VENTILATOR WEANING SYSTEM

This system is designed to:

• Monitor ventilatory performance in critically ill patients being weaned from ventilator control, or, decompensated patients who may need to be placed on ventilators.
  
  
• Assist the spontaneously breathing patient being weaned from ventilator control, by appropriate breathing patterns used in a visual biofeedback manner.
  
  
• Assist the weaning patient's breathing efforts with breathing pattern prompting, while being partially assisted by ventilators of various types, by acting as an intermediary control between patient and ventilator.
  

GENERAL BACKGROUND

Patients with marginal ventilatory capability are a major problem in pulmonary care, and particularly so in the Intensive Care Unit (ICU) environment. Catastrophic ventilatory failure and death in such patients is an undeniable reality, and as such a method to reliably monitor these patients is apparent.

This invention is designed to monitor such patients, whether they are failing and in possible need for intubation and ventilation control, or in the weaning process and coming off ventilatory control.

The system is also designed to assist the spontaneously breathing patient by providing visual breathing pattern prompting, or to be an intermediary assistive device if partial assisted ventilation with various ventilators is required.

The immediate patient care safety implications are apparent. Less obvious is the urgent need to minimize ventilator time, as it is well established that prolonged ventilator time is associated with significant complication rates, morbidity and increased mortality. And likewise there are major economic implications. The ICU environment is extraordinarily expensive, and anything that can be done to minimize this time has financial significance, and particularly so in todays managed care environment.

TECHNICAL BACKGROUND

Though most patients can be weaned from ventilators in a routine manner, some are classified as "hard to wean" patients, and indeed some of these patients are very hard or even impossible to wean. Numerous ventilator assistive techniques have been attempted, and the area is controversial. Bottom line however, whatever ventilatory assistive techniques are employed, ultimately the patient must breathe on their own.

Holliday reported a striking improvement in the weaning problem in a controlled series of "hard to wean" patients by reducing ventilator days from 32.6 to 20.6 days using a simple Tidal Volume visual biofeedback prompting method (Reference: "The Reduction of Weaning Time from Mechanical Ventilation Using Tidal Volume and Relaxation Biofeedback;" Holliday, Jerome E. and Hyers, Thomas M.; American Review of Respiratory Diseases, 1990; v141: pp1214-1220). This method involved a simple bar target display on a computer CRT, with the patient's Tidal Volume indicated by another rising bar, with instructions to make the performance bar equal the target bar before breathing out. In addition, relaxation was promoted by EMG biofeedback of the frontalis muscle. As noted below, this may have been a significant portion of the experimental variables and the favorable results.

Numerous studies have indicated the hard to wean patient usually has an increased neurologic respiratory drive from the Respiratory Center, as estimated from the P 0.1 second ("P100") test, or from integrated diaphragm EMG studies. Until recently, it has been generally presumed that patients were failing in the weaning process due to weakened respiratory muscles being unable to respond to this excessive drive. However, this appears not be the case, or in any event a more complicated situation.

Jubran and Tobin reported on a matched group of successful versus failed weaning trial patients. The patients who succeeded initially showed a slower and deeper breathing pattern, shifting to a rapid and shallow pattern as they became fatigued, again demonstrating the typical defense response of fatiguing respiratory muscles. (Reference: "Pathophysiologic Basis of Acute Respiratory Distress in Patients Who Fail a Trial of Weaning from Mechanical Ventilation"; Amal Jubran and Martin J. Tobin; American Journal Respiratory and Critical Care Medicine, Vol 155, pp 906-915, 1997). However, the patients who failed the weaning trial immediately demonstrated rapid and shallow breathing. This was not due to different degrees of initial muscular fatigue, or substantially different initial pulmonary mechanical factors between the groups (See: parallel reference, pages 916-921). Could these findings perhaps be due to strong but somehow improper Respiratory Center signals?

Again, Holliday and colleagues may have provided fascinating insight into this problem. At the American Association for Respiratory Care convention, at the Respiratory Open Care Forum in San Diego in 1996 they presented a paper on weaning (Reference: "Reduction in Neural Respiratory Drive to Reduce Ventilator Weaning Failures Using Biofeedback"; Holliday, J.E., Haake, R., Range, M.) using a respiratory biofeedback instrument (Computerized Diaphragmatic Breathing Retraining^tm [CDBR^tm]; RBF Technologies, Deerfield Beach, Florida). This device uses visual signals from enclosing visual goggles and auditory signals from earphones, essentially immersing the patient in a audio-visual environment. Originally the device was used to promote relaxation and reduce EEG activity into a lower frequency range. It has been modified for respiratory use by incorporating an infrared radar device that senses chest / abdominal movement. Slow / deep / regular breathing movements produce pleasant audio-visual impressions, while rapid / shallow / irregular breathing movements produce unpleasant sensations. The device has mainly been used in breathing retraining in COPD rehabilitation.

Postulating that a "reduction in high neural respiratory drive" might be beneficial in the weaning process, in an uncontrolled study Holliday and colleagues used the CDBR^tm device on six "hard to wean ventilator patients" being weaned from ventilator control. Time to Extubation appeared to improve (generally 1 to 2 days), in conjunction with a reduction in EEG frequency from about 22.58 to 13.6 Hz (i.e. a frequency range associated with relaxation), and likewise a reduction in respiratory drive as measured by the P 0.1 second ("P100") test. And breathing patterns changed, with a slower respiratory Rate and increased Tidal Volume breaths (i.e. a breathing pattern associated with weaning success). The apparent paradox of this finding should is striking, i.e. reduced ventilatory driving signals resulting in improved ventilatory patterns and a resulting improvement in weaning time. Respiratory Center dysfunction of some sort seems strongly indicated.

What appears to be happening here is a convergence of pulmonary mechanical / breathing pattern needs for weaning, with correction of abnormal excessive and presumably corrupted respiratory drive signals from the Respiratory Center, by use of a neural biofeedback technique.

The weaning device and method of this invention is designed to maximize the weaning process, by providing specific breathing patterns to the patient undergoing the weaning process, by essentially retraining the Respiratory Center with appropriate conditioning breathing patterns. With the capability of the BIS system to generate much more sophisticated breathing patterns this training effect is anticipated to be substantially enhanced, in comparison with the simple Holliday Tidal Volume visual prompting device.

OVERALL METHOD


This is the basic overall system for a spontaneously breathing patient who is undergoing a weaning trial.

The patient's endotracheal tube is attached to a flow transducer, which in turn is sensed by a differential pressure transducer, the output of which is input to a computer for generation of a Tidal Volume breathing signal. This signal is displayed as a standard BIS^tm (Biofeedback Incentive System^tm) display.

NOTE: If you are not familiar with the BIS^tm display and the Phantom Line error detection system you should read the section on same.

Briefly, the BIS^tm system displays Tidal Volume on the "y" axis versus Time on the "x" axis. The central solid line is a simple inspiration / expiration breathing analog synthesized by menu selection, and shows a cursor moving along this Breathing Prescription in the correct time domain, to prompt the patient in correct breathing performance. Essentially therefore the system is an instantaneous breathing flow controller. Below the cursor is a display of real time inspiration breathing performance, in this case slightly below the desired performance. This gives the patient a visual biofeedback signal to correct deficient performance. The dotted lines above and below the desired program analog are so-called Phantom Lines, which are adjustable percentage +/- error limits that optionally may be displayed or hidden. If patient performance falls outside the defined error limit an audio / visual alarm indicates deficient performance, for monitoring and quality control of the process.

It is essential the reader understand the unique nature of the BIS Display ©, which is under copyright protection. Tidal Volume is always internally calibrated to a full scale screen display on the "y" axis, and likewise each respiratory cycle time is displayed full scale on the "x" axis, the entire breathing cycle therefore refreshed every breath. This results in the so-called Primary Breathing Pattern of Tidal Volume and respiratory Rate appearing the same and standardizes the display, whether one is large and breathing slowly with large Tidal Volumes or small and breathing rapidly with small Tidal Volumes. Only the Secondary Breathing Patterns (I:E Ratio, Inspiration and Expiration Breath Hold times, and various Inspiration / Expiration Waveform analogs) used to create subtle waveforms appear different. The display therefore is particularly well suited for patients to train and to imprint learned breathing patterns.

To retrain a Respiratory Center made temporarily dysfunctional by various systemic illnesses such as Shock, Sepsis, etc., the BIS^tm system has unique and powerful advantages to hasten the weaning process.

WEANING WITH VENTILATOR ASSIST

The system is designed to work in conjunction with various ventilators, partially assisting the patient in the weaning process.

Here the real time ventilatory performance is input to a ventilator, which in turn interacts with a computer, to modify ventilator performance if spontaneous respiratory efforts fall below predetermined limits, or if partial assist is desired for other reasons.

The ventilators could be of various types, e.g. the commercial BiPap device, various ventilators supporting Pressure Support Ventilation ("PSV") and/or Intermittent Mandatory Ventilation ("IMV"), Intermittent Positive Pressure Breathing ("IPPB") devices, or Proportional Assist Ventilation ("PAV") ventilators.




The system is also designed to work in conjunction with various external respiratory sensors, e.g. the commercial Respitrace device, both in the ventilator assist mode or the spontaneous breathing mode.











WEANING MONITORING

Whether one is weaning a patient from ventilator control, or observing a patient who may need to be placed on ventilator control, a real time effective monitoring system is essential. Clearly, patients with marginal ventilation are is serious danger of catastrophic ventilatory failure and death.

The BIS^tm system provides an ongoing display means to monitor not only desired ventilatory levels, and in addition to set lower safe limits of ventilation by use of the Phantom Line system. As such, even one dangerously suboptimal breath may be detected in an ongoing manner. For critically ill patients, unsafe ventilatory levels may therefore be detected even before dangerously disordered arterial blood gas changes become apparent.


This is a very simple BIS^tm display, with a linear / constant flow breathing pattern. Note the thicker patient performance line superimposed perfectly on the programmed ideal breathing analog, right behind the cursor. Plus and minus 25% error detection Phantom Lines are shown. Note carefully, the lower limit parameter is calculated to indicate a ventilatory level of marginal or dangerous hypoventilation.

Note also a window indicating Minute Ventilation (this will not be shown in subsequent pictures). This is an important monitoring feature. Even if the patient has several dangerously suboptimal breaths in the previous minute, so long as Minute Ventilation is adequate, the weaning process can be continued with reasonable safety, while the attending staff urge the patient to increase ventilatory performance. And if in doubt, arterial blood gasses may be obtained, and correlated with the observed ventilatory performance. In this manner, the patient may be safely stressed to maximal performance, to hasten the weaning process, and at the same time to be imprinting proper breathing patterns.


Note this breathing pattern has a slightly curvilinear inspiration and expiration waveforms. Also, the I:E Ratio reflects a long expiratory phase, and there is a slight inspiratory pause, and longer expiratory pause (reflecting the Resting Expiratory Level (REL).

Note the patient performance on inspiration is suboptimal, and crossing the lower Phantom Line, therefore triggering audio-visual alarms.





Here the patient ventilatory performance is failing, but still at an adequate level of ventilation to prevent dangerous hypoventilation, as defined by the operator.











Here the patient's ventilation has clearly failed.

If the patient cannot be promptly urged to increase their ventilatory effort, a logical end point of the weaning trial has been reached and the procedure therefore terminated.






MAXIMAL STRESS WEANING TRIALS

Contemporary research indicates the rehabilitation of the fatigued and deconditioned respiratory muscles of respiratory failure patients is best done by short trials of intense effort, followed by appropriate rest. The stress trials should be terminated before debilitating and detrimental stress develops, and further damages these fragile muscles. The following is an optional method to achieve maximal stress in a controlled manner.


This patient is obviously failing in the weaning trial, with rapid and shallow breathing that is falling below a safe level of minimum ventilation.

In this example, the minimum safe level of ventilation performance has been calculated to just prevent hypoventilation, or at most to permit only 3 to 5 mmHg of increased PCO2 levels of hypoventilation.







Here the same patient has been switched to a new breathing prescription, and with new Phantom Line error limits.

Note however, only the Primary Breathing Pattern of Tidal Volume and respiratory Rate have been changed, but the prompting image appears identical to the original. The new "optimal" breathing pattern is now set to the previous level of hypoventilation alarm, and the new lower level Phantom Line alarm is in the dangerous hypoventilation range. But so far as the patient is concerned, the breathing pattern has apparently not changed. Therefore, the patient will continue to train with the desired breathing pattern, while all the time continuing to imprint this pattern.

Note in this example the patient is only marginally able to maintain the lowest safe level of ventilation, as newly defined. If the patient is unable to maintain this level of ventilation, even with the all-important encouragement of skilled ICU staff, then clearly maximal permissible stress has been achieved and the weaning trial must be immediately terminated.

When to terminate a weaning trial has always been a vexing clinical question. This method permits logical definition of the termination point of the weaning trial, while all the time maintaining close monitor control to insure patient safety.

NON-INVASIVE VENTILATION AND MONITORING

While this invention has been mainly directed at the problem of weaning, the same device and general methods could just as well be employed in acute respiratory failure situations, where attempts are being made to treat critically ill patients in a conservative manner, to avoid intubation and controlled ventilation.

The typical patient is one with severe COPD, frequently with chronic respiratory failure, who decompensates with a bronchitic exacerbation. These patients are often critically ill and in immediate danger of dying. However, if invasive intubation and ventilator control can be avoided for the first day of hospitalization, while therapeutic measures stabilize the situation, such patients can frequently be treated conservatively and avoid the hazards (and expense) of intubation and controlled ventilation.

The problem then becomes one of reliable monitoring, and maximizing the effectiveness of non-invasive ventilatory assistive devices.

Here the patient is connected non-invasively via a face mask to the ventilatory device. This could be a standard IPPB device, the commercial BiPap ventilator, etc.

Note the flow transducer will measure ventilatory assistive breaths, as well as any spontaneous breaths through an accessory inspiration port. The monitoring data is input to a computer for display of the BIS^tm device.

All ventilators, and particularly pressure limited ventilators, can only work optimally if the patient is coordinated and cooperating with ventilator action. For example, no ventilator can deliver an optimal breath if the patient is in the act of breathing out, or struggling or coughing. Standard practice is to insure patient cooperation by sedation and/or respiratory paralyzing medications. For the patient who is attempting to avoid intubation this is not an option, as indeed it is imperative these patients be reasonably alert and cooperating with their therapy.

This system provides optimized prompting breathing patterns to insure that any adjunctive ventilatory assist is properly coordinated into the entire air delivery process.

And at the same time, the monitoring capabilities of the system insure patient safety, even if they are resting or sleeping during this critical time.

U.S. Patent VENTILATOR BIOFEEDBACK FOR WEANING AND ASSISTANCE
Patent No. 6,273,088 was granted August 14, 2001.

The patent may be seen at the US Patent Office site http://www.uspto/gov/ On the home page in the pull-down menu, click on "Patents." From there the patent may be found by entering the patent number, or via the search engine.

Further details me be obtained by contacting Sierra Biotechnology.