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Edward Anthony Oppenheimer, M.D.

Noninvasive Ventilation
Oxygen Availability

Dr. Oppenheimer is a pulmonologist specializing in noninvasive ventilation for people with motor neuron diseases. Pneumonia is our number one nemesis. People with ALS don't usually die from respiratory failure initiated by pneumonia.

But good health doesn't just happen. We must take an active role in our health care: learn as much as we can about it, document our findings, then share this information with our physicians.

Normally with respiratory muscle weakness, without pneumonia, noninvasive ventilation achieves improved gas exchange in the alveoli of the lungs. When alveolar ventilation is satisfactory, CO2 is eliminated and oxygen is provided. The arterial oxygen saturation then is usually a good guide to adequate ventilation. However, when pneumonia occurs, the situation is different and more difficult. Areas of pneumonia have the alveolar air exchange units filled with inflammatory fluid (pus) that has to resolve before gas exchange is possible in those areas.

Neither room air nor added oxygen can get into those alveolar units (air sacs), but the blood channels (capillaries) remain open due to mechanical distention and the effect of the inflammatory by-products that cause vasodilatation. The result is that venous (blue) blood low in oxygen "shunts" past these alveolar units which are filled with pneumonia and no gas exchange occurs.

Thus, venous blood returns to the heart from the lung without oxygen uptake, and this is circulated to the body. This is a temporary "shunt" effect, which will decrease as the pneumonia clears. The mechanical ventilation cannot overcome the shunt (this is true for both noninvasive ventilation and tracheotomy ventilation). Added oxygen only has a minor effect because it never reaches the air sacs that are filled with pneumonia.

Fortunately, adults without heart disease can usually manage despite low oxygen saturation if they are getting the right antibiotics and if the CO2 and pH are good. So, it is not a mechanical ventilation problem; it is related to the amount of the lung with pneumonia. Mechanical ventilation provides enough ventilation so that gas exchange in the remainder of the lungs achieves a satisfactory CO2 and pH.

It is very important to assist effective cough to remove any bronchial secretions. Manually assisted cough techniques, and sometimes even using a mechanical "In-Exsufflator cough machine" has been helpful for some people. Dr. John Bach has written two articles about this in the medical journal CHEST in 1994.

One way to prepare for potential respiratory problems down the road is to start noninvasive ventilation earlier, when there are some symptoms related to breathing and the vital capacity has fallen to 50% or less. Starting noninvasive ventilation means learning how to use the equipment, getting some comfort and practice with it, and obtaining better sleep at night without having to sit up. And then if a respiratory infection should occur it is more likely that pneumonia can be avoided because ventilation stays stronger and the assisted ventilation provides a bigger breath in, so that a better cough is possible to eliminate excess secretions.

Pneumonia creates severe problems, regardless of whether you are breathing independently or on a ventilator. Fortunately, most people recover in time and can survive a period of poor arterial oxygen saturation (SaO2). The heart compensates by increasing heart rate and cardiac output in order to deliver more oxygen to the tissues.

The circulation of blood is somewhat like a train. When it is loaded with less oxygen the train circulates more often around the circuit in order to deliver enough oxygen to each point on the way, by making extra trips with a smaller load of oxygen each time. Most people can provide the extra heart work to increase circulation without a problem. Older people or those with heart disease may not do as well. The larger the percent of the lung involved with pneumonia the greater the problem of course. Unfortunately, giving a person more oxygen is not very effective when the decreased SaO2 is due to pneumonia.

It is always better to avoid pneumonia by:

While some people have difficulty with Influenza immunizations, most people do not and definitely will benefit from them if there is an influenza epidemic. They do not give protection from other cold virus and "flu" illnesses.

Key Points

  1. Oxygen saturation levels will remain low, even when using a ventilator, if pneumonia is present.
  2. Learn to use noninvasive ventilation (such as a BiPAP) before problems occur when vital capacity is 50% or less.
  3. Learn assistive cough techniques, either manual or mechanical, to remove secretions.
  4. Prevent illness both by avoiding contact with affected individuals and by immunization.

Edward Anthony Oppenheimer, M.D.
Pulmonary & Critical Care Medicine
Southern California Permanente Medical Group
4950 Sunset Boulevard
Los Angeles, CA 90027-5822

 "In-Exsufflator cough machine"

1-800-252-1414 or
7:30 AM to 4:30 PM ET

Domestic: rob@jhemerson.com
International: kevin@jhemerson.com

J.H. Emerson Co.
22 Cottage Park Avenue
Cambridge, Massachusetts 02140-1691

[Every Breath You Take Part I]

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