|Home | About | Journals | Submit | Contact Us | Français|
Spontaneous breathing during mechanical ventilation improves gas exchange and might prevent ventilator-induced diaphragm dysfunction. In pressure-targeted modes, transpulmonary pressure (PL) is the sum of pressure generated by the ventilator and muscular pressure. When inspiratory effort increases, PL and tidal volume (VT) increase, potentially resulting in lung injury. This effect depends on the degree of inspiratory synchronization (i-sync); pressure-targeted modes can be classified into fully, partially, and non i-sync modes. A bench study  demonstrated that non-i-sync mode resulted in lower PL and VT than other modes, protecting the lungs from injury. We undertook to assess the effect of varying synchronization during pressure-targeted ventilation in critically ill patients.
To compare VT, PL, inspiratory effort (esophageal pressure-time product, PTPeso) and respiratory drive (airway occlusion pressure, P0.1) during three pressure-targeted modes with different degrees of i-sync.
We conducted a randomized cross-over physiological study in spontaneously breathing ventilated patients. Twelve patients were enrolled (1 subsequently withdrew). Three pressure-targeted modes (Evita XL, Draeger, Germany) including fully (PC-CMV), partially (PC-SIMV), and non i-sync (APRV) modes were sequentially applied for 20 minutes in random order using the same driving pressure, PEEP and inspiratory time. Airway, esophageal, and gastric pressures, P0.1, and flow were recorded along with gas exchange and hemodynamics. PL and PTPeso were calculated.
11/12 patients successfully completed the study. VT was significantly lower during non i-sync mode than fully i-sync mode (Table (Table1,1, p = 0.003) and VT variability increased from 13 % to 35 % with decreasing inspiratory synchronization. Maximal PL was significant lower in non-i-sync mode than in partially or fully i-sync modes (p = 0.008). There were no significant differences in gas exchange and hemodynamic parameters between modes. PTPeso was significantly higher with non i-sync modes (Table (Table1,1, p = 0.047). This increase in PTPeso was observed in the 6 patients who were not receiving intravenous sedation; no increase was observed in the 5 patients receiving continuous intravenous sedation (Figure (Figure11).
Non synchronized pressure-targeted ventilation lowers VT and PL in comparison to fully and partially synchronized modes in spontaneously breathing ventilated patients, even with the same driving pressure. Appropriate sedation may be important to alleviate increased patient effort during such modes.
This study was supported by Dr. Brochard Laboratory Research Funding and by a grant from Siriraj Hospital in Bangkok, Thailand.