CARDIORESPIRATORY EFFECTS OF PRESSURE-CONTROLLED VENTILATION WITH ANDWITHOUT INVERSE RATIO IN THE ADULT-RESPIRATORY-DISTRESS-SYNDROME

To assess the cardiorespiratory effects of pressure-controlled ventila tion (PCV) and pressure-controlled inverse ratio ventilation (PC-IRV), we compared pressure-controlled ventilation with an inspiratory-to-ex piratory time ratio (VE) of 1/2 (PCV) and of 2/1 (PC-IRV) to volume-co ntrolled ventilation (VCV) with an I/E of 1/2 in 10 patients suffering from the adult respiratory distress syndrome. In all modes, the inspi ratory oxygen fraction, tidal volume, respiratory rate, and total posi tive end-expiratory pressure (PEEPt = applied PEEP + intrinsic PEEP) w ere kept constant. Each ventilatory mode was applied for 1 h in a rand omized order. No significant differences in PaCO2 were observed among the three modes. The PaCO2 was lower (p<0.05) in PC-IRV (39 +/- 4 mm H g) than in PCV (43 +/- 5 mm Hg) and in VCV (45 +/- 5 mm Hg). The peak airway pressure was significantly lower in PC-IRV than in PCV (P<0.05) and in PCV than in VCV (p<0.05), but plateau pressure was not differe nt in the 3 modes. The mean airway pressure (mPaw) was significantly h igher (p<0.05) in PC-IRV (21.4 +/- 0.7 cm H2O) than in PCV (17.1 +/- 0 .7 cm H2O) and VCV (16.4 +/- 0.5 cm H2O). As a consequence of this inc reased mPaw, PC-IRV induced a decrease in cardiac index (CI) (3.3 +/- 0.2 vs 3.7 +/- 0.2 L/min/m2 in VCV; p<0.05) and hence in oxygen delive ry (Do2) (424 +/- 28 vs 469 +/- 38 ml/min/ml, in VCV; p<0.05). Our res ults suggest that neither PCV nor PC-IRV bring any benefit over VCV in terms of arterial oxygenation. Moreover, the increase in mPaw induced by PC-IRV may be deleterious to the CI and Do2.