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Oxygen therapy

Revision as of 19:46, 27 October 2024 by Nikolas (talk | contribs) (Created page with "<section begin="A&IC" />'''Oxygen therapy''', also called '''oxygen supplementation''', refers to administration of oxygen to the patient. The most common use case is hypoxaemia (type 1 respiratory failure) for any cause, but it is also indicated in CO intoxication, for example. Multiple devices can be used to administer oxygen, the most commonly used being the nasal cannula. Both the flow (in litres per minute) of the gas delivered and the fraction of inspi...")
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Oxygen therapy, also called oxygen supplementation, refers to administration of oxygen to the patient. The most common use case is hypoxaemia (type 1 respiratory failure) for any cause, but it is also indicated in CO intoxication, for example. Multiple devices can be used to administer oxygen, the most commonly used being the nasal cannula. Both the flow (in litres per minute) of the gas delivered and the fraction of inspired oxygen (FiO2) can be adjusted, depending on the device. The FiO2 is the fraction of oxygen gas in the inhaled gas. In room air, the FiO2 is 21%. The devices usually deliver 100% pure oxygen but because the patient also breathes room air, the actual inspired gas is not pure oxygen (100% FiO2).

Excessive oxygen therapy is harmful. For this reason, the oxygen delivered should be titrated to a specific SpO2 range. For healthy people without pulmonary disease, the normal range to aim for is SpO2 94-98%. For people with pulmonary disease, especially COPD or asthma, the range to aim for is 88-92%, to reduce the risk of CO2 narcosis. '

Normal values:

  • O2 pressure in artery (PaO2) ~ 100 mmHg
  • O2 pressure in vein (PvO2) ~ 40 mmHg
  • Alveolo-arterial gradient (PA-aO2) < 20 mmHg

Variable performance oxygen therapy devices

The oxygen delivery of these devices depends on the patient’s own breathing, more specifically their peak inhalatory flow. These devices enrich the inspired air with oxygen during inspiration. There are three types, the nasal cannula, simple face mask, and non-rebreather mask.

Nasal cannula

The nasal cannula lies in the patient's nose. They’re comfortable and cheap, but give a limited amount of oxygen and can dry out the nasal mucosa. By increasing the flow rate of oxygen up to maximum 6 L it can provide a maximum FiO2 of approximately 30%.

Simple face mask

The simple face mask, also called the "50% face mask" can provide an FiO2 of 50% at the maximum. The flow can be adjusted between 5 – 10 L/min of oxygen. If a flow rate og < 5 L/min is used, CO2 may accumulate in the dead space of the mask, causing CO2 retention. The high flow rate can also dry out the oral and nasal mucosa.

Non-rebreather mask

The non-rebreater mask, also called the "100% face mask" could provide an FiO2 of up to 100% in theory, but actually closer to maximum 80% in practice. The flow can be adjusted between 10 – 15 L/min of oxygen.

This type of mask has a reservoir bag which fills with pure oxygen gas between each inhalation, allowing the patient to theoretically breathe 100% pure oxygen (hence the name). A high flow rate is required to fill the reservoir between each breath. The bag has a one-way valve which prevents CO2 from entering the bag and causing CO2 trapping. This type of face mask does not humidify the air either, which is a disadvantage.

Fixed performance oxygen therapy devices

These devices deliver a fixed FiO2 and their efficacy therefore do not depend on the patient’s breathing. More specifically, they provide a higher gas flow than the patient's peak inspiratory flow rate, which is what makes them supply a constant amount of oxygen independent of the patients respiration. They can provide an O2 flow rate of 30 – 60 L/min and for some devices the FiO2 can be adjusted as well. These include the venturi mask and high flow oxygen therapy (HFOT).

These are indicated when a nasal cannula or face mask cannot provide enough oxygen, or when the amount of oxygen should be constant and independent of the patients inspiratory work. This may be useful for COPD, for example.

High flow oxygen therapy

High flow oxygen therapy (HFOT), usually with a high flow nasal cannula (HFNC) and of which Optiflow® is the most commonly known manufacturer, is commonly used. It provides a high flow of oxygen through a nasal cannula or a face mask. The air is humidified and heated by the machine. It can reduce the work of breathing and provide some degree of positive end-expiratory pressure (PEEP), which can keep more alveoli open. It can even wash out the dead space of the airways, decreasing CO2 retention. The oxygen flow can be adjusted between 20-60 L/min and the FiO2 of the inspired gas can be adjusted from 21 - 100%. HFOT is relatively comfortable and the patient can drink and eat.

Venturi mask

A venturi mask is a special type of face mask which uses a special valve that allows the delivery of an exact FiO2. The valve must be exchanged depending on which FiO2 one desires, and the flow rate should be delivered accordingly. For example, if one desires an FiO2 of 60%, 15 L/min should be given and the valve marked "60% 15 L/min" should be used. 60% is the maximum FiO2 a venturi mask can deliver, and 24% is the minimum.