Physiological effects of different recruitment maneuvers in a pig model of ARDS

BACKGROUND: In acute respiratory distress syndrome (ARDS), lung recruitment maneuvers can recruit collapsed alveoli in gravity-dependent lung regions, improving the homogeneity of ventilation distribution. This study used electrical impedance tomography to investigate the physiological effects of different recruitment maneuvers for alveolar recruitment in a pig model of ARDS. METHODS: ARDS was induced in ten healthy male pigs with repeated bronchoalveolar lavage until the ratio of arterial partial pressure of oxygen (PaO(2)) of fraction of inspired oxygen (P/F) was < 100 mmHg and remained stable for 30 min (T(ARDS)). ARDS pigs underwent three sequential recruitment maneuvers, including sustained inflation, increments of positive end-expiratory pressure (PEEP), and pressure-controlled ventilation (PCV) applied in random order, with 30 mins at a PEEP of 5 cmH(2)O between maneuvers. Respiratory mechanics, hemodynamics, arterial blood gas, and electrical impedance tomography were recorded at baseline, T(ARDS), and before and after each recruitment maneuver. RESULTS: In all ten pigs, ARDS was successfully induced with a mean 2.8 ± 1.03 L bronchoalveolar lavages. PaO(2), P/F, and compliance were significantly improved after recruitment with sustained inflation, increments of PEEP or PCV (all p < 0.05), and there were no significant differences between maneuvers. Global inhomogeneity index significantly decreased after recruitment with sustained inflation, increments of PEEP, or PCV. There were no significant differences in global inhomogeneity before or after recruitment with the different maneuvers. The decrease in global inhomogeneity index (ΔGI) was significantly greater after recruitment with increments of PEEP compared to sustained inflation (p = 0.023), but there was no significant difference in ΔGI between increments of PEEP and PCV or between sustained inflation and PCV. CONCLUSION: Sustained inflation, increments of PEEP, and PCV increased oxygenation, and regional and global compliance of the respiratory system, and decreased inhomogeneous gas distribution in ARDS pigs. Increments of PEEP significantly improved inhomogeneity of the lung compared to sustained inflation, while there was no difference between increments of PEEP and PCV or between sustained inflation and PCV.