[Regulation of artificial ventilation in adult respiratory distress syndromes]

Progress in recent years in functionnal investigations of the ventilated patient has made it possible to refine the regulation of artificial ventilation in particular in patients with lesional oedema. The best ventilatory regimen is that which ensures adequate alveolar ventilation at the price of the least mechanical and haemodynamic difficulties. It is also that which ensures the best oxygen transfer and hence to reduce alveolo-arterial oxygen difference. It is now known that the reconstitution of functional residual capacity (FRC) is the essential step. The use of positive pressure at the end of expiration (PEEP) generally makes it possible to achieve this aim. Alveolar function in high critical opening pressure zones requires levels of PEEP for which the maintenance of constant cardiac output is necessary. This may be obtained by combining blood volume expansion with the effect of positive inotropic drugs. Estimation of VD/VT ratio, calculation of P(A - a)O2 and of oxygen transfer indices such as P(a/A)O2 may be used to assess the efficacy of exchanges. Cycle to cycle surveillance of quasi thoracopulmonary compliance offers information concerning the improvement in FRC.