The effect of varying inspiratory to expiratory ratio on gas exchange in partial liquid ventilation.
BACKGROUND
In partial liquid ventilation (PLV), the nondependent lung was observed to be inflated first and the dependent lung later. The inflational time difference between the lung regions can lead to maldistribution of tidal gas and inefficient gas bubbling in the slow-inflating region during PLV. In this situation, increasing the inspiratory to expiratory (I:E) ratio of the mechanical ventilator would lessen the heterogeneity of regional ventilation and improve gas exchange possibly to a greater degree than in gas ventilation (GV).


METHODS
Animal study at the Asan Institute for Life Sciences, Seoul, Korea Subjects: Eighteen rabbits (2.6 +/- 0.5 kg) with acute lung injury by saline solution lavage.


METHODS
Three I:E ratios were tried in GV and then in PLV. I:E ratios were changed by adjusting pause (1:2, 1:1, and 2:1; group 1) or by adjusting inspiratory flow rate (1:3, 1:1, and 2:1; group 2).


RESULTS
With increasing I:E ratio in all animals, PaO(2)/FIO(2) increased (80 +/- 24, 143 +/- 74, and 147 +/- 88 mm Hg; p = 0.001), and PaCO(2) decreased (74 +/- 15, 66 +/- 16, and 66 +/- 15 mm Hg; p = 0.006). The increases of PaO(2)/FIO(2) from 1:2/1:3 to 1:1 (p = 0.006) and from 1:1 to 2:1 (p = 0.036) were both greater in group 1 than in group 2. PaCO(2) decreased with increasing I:E ratio in group 1, but not in group 2. The change of PaO(2)/FIO(2) by varying the I:E ratio was 49 +/- 65% in PLV and 14 +/- 14% in GV (p = 0.003).


CONCLUSIONS
Extending the I:E ratio, especially by adding pause, improved gas exchange in PLV. Oxygenation in PLV was affected by the I:E ratio to a greater degree than in GV.
Lim
C M
CM
Division of Pulmonary and Critical Care Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
Koh
Y
Y
Shim
T S
TS
Lee
S D
SD
Kim
W S
WS
Kim
D S
DS
Kim
W D
WD
D000818:Animals; D019296:Capnography; D005466:Fluorocarbons; D006801:Humans; D007320:Inspiratory Capacity / Q000502:physiology; D008176:Lung Volume Measurements; D011175:Positive-Pressure Respiration; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012123:Pulmonary Ventilation / Q000502:physiology; D011817:Rabbits; D012121:Respiration, Artificial; D012128:Respiratory Distress Syndrome / Q000503:physiopathology*
D005466:Fluorocarbons