Chest
Volume 116, Issue 4, October 1999, Pages 1032-1038
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Laboratory and Animal Investigations
The Effect of Varying Inspiratory to Expiratory Ratio on Gas Exchange in Partial Liquid Ventilation

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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/Fio2increased (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. Paco2decreased 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.

Section snippets

Animal Preparation and Instrumentation

Eighteen New Zealand White rabbits (2.6 ± 0.5 kg) were used for this study. In group 1 (n = 9), the I:E ratio was changed by adjusting the inspiratory pause at a fixed inspiratory flow rate. In group 2 (n = 9), the I:E ratio was changed by adjusting the inspiratory flow rate. The experimental protocol was approved by the Animal Care Committee of our institute, and the rabbits were cared for and handled according to the guidelines of the National Health Institute. The rabbits were placed supine

Results

With increasing I:E ratio in all animals, Pao2/Fio2increased (80 ± 24 mm Hg at 1:2/1:3; 143 ± 74 mm Hg at 1:1; and 147 ± 88 mm Hg at 2:1; p = 0.001) and Paco2 decreased (74 ± 15 mm Hg, 66 ± 16 mm Hg, and 66 ± 15 mm Hg, respectively; p = 0.006). With an increasing I:E ratio in group 1, Pao2/Fio2increased (p = 0.001) and Paco2 and Vd/Vt decreased (both p < 0.05; Table 1). In group 2, on the other hand, Pao2/Fio2at 2:1 was lower than at 1:1 (p < 0.05), and Paco2 and Vd/Vt did not change (Table 2).

Discussion

In at least two animal studies, the superior lung and the inferior lung were observed to be inflated in sequence during PLV.16 The current study was intended to evaluate the effect of an increased I:E ratio on gas exchange in this situation of sequential lung inflation. In our results, extending the I:E ratio in PLV increased oxygenation and decreased Paco2 of acutely injured rabbit lung. In the application of a high I:E ratio in PLV, adding inspiratory pause was superior to lowering

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  • Cited by (10)

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    This study was supported in part by the Asan Institute for Life Sciences, Seoul, Korea.

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