Ventilator-Assisted Living©

Summer 1998, Vol. 12, No. 2

ISSN 1066-534X

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Read selected articles from this issue ...

Why I Don't Have Time to Write an Article for IVUN News
Anthony Giles-Peters, Australian Ventilator Users Network (AVUN), Fairfield, Victoria, Australia

Timothy Clark
Lea Clark, Ironton, Ohio

Ventilators and Bi-Pressure Devices
Alan Fiala, PhD

International Airline Travel
Lori Hinderer, Tucson, Arizona

Which Ventilator to Use?
E.A. Oppenheimer, MD, Los Angeles, California

Trach Changing Tips
Gail Anderson, Worcester, Massachusetts

The Ideal Machine
John W.H. Watt, MB, ChB, FRCA, MD, Southport, England

Bibliography, Calendar, etc.


Ventilators and Bi-Level Pressure Devices

Alan Fiala, PhD, Falls Church, Virginia

I developed respiratory problems in 1984, nearly 32 years after the acute phase of polio. Over the next several years, I worked through a succession of ventilators, seeking the right kind to best treat my particular deficiency. Along the way, I did my homework and learned many lessons from which others may benefit.

Whenever I have time, I monitor several Internet discussion groups for polio survivors and ventilator users. It distresses me to read that people who need help get advice on ventilators based on size, weight, noise, or cost -- without consideration of the function performed. Similarly, I shudder to read stories from people who blithely say something to the effect that "... a sleep study is where they monitor you overnight and then prescribe a CPAP ventilator for you." In this case, the health care professional apparently gives no consideration to function, either.

I have had the good fortune to have health insurance that lets me choose my own physicians. I take the attitude that I am hiring them on consultation, and if they cannot explain to me their diagnosis of my problem, the physiology, and the purpose of a course of treatment, I go to someone else.

If you are having respiratory problems, the effects can sneak up on you insidiously, as happened to me. I deteriorated for two years before reaching a crisis of acute respiratory failure. I think anyone experiencing the late effects of polio should consider having a sleep study done as a preventive diagnostic measure. Most of us are in a weakened state with a narrower margin of health, and we don't need unrecognized and untreated respiratory complications. However, sleep studies must be performed intelligently.

A respiratory problem may be caused by: 1) chronic obstructive pulmonary disease (COPD), which is generalized obstruction of the small airways especially during forced expiration, as in emphysema, chronic bronchitis, and asthma; 2) obstruction or collapse of the upper airway, as in obstructive sleep apnea (OSA); and/or 3) chronic restrictive pulmonary disease (CRPD), which is weakness or limitation in the neuromusculoskeletal structure, as in polio, muscular dystrophy, ALS, etc. Be tested by someone who knows about neuromuscular diseases and who will consider the possibility that your problem is CRPD rather than COPD. In my case, the cause was restriction from kyphoscoliosis. Recognize that you may have a common respiratory problem that is NOT related to post-polio; this is known as co-morbidity.

In respiratory insufficiency, the gases in the blood are out of proportion, thereby providing insufficient oxygenation and perhaps too much CO2. The first step is for the physician to explain what might be causing this, and what might be expected after a course of treatment. The minority of post-polio pulmonary problems are COPD, but pulmonologists like to treat it because it is always the same, and treatment is standard and predictable. Neuromusculoskeletal cases are different from person to person, so a treatment must be chosen and then monitored for effectiveness over time.

One should understand the complete range of treatments and equipment available. Ensure that you understand what your problem is, and that the prescribed treatment will match up with it. In an acute situation, any type of ventilator will deliver air and dream sleep, but it may not resolve the blood gas and respiratory deficiencies in the long run. I experienced this myself when I was hospitalized with respiratory failure. Several types of ventilators were tried on me, and they ALL felt wonderful. Yet the first ventilator prescribed for me was effective only a relatively short time. Beware of respiratory therapists or pulmonologists who prescribe the same type of ventilator for all problems. They may not be knowledgeable, or they may be profiting from the sale.

Different types of ventilators serve different functions and operate with either negative pressure (the iron lung, chest shell or cuirass, and types of body wraps and suits) or positive pressure through a variety of modes currently in vogue. Positive pressure ventilators work noninvasively through an interface, such as a nasal or facial mask, nasal pillows, lipseal, etc., or invasively via a tracheostomy.

A pressure-limited ventilator delivers a continuous positive airway pressure (CPAP) up to the pressure limit set on the machine. The volume varies with an individual's physical condition. This ventilator is typically used in cases of OSA where the airway must be kept open. A bi-level pressure device, e.g. BiPAP® S/T system, delivers a continuous flow of air with pressures set separately for inspiration and expiration. The pressure level tends to make up for air leaks.

A volume ventilator delivers a set volume of air on each cycle. The pressure is then related to chest wall compliance and airway resistance and volume. It changes with physical conditions. In kyphoscoliosis, for example, the lungs expand, but the chest wall is fixed. This system is prone to leakage, but may help to overcome a particular problem such as excessive secretions. A volume ventilator has a range of settings, including range of flow -a setting not available on pressure ventilators.

My physical problem was not an obstructed airway, but thoracic musculature too weak to let me breathe in without assistance while asleep. I needed a strong inspiratory assist to be sufficiently ventilated. I also had some difficulty exhaling completely. I was sent home from the hospital with a negative pressure ventilator (chest shell) and oxygen, for sleeping only. After only a few weeks, this proved insufficient to maintain a correct blood gas balance, and I was switched to a Pulmo-Wrap negative pressure system, still with oxygen. (Note: I was renting these units.) This also proved to be insufficient over time.

After about two years of negative pressure ventilation, my respiratory therapists recommended that I switch to a positive pressure volume ventilator, the PLV-100. This delivers a controlled volume of air in, and lets me breathe out on my own. They also stated that bi-level pressure device ventilation was inappropriate for me, because I needed a device that would trigger to assist inhalation only, and deliver a volume against the resistance of my chest wall.

I did not need assistance to keep my airway open, and could not tolerate continuous pressure working against exhalation. With time, my chest wall compliance was changing. I discontinued oxygen therapy also. I had learned that oxygen was considered counter-productive for people with neuromuscular disease, and when I queried my pulmonologist about it, he said to stop using it to see what happened. I noticed no effect at all, and never used oxygen again.

The fact that my chest wall compliance was changing illustrates another key point. Your ventilatory needs may change over time, and you might have to consider changing the type of equipment used. If at all possible, rent for a long term before buying, and discuss eventual purchase with your insurance carrier. My insurance company finally decided to purchase my ventilator instead of renting it. Fortunately, this happened after I had stabilized on the type of ventilator that best suited me and before the company imposed a lifetime limit on expenditures for medical equipment.

For the first several years that I was using different ventilators, I kept asking the respiratory therapists how to find the optimum settings. The only answer was trial-and-error. I learned about sleep studies through post-polio sources, but then learned that the preponderance of sleep study laboratories would not conduct studies to tinker, but only to prescribe. I finally did find a laboratory in Philadelphia, where I had a two-night study on my own ventilator, and learned that my trial-and-error settings were, indeed, optimum. I was also fortunate that my insurance covered it, as typically only a one-night study would be authorized for detection of sleep apnea. The value of one night is suspect, since there is a strong "first-night" effect, and it doesn't allow for trial of a variety of ventilators and adaptive interfaces.

I have been very fortunate in my learning experiences. The resources of GINI and my local polio society were invaluable. I hope my report will help others in making informed choices when they develop pulmonary problems.

http://www.makoa.org/vent

References

"Post-Polio Breathing and Sleep Problems", Judith R. Fischer and Joan L. Headley, Polio Network News, Fall 1995, Vol. 11, No. 4, p. 2.

"Aging Polio Survivors and Changing Ventilation Needs", Dr. August Alba, Polio Network News, Fall 1997, Vol. 13, No. 4, pp. 6-7.

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