Biologically variable ventilation increases arterial oxygenation over thatseen with positive end-expiratory pressure alone in a porcine model of acute respiratory distress syndrome

Objectives: We compared biologically variable ventilation (BW) (as previous ly described) (1) with conventional control mode ventilation (CV) in a mode l of acute respiratory distress syndrome (ARDS) both at 10 cm H2O positive end-expiratory pressure. Design: Randomized, controlled, prospective study. Setting: University research laboratory. Subjects: Farm-raised 3- to 4-month-old swine. Interventions: Oleic acid (OA) was infused at 0.2 mL/kg/hr with Fio(2) = 0. 5 and 5 cm H2O positive end-expiratory pressure until Pao(2) was less than or equal to 60 mm Hg; then all animals were placed on an additional 5 cm H2 O positive end-expiratory pressure for the next 4 hrs, Animals were assigne d randomly to continue CV (n = 9) or to have CV computer controlled to deli ver RW (variable respiratory rate and tidal volume; n = 8). Hemodynamic, ex pired gas, airway pressure, and volume data were obtained at baseline (befo re GA), immediately after OA, and then at 60-min intervals for 4 hrs, Measurements and Main Results:At 4 hrs after OA injury, significantly highe r Pao(2) (213 +/- 17 vs, 123 +/- 47 mm Hg; mean +/- so), lower shunt fracti on (6% +/- 1% vs, 18% +/- 14%), and lower Paco(2) (50 +/- 8 vs, 65 +/- 11 m m Hg) were seen with BW than with CV, Respiratory system compliance was gre ater by experiment completion with BW (0.37 +/- 0.05 vs, 0.31 +/- 0.08 mL/c m H2O/kg). The improvements in oxygenation, CO2 elimination, and respirator y mechanics occurred without a significant increase in either mean airway p ressure (14.3 +/- 0.9 vs, 14.9 +/- 1.1 cm H2O) or mean peak airway pressure (39.3 +/- 3.5 vs, 44.5 +/- 7.2 cm H2O) with RW, The oxygen index increased five-fold with OA injury and decreased to significantly lower levels over time with BW, Conclusions: In this model of ARDS, BW with 10 cm H2O positive end-expirato ry pressure improved arterial oxygenation over and above that seen with CV with positive end-expiratory pressure alone. Proposed mechanisms for RW eff icacy are discussed.