Regional ventilation redistribution measured by electrical impedance tomography during spontaneous breathing trial with automatic tube compensation**This study was endorsed by the Far Eastern Memorial Hospital Research Ethics Review Committee, approval number: FEMH-IRB-103133-E.

Abstract

Objective. Automatic tube compensation (ATC) was developed to overcome the flow resistance of endotracheal tube and decrease the imposed work of breathing. Although ATC is used as an evidence-based strategy to predict successful weaning from assisted ventilation, the changes in regional ventilation distribution induced by this technique are not known. We hypothesized that continuous positive airway pressure plus ATC (CPAP + 100%ATC) could reactivate the respiratory muscles in patients with prolonged mechanical ventilation (PMV) more effectively than volume assist-control mandatory ventilation (ACMV). Approach. A total of 16 PMV patients were included. Patients were ventilated under volume ACMV mode and subsequently under CPAP + 100%ATC for 50 min. Two periods of 5 min electrical impedance tomography (EIT) data at the end of each mode were analyzed. Main results. Tidal variations of electrical impedance determined by EIT during CPAP + 100%ATC were significantly smaller than during ACMV (p < 0.001), while no significant differences in end-expiratory lung impedance were found. Regional ventilation was distributed significantly more towards dorsal regions during CPAP + 100%ATC as indicated by the EIT-based index center of ventilation (46.2 ± 5.8 during ACMV versus 51.7 ± 6.5 during CPAP + 100%ATC, values in %, p < 0.001). However, the overall degree of ventilation inhomogeneity was not improved as indicated by the global inhomogeneity index (0.42 ± 0.09 during ACMV versus 0.42 ± 0.06 during CPAP + 100%ATC). The onset of ventilation was significantly less delayed during CPAP + 100%ATC in both ventral and dorsal regions as indicated by the ventilation delay index (ACMV versus CPAP + 100%ATC, 53.0 versus 42.6 in ventral; 50.2 versus 39.3 in dorsal regions; values in %, p < 0.001). Significance. Dorsal redistribution of ventilation and reduction of ventilation delay as identified by EIT indicate that CPAP + 100%ATC was effective in reactivating the respiratory muscles in the PMV patients of the present study.