Improved arterial oxygenation with biologically variable or fractal ventilation using low tidal volumes in a porcine model of acute respiratory distress syndrome

We compared biologically variable ventilation ((V)over dot(bv); n = 9) with control mode ventilation ((V)over dot(c); n = 8) at low tidal volume (VT)-initial 6 ml/kg-in a porcine model of acute respiratory distress syndrome (ARDS). Hemodynamics, respiratory gases, airway pressures, and VT data were measured. Static P-V curves were generated at 5 h. Interleukin (IL)-8 and IL-10 were measured in serum and tracheal aspirate. By 5 h, higher Pa-O2 (173 +/- 30 mm Hg versus 119 +/- 23 mm Hg; mean +/- SD; p < 0.0001 group x time interaction [G x T]), lower shunt fraction (6 +/- 1% versus 9 +/- 3%; p = 0.0026, G x T) at lower peak airway pressure (21 +/- 2 versus 24 +/- 1 cm H2O; P = 0.0342; G x T) occurred with (V)over dot(bv). IL-8 concentrations in tracheal aspirate and wet:dry weight ratios were inversely related; p = 0.011. With (V)over dot(c), IL-8 concentrations were 3.75-fold greater at wet:dry weight ratio of 10. IL-10 concentrations did not differ between groups. In both groups, ventilation was on the linear portion of the P-V curve. With (V)over dot(bv), VT variability demonstrated an inverse power law indicating fractal behavior. In this model of ARDS, (V)(bv) improved Pa-O2 at lower peak airway pressure and IL-8 levels compared with (V)over dot(c).