Water out alarm determination

1. A respiratory assistance system for humidifying a flow of gases, the respiratory assistance system comprising:

a heater configured to provide heat to a quantity of water held in a humidification chamber;

a flow sensor;

a temperature sensor configured to sense a temperature of the gases proximal to an outlet of the humidification chamber; and

a controller in electronic communication with the heater, the flow sensor and the temperature sensor,

wherein the controller is configured to determine at least one operational state from a plurality of predetermined operational states based on at least one of a temperature of the heater, a temperature of the gases proximal to the outlet of the humidification chamber, or a therapy mode and a flow rate, and

wherein the controller is further configured to select at least one independently selectable water out detection method from a plurality of water out detection methods based on the determined operational state, wherein the at least one water out detection method is selected from one or more predetermined water out detection methods associated with the determined operational state.

2. The respiratory assistance system of claim 1 , wherein the operational state is dependent on the flow rate in relation to a flow rate threshold.

3. The respiratory assistance system of claim 1 , wherein the flow sensor detects the flow rate, the flow sensor proximal an inlet or the outlet of the humidification chamber.

4. The respiratory assistance system of claim 1 further comprising a user interface configured to permit a person to select the therapy mode from a predetermined list of therapy modes,

wherein the predetermined list comprises an invasive mode, a non-invasive mode, and a high flow, unsealed mode, and

wherein the high flow, unsealed mode comprises a high flow rate through unsealed interface.

5. The respiratory assistance system of claim 4 , wherein the therapy mode comprises a plurality of set points.

6. The respiratory assistance system of claim 5 , the non-invasive mode comprising set point of 31 degrees, 29 degrees, and 27 degrees Celsius; and/or the high flow, unsealed mode comprising set points of 37 degrees, 35 degrees, and 33 degrees Celsius; and/or the invasive mode comprising a set point of 37 degrees Celsius.

7. The respiratory assistance system of claim 1 , the predetermined plurality of operational states comprise:

a startup operational state relating to the temperature of the heater below a defined temperature threshold and/or the temperature for the outlet of the humidification chamber below a defined temperature threshold,

a first operational state relating to a no flow state,

a second operational state relating to a therapy mode having a high set point and a medium high or high flow rate,

a third operational state relating to a therapy mode having the high set point and a medium low or low flow rate,

a fourth operational state relating to a therapy mode having a low set point.

8. The respiratory assistance system of claim 7 , wherein:

the high set point has a temperature above 31 degrees Celsius and the low set point has a temperature between and including 25 degrees and 31 degrees Celsius; and/or

the defined temperature threshold of the heater is greater than or equal 30 degrees Celsius and/or is 40 degrees Celsius; and/or

the defined temperature threshold for the outlet of the humidification chamber is greater than or equal to 30 degrees Celsius and/or is 37 degrees Celsius; and/or

the no flow state has a flow rate between 0 1/min and 3.5 1/min, the low flow rate has a flow rate between 3 1/min and 7 1/min, the medium low flow rate has a flow rate between 5 1/min and 15 1/min, the medium high flow rate has a flow rate between 13 1/min and 35 1/min, and the high flow rate has a flow rate greater than 301/min.

9. The respiratory assistance system of claim 7 , wherein the controller is configured to perform at least one of the following:

disable the water out detection method when in the first operational state,

select a passive water out detection method when in the second operational state, or

select the passive water out detection method when in the third or fourth operational state.

10. The respiratory assistance system of claim 1 , the at least one independently selectable water out detection method from a plurality of water out detection methods comprising a passive water out detection method, an active water out detection method, and the passive water out detection method in conjunction with the active water out detection method.

11. The respiratory assistance system of claim 10 , the passive water out detection method comprising:

calculating an estimated water level;

comparing the estimated water level to a threshold; and

determining a water out condition when the estimated water level is less than the threshold.

12. The respiratory assistance system of claim 11 , the estimated water level comprising a ratio of an amount of power supplied to the heater divided by the difference between a temperature of the heater minus a temperature of humidified gases proximal to the outlet.

13. The respiratory assistance system of claim 12 , wherein the power supplied to the heater is determined by a heater plate power sensor, wherein the heater plate power sensor comprises a PMIC.

14. The respiratory assistance system of claim 10 , the active water out detection method comprising:

controlling the temperature of the heater to a baseline;

supplying an amount of power to the heater until a target is achieved;

monitoring the heater temperature until a maximum is reached; comparing the maximum heater temperature to a threshold; and determining a positive test result when the maximum heater temperature is greater than the threshold.

15. The respiratory assistance system of claim 10 , the passive water out detection method in conjunction with the active water out detection method comprising:

determining a water out condition through the passive water out detection method; and

confirming the water out condition through the active water out detect method if the passive water out detection method provided a positive outcome.

16. The respiratory assistance system of claim 1 , the therapy mode relating to a mode value received by the controller and/or the therapy mode selected by a user.

17. The respiratory assistance system of claim 1 further comprising the humidification chamber, wherein the humidification chamber is adapted to hold the quantity of water, the humidification chamber having an inlet and the outlet to allow gases to pass through the humidification chamber, and the flow sensor is positioned on the humidification chamber.

18. The respiratory assistance system of claim 9 , wherein the controller is configured to perform at least one of the following:

select an active water out detection method when in the third or fourth operational state if the passive water out detection method returns a water out condition, or

select a time-based active water out detection method when in the fourth operational state.