Decrease in Lung Volume Depends on End-Expiratory Pressure in a Rabbit Model of Airway Lavage

Background: In the past, the rabbit model of repeated airway lavage has been extensively used to induce a decrease in lung volume accompanied by impairment in lung mechanics and gas exchange. Objectives: The rationale of our study was to investigate the influence of different end-expiratory pressure (EEP) levels (0.4–4.2 cm H 2 O) on changes in functional residual capacity (FRC) and the efficacy of lavages administered. Methods: Forty-five rabbits were subjected to 2–8 lavages with 20 ml/kg warm normal saline until arterial/alveolar oxygen tension (a/A ratio) had decreased to ≤0.12. Results: FRC and dynamic compliance of the respiratory system (C rs ) decreased significantly (both p < 0.001; from 19.1 ± 4.2 to 10.5 ± 5.6 ml/kg and from 1.17 ± 0.27 to 0.47 ± 0.10 ml/cm H 2 O, respectively, means ± SD). The decrease in FRC was significantly influenced by EEP (–28.6 ± 15.8% at EEP = 1 cm H 2 O vs. –58.7 ± 12.9% at EEP = 3 cm H 2 O, p < 0.0001). There was a significant correlation between the number of lavages and EEP (p < 0.01), indicating that successive lavages at higher EEP became ineffective in lowering FRC compared to those at lower EEP. Conclusions: We conclude that the EEP levels used in this model are of critical importance for the prediction of a decrease in lung volume (FRC) and the efficacy of lavages.