Am. J. Respir. Crit. Care Med., Vol 152, No. 4, 10 1995, 1241-1247.
Effects of PEEP on acinar gas transfer in healthy and lung-injured dogs
GM Barnas, PL Donahue, CS Kong, IG Ryder, DH Choi, BH Hoff and CF Mackenzie
Department of Anesthesiology, University of Maryland, Baltimore 21201, USA.
We measured cardiorespiratory variables and 133xenon washout from a
nonperfused lung region (XeW) in six anesthetized/paralyzed dogs,
mechanically ventilated with 60% O2 at different positive end- expiratory
pressures (PEEP). XeW in this technique represents directly measured acinar
gas transfer (3). Measurements were repeated after induction of lung injury
by lavaging the lungs 11 to 13 times with 600 ml saline. In control dogs,
lung compliance (CL), alveolar ventilation (Valv), and XeW all decreased
with increasing PEEP from 0 to 25 cm H2O (p < 0.05), while lung
resistance (RL) did not change. After lavage, CL, Valv, and XeW below 15 cm
H2O PEEP were all less than control values (p < 0.05), while RL was
higher than control values. As PEEP increased from 0 to 20 cm H2O, Valv and
XeW increased, but CL did not change; RL decreased only from 0 to 5 cm H2O.
At 20 cm H2O PEEP, Valv and CL were not different from control values (p
> 0.05), and XeW was higher than control values (p < 0.05). At
estimated alveolar volumes above 400 ml, values for XeW before and after
lavage were similar. We conclude that, during severe lung injury: (1)
increasing PEEP to moderate levels will increase acinar gas transfer but,
after a certain lung volume is reached, further increases in PEEP will have
effects similar to the healthy condition; (2) overall mechanical properties
of the lung do not reflect the responses to PEEP of the lung periphery.
