Volume-pressure curve of the respiratory system predicts effects of PEEP in ARDS: "occlusion" versus "constant flow" technique.
The effects of positive end-expiratory pressure (PEEP) on static ("rapid airway occlusion" technique) and dynamic ("constant flow" technique) volume-pressure (V-P) curves were studied in 19 patients with adult respiratory distress syndrome (ARDS). To describe the shape of both curves, the nonlinear coefficient of a second-order polynomial equation fitted to the static (static nonlinear coefficient) and dynamic (dynamic nonlinear coefficient) V-P curves on zero end-expiratory pressure (ZEEP) was used. Two distinct patterns were observed: (1) in ten patients, the static and dynamic V-P curves on ZEEP exhibited a convex shape with a progressive decrease in slope with increasing inflation volume (nonlinear coefficients: negative). In these patients PEEP induced a volume displacement along the static and dynamic V-P curves on ZEEP (hyperinflation). (2) In nine patients, the static and dynamic V-P curves on ZEEP showed a concave shape with a progressive increase in slope with increasing volume (nonlinear coefficients: positive) and PEEP shifted both curves upward along the volume axis (alveolar recruitment). A correlation (p < 0.0001) between static and dynamic nonlinear coefficients was found at all levels of PEEP. Both static and dynamic nonlinear coefficients on ZEEP were correlated (p < 0.0001) with the amount of lung volume recruited with PEEP, and the variations of cardiac index (CI), O2 delivery (DO2), right-to-left venous admixture (Qs/Qt), and PaO2 with PEEP. Besides, the effects of PEEP on Cl, DO2, Qs/Qt, and PaO2 were less pronounced (p < 0.001) in patients with convex V-P curves than in patients with concave V-P curves.(ABSTRACT TRUNCATED AT 250 WORDS)
Ranieri
V M
VM
Istituto di Anestesiologia e Rianimazione, Policlinico, Università di Bari, Italy.
Giuliani
R
R
Fiore
T
T
Dambrosio
M
M
Milic-Emili
J
J
D000368:Aged; D000704:Analysis of Variance; D001784:Blood Gas Analysis; D005260:Female; D006439:Hemodynamics; D006801:Humans; D016018:Least-Squares Analysis; D008170:Lung Compliance; D008297:Male; D008433:Mathematics; D008875:Middle Aged; D011175:Positive-Pressure Respiration / Q000379:methods*; D011237:Predictive Value of Tests; D011312:Pressure; D011650:Pulmonary Alveoli / Q000503:physiopathology*; D011659:Pulmonary Gas Exchange; D012115:Residual Volume; D012128:Respiratory Distress Syndrome / Q000097:blood / Q000401:mortality / Q000503:physiopathology* / Q000628:therapy*; D015996:Survival Rate