Biologically variable ventilation increases arterial oxygenation over thatseen with positive end-expiratory pressure alone in a porcine model of acute respiratory distress syndrome
Wac. Mutch et al., Biologically variable ventilation increases arterial oxygenation over thatseen with positive end-expiratory pressure alone in a porcine model of acute respiratory distress syndrome, CRIT CARE M, 28(7), 2000, pp. 2457-2464
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.