Development of a time-cycled volume-controlled pressure-limited respiratorand lung mechanics system for total liquid ventilation

Total liquid ventilation can support gas exchange in animal models of lung injury. Clinical application awaits further technical improvements and perf ormance verification. Our aim was to develop a liquid ventilator, able to d eliver accurate tidal volumes, and a computerized system for measuring lung mechanics. The computer-assisted, piston-driven respirator controlled vent ilatory parameters that were displayed and modified on a real-time basis. P ressure and temperature transducers along with a lineal displacement contro ller provided the necessary signals to calculate lung mechanics. Ten newbor n lambs (<6 days old) with respiratory failure induced by lung lavage, were monitored using the system. Electromechanical, hydraulic, and data acquisi tion/analysis components of the ventilator were developed and tested in ani mals with respiratory failure. All pulmonary signals were collected synchro nized in time, displayed in real-time, and archived on digital media. The t otal mean error (due to transducers, analog-to-digital conversion, amplifie rs, etc.) was less than 5 % compared with calibrated signals. Components (t ubing, pistons, etc.) in contact with exchange fluids were developed so tha t they could be readily switched, a feature that will be important in clini cal settings. Improvements in gas exchange and lung mechanics were observed during liquid ventilation, without impairment of cardiovascular profiles. The total liquid ventilator maintained accurate control of tidal volumes an d the sequencing of inspiration/expiration. The computerized system demonst rated its ability to monitor in vivo lung mechanics, providing valuable dat a for early decision making.