Oxygen is a gas that makes up about 21% of the air we breathe. The lungs take oxygen from the air and transfer it to the bloodstream (see Exchanging Oxygen and Carbon Dioxide). Oxygen is needed to burn fuel to release energy, such as in a car engine. Similarly, all living tissue needs oxygen to provide energy for the body. Without enough oxygen, cells function poorly and eventually die.
Many diseases, particularly lung diseases, decrease the amount of oxygen in the bloodstream. In such cases, people may benefit from being given extra oxygen. Doctors used to give extra oxygen to many sick people. However, evidence has shown that oxygen is not helpful unless a person's oxygen level is actually low. Breathing too much oxygen can actually damage the lungs after a period of time.
To ensure that oxygen is given only to people who need it, doctors check the level of oxygen in their bloodstream using a blood test or a fingertip sensor (pulse oximetry). Once the level of oxygen is determined, oximetry may be used to adjust oxygen flow settings (how much oxygen the person gets per minute) over time.
When oxygen is used
Some people with chronic lung disease need only a brief period of oxygen therapy during an acute flare up (exacerbation) of their lung disease. (See also Overview of Pulmonary Rehabilitation.) Others, in whom oxygen levels in the blood are consistently low (such as some people with severe COPD), may require oxygen therapy all the time.
In people with severely low oxygen levels, long-term oxygen therapy increases survival time. The more hours a day the oxygen is used, the better the result. People survive longer when 12 hours of oxygen are used than when no oxygen is used. People survive even longer when oxygen is used continuously (24 hours per day). However, in people with moderate or slightly low oxygen levels due to chronic lung disease, long term-term oxygen use does not decrease risk of death. Regardless of the effects on mortality, long-term oxygen use may decrease shortness of breath and reduces the strain on the heart that lung disease causes. Both sleep quality and the ability to exercise tend to improve.
Some people with chronic lung disease have low levels of oxygen only when they physically exert themselves. These people can limit their oxygen use to periods of exertion. Other people have low oxygen levels only when they are sleeping. These people can limit their oxygen use to overnight hours.
Oxygen delivery systems
Oxygen for long-term home use is available from three different delivery systems:
- Oxygen concentrators
- Liquid oxygen systems
- Compressed gas systems
An oxygen concentrator is an electrically powered device that separates the oxygen from the nitrogen in the air, allowing a person with lung disease to receive purified oxygen. Because the system pulls oxygen from the room air, the person does not need to receive deliveries of oxygen. Although many of the devices also operate by battery as well, people should have a supply of oxygen available in case of a power or battery failure.
With a liquid oxygen system, oxygen is stored as a very cold liquid. Much more oxygen can be stored as a liquid than as a gas, so a given size container can hold much more liquid oxygen. As the liquid oxygen is released, it turns back into a gas, and the person can breathe it in.
With a compressed gas system, oxygen is stored in a metal tank under pressure and is released as the person breathes in.
Inside the home, liquid and compressed gas systems use large tanks to store oxygen. These tanks are periodically refilled by a home care company. Small, portable tanks of compressed or liquid oxygen or a portable oxygen concentrator may be used outside the home. Each system has advantages and disadvantages.
Oxygen sources should be closed tightly when not in use. Because oxygen is flammable and can cause an explosion, it is also important to keep tanks away from any sources of ignition, such as matches, heaters, or hair dryers. No one in the house should smoke when oxygen is in use.
Oxygen is typically administered through a two-pronged nasal tube (cannula) with either continuous flow or a demand-type system. To improve efficiency and increase mobility in people requiring high amounts of supplemental oxygen, several devices, including reservoir cannulas and transtracheal catheters, can be used.
When a person exhales, a reservoir cannula stores oxygen in a small chamber, and then returns the oxygen when the person inhales.
Demand-type systems deliver oxygen only when triggered by the machine's user (such as when a person inhales or presses on the device). They do not deliver oxygen continuously. Some have small reservoirs.
A transtracheal catheter is a small tube that is inserted through the skin directly into the windpipe. Oxygen is then delivered directly to the windpipe. Usually, a respiratory therapist or physician instructs the person about proper oxygen use.