Liquid Ventilator

Liquid Ventilator

A liquid ventilator functions similarly to a conventional medical ventilator but is specifically designed to facilitate total liquid ventilation using a breathable liquid, typically a perfluorocarbon (PFC). While liquid ventilators have been utilized in animal experiments, experts advocate for further development to adapt them for clinical use.

Function and Technology

Driving Liquid

In total liquid ventilation (TLV), the lungs are entirely filled with a perfluorocarbon (PFC) liquid while the liquid ventilator refreshes the tidal volume of PFC. The ventilator operates in mandatory mode, actively moving the PFC in and out of the lungs using a pumping system.

During the inspiratory phase, the pump creates a positive driving pressure in the trachea to facilitate the insertion of the PFC tidal volume.

During the expiratory phase, the pump generates a negative driving pressure in the trachea to facilitate the withdrawal of the PFC tidal volume.

The pumping system can be a peristaltic pump in simpler liquid ventilators or two piston pumps in more advanced models.

Due to the viscosity of the PFC, the choked flow phenomenon may occur during expiration, leading to compromised minute ventilation and gas exchange. To mitigate this, liquid ventilators incorporate control mechanisms for the pumping system.

Controlling Liquid Ventilator

The integration of computers allows for various control modes and monitoring functions, providing valuable data for decision-making.

The liquid ventilator operates in a volume-controlled mode to ensure precise delivery and retrieval of the specified tidal volume of PFC. It is also pressure-limited to halt the inspiratory or expiratory phase if the driving pressure deviates from specified limits.

During expiration, the expiratory flow can be controlled by either an open-loop or closed-loop controller. In open-loop control, the flow is initially rapid and progressively slows down to minimize the risk of collapse generation. In closed-loop control, the flow is adjusted in real-time to maintain a specified driving pressure, preventing collapse.

Similarly, during inspiration, the volume-controlled mode is achieved through either open-loop or closed-loop control of the PFC flow.

Oxygenating and Heating Liquid

The liquid ventilator removes carbon dioxide (CO2) from the PFC by saturating it with oxygen (O2) and medical air. This can be accomplished using a membrane oxygenator or a bubble oxygenator.

The PFC is heated to body temperature by a heat exchanger connected to the oxygenator or by integrated heaters within the oxygenator.

To minimize evaporation loss, the vapor produced by the oxygenator and heater is recovered using a condenser, as PFC is a greenhouse gas.

Studies have demonstrated the efficacy and safety of liquid ventilation, particularly in newborns with normal, mature, and immature lungs. Liquid ventilation improves gas exchange, lung compliance, and helps prevent ventilation-induced lung injury.

In conditions like acute respiratory distress syndrome (ARDS), liquid ventilation has shown clear benefits, potentially offering a therapeutic option for newborns with severe neonatal respiratory distress syndrome, particularly those at risk of intracranial hemorrhage.

Liquid ventilation can also facilitate therapeutic lung lavage without suspending ventilation support, offering a promising approach for conditions such as meconium aspiration syndrome (MAS). Studies in neonatal lambs have demonstrated the efficacy of liquid ventilation in this context.