Oxygen Therapy: Everything You Need to Know

Oxygen therapy is used to immediately or long-term address certain conditions that prevent oxygen from reaching the patient's tissues.

Written and verified by el biólogo Samuel Antonio Sánchez Amador.

Last update: 16 December, 2022

The term oxygen therapy refers to any technique that uses the administration of oxygen (O2) for therapeutic purposes. The purpose of this approach is to provide the patient with gas in concentrations higher than those in the environment. It’s used for hypoxic conditions, in which the patient isn’t able to transport enough quantity to their tissues.

In this scenario, oxygen’s considered a drug, as it has precise indications, must be used in protocolized doses and intervals, reports adverse effects, and requires clinical and laboratory criteria. In the short and long term, the goals of oxygen therapy are to improve oxygenation, decrease or prevent hypoxemia, and prevent or correct hypoxia.

Outside the medical field, oxygen therapy also finds its place in the homes of the chronically ill, in the form of chronic home oxygen therapy. If you want to know more about this set of techniques, keep reading.

What is oxygen therapy?

Oxygen therapy is a therapeutic measure that consists of administering oxygen at concentrations higher than ambient. As indicated by the Universidad Clínica Navarra, the objective of this approach is to maintain adequate oxygen pressure.

Under normal environmental conditions, air contains 21% oxygen. In normobaric oxygen therapy, oxygen—actually dioxygen—is administered at a concentration of 21 to 100% using masks, nasal cannulas, and other devices. On the other hand, in the hyperbaric variant, 100% O2 is supplied with special devices, in a hyperbaric chamber.

According to medical documents, the need for oxygen therapy in the patient is determined based on the arterial partial pressure of oxygen (PaO2), which in turn correlates with the low oxygen saturation in the hemoglobin of red blood cells. This set of techniques is prescribed when the PaO2 in arterial blood is less than 60 millimeters of mercury (mm Hg) or the hemoglobin saturation in peripheral blood is less than 93-95%.

Glossary of terms

Before continuing with the types and uses of oxygen therapy, we want to introduce some medical terms that aren’t well known among the general population:

• Fraction of inspired oxygen (FiO2): The percentage of O2 dissolved in inspired air, expressed in concentration, and measured in percentage. In ambient air, the standard FiO2 is 21%.
• PaO2: Arterial oxygen pressure. Normal results range from 75 to 100 mm Hg. This value can only be analyzed in the blood that runs through the arteries.
• PaCO2: The blood pressure of carbon dioxide. Normal results range from 38 to 42 mm Hg.
• Hypoxia: A decreased supply of O2 to the patient’s tissues. Hypoxia can be hypoxemic, circulatory, anemic, and histotoxic.
• Hypoxemia: A decrease in dissolved O2 in arterial blood. In other words, it’s a decrease in PaO2 below 60 mm Hg. In turn, this value corresponds to an O2 saturation of 90%.
• Flow: The amount of oxygen delivered by a certain mechanism. It’s measured in liters per minute (bpm).
• Ventilation/perfusion ratio (V/Q ratio): This term refers to the relationship between the ventilation of the alveoli and the transportation of blood by their arterioles. Normal values are 4.2 liters per minute (L/min) for V and 4-5 L/min for Q.
• Respiratory failure: A condition in which the respiratory system fails to transport enough oxygen to the blood or when the lungs don’t release a certain amount of carbon dioxide from it. At this stage, PaO2 is less than 60 mm Hg (hypoxemia) and PaCO2 is greater than 50 mm Hg (hypercapnia).

What are the uses of oxygen therapy?

Oxygen therapy is prescribed in cases of respiratory failure, that is, when PaO2 is less than 60 mm Hg. In any case, there’s no justification for waiting to measure these variables to start treatment.

A bluish tone of the lips and mucous membranes (central cyanosis) indicates a PaO2 of less than 50 mm Hg and a hemoglobin saturation of less than 85%. If the patient displays this clinical sign, it’s more than enough reason to start oxygen therapy.

Hypoxia in the cellular environment can be due to many conditions: Decreased O2 in the inspired air, altered alveolar ventilation, imbalances in the ventilation/perfusion ratio, impaired gas transfer, decreased cardiac output, shock, or hypovolemia. Here are some of the uses of oxygen therapy based on these conditions.

Atmospheric hypoxia

Up to about 12,000 meters above sea level, the atmospheric oxygen concentration remains at 21%. In any case, as the altitude increases, the atmospheric pressure decreases and therefore, the O2 concentration. Transportable oxygen therapy devices can provide oxygen in these situations.

Hypoxia due to hypoventilation

Hypoventilation is very shallow and slow breathing, which always causes an increase in PaCO2 and a decrease in PaO2. In these situations, oxygen therapy can increase the oxygen available to the patient up to 5 times. In any case, as indicated by the Anales de Pediatría website, the ultimate goal is to restore the normal ventilatory mechanism.

Chronic diseases

Oxygen therapy is very useful in patients with chronic obstructive pulmonary disease (COPD). This condition is characterized by progressive and irreversible airway obstruction. Since lung damage can’t be resolved, the patient requires lifelong oxygen therapy.

Another chronic condition in which long-term oxygen therapy is helpful is sleep apnea. In this condition, breathing repeatedly stops and starts again during the night, which can seriously endanger the patient’s life. Portable oxygen concentrators are a tool that allows people with apnea to breathe easier.

Acute illnesses

Oxygen therapy is widely used in the medical field, either in hospital wards or in emergency situations. In the pre-hospital patient, hypoxia usually occurs from severe trauma, heavy bleeding, anaphylactic shock, seizures, and hypothermia.

It’s also used in patients with abnormally low oxygen levels, derived from another acute condition. When the treatment is finished, the patient should be able to breathe normally again.

Devices for oxygen therapy

The devices used in these approaches are divided into 2 categories: Low-flow and high-flow. We’ll explore each of the variants below.

Low-flow devices

As professional documents indicate, low-flow devices deliver less than 40 liters of gas per minute (lpm). They don’t provide all the inspired air to the patient, and therefore, the supplied gas mixes with the ambient gas.

We’ll tell you about some of the most common low-flow devices to carry out oxygen therapy in the medical field:

• Nasopharyngeal tube (1 to 6 bpm and 24-40% 02): This is a catheter that’s inserted from a nostril to the oropharynx. This mechanism allows the patient to move, talk and eat during treatment, so it’s recommended in long-term hospital stays.
• Nasal cannula (1 to 6 bpm t 24-40% O2): This is one of the most common variants. These are 2 nasal glasses that are placed in the holes and connected by a tube to the O2 source and a humidifier. It’s a very comfortable option, but its effectiveness depends on the patient’s respiratory capacity and doesn’t allow the FiO2 to be known.
• Simple face mask (from 5 to 6 bpm and 40% O2): This device lacks reservoirs and complex mechanisms and only has 2 lateral orifices that act as a place for gas exchange between the patient and the environment. It allows the release of higher O2 concentrations than the previous options, but prevents expectoration and makes speech difficult.
• Mask with partial recirculation and a reservoir bag (5 to 8 bpm and 40-60% O2): A mask with 2 lateralized holes that act as vents. In addition, by including a reservoir bag in the inlet circuit, O2 concentrations of up to 60% can be achieved.

High-flow devices

High-flow devices deliver all of the air the patient inspires. There are no mixtures with ambient gases and FiO2 is independent of the ventilatory pattern, remaining constant over time.

An example is a Venturi-type mask. It’s a system that allows the constant and exact administration of the necessary oxygen concentration, with FiO2 values of 24 to 60%, independent of the patient’s ventilatory pattern and the environment.

Other devices

In hyperbaric oxygen therapy, 100% oxygen is administered to the patient, at 2 or 3 times the atmospheric pressure at sea level. It’s done inside a hyperbaric chamber. The aim is to increase the partial pressure of O2 in the tissues, as it reaches a figure much higher than expected, breathing pure oxygen under normobaric conditions.

The dangers of oxygen therapy

Oxygen therapy is generally well tolerated but as with all treatment, there are a number of considerations and threats that must be taken into account. As studies have pointed out, there are cases in which oxygen therapy isn’t only discouraged, but can also have harmful effects.

Here are some of the possible side effects:

• Toxicity: Breathing very high concentrations of oxygen at atmospheric pressure causes serious lung damage if exposure is long (24 to 48 hours). A mixture with an FiO2 greater than 60% can cause damage to the cells of the tracheobronchial tree and alveoli after 24 hours of exposure.
• CO2 retention: In some patients with defective ventilatory mechanisms, oxygen therapy can depress responses to hypoxia, and therefore, cause the storage of CO2 in the blood (hypercapnia). If this condition isn’t taken into account, the patient can suffer respiratory acidosis with serious consequences.
• Accidents: As with any type of machinery, accidents can occur when operating these devices. In any case, hospital professionals can avoid accidents through proper preparation. It’s important to remember that oxygen at high concentrations is a major fuel for a fire.
• Dryness of the mucous membranes and irritation: A constant flow of gases can irritate and dry the mucous membranes of the upper respiratory tract, which must be moist. To avoid this, oxygen should be adequately humidified before it reaches the patient’s respiratory system.

Furthermore, oxygen therapy isn’t recommended in people with pulmonary fibrosis resulting from treatment with bleomycin–an anticancer drug–or in the pediatric population for a long time. In children who are born prematurely, these approaches can cause retinopathy of prematurity (ROP), which is blindness due to the overgrowth of ocular blood capillaries.

Oxygen therapy is useful, but not without precautions

In general, oxygen therapy is very well tolerated in the adult population, whether administered in the short or long term. It prevents death from hypoxia/hypoxemia and hypercapnia, so it’s usually the first medical approach taken into account when a patient arrives at the emergency room with some type of respiratory failure or signs of cyanosis.

This supportive treatment is useful in keeping the person alive, but looking for the cause of the hypoxia and finding a solution are always necessary once the vital signs stabilize. Without a doubt, this set of techniques saves thousands of people a year.