Positive End-expiratory Pressure Effects to Predict Fluid Responsiveness

Volume expansion is one of the main treatments for shock, with the goal of increasing cardiac preload and, consequently, cardiac output. However, this increase only occurs if there is a preload-dependence of cardiac output, which is present in 50% of cases. A test to predict the effectiveness of volume expansion prior to administration would avoid the need for excess treatment if it proves to be unnecessary. The end-expiratory pressure test (PEEP) would be to vary the PEEP in patients in shock conditions placed under mechanical ventilation. PEEP is the positive pressure maintained in the airways at the end of expiration. It opposes systemic venous return and lowers cardiac preload. It also distends the pulmonary vessels, increases their resistance and opposes the ejection of the right ventricle. The decrease in PEEP could alleviate the obstacle to venous return and thus increase cardiac preload, mimicking a volume expansion, increasing cardiac output only in the case of preload dependence. This test would be an easy alternative to the tests used in current practice. To evaluate the ability of the PEEP test to detect a preload-dependence condition, defined by a passive passive leg raising test, in patients in shock.

The primary endpoint will be the area under the receiver operating characteristic (ROC) curve constructed to describe the ability of the PEEP test to detect a preload-dependency condition. We measure cardiac output by analysis of the pulse wave contour before and after the passive leg raising and PEEP test tests, then according to these tests, measurement of the cardiac output before and after volume expansion.