Vm. Ranieri et al., VOLUME-PRESSURE CURVE OF THE RESPIRATORY SYSTEM PREDICTS EFFECTS OF PEEP IN ARDS - OCCLUSION VERSUS CONSTANT FLOW TECHNIQUE, American journal of respiratory and critical care medicine, 149(1), 1994, pp. 19-27
Citations number
30
Categorie Soggetti
Emergency Medicine & Critical Care","Respiratory System
The effects of positive end-expiratory pressure (PEEP) on static (''ra
pid airway occlusion'' technique) and dynamic (''constant flow'' techn
ique) volume-pressure (V-P) curves were studied in 19 patients with ad
ult respiratory distress syndrome (ARDS). To describe the shape of bot
h curves, the nonlinear coefficient of a second-order polynomial equat
ion fitted to the static (static nonlinear coefficient) and dynamic (d
ynamic nonlinear coefficient) V-P curves on zero end-expiratory pressu
re (ZEEP) was used. Two distinct patterns were observed: (1) In ten pa
tients, the static and dynamic V-P curves on ZEEP exhibited a convex s
hape with a progressive decrease in slope with increasing inflation vo
lume (nonlinear coefficients: negative). In these patients PEEP induce
d a Volume displacement along the static and dynamic V-P curves on ZEE
P (hyperinflation). (2) In nine patients, the static and dynamic V-P c
urves on ZEEP showed a concave shape with a progressive increase in sl
ope with increasing volume (nonlinear coefficients: positive) and PEEP
shifted both curves upward along the volume axis (alveolar recruitmen
t). A correlation (p < 0.0001) between static and dynamic nonlinear co
efficients was found at all levels of PEEP. Both static and dynamic no
nlinear coefficients on ZEEP were correlated (p < 0.0001) with the amo
unt of lung volume recruited with PEEP, and the variations of cardiac
index (Cl), O-2 delivery (Do(2)), right-to-left venous admixture (Qs/Q
t), and Pao(2) with PEEP. Besides, the effects of PEEP on Cl, Do(2), Q
s/Qt, and Pao(2) were less pronounced (p < 0.001) in patients with con
vex V-P curves than in patients with concave V-P curves. We conclude t
hat analysis of the dynamic V-P curve (''constant flow'' method) may r
eplace the use of the static V-P curve (''occlusion technique'') to as
sess the elastic properties of the respiratory system in ARDS patients
. The dynamic V-P curve represents a simple and noninvasive clinical t
ool which detects hyperinflation and predicts the effects of PEEP on a
lveolar recruitment, hemodynamics, and gas exchange in ARDS patients.