Cardiovascular responses to high-frequency oscillatory ventilation during acute lung injury in sheep.
OBJECTIVE
The present study was designed to evaluate pulmonary and systemic hemodynamics and blood gas changes on switching from conventional mechanical ventilation (CMV) to high-frequency oscillatory ventilation (HFOV) in a large animal model of acute lung injury.


METHODS
Eleven anesthetised sheep chronically instrumented with vascular monitoring were prepared. Animals received oleic acid (0.08 ml x kg(-1)) intravenously and were ventilated for 4 h h after the administration of oleic acid. The animals were then randomized into the two following different ventilation modes: CMV (tidal volume [V(T)], 6 ml x kg(-1); respiratory rate [RR], 25 x min(-1)) with positive end-expiratory pressure (PEEP) of 12 cmH(2)O; or CMV under the same settings without PEEP. HFOV was then switched. The setting of mean airway pressure with a fixed stroke volume was changed between 25, 18, and 12 cmH(2)O every 20 min. Mean pulmonary artery pressure, pulmonary artery occlusive pressure (Paop), left atrium pressure, systemic arterial pressure, cardiac output (CO), and blood gas composition under each setting were measured before and after HFOV.


RESULTS
Switching to HFOV, from without PEEP, resulted in significant increases in Paop and PaO2 and a decrease in CO at higher (25, 18 cmH(2)O) mean airway pressure. However, when changed from low V(T) and PEEP, HFOV produced further improvements in oxygenation without any deterioration of cardiovascular depression. Thus, switching to HFOV from CMV with low V(T) and high PEEP may have little influence on pulmonary or systemic hemodynamics in acute lung injury.


CONCLUSIONS
We conclude that hemodynamic responses are dependent on the predefined setting of PEEP during CMV, and on applied mean airway pressure during HFOV.
Anesthesiology and Resuscitation, Shinshu University School of Medicine, Matsumoto, Japan.
Rikimaru
R
Nakagawa
Tomonobu
T
Koizumi
Koichi
K
Ono
Kenji
K
Tsushima
Sumiko
S
Yoshikawa
Keishi
K
Kubo
Tetutarou
T
Otagiri
D000704:Analysis of Variance; D000818:Animals; D001784:Blood Gas Analysis; D001794:Blood Pressure / Q000502:physiology*; D002302:Cardiac Output / Q000502:physiology*; D004195:Disease Models, Animal; D006612:High-Frequency Ventilation / Q000379:methods*; D019301:Oleic Acid; D011175:Positive-Pressure Respiration / Q000379:methods*; D011897:Random Allocation; D012128:Respiratory Distress Syndrome / Q000097:blood / Q000139:chemically induced / Q000628:therapy*; D012756:Sheep; D014655:Vascular Resistance / Q000502:physiology*
D019301:Oleic Acid