Oxygen: for Some, a Vital Drug

WHAT IS OXYGEN?

Oxygen is a colorless, odorless gas that is vital to life. Without it we would all die within minutes. We normally have more than enough oxygen in our blood, from the air that surrounds us, wherever we are. At all altitudes, air contains 21% oxygen (the other 79 percent is mostly nitrogen). A patient who requires oxygen for treatment therefore needs more than the 21% normally available. Such patients do not have enough oxygen in their blood from breathing ordinary air.

WHEN IS OXYGEN USED?

Giving oxygen is like administering any other drug. There are situations where it is definitely needed and others where it might actually be harmful. Some patients will benefit from this drug, although the vast majority of non-hospitalized patients don't require it.

The best way to show a need for extra oxygen is by a simple test, called a pulse oximetry. This measures the SaO₂, which stands for the saturation (S) of oxygen (O₂) in the arterial blood (a). Its value tells us if the lungs are working properly to bring in enough oxygen. If the SaO₂ is very low the physician must determine if supplemental oxygen will help and how much to give. Since every patient is automatically breathing at least 21% O₂ (from the air around us), the decision to administer extra oxygen means choosing an amount between 21% and 100% (the maximum). Often the SaO₂ measurement has to be repeated while the patient is receiving supplemental oxygen. In fact, except in brief emergency situations, oxygen should only be used where the dose can be controlled and the level in the blood (SaO₂) easily measured.

Oxygen is most commonly used in hospitalized patients who are acutely ill with respiratory disease. For most patients, once the acute illness is over there is no longer a need for supplemental O₂. Considering the large number of respiratory patients in the United States, only a small percentage will ever require supplemental O₂.

HOW IS OXYGEN ADMINISTERED?

No matter how oxygen is delivered there must be some method of actually getting the gas to the patient so it can be inhaled.

For most patients, oxygen is simply delivered to the region of the face where it is inhaled. In all systems currently used, a long thin hose leads from the oxygen source (a tank, wall outlet in a hospital, oxygen extractor designed for home use, and so forth) to some facial appliance worn by the patient. In adults this appliance takes one of two typical forms: either a nasal cannula (thin, hollow tube) that fits inside the nostrils, or a face mask that fits loosely over both the mouth and nose.

In most delivery systems, oxygen flowing through the thin hose to the facial appliance is pure, or 100 percent, oxygen. By the time the patient actually inhales the oxygen it has become mixed with surrounding room air (containing 21% O₂), so the patient actually receives less than 100% oxygen. By varying the flow rate of oxygen through the hose and the specific design of the appliance (there are several types of face masks), physicians can order virtually any concentration of oxygen for the patient, from about 24% to 90+%.

In infants and small children oxygen tents are sometimes used. These work on the same principle as face masks, but the patient does not actually have anything touching the face. Tents are considered impractical for adults because of their size and requisite need for large amounts of oxygen to be effective.

CAN OXYGEN BE DELIVERED ANYWHERE?

Oxygen can be administered just about anywhere. It can be dispensed from special portable oxygen tanks at the scene of an accident or fire. Oxygen can also be set up for long-term use in a patient's home or in a nursing facility. Apparatus is available so that patients with a continuous need can be ambulatory while receiving oxygen. Oxygen is more and more being prescribed for home use in patients with severe chronic lung disease.

HOW CAN A PATIENT KNOW IF SUPPLEMENTAL OXYGEN IS NEEDED?

This question is often asked by patients who are chronically short of breath or have a chronic respiratory illness. However, outside the hospital oxygen is not prescribed lightly. This is for several reasons. Perhaps the most important is that non-hospitalized patients with respiratory disease will usually not benefit from oxygen administration.

Patient symptoms are an unreliable guide to the need for supplemental oxygen. Out of 10 patients with chronic lung disease and identical symptoms (cough, shortness of breath, and so forth), perhaps one will actually be low in O₂ and benefit from receiving it. Patients can have severe, even incapacitating lung disease and still not be deficient in oxygen. In such patients the incapacitation is usually due to difficulty in moving air in and out of the lungs; they have sufficient oxygen in their blood and giving them more would not help.

Of course, there is a definite group of patients deficient in oxygen who will benefit from receiving it at home. However, there is no way for the patient to know if he or she will benefit from O₂. In fact, there is no way for a physician to know without measuring the oxygen in the patient's blood. This can be done with a pulse oximeter and is routine if the doctor suspects severe respiratory disease or interference with gas exchange.

There are also disadvantages of chronic oxygen therapy, discussed in a subsequent section.

HOW IS OXYGEN GIVEN IN THE HOME?

Hospitals generally have a sophisticated liquid oxygen system that pipes O₂ into all hospital rooms. For home use there are three types of systems, all widely used; they are illustrated in Figure 1. The oldest in use is oxygen tanks. These large, upright cylinders, always colored green, contain oxygen gas in compressed form. The tank can be delivered and continuously changed by a local oxygen supply company, with delivery frequency determined by how much the patient is using. (For limited portability, smaller tanks can be provided on wheels; one is shown in Figure 1). The oxygen is released from the tank by a series of valves and travels safely from the tank via a long, thin hose to either a nasal cannula or face mask. The oxygen is odorless, although sometimes one can smell the plastic of the facial appliance.

Figure 1. Equipment used to deliver oxygen in the home. Represents three different systems. (Reproduced by permission, Linde Homecare Medical Systems, Inc.)

A second method is a portable liquid oxygen system, designed for home use. A liquid oxygen container (the two large canisters in Figure 1; see also Figure 2) is placed in the patients's home and is filled periodically from a truck brought to the residence. Liquid oxygen has the advantage of allowing more oxygen to be stored at one time compared to tanks of compressed oxygen. An additional advantage is that portable walking containers can be filled from the liquid oxygen system, something not possible with the other two systems (Figure 1 and 3).

The third delivery method of home O₂ is via an oxygen extractor, also called an oxygen concentrator, an ingenious device that works from normal house current (in Figure 1, it is the large box-like unit next to the tall oxygen tank). This machine extracts oxygen from air by eliminating the nitrogen, effectively concentrating the oxygen and converting it from 21% to over 90% of the air. As with the other two systems, the actual amount received by the patient will be determined by the liter flow rate ordered by the physician. The therapeutic advantage of all oxygen systems is the delivery to the patient of more that 21% oxygen.

Figure 2. A woman sitting by the fireplace, using a liquid oxygen system. Note the oxygen tubing leading from the canister to her nose. (Reproduced by permission, Linde Homecare Medical systems, Inc.)

Figure 3. A woman shopping, while using a portable oxygen system. This system was filled from a canister like the one shown in Figure 2; it allows for continuous oxygen use for several hours outside the home. Such portable oxygen systems are continually being made lighter and more convenient to carry. (Reproduced by permission, Linde Homecare Medical Systems, Inc.)

WHAT ARE THE DISADVANTAGES OF USING HOME OXYGEN?

Assuming the need for oxygen is established, there are several disadvantages:

1. Continuous Need. The need for O₂ is continuous since the body does not store it. Only a few minutes' supply is available in circulating blood; once that supply is exhausted, death ensues. This is marked contrast to food, which is stored as protein and fat and can keep a fasting person alive for many days. When patients are low on O₂ they would logically benefit from receiving supplemental O₂ all the time. This is impractical because of inconvenience and cost.

2. Inconvenience. The extra O₂ must come from either heavy tanks or a cumbersome electrical apparatus and hence is confining. Practically speaking, patients must be sedentary for continuous oxygen or carry bulky equipment if they are ambulatory (Figure 3). In addition, these small canisters do not allow excursions for more than a few hours. Unfortunately, oxygen is available only in gaseous form; there is no pill or elixir one can swallow.

Because of the inconvenience, most patients compromise. They use oxygen mainly at night and during the day when they feel they need it or it is otherwise inconvenient to use. Many suffer the symptoms of low oxygen rather than be confined, carry bulky equipment, or be seen in public with tubes in their noses. Certainly, both the inconvenience and the stigma some patients feel are an obstacle to continuous O₂ use. Conversely, continuous need is an obstacle to truly effective O₂ therapy.

3. Cost. This varies depending on the amount and duration of use. Oxygen at 2 liters per minute for 12 hours a day can range from $100 to more than $300 a month. For some patients a large percentage of the total cost will be subsidized by insurance carriers or Medicare.

4. Discomfort. Continuous oxygen is given either by nasal cannula or face mask (unless the patient is connected to an artificial ventilator.). Prolonged use by either appliance tends to cause irritation and erythema (redness) in the areas of facial contact. Some patients receiving nasal oxygen also complain of a headache, particularly after several hours of high flow oxygen, and find no relief unless they remove the cannula.

5. Toxicity. Improperly used, oxygen can be toxic. As with any medication, too much can be harmful to health and can even cause lung disease worse than the underlying condition. This is why O₂ should only be prescribed after blood gas analysis and full evaluation of the patient's respiratory problem.

In summary, determining who will benefit from oxygen requires a thorough evaluation including arterial blood gas analysis. Except in emergency situation, continuous O₂ therapy should never be ordered for a patient without such an evaluation. [Return to Table of Contents]