Water out alarm

1. An apparatus for supplying gases to a patient comprising:

a casing;

a flow generator including a fan configured to provide a flow of gases;

a humidifier with a heater plate,

an unsealed nasal cannula for a patient,

a controller, and

a valve operable as a flow control mechanism to control an O2 fraction provided to the patient,

wherein

the humidifier and flow generator are integrated in the casing, and

the controller is configured to:

adjust an output of the flow generator by controlling a fan speed,

monitor system conditions during use of the apparatus, and

interrupt a normal control of the apparatus in response to a control interruption condition having been detected so as to determine a possible absence of water in a humidifier chamber based on confirmation or contradiction of the monitored system conditions during the interruption of the normal control of the apparatus.

2. The apparatus of claim 1 , wherein the controller is configured to determine a possible absence of water by:

monitoring a temperature of gases leaving the humidifier chamber,

monitoring power applied to the heater plate, and

determining a possible absence of water based on a function of the temperature of gases leaving the humidifier and the power applied to the heater plate.

3. The apparatus of claim 1 , wherein the controller is configured to determine a possible absence of water by:

making a primary determination of an absence of water, and

making a secondary determination of an absence of water.

4. The apparatus of claim 3 , wherein in making the secondary determination the controller is configured to interrupt the normal control of the apparatus and take over control of a power input of the humidified heater.

5. The apparatus of claim 1 , wherein the controller is configured to output the absence of water determination to activate a user alert.

6. The apparatus of claim 1 , further comprising a delivery conduit.

7. The apparatus of claim 6 , wherein the delivery conduit comprises a heater wire.

8. The apparatus of claim 1 , wherein the controller is configured to operate the apparatus to provide O2 or an O2 fraction to the patient.

9. The apparatus of claim 1 , further comprising an ambient temperature sensor located within, near or on the casing.

10. The apparatus of claim 1 , further comprising a humidifier exit port sensor at or proximal to an exit of the humidifier chamber.

11. The apparatus of claim 10 , wherein the humidifier exit port sensor is at the exit of the humidified chamber.

12. The apparatus of claim 6 , further comprising a humidifier exit port sensor at an apparatus end of the delivery conduit.

13. The apparatus of claim 10 , wherein the humidifier exit port sensor is a temperature sensor.

14. The apparatus of claim 1 , further comprising a heater plate temperature sensor.

15. The apparatus of claim 1 , further comprising a flow probe configured to measure a gases flow rate.

16. The apparatus of claim 6 , further comprising a patient end temperature sensor at or close to a patient end of the delivery conduit.

17. The apparatus of claim 1 , further comprising a patient end temperature sensor in or on the cannula.

18. The apparatus of claim 1 , further comprising the humidifier chamber for water.

19. The apparatus of claim 16 , wherein the controller is configured to reduce or remove power to the heater plate on determination of the absence of water.

20. The apparatus of claim 1 , wherein the control interruption condition is a water-out interruption condition.