SYSTEM AND METHOD FOR DETERMINING VENTILATOR LEAKAGE DURING STABLE PERIODS WITHIN A BREATH

• US 20110259330A1
• Filed: 03/30/2009
• Published: 10/27/2011
• Est. Priority Date: 03/31/2008
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett LLC (Medtronic Plc)
• Inventors: Jafari, Mehdi, Aviano, Jeffrey, Upham, Gail, Jimenez, Rhomere
• Granted Patent: US 10,207,069 B2
• Time in Patent Office: Days
• US Class Current: 128/204.18
• CPC Class Codes: A61M 16/0063 Compressors
• CPC Class Codes: A61M 16/024 including calculation means, e.g. using a processor
• CPC Class Codes: A61M 2016/0021 with a proportional output signal, e.g. from a thermistor
• CPC Class Codes: A61M 2016/0027 pressure meter
• CPC Class Codes: A61M 2016/0033 electrical
• CPC Class Codes: A61M 2205/15 Detection of leaks
• CPC Class Codes: A61M 2205/50 with microprocessors or computers
• CPC Class Codes: A61M 2205/505 Touch-screens; Virtual keyboard or keypads; Virtual buttons; Soft keys; Mouse touches
• CPC Class Codes: A61M 2230/46 Resistance or compliance of the lungs

Abstract

This disclosure describes systems and methods for compensating for leaks in a ventilation system based on data obtained during periods within a breath in which the patient is neither inhaling nor exhaling. The methods and systems described herein more accurately and quickly identify changes in leakage. This information is then to estimate leakage later in the same breath or in subsequent breaths to calculate a more accurate estimate of instantaneous leakage based on current conditions. The estimated leakage is then used to compensate for the leak flow rates, reduce the patient'"'"'s work of breathing and increase the patient'"'"'s comfort (patient-ventilator breath phase transition synchrony).

Claims

1. A method for identifying leakage in a respiratory gas supply system comprising:

monitoring data indicative of at least one of pressure and flow in the respiratory gas supply system;

identifying that the data meet at least one stability criterion indicating that pressure and flow conditions have been stable for a period of time within a breath;

in response to the identifying operation, calculating leakage information based at least in part on the data taken during the period of time within the breath; and

determining a leakage rate after the period of time based at least in part on the leakage information.

2. The method of claim 1 further comprising:

compensating, after the period of time, at least one of an estimated lung flow and a bias flow based on the calculated leakage rate.

3. The method of claim 1 further comprising:

displaying the leakage rate to a user.

4. The method of claim 1 wherein determining a leakage rate further comprises:

determining an instantaneous leakage rate after the period of time using only the leakage information and a pressure measurement taken after the period of time.

5. The method of claim 1 wherein determining a leakage rate further comprises:

determining an instantaneous leakage rate after the period of time using the leakage information and at least one current pressure measurement in the respiratory gas supply system.

6. The method of claim 1 further comprising:

monitoring data indicative of pressure at two different locations in a patient circuit.

7. The method of claim 1 further comprising:

monitoring data indicative of flow at two different locations in the patient circuit.

8. The method of claim 1 further comprising:

monitoring data indicative of at least one of pressure and flow at different locations in the patient circuit.

9. The method of claim 1 wherein identifying comprises:

calculating a first value indicative of a rate of change of pressure during at least a portion of the period of time;

comparing the first value to a first stability criterion; and

based at least in part on a result of the comparing operation, classifying the period of time as stable.

10. The method of claim 9 wherein identifying comprises:

calculating a second value indicative of a rate of change of flow during at least a portion of the period of time;

comparing the second value to a second stability criterion; and

based at least in part on a result of the comparing operation, classifying the period of time as stable.

11. The method of claim 1 wherein calculating leakage information comprises:

calculating at least one constant based on data taken during the period of time, wherein the constant relates pressure to leakage rate in the respiratory gas supply system.

12. The method of claim 1 wherein calculating leakage information comprises:

calculating a first orifice constant representing the relationship between leakage flow through a hypothetical orifice and pressure in the respiratory gas supply system based on data taken during the period of time.

13. The method of claim 1 wherein identifying further comprises:

periodically analyzing, while providing therapy to a patient, a window of the most recent data to determine if the data in the window meet the at least one stability criterion.

14. A respiratory gas supply system comprising:

a pressure generating system capable of controlling the flow of breathing gas through a patient circuit and a patient interface to a patient;

a stable period identification module that identifies a stable period within either an inhalation or an exhalation phase of a breath; and

a leak compensation module that calculates leakage information using data obtained during the stable period identified by the stable period identification module and that calculates, during unstable periods within the breath or a later breath, an instantaneous leakage rate based on the leakage information.

15. The respiratory gas supply system of claim 14 wherein the leak compensation module further changes the flow of breathing gas based on the instantaneous leakage rate.

16. The respiratory gas supply system of claim 14 wherein the stable period identification module compares a window of recent pressure and flow data to a first set of one or more stability criteria during the inhalation phase.

17. The respiratory gas supply system of claim 16 wherein the first set of one or more stability criteria includes at least one criterion selection from a first criterion identifying a minimum pressure, a second criterion identifying a maximum pressure variation within the window, a third criterion identifying a maximum flow variation within the window and a fourth criterion based on a patient circuit type.

18. The respiratory gas supply system of claim 14 wherein the stable period identification module compares the window of recent pressure and flow data to a second set of one or more stability criteria during the exhalation phase.

19. The respiratory gas supply system of claim 18 wherein the second set of one or more stability criteria includes at least one criterion selected from a fifth criterion identifying a pressure threshold, a sixth criterion identifying a minimum time since the patient began to exhale, a seventh criterion identifying a minimum flow, a eighth criterion identifying a maximum pressure variation within the window and a ninth criterion identifying a maximum flow variation within the window.

20. A method for determining leakage from a respiratory gas supply system providing respiratory gas to a breathing patient comprising:

identifying at least one stable period within a patient breath;

calculating leakage information from pressure and flow data obtained during the at least one stable period; and

subsequent to the stable period, estimating the leakage from the respiratory gas supply system based on the leakage information and current data.

21. The method of claim 20 wherein calculating leakage information further comprises:

calculating a net leakage from the respiratory gas supply system during the stable period based on measurements of respiratory gas flow to the patient and respiratory gas flow exiting the respiratory gas supply system.

22. The method of claim 20 wherein calculating leakage information further comprises:

calculating a representative pressure in the respiratory gas supply system during the stable period based on measurements of pressure.

23. The method of claim 20 wherein calculating leakage information further comprises:

determining leakage information based on the net leakage from the respiratory gas supply system and the representative pressure.

24. The method of claim 22 wherein calculating a representative pressure comprises:

calculating a square root of an average pressure in the respiratory gas supply system during the stable period.