Controlled
mechanical ventilation (CMV) may contribute to impaired hemodynamics in patients with
respiratory failure. It is rational to assume that hybrid modalities of
mechanical ventilation have fewer hemodynamic side-effects when spontaneous respiratory activity is allowed during the application of positive airway pressure.
Partial liquid ventilation (PLV) has been shown to improve gas exchange in subjects with severe alveolar
lung disease. We have shown that spontaneous respiratory efforts during
proportional assist ventilation (PAV) is possible in experimental animals without
lung disease whose lungs are partially filled with
perfluorocarbons. In another series of experiments we demonstrated that PLV improves oxygenation and lung compliance in adult rabbits with severe
surfactant deficiency, and in rabbits with
meconium aspiration. In animals with
meconium aspiration mortality, work of breathing and the degree of
lung injury, as assessed by histological analysis, were reduced. In another two series of animals with and without
surfactant deficiency spontaneous breathing supported by PAV was associated with increased cardiac output, stroke volume and
oxygen transport, as compared to CMV after pharmacologically induced muscle
paralysis. An increased arterial and venous pH in animals with
surfactant deficiency during spontaneous breathing supported by PAV suggests improved tissue perfusion. Furthermore, gas exchange was improved during spontaneous breathing supported by PAV as compared to CMV and muscle
paralysis.