Cardiopulmonary Effects of Positive

Study objectives: To assess the gas exchange and hemodynamic effects of pressure-limited ventilation (PLV) strategies in acute lung injury (ALI). We hy¬ pothesized that in ALI, the reduction ofplateau airway pressure (Paw) would be associated with less alveolar overdistention and thus have better hemodynamic and gas exchange characteristics than larger tidal volume (Vt) ventilation. Setting: Laboratory. Design: Prospective time-controlled sequential animal study. Measurements: Right atrial, pulmonary artery, left atrial, arterial, lateral pleural (Ppl), and pericardial (Ppc) pressures, Paw, ventricular stroke volume, mean expired CO2, and arterial and mixed venous oxygen contents. Airway resistance and static lung compliance were also measured. Interventions: Intermittent positive pressure ventila¬ tion (IPPV) given before (control) and after induction ofALI by oleic acid infusion (0.1 mL/kg). IPPV at FIo2 of 1, Vt of 12 mL/kg, and frequency adjusted to main¬ tain normocarbia. ALI PLV was given during ALI and defined as that Vt which gave a similar plateau Paw to that of control IPPV. High-frequency jet ventilation (HFJV) and ALI HFJV were also given and defined as frequency within 10% of heart rate and mean Paw similar to that during control IPPV. Results: After ALI, static lung compliance, PaC>2, and pH decreased, whereas airway resistance and PaCC>2 increased. For a constant lung volume, Ppl and Ppc were not different between control and ALI. Both ab¬ solute dead space (Vd) and intrapulmonary shunt fraction increased afterALI, but absoluteVd was lower with ALI PLV andALI HFJVwhen compared with ALI IPPV. Ventilation did not alter hemodynamics during ALI.