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(Chest. 1999;116:1032-1038.)
© 1999 American College of Chest Physicians

The Effect of Varying Inspiratory to Expiratory Ratio on Gas Exchange in Partial Liquid Ventilation*

Chae-Man Lim, MD; Younsuck Koh, MD; Tae S. Shim, MD; Sang D. Lee, MD; Woo S. Kim, MD; Dong S. Kim, MD and Won D. Kim, MD, FCCP

* From the Division of Pulmonary and Critical Care Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.

Correspondence to: Chae-Man Lim, MD, Division of Pulmonary and Critical Care Medicine, Asan Medical Center, Songpa PO Box 145, Seoul, Korea, 138–600

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).

Design and setting: 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.

Interventions: 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).

Measurements and results: With increasing I:E ratio in all animals, PaO2/FIO2 increased (80 ± 24, 143 ± 74, and 147 ± 88 mm Hg; p = 0.001), and PaCO2 decreased (74 ± 15, 66 ± 16, and 66 ± 15 mm Hg; p = 0.006). The increases of PaO2/FIO2 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. PaCO2 decreased with increasing I:E ratio in group 1, but not in group 2. The change of PaO2/FIO2 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.

Key Words: gas exchange • inspiratory flow rate • inspiratory pause • inspiratory to expiratory ratio • partial liquid ventilation






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