Method and device for monitoring and improving patient-ventilator interaction

Abstract

Method and apparatus for non-invasively determining the time onset (T onset ) and end (T end ) of patient inspiratory efforts. A composite pressure signal is generated comprising the sum of an airway pressure signal, a gas flow pressure signal obtained by applying a gain factor (K f ) to a signal representing gas flow rate and a gas volume pressure signal obtained by applying a gain factor (K v ) to a signal representing volume of gas flow. K f and K v values are adjusted to result in a desired linear trajectory of composite pressure signal baseline in the latter part of the exhalation phase. The current composite pressure signal is compared with (i) selected earlier composite pressure signal values and/or (ii) value expected at current time based on extrapolation of composite pressure signal trajectory at specified earlier times and/or (iii) the current rate of change in the composite pressure signal with a selected earlier rates of change. The differences obtained by the comparison are compared with selected threshold values. T onset is identified when at least one of the differences exceeds the threshold values.

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       20 . A method for cycling off the inflation phase of a mechanical ventilator comprising:
 measuring the average interval between patient inspiratory efforts in a patient in a suitable number of elapsed breaths (T TOT ) with said average being updated at suitable intervals;   identifying onset of current inspiratory effort;   monitoring time from said onset of inspiratory effort; and   generating a signal that causes the ventilator to cycle off when time elapsed since onset of inspiratory effort exceeds a specified fraction of T TOT .   
   
   
       21 . The method of  claim 20  wherein the time to generate a signal to cycle off the ventilator is calculated from the trigger time of current ventilator cycle plus a specified fraction of T TOT . 
   
   
       22 . A method for cycling off the inflation phase of a ventilator in pressure support ventilation comprising:
 measuring the interval between successive inspiratory efforts in a suitable number of elapsed breaths (T TOT );   measuring inspiratory flow rate at specified times in those elapsed breaths which triggered ventilator cycles, said specified times corresponding to a specified fraction of the T TOT , measured from the onset of inspiratory effort of said each breath or from the trigger time of the ventilator;   calculating the average of the flow values obtained at said specified times in said elapsed breaths; and   generating a signal that causes the ventilator to cycle off when inspiratory flow in the current inflation phase decreases below said average flow value.   
   
   
       23 . The method of  claim 1  wherein results concerning patient ventilator interaction are displayed, such results including displays of at least one of the composite pressure signal itself, T onset  and T end  markers, and trigger delay, cycling-off errors, patient respiratory rate, number and frequency of ineffective efforts, and frequency and duration of central apneas, desirable duration of inflation phase, and flow at a specified fraction of T TOT  of the patient in the pressure support ventilation mode. 
   
   
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       38 . A device for estimating a desirable duration of inflation phase of a ventilator, comprising:
 circuitry to identify inspiratory efforts of a patient;   means to calculate the time difference between patient inspiratory efforts (patient T TOT );   means for displaying a value corresponding to a specified fraction of patient T TOT , said specified fraction being a user input or a default value between 0.3 and 0.5.   
   
   
       39 . The device of  claim 38  where a signal is generated to cycle off the inflation phase of the ventilator when said desirable duration has elapsed after ventilator triggering. 
   
   
       40 . The device of  claim 38  wherein a signal is generated to cycle off the inflation phase of the ventilator when said desirable duration has elapsed after onset of inspiratory effort in current breaths or after a point intermediate between onset of effort and ventilator triggering. 
   
   
       41 . The device of  claim 39  wherein a user input is provided for inputting patient T TOT  or its reciprocal, patient respiratory rate, and said input is used by the device, in lieu of device-determined patient T TOT , to determine desirable duration of inflation phase. 
   
   
       42 . A device for determining the desirable inspiratory flow threshold for terminating inflation cycles in the pressure support ventilation mode comprising:
 circuitry for estimating desirable duration of inflation phase of the ventilator;   means to measure inspiratory flow in recently elapsed breaths after said desirable duration has elapsed from the ventilator's trigger time, or from the onset of inspiratory effort preceding triggered breaths, or from a specified point in between the latter two points; and   means for displaying the value of said measured flow.   
   
   
       43 . The device of  claim 42  wherein the value of said measured flow is communicated to cycling mechanism of the ventilator to effect termination of the inflation phase when said measured flow, or a reasonable approximation thereof, is reached during the inflation phase. 
   
   
       44 . The device of  claim 24  wherein values relevant to patient ventilator interaction are calculated and displayed, such values including displays of at least one of the composite pressure signal itself, T onset  and T end  markers and displays or outputs indicating trigger delay, cycling-off errors, patient respiratory rate, number and frequency of ineffective efforts, frequency and duration of central apneas, desirable duration of inflation phase, and flow at a specified fraction of patient's T TOT  in the pressure support ventilation mode. 
   
   
       45 . The device of  claim 24  wherein the output of the device is used for closed-loop control of ventilator settings. 
   
   
       46 . The device of  claim 24  wherein functions executed by electrical circuitry are executed in whole or in part by digital techniques.