EFFECTS OF PRESSURE-CONTROLLED WITH DIFFERENT I E RATIOS VERSUS VOLUME-CONTROLLED VENTILATION ON RESPIRATORY MECHANICS, GAS-EXCHANGE, AND HEMODYNAMICS IN PATIENTS WITH ADULT-RESPIRATORY-DISTRESS-SYNDROME/

Background: Pressure-controlled (PCV) and pressure-controlled inverse ratio ventilation (PCIRV) have been proposed instead of volume-control led conventional ratio ventilation (VC) with positive end-expiratory p ressure (PEEP) for patients with adult respiratory distress syndrome ( ARDS). The advantages advocated with the use of PCIRV are to decrease airway pressures and to improve gas exchange. However, most studies di d not compare PCIRV and VC while keeping both the level of ventilation and end-expiratory alveolar pressure (total-PEEP) constant. Methods: Nine patients with moderate to severe ARDS (lung injury score 2.83+/-0 .18) had their lungs ventilated with VC, PCV with a conventional ratio (I:E 1:2; PC 1/2), and PCIRV (I: E 2:1 and 3:1; PC 2/1 and PC 3/1, re spectively). Ventilator settings were adjusted to keep tidal volume, r espiratory rate, Fi(O2), and total-PEEP constant in every mode. With e ach mode, a complete set of ventilatory, hemodynamic, and gas exchange parameters was obtained after 30 min. Results: In PC 3/1, the data ob tained could not be strictly compared to the other modes because total -PEEP was higher despite external-PEEP being set at zero. For the othe r modes (VC, PC 1/2, and PC 2/1), despite differences in peak airway p ressures, no difference was noted for end-inspiratory and end-expirato ry static airway pressures (which better reflect alveolar pressures) n or for lung and respiratory system compliance. Arterial oxygenation de teriorated slightly with PC 2/1 despite a higher mean airway pressure, whereas alveolar ventilation tended to be slightly, but not significa ntly, improved (lower Pa-CO2). A decrease in systolic and mean arteria l pressure also was observed with PC 2/1 without other significant hem odynamic change. Conclusions: In this prospective controlled study, no shortterm beneficial effect of PCV or PCIRV could be demonstrated ove r conventional VC with PEEP in patients with ARDS.