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Oxygen as a drug in some respiratory diseases

Posted Jul 01 2008 4:10pm


Oxygen is a key element for our body to work properly. All the effort of breathing is made to keep the levels of this gas in the appropriate range. The healthy human being does not realize of the physical breathing process as a routine when the entire body is working in the positive balance of oxygen taking. However a challenge to the environment is accompanied by an increase need in oxygen so our muscles can work for running away, jumping, cycling, climbing stairs quickly, making strides, etc.

Oxygen as a excess requirement

Respiratory ill patients like those with pulmonary fibrosis, chronic obstructive disease and asthma, pneumonia, rib fractures, etc. have a diminished surface to exchange oxygen and CO2 with the atmosphere. Although the surface for exchange may be big enough to favor CO2 release, some times oxygen will not find sufficient permeable tissue to get into the blood. That’s the reason why some patients must need supplemental oxygen and others may have a delayed requirement.

Lower level of activities acting as indicators

The respiratory imposed condition may not wait for for typical exhausting tasks to add symptoms or make the reduced level of oxygen more diminished. These diseases may make the oxygen need more apparent when getting up, walking, carrying a bag with groceries, or taking a shower. For some patients, just lying on bed may reduce the surface for exchange due to obesity, diafragm weakness, occlusive upper airway (as in sleep apnea/hypopnea) or enlarged heart (just some examples).

Basement of Oxygen prescription

To indicate oxygen therapy, physicians base their decision on objective oxygen measurement that may be non-invasive or invasive. The non-invasive procedure is the Pulse Oxymetry that assesses only oxygen through the skin. The invasive procedure implies a blood sample taken from an peripheral artery (with blood coming from the heart after taking oxygen from the lungs). With the measurement of Gases of Arterial Blood it comes also the levels of CO2, as well as HCO3, and pH (among other values).

Once the reduced arterial blood oxygen level is confirmed low (hypoxemia), the election is made. Of course the supplemental oxygen is not administered to correct hypoxemia only. The oxygen therapy is started to decrease the intensity of symptoms and to reduce the workload imposed to the cardiopulmonary system when it is trying to get its best for maintaining oxygen in the best range.

Oxygen Therapy Precautions 

The oxygen therapy has potential complications although it is clearly indicated. It needs to be re-assessed on a regular basis to avoid the complications. When the right level is reached re-assessments are less frequent.

One of the most feared complications of oxygen therapy is depression of ventilatory centers (chemically confused due to the new excessive amount of oxygen supplied). Unfortunately it may appear in patients with more requirement of oxygen like those with elevated CO2 levels. This tends to appear in the most serious cases of hypoxemia: advanced stages of COPD, severe persistent asthma, obstructive sleep apnea.

When the inspired fraction of oxygen is increased over the normal atmospherical level, there’s a described risk of atelectasis (colapse of lung units where the oxygen is taken). Other risk is oxygen toxicity.

Oxygen Toxicity: special chapter

Oxygen toxicity occurs due to its chemical effect on a cellular level. This excessive oxidation leads to death of cells where the impact occurs. Actually, this effect is correlated with time of exposure and what happens is an inflammatory reaction. First with the irritating action may appear the inflammation of the trachea and bronchi with middle chest pain. Then it may be followed by reduced lung space for exchange, rigidity of local tissues, altered balance of oxygen between air and blood, hypoxemia during exercise, and reduced diffusing capacity of gases that leads to CO2 retention and no oxygen is taken.

All this occurs while the injure is being established with lession of capillaries, swelling of the lungs, and cellular destruction.

Amount and Time

As the levels and time of continuous exposure represent a risky situation, the prescription of oxygen is regulated in terms of Liters of Oxygen and hours of exposure. This needs to be clearly communicated to patients with oxygen therapy and care givers to avoid toxicity and imbalance in blood gases that may lead to confusion at respiratory centers, for instance in the Central Nervous System, with CO2 retention and worsening hypoxemia.

Oxygen may be considered a drug as it has been described with biological effects and benefits as well as potential adverse effects and events that imply warnings and precautions.

Long term Oxygen Therapy in COPD

Patients with COPD have necessary long term supplemental oxygen indicated when they have severe COPD and arterial oxygen levels less than 7.3 kPa (55 mm Hg) with or without CO2 retention or if they have arterial oxygen levels in the range of 7.3 kPa to 8 kPa (60 mm Hg) with evidence of pulmonary arterial hypertension or peripheral edema (swelling) and increased red blood cells (also called erithrocytosis, erithrocythemia more appropriately, or polycithemia) as an exaggerated response to chronic reduced arterial oxygen.

A summary

In summary, respiratory conditions may reduce the oxygen in the circulating blood. This implies that some patients may require supplemental oxygen administration. In those patients, oxygen may be required for better performance of a wide range of physical tasks. Oxygen may be injuring if given in high amounts and for extended periods of time. The administration may be required for short or long periods of time and is based on body levels of oxygen.

Previous steps?

This may be a reason to think more about Pulmonary Rehabilitation when considering to adapt to some chronic respiratory conditions.

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