Methods and apparatus for varying the back-up rate for a ventilator

• US 20040231670A1
• Filed: 03/05/2004
• Published: 11/25/2004
• Est. Priority Date: 03/07/2003
• Status: Active Grant

• Current Assignee: ResMed Pty Ltd. (ResMed Incorporated)
• Original Assignee: Resmed Limited (ResMed Incorporated)
• Inventors: Bassin, David John
• Granted Patent: US 7,255,103 B2
• Time in Patent Office: Days
• US Class Current: 128/204.18
• CPC Class Codes: A61M 16/00 Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes stimulating the respiratory movement by mechanical, pneumatic or electrical means, iron lungs combined with gas breathing means A61H31/00
• CPC Class Codes: A61M 16/0003 Accessories therefor, e.g. sensors, vibrators, negative pressure
• CPC Class Codes: A61M 16/0066 Blowers or centrifugal pumps
• CPC Class Codes: A61M 16/0069 the speed thereof being controlled by respiratory parameters, e.g. by inhalation
• CPC Class Codes: A61M 16/024 including calculation means, e.g. using a processor
• CPC Class Codes: A61M 16/04 Tracheal tubes catheters in general A61M25/00
• CPC Class Codes: A61M 16/06 Respiratory or anaesthetic masks
• CPC Class Codes: A61M 16/0875 Connecting tubes
• CPC Class Codes: A61M 16/20 Valves specially adapted to medical respiratory devices
• CPC Class Codes: A61M 2205/3334 Measuring or controlling the flow rate
• CPC Class Codes: A61M 2205/50 with microprocessors or computers
• CPC Class Codes: A61M 2205/502 User interfaces, e.g. screens or keyboards
• CPC Class Codes: A61M 2230/005 Parameter used as control input for the apparatus
• CPC Class Codes: A61M 2230/40 Respiratory characteristics

Abstract

A ventilator device delivers ventilatory support to a patient in a back up timed mode when patient respiration is not detected or a spontaneous mode when patient respiration is detected. The timing threshold governing the back-up mode is chosen to deviate from normal expected respiration time for the patient to promote patient initiated ventilation in the spontaneous mode but permit back-up ventilation in the event of apnea. Automated adjustments to the timing threshold during the timed mode are made from the less vigilant timing threshold to a more vigilant threshold at or near a timing of normal expected breathing of the patient. Such adjustments may be made from a minimum to a maximum vigilance timing settings or incrementally there between as a function of time in the timed mode which is preferably the number of delivered machine breaths.

Claims

1. A method for setting back up support ventilation for a patient comprising the steps of:

delivering pressure support ventilation to a patient during inspiratory and expiratory portions of a breathing cycle of the patient;

detecting a recurrent respiratory event in a cycle of the patient'"'"'s respiration;

setting a timing threshold for controlling the delivery of pressure support ventilation subsequent to the recurrent respiratory event and in an absence of a detection of a subsequent recurrent respiratory event;

controlling a delivery of pressure support according to the timing threshold in the absence of a detection of a recurrent respiratory event subsequent to a detected recurrent respiratory event;

wherein the step of setting a timing threshold, said timing threshold is chosen to deviate from a normal expected respiration timing for the patient in a manner that promotes patient initiated synchronization of the pressure support ventilation but permits back-up ventilation in the event of an apnea.

2. The method of claim 1 further comprising the step of automatically adjusting the timing threshold in the absence of a detection of a subsequent recurrent respiratory event to normalize the timing threshold toward an expected normal respiration timing for the patient.

3. The method of claim 2 wherein the timing threshold adjusts stepwise as a function of a number of delivered cycles of ventilation delivered in response to the timing threshold.

4. The method of claim 2 further comprising the step of automatically adjusting the timing threshold in the presence of a detection of a subsequent recurrent respiratory event to adjust the timing threshold towards a timing threshold chosen to deviate from a normal expected respiration timing for the patient.

5. The method of claim 4 wherein the timing threshold adjusts stepwise as a function of a number of delivered cycles of ventilation delivered in response to detected patient respiration.

6. The method of claim 5 wherein in response to a detection of a single respiratory cycle by the patient, the timing threshold returns to an original timing threshold chosen to deviate from a normal expected respiration timing for the patient.

7. The method of claim 6 wherein the timing threshold is a respiratory rate, and in the step of automatically adjusting the timing threshold in the absence of a detection of a subsequent recurrent respiratory event, said respiratory rate increases from a rate chosen to deviate from a normal expected respiration rate for the patient toward a normal expected respiration rate.

8. The method of claim 7 wherein automated adjustments to the timing threshold are restricted by a maximum respiratory rate that is about 50 percent faster than the rate chosen to deviate from a normal expected respiration rate.

9. The method of claim 7 wherein automated adjustments to the timing threshold are restricted by a minimum respiratory rate that is calculated as a fraction of a normal respiratory rate determined during a learning period.

10. The method of claim 9 wherein the fraction is about 67%.

11. The method of claim 6 wherein the timing threshold is a respiratory period, and in the step of automatically adjusting the timing threshold in the absence of a detection of a subsequent recurrent respiratory event, said respiratory period decreases from a period chosen to deviate from a normal expected respiration period for the patient toward a normal expected respiration period.

12. The method of claim 2 further comprising the step of determining adequacy of the patient'"'"'s ventilation and wherein automated adjustments to the timing threshold are a function of the adequacy of the patient'"'"'s ventilation.

13. The method of claim 12 wherein the function of the adequacy of the patient'"'"'s ventilation includes a ratio of a measured ventilation and a target ventilation.

14. The method of claim 13 wherein the measured ventilation is a minute ventilation and the function is piecewise linear on a ratio of a measured minute ventilation to a target minute ventilation.

15. The method of claim 2 further comprising the step of automatically periodically returning the normalized timing threshold to the timing threshold chosen to deviate from a normal expected respiration in the absence of a detection of a subsequent recurrent respiratory event.

16. The method of claim 15 further comprising the step of changing the timing threshold back towards the normalized timing threshold after delivering a machine breath if a subsequent recurrent respiratory event remains undetected during application of the the timing threshold chosen to deviate from a normal expected respiration.

17. The method of claim 16 wherein the periodic return occurs as a function of a number of delivered machine breaths.

18. An apparatus for providing back up ventilation to a patient comprising:

a ventilator adapted to generate and deliver ventilatory support to a patient; and

a controller configured to control the ventilatory support provided by the ventilator,

wherein the controller is configured with a spontaneous mode in which synchronized cyclical ventilatory support is initiated by detecting the presence of a respiratory cycle of the patient;

wherein the controller is further configured with a timed mode in which cyclical ventilatory support is delivered in accordance with a timing threshold in the absence of detecting a respiratory cycle of the patient, and

wherein the controller is configured to set the timing threshold as a function of normal expected respiratory timing for the patient, said function chosen to deviate the timing threshold from the normal expected respiration timing for the patient in a manner that promotes patient initiated synchronization of the ventilatory support but permits back-up ventilation in the event of an apnea.

19. The apparatus of claim 18 wherein the controller is further configured to automatically adjust the timing threshold in a timed mode in the absence of detecting a respiratory cycle of the patient from a timing threshold deviating from a normal expected respiration timing for a patient toward a normal expected respiration timing for the patient.

20. The apparatus of claim 19 wherein the timing threshold adjusts stepwise as a function of a number of delivered cycles of ventilation delivered in response to the timing threshold.

21. The apparatus of claim 20 wherein the controller is further configured to automatically change the timing threshold upon the detection of the presence of a respiratory cycle of the patient by adjusting the timing threshold towards a timing threshold deviating from a normal expected respiration timing for the patient.

22. The apparatus of claim 21 wherein the timing threshold adjusts stepwise as a function of a number of delivered cycles of ventilation delivered in response to detected respiratory cycles of the patient.

23. The apparatus of claim 22 wherein in response to a detection of a single respiratory cycle by the patient, the timing threshold returns to an original timing threshold chosen to deviate from a normal expected respiration timing for the patient.

24. The apparatus of claim 19 wherein the timing threshold is a respiratory rate, and the controller in automatically adjusting the timing threshold in the timed mode increases the timing threshold from a minimum rate lower than a normal expected respiration rate for the patient toward a maximum higher rate approximately that of normal expected patient respiration.

25. The apparatus of claim 24 wherein the automated adjustments to the timing threshold are restricted by a maximum respiratory rate that is about 50 percent faster than the minimum rate.

26. The apparatus of claim 24 wherein the minimum respiratory rate is calculated as a fraction of a normal respiratory rate determined during a learning period.

27. The apparatus of claim 26 wherein the fraction is about 67%.

28. The apparatus of claim 18 wherein the function of normal expected respiratory rate for the patient is a fixed percent of a learned respiratory rate for the patient.

29. The apparatus of claim 28 wherein the fixed percent is about 67%.

30. The apparatus of claim 19 wherein the timing threshold is a respiratory period, and the controller in automatically adjusting the timing threshold decreases it from a maximum period deviating from a normal expected respiration period toward a minimum lower period approximately that of normal expected respiration.

31. The apparatus of claim 18 wherein the controller is further configured to determine adequacy of the patient'"'"'s ventilation and adjust the timing threshold as a function of the adequacy of the patient'"'"'s ventilation.

32. The apparatus of claim 31 wherein the function of the adequacy of the patient'"'"'s ventilation includes a ratio of a measured ventilation and a target ventilation.

33. The apparatus of claim 32 wherein the measured ventilation is a minute ventilation and the function of the adequacy of the patient'"'"'s ventilation is piecewise linear on a ratio of a measured minute ventilation to a target minute ventilation.

34. The apparatus of claim 18 wherein the controller is further configured in the absence of a detection of a respiratory cycle of the patient to automatically periodically return the timing threshold from a more vigilant threshold approximating normal expected respiration timing to a less vigilant threshold deviating from normal expected respiration timing.

35. The apparatus of claim 34 wherein the controller is further configured to change the timing threshold to the more vigilant threshold from the less vigilant timing threshold after delivering a machine breath if a subsequent respiratory cycle of the patient remains undetected during application of the less vigilant timing threshold.

36. The apparatus of claim 34 wherein the controller periodically returns the timing threshold as a function of a number of consecutive delivered machine breaths.

37. An apparatus for providing back up ventilation to a patient comprising:

a patient interface and conduit coupled for delivering a controlled supply of breathable gas to a patient;

a controllable blower device coupled to the conduit to generate the supply of breathable gas, the supply of breathable gas providing ventilatory support for the patient;

a pressure transducer configured to detect a measure of patient respiration through the interface and generate a signal indicative of the measure; and

a processor coupled with the blower device and transducer to control the delivery of the supply of breathable gas to the patient,

wherein the processor includes coded instructions to control a spontaneous mode in which synchronized cyclical ventilatory support is initiated by detecting the presence of a respiratory cycle of the patient from the signal from the pressure transducer;

wherein the controller is further includes coded instructions to control a timed mode in which cyclical ventilatory support is delivered in accordance with a timing threshold in the absence of detecting a respiratory cycle of the patient from the signal from the pressure transducer, and

wherein the processor further includes coded instructions to set the timing threshold as a function of normal expected respiratory timing for the patient, said function chosen to deviate the timing threshold from the normal expected respiration timing for the patient in a manner that promotes patient initiated synchronization of the ventilatory support but permits back-up ventilation in the event of an apnea.

38. The apparatus of claim 37 wherein the processor further includes coded instructions to automatically adjust the timing threshold in a timed mode in the absence of detecting a respiratory cycle of the patient from a timing threshold deviating from a normal expected respiration timing for a patient toward a normal expected respiration timing for the patient.

39. The apparatus of claim 38 wherein the timing threshold adjusts stepwise as a function of a number of delivered cycles of ventilation delivered in response to the timing threshold.

40. The apparatus of claim 39 wherein the processor further includes coded instructions to automatically change the timing threshold upon the detection of the presence of a respiratory cycle of the patient to adjust the timing threshold towards a timing threshold deviating from a normal expected respiration timing for the patient.

41. The apparatus of claim 40 wherein the timing threshold adjusts stepwise as a function of a number of delivered cycles of ventilation delivered in response to detected respiratory cycles of the patient.

42. The apparatus of claim 41 wherein in response to a detection of a single respiratory cycle by the patient, the timing threshold returns to an original timing threshold chosen to deviate from a normal expected respiration timing for the patient.

43. The apparatus of claim 38 wherein the timing threshold is a respiratory rate, and the coded instructions of the processor control automatically adjusting of the timing threshold in the timed mode to increase the timing threshold from a minimum rate lower than a normal expected respiration rate for the patient toward a maximum higher rate approximately that of normal expected respiration.

44. The apparatus of claim 43 wherein automated adjustments to the timing threshold are restricted by a maximum respiratory rate that is about 50 percent faster than the minimum rate.

45. The apparatus of claim 44 wherein coded instructions of the processor calculate the minimum respiratory rate as a fraction of a normal respiratory rate determined during a learning period.

46. The apparatus of claim 45 wherein the fraction is about 67%.

47. The apparatus of claim 37 wherein the function of normal expected respiratory rate for the patient is a fraction of a learned respiratory rate for the patient.

48. The apparatus of claim 47 wherein the fraction is about 67%.

49. The apparatus of claim 38 wherein the timing threshold is a respiratory period, and the coded instruction of the processor control automatically adjusting the timing threshold by decreases it from a maximum period deviating from a normal expected respiration period toward a minimum lower period approximately that of normal expected respiration.

50. The apparatus of claim 37 wherein the processor further includes coded instructions to determine adequacy of the patient'"'"'s ventilation from a signal from the pressure transducer and adjust the timing threshold as a function of the determined adequacy of the patient'"'"'s ventilation.

51. The apparatus of claim 50 wherein the function of the adequacy of the patient'"'"'s ventilation includes a ratio of a measured ventilation and a target ventilation.

52. The apparatus of claim 51 wherein the measured ventilation is a minute ventilation and the function of the adequacy of the patient'"'"'s ventilation is piecewise linear on a ratio of a measured minute ventilation to a target minute ventilation.

53. The apparatus of claim 37 wherein the processor further includes coded instructions to control in the absence of a detection of a respiratory cycle of the patient an automatic periodic return of the timing threshold from a more vigilant threshold approximating normal expected respiration timing to a less vigilant threshold deviating from normal expected respiration timing.

54. The apparatus of claim 53 wherein the coded instructions further control a change of the timing threshold to the more vigilant threshold from the less vigilant timing threshold after delivering a machine breath if a subsequent respiratory cycle of the patient remains undetected.

55. The apparatus of claim 53 wherein the coded instructions control the automatic periodic return of the timing threshold as a function of a number of consecutive delivered machine breaths.