Am. J. Respir. Crit. Care Med.,
Volume 161, Number 6, June 2000, 1797-1804
Biologic Variability in Mechanical Ventilation Rate and
Tidal Volume Does Not Improve Oxygenation or Lung
Mechanics in Canine Oleic Acid Lung Injury
ARTHUR J.
NAM,
ROY G.
BROWER,
HENRY E.
FESSLER,
and
BRETT A.
SIMON
Departments of Environmental Physiology, Pulmonary/Critical Care Medicine, and Anesthesiology/Critical Care Medicine,
Johns Hopkins Medical Institutions, Baltimore, Maryland
Mechanical ventilation in patients with acute respiratory distress
syndrome and acute lung injury (ALI) remains a difficult challenge
because of the conflict between maintaining adequate gas exchange and furthering lung injury via overdistention. In a recent
study, Lefevre and colleagues (Am. J. Respir. Crit. Care Med. 1996;154:
1567-1572) suggested that mechanical ventilation with natural
biologic variability (BV) in breath-to-breath respiratory frequency
(f) and VT could reduce lung injury and improve gas exchange
without increases in mean airway pressure (Paw) or peak inspiratory pressure (PIP). However, significant differences in cardiac
output (CO), PaCO2, pH, and delivered VT between the treatment groups in their study could have influenced these results. Because of the potential implications of these findings for patient care, we
attempted to confirm these findings by Lefevre and colleagues in
a canine model of oleic acid-induced lung injury. Eighteen mongrel dogs were anesthetized in the supine position, paralyzed, and
mechanically ventilated with 50% O2 at f = 15 breaths/min, and
VT was adjusted to achieve an end-tidal CO2 of 30 to 35 mm Hg.
Lung injury was produced by infusion of 0.06 ml/kg oleic acid solution into the right atrium over a 30-min period. Animals were then
randomized to either conventional ventilation at the baseline settings (n = 9) or to BV at the same mean VT and f (n = 9). Both groups received comparable degrees of injury, and hemodynamic and ventilatory parameters were closely matched, with no differences in mean VT, PIP, mean Paw, PaCO2, pH, CO, pulmonary artery
occlusion pressure, or arterial pressure (Pa). However, no differences between the two groups were found in PaO2, shunt, or static
compliance over a 4-h period. When hemodynamic and ventilatory parameters were well matched in a canine model of ALI, BV
showed no advantage over conventional ventilation at constant VT
and f.
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Copyright © 2000 American Thoracic Society
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