Synchrony between end of ventilator cycles and end of a patient efforts during assisted ventilation

• US 20060278223A1
• Filed: 03/15/2004
• Published: 12/14/2006
• Est. Priority Date: 03/14/2003
• Status: Active Grant

• Current Assignee: Magdy Younes
• Original Assignee: Magdy Younes
• Inventors: Younes, Magdy
• Granted Patent: US 7,819,815 B2
• Time in Patent Office: Days
• US Class Current: 128/204.230
• 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 2016/003 with a flowmeter
• CPC Class Codes: A61M 2016/0036 in the breathing tube and used in both inspiratory and expiratory phase
• CPC Class Codes: A61M 2016/0039 in the inspiratory circuit
• CPC Class Codes: A61M 2016/0042 in the expiratory circuit
• CPC Class Codes: A61M 2205/52 with memories providing a history of measured variating parameters of apparatus or patient
• CPC Class Codes: A61M 2230/08 Other bio-electrical signals
• CPC Class Codes: A61M 2230/42 Rate

Abstract

Automatic ongoing adjustment of the cycling-off time of ventilator inflation phase during assisted ventilation in accordance with true respiratory rate of a patient. Electrical signals are generated corresponding to the gas flow exchanged between patient and ventilator (flow) and/or to airway pressure (P_aw) and the true respiratory rate of the patient (patient RR) is determined on an ongoing basis from the flow and/or P_aw. The current average cycle duration of patient respiratory efforts (current patient T_TOT) is estimated from patient RR. A current desirable duration of the inhalation phase (desirable T_I) is calculated from the product of current patient T_TOT a T_I/T_TOT ratio chosen to be in the physiological range, usually 0.25 to 0.50. The ventilator phase is caused to terminate in accordance with the desirable T_I.

Claims

1. A method for automatic ongoing adjustment of the cycling-off time of ventilator inflation phase during assisted ventilation in accordance with true respiratory rate of a patient, comprising:

generating electrical signal(s) corresponding to rate of gas flow exchanged between patient and ventilator (flow) and/or to airway pressure (P_aw);

determining true respiratory rate of patient (patient RR) on an ongoing basis from said flow and/or P_aw signals;

estimating current average cycle duration of patient respiratory efforts (current patient T_TOT) from said patient RR;

calculating a current desirable duration of the inhalation phase (desirable T_I) from the product of current patient T_TOT and a T_I/T_TOT ratio chosen to be in the physiological range (usually 0.25 to 0.50); and

causing ventilator inflation phase to terminate in accordance with said desirable T_I.

2. The method of claim 1 wherein ongoing patient RR is estimated from the sum of patient-triggered ventilator cycles, ineffective efforts during exhalation and additional efforts during the ventilator'"'"'s inflation phase.

3. The method of claim 2 wherein ineffective efforts are estimated from the derivative of the flow signal (Δ

flow/Δ

t), and identifying negative transients in said signal that meet specified duration criteria, and/or from the derivative of the P_aw signal (Δ

P_aw/Δ

t) and identifying positive transients in said signal that meet specified duration criteria.

4. The method of claim 1 wherein ongoing patient RR is determined from a composite signal incorporating both flow and P_aw.

5. The method of claim 1 wherein ongoing patient RR is determined by spectral analysis of the flow and/or P_aw signal.

6. The method of claim 1 wherein ongoing patient RR is determined from electrical inductance or impedance of the chest wall, strain gauges placed on chest wall, or from signals measuring electrical activity of respiratory muscles.

7. The method of claim 1 wherein periods of central apnea are excluded when estimating patient RR and patient T_TOT.

8. The method of claim 1 wherein a minimum and/or maximum limit is placed on the calculated desirable T_I.

9. The method of claim 1 wherein the T_I/T_TOT ratio to be used in calculating desirable T_I is a user input.

10. The method of claim 1 wherein the T_I/T_TOT ratio to be used in calculating desirable T_I is a default value or a default function of patient RR.

11. The method of claim 1 wherein calculated desirable T_I is used to directly determine the duration of the inflation phase of the ventilator (ventilator T_I).

12. The method of claim 11 wherein ventilator T_I is set to equal desirable T_I plus a specified amount or a specified percent.

13. The method of claim 1 wherein actual T_I is also determined in a number of recently elapsed breaths from the difference between cycling off time and either trigger time or time of onset of inspiratory effort, and a T_I error signal corresponding to the difference between actual and desirable T_I is generated.

14. The method of claim 13 wherein said T_I error signal is used to adjust the flow threshold for cycling off in the pressure support mode.

15. The method of claim 14 wherein adjustment of flow threshold is effected by fixed step increases or decreases in said threshold with polarity of said step changes being determined by polarity of the T_I error signal.

16. The method of claim 14 wherein adjustment of flow threshold is effected by variable step increases or decreases in said threshold with magnitude of said variable step changes being determined by magnitude of T_I error signal and the estimated rate of change in flow in the terminal part of the ventilator'"'"'s inflation phase.

17. The method of claim 14 wherein the greater of the results of the two methods of claims 15 and 16 is used to effect the change in flow threshold.

18. The method of claim 14 wherein flow threshold for cycling off is adjusted based on the magnitude of a composite signal consisting of the T_I error signal and/or the integral of the T_I error signal and/or the derivative of the T_I error signal.

19. The methods of any one of claims 1 to 18 wherein changes in ventilator T_I resulting from application of said methods are automatically accompanied by changes in the delivered flow rate (in volume-cycled ventilation) or in delivered pressure support (in pressure support ventilation) intended to partially or completely offset the expected change in delivered tidal volume.

20. A device for automatic ongoing adjustment of the cycling-off time of ventilator inflation phase during assisted ventilation in accordance with true respiratory rate of the patient, comprising:

circuitry for generating electrical signal(s) corresponding to the flow exchanged between patient and ventilator (flow) and/or to airway pressure (P_aw);

digital or analog circuitry means for determining true respiratory rate of patient (patient RR) on an ongoing basis from said flow and/or P_aw signals;

digital or analog circuitry means for estimating current average cycle duration of patient respiratory efforts (current patient T_TOT) from said patient RR;

digital or analog circuitry means for calculating a current desirable duration of the inhalation phase (desirable T_I) from the product of current patient T_TOT and a T_I/T_TOT ratio chosen to be in the physiological range (usually 0.25 to 0.50); and

means to cycle off ventilator inflation phase in accordance with said desirable T_I.

21. The device of claim 20 wherein ongoing patient RR is estimated from the sum of patient-triggered ventilator cycles, ineffective efforts during exhalation and additional efforts during the ventilator'"'"'s inflation phase.

22. The device of claim 21 wherein ineffective efforts are estimated from the derivative of the flow signal (Δ

flow/Δ

t), and identifying negative transients in said signal that meet specified duration criteria, and/or from the derivative of the P_aw signal (Δ

P_aw/Δ

t) and identifying positive transients in said signal that meet specified duration criteria.

23. The device of claim 20 wherein ongoing patient RR is determined from a composite signal incorporating both flow and P_aw signals.

24. The device of claim 20 wherein ongoing patient RR is determined by spectral analysis of the flow and/or P_aw signal.

25. The device of claim 20 wherein ongoing patient RR is determined from electrical inductance or impedance of the chest wall, strain gauges placed on chest wall, or from signals measuring electrical activity of respiratory muscles.

26. The device of claim 20 wherein periods of central apnea are excluded when estimating patient RR and patient T_TOT.

27. The device of claim 20 wherein a minimum and/or maximum limit is placed on the calculated desirable T_I.

28. The device of claim 20 wherein the T_I/T_TOT ratio to be used in calculating desirable T_I is a user input.

29. The device of claim 20 wherein the T_I/T_TOT ratio to be used in calculating desirable T_I is a default value or a default function of patient RR.

30. The device of claim 20 wherein calculated desirable T_I is used to directly determine the duration of the inflation phase of the ventilator (ventilator T_I).

31. The device of claim 30 wherein ventilator T_I is set to equal desirable T_I plus a specified amount or a specified percent.

32. The device of claim 20 wherein actual T_I is also determined in a number of recently elapsed breaths from the difference between cycling off time and either trigger time or time of onset of inspiratory effort, and a T_I error signal corresponding to the difference between actual and desirable T_I is generated.

33. The device of claim 32 wherein said T_I error signal is used to adjust the flow threshold for cycling off in the pressure support mode.

34. The device of claim 33 wherein adjustment of flow threshold is effected by fixed step increases or decreases in said threshold with polarity of said step changes being determined by polarity of the T_I error signal.

35. The device of claim 33 wherein adjustment of flow threshold is effected by variable step increases or decreases in said threshold with magnitude of said variable step changes being determined by magnitude of T_I error signal and the estimated rate of change in flow in the terminal part of the ventilator'"'"'s inflation phase.

36. The device of claim 33 wherein the greater of the results of the two methods of claims 34 and 35 is used to effect the change in flow threshold.

37. The device of claim 33 wherein flow threshold for cycling off is adjusted based on the magnitude of a composite signal consisting of the T_I error signal and/or the integral of the T_I error signal and/or the derivative of the T_I error signal.

38. The devices of any one of claims 20 to 37 wherein changes in ventilator T_I resulting from application of said methods are automatically accompanied by changes in the delivered flow rate (in volume-cycled ventilation) or in delivered pressure support (in pressure support ventilation) intended to partially or completely offset the expected change in delivered tidal volume.

39. The devices of any one of claims 20 to 38 wherein values of any or all of ineffective efforts, additional efforts, patient RR, desirable T_I, T_I error, and/or recommended flow threshold for cycling off, or recommended change thereof, are displayed to the user.