A numerical model of an intensive care ventilator-humidifier system

Improved control of gas humidity in neonatal intensive care ventilators

Difficulties experienced by nursing staff in controlling humidity in neonatal intensive care ventilators are shown to originate in the use of a single control, namely a heater, to condition two parameters, namely temperature and humidity, at the inlet to the inspiratory tube. It is shown that better control can be achieved by separating the gas flow through the humidifier into two streams, only one of which is humidified. It is proposed that the temperature along most of the inspiratory tube should be maintained about 3-5 degrees C higher than the target delivery temperature. This eliminates the risk of condensation in the tube, a second commonly occurring problem in existing systems. It is shown why the control of ventilator systems should be based on absolute humidity, not relative humidity, even though the latter may be preferred for monitoring purposes.