HEMODYNAMIC-EFFECTS OF DIFFERENT MODES OF MECHANICAL VENTILATION IN ACUTE CARDIAC AND PULMONARY FAILURE - AN EXPERIMENTAL-STUDY

Objective: To determine the hemodynamic effects of four different mode s of mechanical ventilation in an animal model of acute cardiac and pu lmonary failure.Design: Prospective, randomized, crossover design. Set ting: University research laboratory. Subjects: Twelve piglets weighin g 10 to 16 kg. Interventions: The experimental protocol consisted of t hree stable 30-min periods: when ventricular and pulmonary functions w ere normal (control), after the induction of acute cardiac failure by the administration of a beta-adrenergic receptor blocker, and after pu lmonary failure induced by repeated lung lavage. Modes of mechanical v entilation included controlled mechanical ventilation, high-frequency oscillation, synchronized high-frequency jet ventilation, and external negative pressure oscillation combined with pressure support ventilat ion. Each mode of respiratory support was randomly and sequentially ap plied to each animal with the assessment of cardiopulmonary function a t the end of each period. Measurements and Main Results: Continuous mo nitoring included electrocardiogram, right atrial, left ventricular en d-diastolic, pulmonary arterial, intrathoracic aortic, arterial, esoph ageal, and transpulmonary pressures and arterial and mixed venous oxyg en saturation measurements. In addition, cardiac output using the ther modilution technique was measured intermittently. Whereas in the contr ol period cardiac index was significantly (p < .05) higher during sync hronized high-frequency jet ventilation (193 +/- 19.3 ml/kg/min) than during controlled mechanical ventilation (151 +/- 12.1 mL/kg/min) and high-frequency oscillation (151 +/- 18.1 mL/kg/min), there was no sign ificant hemodynamic difference between the four modes of mechanical ve ntilation in the cardiac and pulmonary failure periods. In the pulmona ry failure period, transpulmonary pressure was significantly higher du ring high-frequency oscillation (7.1 +/- 1.6 mm Hg) than during contro lled mechanical ventilation (5.6 +/- 0.6 mm Hg), high-frequency ventil ation (4.1 +/- 0.4 mm Hg), and external negative pressure oscillation combined with pressure support ventilation (5.3 +/- 0.5 mm Hg). Conclu sions: Synchronized high-frequency ventilation improves cardiac perfor mance in control conditions. No hemodynamic difference is present betw een the four modes of mechanical ventilation in the cardiac and pulmon ary failure periods. External negative pressure oscillation combined w ith pressure support ventilation has moderate hemodynamic advantages o ver controlled mechanical ventilation and high-frequency oscillation i n different clinical settings, but it also results in a deterioration of pulmonary gas exchange during the pulmonary failure period.