CENTRAL  SOUTH  DAKOTA  MEDICAL NEWS
THE CLINICAL VIEW
By: Phillip E. Hoffsten, M.D.
28  JUNE  2001

When and How to use Oxygen Treatments

Chronic lung disease and heart failure are two of the major causes of disability and discomfort in the United States. Not being able to breathe or having the breathing that you are doing just not work is a horrible feeling. This is what happens to people who have heart failure where blood backs up into the lungs and takes up air space or when a person has emphysema meaning that the amount of lung tissue that would normally be present has simply been destroyed and is gone.

The way the system works is to have blood run through the lungs. In the lungs, there is a huge surface area where tiny blood vessels run next to air sacs with a hair-thin membrane between the two. This membrane is very special in that it keeps the blood in the blood vessels and the air in the air sacs but lets carbon dioxide come out of the blood to be breathed out and lets oxygen come into the blood to be carried off for the body's use. When the blood flow is too slow as in heart failure or when the lungs have been damaged as in emphysema, this exchange of carbon dioxide and oxygen does not occur fast enough, and the person's body does not get enough oxygen to make it work. Oxygen can be thought of rather like gasoline is to a car. Oxygen makes the body run.

The most critical place that oxygen is needed is in the brain. After about 8 seconds of inadequate blood supply to the brain, a person will lose consciousness. By the same token, the slower the blood flow to the brain and the less oxygen it gets, the less well it works.  Conceptually, one of the best ways to take care of this problem is to put more oxygen in the air that the person is breathing. Normally, air is about 20% oxygen and has almost no carbon dioxide in it. The air that a person breathes back out is about 5% carbon dioxide and only 12% to 15% oxygen. One of the basic laws of natural physics is that the more oxygen you put in the air that a person breathes, the more that will diffuse into the blood for the persons use. Back when I was in medical school 40 years ago, the use of oxygen at home was something unusual. Now, because of the severe epidemic of lung disease from cigarettes and industrial exposure and other illnesses, many, many people use home oxygen and it has become a major expense for Medicare.

There are some important considerations in using oxygen treatments in the hospital or at home. One of the most common questions that patients ask, "How long should I use the oxygen?". This has been studied over a long period of time and it is very clear that when a person needs home oxygen therapy, they need to use it continuously. Patients have been followed over several years' time and it has been shown very clearly that those who use the oxygen longer each day do better than those who try to just use the oxygen once in awhile. Using oxygen "just when I need it" is not a good strategy. The best measure of effectiveness of oxygen therapy is the maintenance of a person's mental function. Those patients who use the oxygen continuously are able to remain in their homes and carry on their activities of daily living longer and more comfortably than patients who do not use their oxygen continuously. Using the oxygen all day long and all night long is a critical and important part of oxygen therapy.

The second most common question we hear is, "What should the flow rate of oxygen be?". If a person uses a nasal canula or tube to deliver the oxygen directly into the nose. The most commonly prescribed flow rate is 2 liters of oxygen per minute. This raises the percent of oxygen in the inspired air to about 28% which is up from 20%. While this may not sound like much, it is a 40% increase in the oxygen delivery pressure to the individual and is often enough to compensate the person's oxygen needs. For some individuals, this is not enough. A test using an oxygen saturation meter placed on the person's finger can help determine the best flow rate for each individual person. Usually, the flow rate is between 2 to 3 liters per minute.

An additional consideration is the provision of moisture with the oxygen. When a person uses dry oxygen without a humidifier in the line, the person's nose can become very dry and cracked and then nosebleeds and irritation develop. The use of a bottle of water in the line so that the oxygen bubbles through this is helpful in preventing drying of the nasal passages. Another question commonly asked is, "Can a person get too much oxygen?". The answer to that is yes, but it is unusual. The problem relates to the force that makes us breathe. Most people do not have to think about breathing. There is a mechanism in the bottom of the brain that tells them when to breathe and how fast to breathe and this is regulated by the amount of carbon dioxide in the person's blood. If a person goes out and runs around the block, they will produce a great deal more carbon dioxide than they would sitting still and thus they breathe faster and harder and deeper than if they had just been sitting in the easy chair. So breathing is primarily regulated through carbon dioxide blood levels. In some people with chronic lung disease, the amount of carbon dioxide in the blood tends to drift upward because the lungs just do not have enough surface area to get rid of all of the carbon dioxide being produced. As this occurs, the body has a backup mechanism to regulate breathing. When carbon dioxide levels build up too high in the blood, breathing is then driven by the amount of oxygen in the blood. Shifting from oxygen drive to carbon dioxide drive or back again is a slow process. Thus if a person is on oxygen drive because their carbon dioxide levels are already quite high, giving this person too much oxygen will slow their respiratory rate because oxygen will be adequately provided with the increased levels in the inspired air. Unfortunately, the carbon dioxide level then builds up higher yet as the person breathes more slowly. It is a little known medical fact that carbon dioxide is like an anesthetic and when the levels get too high, the person goes to sleep and breathing can then become dangerously slowed. As this occurs, the carbon dioxide levels build up higher yet and the situation can be fatal. Thus for patients who have chronic lung disease, a little bit of oxygen help is a good thing but pushing the levels up too high can be a disastrous mistake. The respiratory therapist and the health care professionals who help set up home oxygen therapy are skilled at setting the oxygen levels at the right point and avoiding this problem. Patients should not be tinkering with the oxygen flow rates on their machines without careful instruction and counseling from the respiratory therapist.

Other uses of oxygen therapy include treating sleep apnea in which patients stop breathing at night because they are asleep. There are special machines called CPAP devices which use oxygen therapy if needed to prevent the person from stopping breathing while they are asleep. Lastly, oxygen is somewhat helpful in people who have an acute asthmatic attack because it does help relax the bronchial airways and allow better airflow. The health care professionals at your local clinic are aware and skilled at these considerations and can be a major help in both prescribing oxygen therapy when needed and regulating the oxygen prescription for home use.