DETERMINATION OF PATIENT CIRCUIT DISCONNECT IN LEAK-COMPENSATED VENTILATORY SUPPORT

• US 20100147303A1
• Filed: 12/12/2008
• Published: 06/17/2010
• Est. Priority Date: 03/31/2008
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett LLC (Medtronic Plc)
• Inventors: Upham, Gail F., Jafari, Mehdi M., Jimenez, Rhomere S.
• Granted Patent: US 8,746,248 B2
• Time in Patent Office: Days
• US Class Current: 128/204.230
• CPC Class Codes: A61M 16/0051 with alarm devices
• CPC Class Codes: A61M 16/0063 Compressors
• CPC Class Codes: A61M 16/026 specially adapted for predicting, e.g. for determining an information representative of a flow limitation during a ventilation cycle by using a root square technique or a regression analysis
• CPC Class Codes: A61M 2016/0015 inhalation detectors
• CPC Class Codes: A61M 2016/0027 pressure meter
• CPC Class Codes: A61M 2016/003 with a flowmeter

Abstract

This disclosure describes systems and methods for detecting disconnect conditions in a ventilator. The disclosure describes a model-based enhancement to conventional disconnect detection. The methods and systems described herein compensate for the additional leakage that occurs due to inelastic and elastic leaks in the ventilation system. One method described includes calculating the actual leakage from the ventilation system including leaks from elastic leakage and inelastic leakage based on measurements of pressure and flow in the ventilation system for a breath and then comparing this leakage to a calculated hypothetical maximum allowable leakage determined based on an operator-selected maximum allowable leakage and the measurements of pressure for the same breath. Disconnection is assumed if the actual leakage is greater than the maximum allowable leakage.

Claims

1. A method of detecting disconnection of a ventilation system during delivery of gas from a medical ventilator to a patient comprising:

developing an actual leakage equation describing leakage from the ventilation system as a function of pressure in the ventilation system;

developing a maximum leakage equation describing a maximum allowed leakage from the ventilation system as a function of pressure in the ventilation system;

monitoring pressure in the ventilation system during delivery of gas to the patient during a breath;

calculating an actual leakage from the ventilation system during the breath based on the current pressure using the actual leakage equation;

calculating a maximum allowed leakage from the ventilation system during the breath based on the current pressure using the maximum leakage equation; and

comparing the calculated maximum allowed leakage and the actual leakage.

2. The method of claim 1 further comprising:

identifying that the ventilation system has been disconnected from the patient based on results of the comparing operation.

3. The method of claim 1 wherein developing an actual leakage equation further comprises:

taking one or more measurements of instantaneous pressure or instantaneous flow in ventilation system during a period of delivery of gas to the patient;

determining an actual leakage from the ventilation system during the period;

based on the one or more measurements and the actual leakage for the period, modeling the actual leakage as a first leakage component through a first orifice of a fixed size and a second leakage component through a second orifice of a varying size, wherein the first and second leakage components are different functions of pressure in the ventilation system; and

developing the actual leakage equation based on the first and second leakage components.

4. The method of claim 3 further comprising:

calculating the actual leakage from the ventilation system based on the monitored pressure, the first leakage component and the second leakage component.

5. The method of claim 1 wherein developing a maximum leakage equation further comprises:

receiving a maximum allowed leak flow at a selected therapy setting; and

developing the maximum leakage equation based on the maximum allowed leak flow and the selected therapy setting.

6. The method of claim 5 wherein developing a maximum leakage equation further comprises:

based on the maximum allowed leakage value and selected therapy setting, modeling the maximum leakage as a third leakage component through a third orifice of a fixed size and a fourth leakage component through a fourth orifice of a varying size, wherein the third and fourth leakages are different functions of pressure in the ventilation system; and

developing the actual leakage equation based on the third and fourth leakage components.

7. The method of claim 6 further comprising:

calculating the maximum leakage from the ventilation system based on the current pressure, the third leakage component and the fourth leakage component.

8. The method of claim 5 further comprising:

receiving the maximum allowed leak flow value and the selected therapy setting from an operator of the ventilator.

9. The method of claim 5 further comprising:

identifying a pressure value associated with the selected therapy setting.

10. The method of claim 5 wherein the selected therapy setting is an operator-selected positive end expiratory pressure.

11. The method of claim 2 wherein identifying further comprises:

initiating a disconnect alarm.

12. A method of detecting disconnection of a ventilation system during delivery of therapy to a patient comprising:

generating an actual leak equation based on a leak model and measurements taken during the delivery of therapy to the patient;

generating a maximum leak equation based on the leak model, and a maximum allowed leakage at a specified pressure;

measuring pressure in the ventilation system during a current therapy period; and

calculating an actual leak from the ventilation system for the current therapy period based on the pressure using the actual leak equation;

calculating a maximum allowable leak from the ventilation system for the current therapy period based on the pressure using the maximum leak equation; and

selecting, based on a comparison of the actual leak and the maximum allowable leak, one of at least two ventilator connection states.

13. The method of claim 12 wherein selecting further comprises:

selecting a second state indicating that the patient is connected to the ventilation system.

14. The method of claim 12 wherein selecting further comprises:

selecting a first state indicating that the patient is disconnected from the ventilation system.

15. The method of claim 14 further comprising:

initiating a disconnect alarm.

16. The method of claim 12 wherein generating an actual leak equation further comprises:

monitoring pressure and flow in the ventilation system during a previous therapy period different from the current therapy period;

estimating the leakage from the ventilation system during the previous therapy period based on the measured flow;

generating the actual leak equation based on the leak model, the pressure for the previous therapy period and the estimated leakage for the previous therapy period.

17. The method of claim 12 wherein the leak model models leakage from the ventilator circuit as a first leakage component through a first orifice of a fixed size and a second leakage component through a second orifice of a varying size, wherein the first and second leakage components are different functions of pressure in the ventilation system.

18. A pressure support system comprising:

a pressure generating system adapted to generate a flow of breathing gas;

a ventilation system including a patient interface device;

one or more sensors operatively coupled to the pressure generating system or the ventilation system, each sensor capable of generating an output indicative of a pressure of the breathing gas;

a processor;

an actual leak estimation module that calculates actual leakage in the ventilation system based on pressure and a predetermined actual leak equation;

a maximum allowable leak estimation module that calculates maximum allowable leakage in the ventilation system based on pressure and a predetermined maximum allowable leak equation; and

a disconnect monitoring module that generates one or more alarms based on a comparison of the actual leakage and the maximum allowable leakage.

19. The system of claim 18 wherein the pressure is measured during a current therapy cycle and the actual leak estimation module is further adapted to generate the actual leak equation based on a leak model and pressure and flow data measured during a previous therapy cycle.

20. The system of claim 19 wherein the actual leak estimation module calculates actual leakage due to elastic and inelastic leaks in the ventilation system.

21. The system of claim 18 wherein the maximum allowable leak estimation module is further adapted to generate the maximum allowable leak equation based on the leak model and an operator-selected maximum allowable leakage from ventilator system at a specified pressure.

22. The system of claim 18 wherein the disconnect monitoring module that generates one or more alarms when the actual leakage is greater than the maximum allowable leakage.

23. The system of claim 18 further comprising:

a monitoring module that monitors at least one output of the one or more sensors and provides data indicative of the pressure of the breathing gas to at least one other module in the system.

24. A controller for a medical ventilator comprising:

a microprocessor; and

a disconnect monitoring module that determines if the medical ventilator is disconnected from a patient based on an actual leakage estimate and a maximum allowable leakage estimate, wherein the actual leakage estimate is calculated using a first equation based on pressure in a ventilation system and the maximum allowable leakage estimate is calculated using a second equation different from the first equation based on the pressure in the ventilation system.

25. A computer-readable medium comprising computer-executable instruction for performing a method of detecting disconnection of a ventilation system during delivery of therapy to a patient, the method comprising:

generating an actual leak equation based on a leak model and measurements taken during the delivery of therapy to the patient;

generating a maximum leak equation based on the leak model, and a maximum allowed leakage at a specified pressure;

measuring pressure in the ventilation system during a current therapy period; and

calculating an actual leak from the ventilation system for the current therapy period based on the pressure using the actual leak equation;

calculating a maximum allowable leak from the ventilation system for the current therapy period based on the pressure using the maximum leak equation; and

selecting, based on a comparison of the actual leak and the maximum allowable leak, one of at least two ventilator connection states.