[Effect of artificial ventilation with an end-expiratory plateau on gas exchange amd hemodynamics in chronic respiratory failure].

Previous studies of pulmonary models and with animals have shown that in obstructive disease of the airways, ventilation with an end-expiratory plateau improves ventilation distribution. Paradoxically, there has been no data published on patients with obstructive disease. For this reason, we examined the effects of mechanical ventilation with an end-expiratory plateau on gas exchange and haemodynamics in 12 patients presenting acute exacerbations of chronic respiratory failure. Following a period of conventional controlled ventilation, two plateaux of 0.3 and 0.5 s respectively are successively introduced while the I/E ratio (1/2.5) and then inspiratory flow (respiratory frequency and end-tidal volume remaining the same) are kept constant. PaCO2 decreases by approximately 10% with the addition of each plateau. In spite of a moderate increase in mean airway pressure (+8%), greatest improvement in gas exchange is observed with the longer plateau (0.5 s), maintaining expiration time (I/E constant) : a decrease in PaCO2 and in VD/VT (approximately - 14%), an increase in PaO2 (+7%) and a decrease of venous admixture (shunt + shunt effect : - 18.5%). The plateau tends to reduce ventilation/perfusion mismatch, whereas maintaining prolonged expiration assures "emptying" of slow alveoli. However, no matter which plateau is used, cardiac output decreases by more than 10% in six patients, probably due to a drop in systemic venous return. PaCO2 increase is too slight to hinder a decrease in arterial oxygen transport. The variability of these results accounts for patient diversity and restricts the indication of end-expiratory plateau to patients with severe ventilatory distribution disturbances who can benefit from close cardiorespiratory monitoring.