Method and apparatus for detecting ineffective inspiratory efforts and improving patient-ventilator interaction
View Patent ↗A method and system for detecting an ineffective effort of a patient being mechanically ventilated by a ventilator comprises (i) monitoring a respiratory flow of air of the patient after said ventilator has cycled; (ii) creating a signal indicative of said flow; (iii) removing artifact from said signal; (iv) monitoring said signal for perturbations; and (v) determining that an ineffective effort has occurred when said perturbation is significant.
1. A method of detecting an ineffective effort of a patient being mechanically ventilated by a ventilator, the method comprising:
monitoring a respiratory flow of air of the patient during expiration by the patient after said ventilator has cycled and before the ventilator has triggered;
generating a signal indicative of said flow of the patient during expiration;
outputting the generated signal to a processing system;
determining a peak expiratory flow (PEF) of the patient based on the generated signal;
calculating, via a processing system that includes at least one processor, a value of a second derivative of the signal that is indicative of the respiratory flow;
determining an occurrence of a significant declivity within the signal when the value of the second derivative of the signal is greater than a negative threshold value;
detecting perturbations within the generated signal by classifying the perturbations between at least ineffective efforts and non-ineffective efforts based on determination of the occurrence of the significant declivity within the signal; and
adjusting at least one setting of the ventilator based on classification of the ineffective efforts.
2. The method of claim 1 , further comprising removing a signal representative of cardiogenic oscillation from the generated signal.
3. The method of claim 2 , further comprising down-sampling or noise-filtering the generated signal to remove the signal representative of cardiogenic oscillation from the generated signal.
4. The method of claim 2 , further comprising distinguishing cardiogenic oscillations in the generated signal on the basis of amplitude.
5. The method of claim 4 , wherein distinguished cardiogenic oscillations in the generated signal are assumed to have an amplitude of less than 4 L per minute.
6. The method of claim 1 , further comprising determining whether a cough has occurred.
7. The method of claim 1 , further comprising modifying the generated signal by removing signals that are indicative of secretions.
8. The method of claim 1 , further comprising applying a noise filter to the generated signal.
9. The method of claim 1 , further comprising detecting a local maximum within the generated signal.
10. The method of claim 9 , further comprising determining a flow value that is associated with said local maximum.
11. The method of claim 10 , further comprising determining that a potential swallow has occurred when the flow value associated with the local maximum is near zero.
12. The method of claim 11 , further comprising starting a swallow timer when the flow value associated with the local maximum is near zero.
13. The method of claim 12 , further comprising determining that a swallow has occurred when said swallow timer is greater than about 500 ms.
14. The method of claim 1 , further comprising determining whether a potential swallow has occurred.
15. The method of claim 1 , further comprising determining a time period since onset of a potential swallow.
16. The method of claim 1 , further comprising determining that a cough has occurred when the PEF exceeds a threshold.
17. The method of claim 16 , whereby said threshold is approximately 200 L per minute.
18. The method of claim 1 , further comprising calculating a standard deviation of the second derivative of the generated signal, wherein said negative threshold is a percentage of the standard deviation.
19. The method of claim 18 , whereby said percentage is 33%.
20. The method of claim 1 , further comprising:
detecting a local minimum in the generated signal; and
determining an end of the significant declivity based on the detected local minimum.
21. The method of claim 20 , further comprising determining an amplitude of the significant declivity.
22. The method of claim 21 , further comprising determining that a cough has occurred when the amplitude of the significant declivity is greater than a threshold.
23. The method of claim 22 , whereby said threshold is the PEF.
24. The method of claim 22 , whereby said threshold is 200 L/min.
25. The method of claim 20 , further comprising subtracting a flow value at said local minimum from a flow value at a local maximum.
26. The method of claim 1 , wherein the adjustment of the at least one setting is automated.