LONG-TERM EFFECTS OF 2 DIFFERENT VENTILATORY MODES ON OXYGENATION IN ACUTE LUNG INJURY - COMPARISON OF AIRWAY PRESSURE RELEASE VENTILATION AND VOLUME-CONTROLLED INVERSE RATIO VENTILATION

A total of 18 patients with acute lung injury (ALI) were sequentially Ventilated with two different modes of mechanical ventilation, each ap plied for a period of 24 h: (1) volume-controlled inverse ratio ventil ation (VC-IRV), (2) airway pressure release ventilation (APRV). The in dividual sequence of both ventilatory modes was randomized. Ventilator y minute volume was adjusted for a Pace, of 35 to 45 mm Hg at the begi nning of the study during the first ventilatory mode and then kept con stant within preset limits. Hemodynamic variables were stable and simi lar during the 24-h periods of VC-IRV and APRV as well. Despite the lo wer sedation and spontaneous breathing during APRV, oxygen uptake was similar during both ventilatory modes. During the 24-h period of VC-IR V there was no relevant change of either airway pressures, alveolo-art erial O-2 tension difference (AaDo(2))/fraction of inspired oxygen (Fl o(2)) or venous admixture. In contrast, peak airway pressures (Paw(max )) during APRV were significantly lower (about 30%; p < 0.01), and dec reased further within 24 h (p < 0.05). During APRV AaDO(2)/Flo(2) and venous admixture improved significantly with time after more than 8 h (AaDo(2)/Flo(2): 487 versus 414 mm Hg; p < 0.01; venous admixture: 20. 6 versus 13.9%; p < 0.01; medians of onset versus end). The improvemen t was significantly different between both ventilatory modes (p < 0.01 ). We conclude that this indicates a progressive alveolar recruitment over time during ventilation with APRV. The results of our study indic ate that VC-IRV and APRV as well were able to provide sufficient venti lation and oxygenation in our patients with moderate to severe acute l ung injury over a period of 24