEP.


METHODS
We analyzed data from a database of 68 patients with acute lung injury or ARDS who underwent whole-lung computed tomography at 5, 15, and 45 cm H(2)O airway pressure.


RESULTS
End-inspiratory nonaerated lung tissue was estimated from computed tomography pressure-volume curves. Alveolar strain and opening and closing lung tissue were computed at 5 and 15 cm H(2)O PEEP. In patients with a higher percentage of potentially recruitable lung, the increase in PEEP markedly reduced opening and closing lung tissue (P < 0.001), whereas no differences were observed in patients with a lower percentage of potentially recruitable lung. In contrast, alveolar strain similarly increased in the two groups (P = 0.89). Opening and closing lung tissue was distributed mainly in the dependent and hilar lung regions, and it appeared to be an independent risk factor for death (odds ratio, 1.10 for each 10-g increase).


CONCLUSIONS
In ARDS, especially in patients with higher lung recruitability, the beneficial impact of reducing intratidal alveolar opening and closing by increasing PEEP prevails over the effects of increasing alveolar strain.
Caironi
Pietro
P
Dipartimento di Anestesiologia, Fondazione Istituto Di Ricovero e Cura a Carattere Scientifico - Ospedale Maggiore Policlinico, Università degli Studi di Milano, Milan, Italy.
Cressoni
Massimo
M
Chiumello
Davide
D
Ranieri
Marco
M
Quintel
Michael
M
Russo
Sebastiano G
SG
Cornejo
Rodrigo
R
Bugedo
Guillermo
G
Carlesso
Eleonora
E
Russo
Riccarda
R
Caspani
Luisa
L
Gattinoni
Luciano
L
D000704:Analysis of Variance; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D008875:Middle Aged; D016017:Odds Ratio; D011175:Positive-Pressure Respiration / Q000009:adverse effects* / Q000379:methods; D012128:Respiratory Distress Syndrome / Q000503:physiopathology* / Q000628:therapy*; D012129:Respiratory Function Tests / Q000379:methods; D012307:Risk Factors; D014057:Tomography, X-Ray Computed / Q000379:methods; D055397:Ventilator-Induced Lung Injury / Q000000981:diagnostic imaging* / Q000209:etiology