Diverse types of tidal liquid ventilators have been developed for conducting animal experiments. Regardless of the technologies used, a liquid ventilator must perform the following essential functions: insert and withdraw the tidal volume of perfluorochemical liquid (PFC) from the lungs, oxygenate and maintain the PFC at a desired temperature. The latest system developments on the Inolivent prototype are described. For its simplicity and low cost, a bubble gas exchanger was built. It is divided into two sections such that the PFC exiting the lungs is not in contact with the PFC entering the lungs. The equivalent gas exchange area is around 0.8m2 for two oxygenators in series, which is equivalent to an ECMO for children less than 10kg. The heating system is incorporated in the metallic base of the gas exchanger, and a heat sink-type condenser is placed on top of the exchanger to retrieve PFC vapours. Its efficiency is 75%, yielding a net PFOB loss of about 21ml/h, using perfluorooctylbromide. This condenser-heater-oxygenator configuration minimizes the priming volume and simplifies the assembly. This unit is also modular and can be easily adapted for an adult patient. In order to insert and withdraw PFC liquid from the lung, two independent piston pumps are volume controlled and pressure limited. The latter produces steady flows, although the main interest of a piston pump is to achieve perfect volume-controlled ventilation. Measurable pumping errors are corrected by a programmed supervisor module, which modifies the inserted or withdrawn volume. Pump independence also permits easy FRC modifications during ventilation, without altering the ventilation scheme. Different cycles are available on the ventilator. A preparation cycle allows the movement of the liquid in a closed loop to warm and oxygenate the PFC. A filling sequence serves to fill the patient's lungs using one pump. Finally, the respiratory cycle is used to carry out TLV. All of those cycles and their adjustable parameters are accessible and can be changed via a human-ventilator interface. The Inolivent tidal liquid ventilator was tested on 8 healthy newborn lambs. The results demonstrate the efficiency and safety of the prototype in maintaining adequate gas exchange, normal acido-basis equilibrium, and cardiovascular stability during a short 2 hours TLV.
The team is supported in part by the Foundation for Research into Children's Diseases and by the Fonds Québécois pour la Recherche sur la Nature et les Technologies.