Leak-compensated respiratory mechanics estimation in medical ventilators

• US 8,424,521 B2
• Filed: 02/27/2009
• Issued: 04/23/2013
• Est. Priority Date: 02/27/2009
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Covidien LP (Medtronic Plc)
• Inventors: Jafari, Mehdi M., Jimenez, Rhomere S., Upham, Gail F., Aviano, Jeffrey K.
• Primary Examiner(s): Thanh, Loan
• Assistant Examiner(s): DITMER, KATHRYN ELIZABETH
• Application Number:
  US12/395,332
• Publication Number:
  US 20100218767A1
• Time in Patent Office: 1,516 Days
• Field of Search: 128/204.18, 128/204.21, 128/204.23
• US Class Current: 128/204.21
• 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 2016/0021 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 2205/502 User interfaces, e.g. screens or keyboards
• CPC Class Codes: A61M 2205/52 with memories providing a history of measured variating parameters of apparatus or patient
• CPC Class Codes: A61M 2230/46 Resistance or compliance of the lungs

Abstract

This disclosure describes systems and methods for compensating for leakage when determining the respiratory mechanics of a patient during delivery of gas from a medical ventilator to a patient. The systems and methods include monitoring an instantaneous flow in the ventilation system based on one or more measurements of pressure and flow in ventilation system. The leakage is modeled using a predetermined leakage model. A leak-compensated instantaneous lung flow of gas inhaled or exhaled by the patient is estimated. Using the leak-compensated lung flow and a predetermined respiratory mechanics model, the respiratory mechanics of a patient may be estimated including at least one of a leak-compensated lung compliance and a leak-compensated lung resistance. The method may include using a dynamic respiratory mechanics model or a static respiratory mechanics model that requires use of a pause maneuver to collect the necessary data.

Claims

1. A method of compensating for leakage in a ventilation system during delivery of gas from a medical ventilator to a patient comprising:

monitoring an instantaneous flow in the ventilation system based on one or more measurements of pressure and flow in ventilation system;

modeling, by the medical ventilator, 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 instantaneous pressure in the ventilation system;

estimating a leak-compensated instantaneous lung flow of gas inhaled or exhaled by the patient based on the one or more measurements, the first leakage component and second leakage component; and

using the leak-compensated lung flow and a predetermined respiratory mechanics model to estimate at least one of a leak-compensated lung compliance and a leak-compensated lung resistance.

2. The method of claim 1 wherein the method uses a dynamic respiratory mechanics model and the method further comprises:

detecting a condition indicating that leak-compensated lung compliance should be calculated;

retrieving one or more previously estimated leak-compensated instantaneous lung flows;

estimating a leak-compensated lung compliance and a leak-compensated lung resistance using the dynamic respiratory mechanics model and the retrieved one or more previously estimated leak-compensated instantaneous lung flows.

3. The method of claim 2 wherein the dynamic respiratory mechanics model requires input of a lung volume change over a predetermined time period and the method further comprises:

calculating a leak-compensated lung volume for the predetermined time period based on leak-compensated lung flows associated with the predetermined time period.

4. The method of claim 1 wherein the method calculates at least the leak-compensated lung compliance and the method further comprises:

calculating a leak-compensated lung volume based on the leak-compensated lung flow during an inspiratory phase;

stabilizing the delivery of gas so that the medical ventilator delivers a stable flow of gas at a stable pressure, wherein the stable flow and stable pressure are determined based on the first leakage component and second leakage component at the stable pressure;

maintaining the stable flow of gas at the stable pressure for at least a predetermined time interval; and

calculating the leak-compensated lung compliance based on the leak-compensated lung volume and the stable pressure.

5. The method of claim 4 wherein stabilizing further comprises:

stabilizing the delivery of gas by adjusting the instantaneous flow of gas to be within a predetermined amount of the first leakage component and second leakage component at the instantaneous pressure.

6. The method of claim 4 wherein stabilizing further comprises:

stabilizing the delivery of gas so that the stable flow of gas is equivalent to the first leakage component and second leakage component at the stable pressure.

7. The method of claim 6 wherein stabilizing further comprises:

stabilizing the delivery of gas so that the lung flow is practically zero.

8. The method of claim 4 further comprising:

calculating a leak-compensated lung resistance based on the leak-compensated lung compliance and one or more of a previously calculated leak-compensated lung flow, a previously calculated leak-compensated lung volume and a previously measured pressure.

9. The method of claim 4 wherein the stabilizing and maintaining operations are performed at the end of the inspiratory phase.

10. The method of claim 1 wherein the method calculates at least the lung compliance and the method further comprises:

calculating a leak-compensated lung volume based on the leak-compensated lung flow during an inspiratory phase and expiratory phase;

stabilizing the delivery of gas so that the medical ventilator delivers a stable flow of gas at a stable pressure, wherein the stable flow and stable pressure are determined based on the first leakage component and second leakage component at the stable pressure;

maintaining the stable flow of gas at the stable pressure for at least a predetermined time interval; and

calculating the leak-compensated lung compliance based on the leak-compensated lung volume and the stable pressure.

11. The method of claim 1 wherein the method first calculates a leak-compensated lung compliance and then, based on the leak-compensated lung compliance, calculates a leak-compensated lung resistance.

12. A method of compensating for leakage in a ventilation tubing system during delivery of gas from a medical ventilator to a patient comprising:

identifying, by the medical ventilator, an inelastic leakage in the ventilation system as a first function of at least one of a pressure measurement and a flow measurement in the ventilation tubing system;

identifying, by the medical ventilator, an elastic leakage in the ventilation system as a second function of at least one of the pressure measurement and the flow measurement in the ventilation tubing system;

estimating circuit compliance and circuit resistance of the ventilation tubing system; and

estimating one or more of a lung compliance of the patient and a lung resistance of the patient based on the inelastic leakage, the elastic leakage, the circuit compliance, circuit resistance and the at least one of the pressure measurement and the flow measurement in the ventilation system.

13. The method of claim 12 wherein estimating lung compliance further comprises:

generating a plurality of leak-compensated lung flows associated with a period of time based on the elastic leakage and at least one of the pressure measurements and the flow measurements associated with the period of time;

generating a leak-compensated net delivered lung volume for the period of time based on the plurality of leak-compensated lung flows; and

calculating lung compliance using the leak-compensated net delivered lung volume.

14. The method of claim 12 wherein estimating lung compliance and lung resistance further comprises:

generating a plurality of leak-compensated lung flows associated with a period of time based on the elastic leakage and at least one of pressure measurements and the flow measurements associated with the period of time;

generating a leak-compensated net delivered lung volume for the period of time based on the plurality of leak-compensated lung flows; and

calculating lung compliance and lung resistance using the leak-compensated net delivered lung volume, the plurality of leak-compensated lung flows for the period of time and the pressure measurements associated with the period of time.