Assessment of PEEP-induced reopening of collapsed lung regions in acute lung injury: are one or three CT sections representative of the entire lung?

Objectives: To study whether PEEP-induced reopening of collapsed lung regio ns - defined as the decrease in nonaerated lung volume measured on a single or three computerized tomographic (CT) sections - is representative of the decrease in overall nonaerated lung volume. Design: Review of 39 CT scans obtained in consecutive patients with Acute L ung Injury. Settings: Fourteen-bed surgical intensive care unit of a University Hospita l. Measurements and results: PEEP-induced decrease in nonaerated lung volume w as measured in 39 patients with ALI on a single juxtadiaphragmatic CT secti on, on three CT sections - apical, hilar, and juxtadiaphragmatic - and on c ontiguous apex-to-diaphragm CT sections. The percentage of decrease in nona erated lung volume following PEEP, was compared between one, three and all CT sections using a linear regression analysis and Bland and Altman's metho d. The decrease in nonaerated lung volume measured on a single and three CT sections was significantly correlated with the de-crease in nonaerated lun g volume measured on all CT sections: R = 0.83, P < 0.0001 for one CT secti on and R = 0.92, P < 0.0001 for three CT sections. However, measurements pe rformed on a single CT section were poorly representative of the overall lu ng: bias -6 %, limits of agreement ranging between -37 % and +25 %. Measure ments performed on three CT sections overestimated by 11 % the overall decr ease in nonaerated lung volume: bias -11 %, limits of agreement ranging bet ween -29 % and +7 %. Conclusions: PEEP-induced reopening of collapsed lung regions measured on a single or three CT sections sensibly differs from the reopening of collaps ed lung regions measured on the overall lung. The inhomogeneous distributio n of PEEP-induced reopening of collapsed lung regions along the cephalocaud al axis probably explains these discrepancies.