IMPROVED ARTERIAL OXYGENATION AFTER OLEIC-ACID LUNG INJURY IN THE PIGUSING A COMPUTER-CONTROLLED MECHANICAL VENTILATOR

We compared computer-controlled mechanical ventilation programmed for biologic variability of respiratory rate (RR) and tidal volume (VT) wi th conventional intermittent positive-pressure ventilation (IPPV) in a n oleic acid (OA) lung injury model. Seventeen pigs were ventilated wi th an Ohio 7000 anesthesia ventilator. Minute ventilation (V over dot E) was adjusted to maintain Pa-CO2 at 30 to 35 mm Hg at baseline and w as not altered further. OA was infused at 0.2 ml/kg/h until Pa-O2 decr eased to less than or equal to 125 mm Hg (FIO2 = 0.5). Animals were ra ndomly assigned to continue with conventional IPPV (control group; n = 8) or had IPPV computer-controlled (computer group; n = 9). Hemodynam ic, respiratory gas, airway pressure, and volume data were obtained at baseline (before OA infusion), at Time 30 (after infusion), and at 30 -min intervals for 240 min after OA. At experiment completion, the lun gs were removed to determine the wet:dry weight ratios. The control gr oup had RR fixed at 20 breaths/min. The computer group had a RR of 20 +/- 2.3 breaths/min (range, 15 to 27 breaths/min), comprising 369 diff erent RR values with reciprocal changes in VT over 1,089 s before the program looped to repeat itself. There was no difference between group s in the volume of OA infused. By 120 min after lung injury, animals i n the computer group had significantly greater Pa-O2, associated with a lower Q over dot s/Q over dot T. Mean airway pressures and mean peak airway pressures were not different in the two groups. By 180 min, re spiratory system compliance (Crs) was significantly lower in the contr ol group. The wet:dry lung weight ratios were greater in the control g roup. Thus, in a porcine model of OA lung injury, computer-controlled mechanical ventilation, which is programmed for biologic variability, resulted in improved blood oxygenation without increasing mean airway pressures when compared with conventional IPPV.