Many biochemical reactions in the body depend on oxygen utilization. Supply of oxygen to the tissues depends on many factors like ventilation, diffusion across alveolar-capillary membrane, hemoglobin, cardiac output, and tissue perfusion. Oxygen therapy is required for respiratory failure in many conditions like severe asthma, chronic bronchitis, pneumonia, and myocardial infarction, etc. Oxygen therapy is the administration of oxygen as a therapeutic modality. Oxygen therapy benefits the patient by increasing the supply of oxygen to the lungs and thereby increasing the availability of oxygen to the body tissues. Appropriate levels of oxygen are vital to support cell respiration. High blood and tissue levels of oxygen can be helpful or damaging, depending on circumstances. Hyperbaric oxygen therapy is the use of high levels of oxygen for treatment of specific diseases. High levels of oxygen given to infant's cause's blindness by promoting overgrowth of new blood vessels in the eye obstructing sight. This is Retinopathy of prematurity (ROP). Administration of high levels of oxygen in patients with severe emphysema and high blood carbon dioxide reduces respiratory drive, which can precipitate respiratory failure and death.

Respiratory system

The respiratory system is concerned with the delivery of an adequate amount of oxygen to and elimination of a corresponding amount of carbon dioxide from the cells of the body and maintenance of normal acid-base balance in the body. Adequate supply of oxygen and elimination of carbon dioxide from various tissues of the body depends on the optimal functioning of various parts of the respiratory system like chest wall and respiratory muscles, airways and lungs, CNS (including medullary respiratory centres), spinal cord and endocrine system. A disorder in any portion of these systems can lead to respiratory failure.

Respiratory failure

During respiratory failure, there is an inability to keep the arterial blood gases at normal level. Respiratory failure may be acute or chronic. Acute respiratory failure develops suddenly or slowly if lungs are already diseased; while chronic respiratory failure develops slowly due to underlying lung disease. Respiratory failure may occur even if lungs are normal as in diseases of nervous system, chest wall, or upper airways. Inadequate gas exchange is associated with hypoxaemia with or without hypercarbia.

(Type-1 respiratory failure or lung failure), while inadequate ventilation leads to hypoxaemia with hypercarbia (Type-2 or ventilatory failure). Type- 1 respiratory failure occurs when there is disease of peripheral gas exchanging parts of body and type-2 in COPD, bronchial asthma, neuromuscular disease, and chest wall disorders.

Management

The aims of therapy in respiratory failure are to achieve and maintain adequate gas exchange and reversal of the precipitating process that led to the failure. In type-1 respiratory failure, high concentration of oxygen is given to correct hypoxaemia. At the outset it should be determined whether the hypoxaemia can be relieved by oxygen therapy alone or it needs oxygen and ventilatory intervention. The decision is made on the presence or absence of hypercapnia and of lung disease. In type-2 respiratory failure with previous normal lungs, there is inadequate alveolar ventilation and in these patients ventilatory assistance is needed. In patients with previous lung disease as in acute exacerbation of COPD, controlled oxygen therapy is needed. Mechanical ventilation should be avoided in patients with COPD as the weaning from the ventilator is very difficult.

Hypoxia and hypoxaemia

Hypoxia is lack of oxygen at the tissue level while hypoxaemia implies a low arterial oxygen tension below the normal expected value (85-100 mmHg).

Acute severe bronchial asthma

Patients with acute severe asthma or status asthmaticus have severe air ways obstruction and inflammation. They are generally hypoxaemic. Hypoxaemia is corrected by giving oxygen via nasal cannula or face mask at a flow rate of 4-6 L/min to achieve FiO2 of 35-40%. Flow rate may be adjusted to maintain PaO2 of about 80 mmHg or more. The risk of hypercarbia and CO2 narcosis is more in COPD rather than acute severe asthma and in such cases assisted ventilation is required. Administration of sedatives and tranquilizers must be avoided. Sedatives may precipitate the CO2 retention not only in patients with COPD but also in asthma.

Severe pneumonia

In severe acute viral or bacterial pneumonias, there may be hypoxaemia and respiratory failure. Oxygen is given at a flow rate of 4-6 L/min to achieve PaO2 above 60 mmHg. Bronchial hygiene and treatment with antibiotics and other drugs is meanwhile continued.

Interstitial lung disease

Patients may have respiratory failure due to fulminant onset or because of intercurrent infection. The lungs are stiff and compliance is low. As these patients need oxygen for prolonged periods, one should wean oxygen to FiO2 of about 40% as early as possible. Some patients may become dysphonic even after mild exertion and such cases benefit from oxygen administration before and after physical activity.

Administration

Various devices are used for administration of oxygen.

1.

The nasal cannula (NC) is a thin tube with two small nozzles that protrude into the patients nostrils. It can only provide oxygen at low flow rates, 2-6 litres per minute (LPM), delivering a concentration of 28-44%.

2.

The simple face mask (SFM) is a basic mask used for non-life-threatening conditions but which may progress in time, such as chest pain, dizziness, and minor hemorrhages. It is often set to deliver oxygen between 6-10 LPM.

3.

The non-rebreather mask (NRB) is utilized for patients who require high-flow oxygen, but do not require breathing assistance. It has an attached reservoir bag where oxygen fills in between breaths, and a valve that largely prevents the inhalation of room or exhaled air.

4.

The bag-valve-mask (BVM) is used for patients in critical condition who are either breathing extremely inefficiently, or not breathing at all. An oxygen reservoir bag is attached to a central cylindrical bag, attached to a valved mask that administers almost 100% concentration oxygen at 8-15 lpm.

5.

The anaesthetic machine is a machine used during anesthesia that allows a variable amount of oxygen to be delivered, along with other gases including air, nitrous oxide and inhalational anaesthetics.

6.

Aviator type and other specialized tight fitting oxygen masks are used in hyperbaric oxygen chambers and to provide oxygen to carbon monoxide victims.

Dangers of oxygen therapy

There are three types of risks associated with oxygen use.

1. Physical risks

Oxygen being combustible, fire hazard and tank explosion is always there. This is more with high concentration of oxygen, use of pressure chambers, and in smokers. Catheters and masks can cause injury to the nose and mouth. Dry and non-humidified gas can cause dryness and crusting.

2. Functional risks

Patients who have lost sensitivity to CO2 and are upon the hypoxic drive are in danger of ventilatory depression as seen in patients of COPD. Hypoventilation can lead to hypercapnia and CO2 narcosis although the risk is small with low flow oxygen therapy.

3. Cytotoxic damage

COPD patients on long term oxygen therapy, on autopsy, show proliferative and fibrotic changes in their lungs. In acute conditions, most of the structural damage occurs from high FiO2 as the oxygen can lead to the release of various reactive species which attack the DNA, lipids, and SH-containing proteins.

What conditions or diseases can be helped with oxygen therapy?

Cancer. Oxygen therapies have great potential in the treatment of cancer. As early as 1931 Dr. Otto Warburg won the Nobel Prize in his work of what causes cells to become cancerous. "Cancer has only one prime cause. The prime cause of cancer is the replacement of normal oxygen respiration of body cells by an anaerobic (lacking in oxygen) cell respiration." It is well known that cancer cells thrive under conditions of low oxygen and high acidity.

Heart conditions. The heart goes into spasm largely due to lack of oxygen. The better the breathing is the more oxygen exists and less the heart has to work.

Bacterial diseases. Ozone is able to destroy many kinds of bacteria. It produces peroxides within the body, which destroys the cell membrane of bacteria but does not affect healthy cells. Scientific experiments have shown that E. coli is completely destroyed after one minute of being exposed to an ozone solution. Similar experiments have shown reduction in staphylococcus, streptococci, and mycobacterium tuberculosis. Because many strains of bacteria have recently been shown to be resistant to antibiotics, oxygen therapy may offer an effective alternative.

Viral diseases. Antibiotics are not effective in viral infections but. Oxygen therapies have proved successful. Some of the diseases caused by viruses are flu, mumps, measles, polio, herpes, AIDS, hepatitis. Ozone can destroy the protein coat of the virus cell wall and once inside can disrupt its DNA. Studies have shown ozone to inactivate 97 to 100 percent of the HIV virus.

Parasitic infections. Studies of the effective use of ozone and hydrogen peroxide destroying parasites have been very successful. Malaria parasites were killed with even slight concentrations of hydrogen peroxide in animal and laboratory studies. In a study of Giardia lamblia, a parasite that can infest the intestinal tract and cause severe symptoms of diarrhea, nausea, and cramps, patients were given either ozonated water or ozonated oil. The symptom reduction was very a successful 97.5% for each group.