ResMed Astral Series Clinical Manual page 56

Accessories
To attach a humidifier to a patient circuit:
1. Connect a length of air tubing to the inspiratory port on the device.
2. Connect the other end of the air tubing to the inlet port on the humidifier.
3. Connect the patient circuit to the outlet port on the humidifier.
The image below shows proper use of a humidifier in combination with a double limb circuit.
When using heated humidification with a double limb circuit, condensation may form in the expiratory
flow sensor if the air is cooled to below its dew point. Condensation may also form in the patient circuit
and is most likely to form at high humidity settings and low ambient temperatures.
Condensation forming in the expiratory flow sensor may cause a loss of expiratory flow measurement
and compromised therapy (ie, auto-triggering, increased PEEP and activation of the leak alarm.
To prevent condensation at the Expiratory flow sensor, always follow the humidifier manufacturer's
instructions on how to prevent condensation and regularly check the patient circuit for condensation.
To ensure accurate therapy, Astral's Learn Circuit function should be performed prior to filling the water
tub.
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