Oxygen and COVID-19: what you need to know
Not every patient with COVID-19 who is admitted to hospital needs to be put on a ventilator. Other options are available.
According to the World Health Organization, while most people with COVID-19 develop only mild or uncomplicated illness, around 14% develop severe disease that requires hospitalisation and oxygen support, and 5% require admission to an intensive care unit.
Dr Emmanuel Taban, a pulmonologist at Mediclinic Midstream, says 80% of patients with COVID-19 admitted to hospital don’t need to be put on life support (a ventilator). ‘This is because we can correct their oxygen by giving it to them in a different way, such as a nasal cannula – a small tube that fits into each nostril – or via a face mask. This method has a low flow rate and is much more accessible and less invasive than a ventilator. Most patients with COVID-19 can be managed with oxygen, anticoagulation therapy (drugs that prevent blood clots), and by placing them in the prone position (lying flat on their stomach). Placing patients in the prone position early can prevent the need for a ventilator and shorten the length of ICU stay.’
Dr Taban adds that 17% of patients admitted to Mediclinic Midstream ICU currently require mechanical ventilation.
‘Most patients with COVID-19 are first put on oxygen (face mask or rebreather mask) and if they don’t cope, we then put them on a high-flow oxygen device. We only consider intubation if the patient is showing signs of respiratory failure as evidenced by: their oxygen saturations dropping below 90%; if they’re breathing too fast and getting tired while on oxygen; or they’re confused. In some patients we can use a non-invasive form of ventilation that doesn’t require insertion of a tube through the mouth or nose.’
Low-flow oxygen delivery systems provide lower oxygen flow than the actual inspiratory flow of the patient. When the patient breathes, the oxygen is diluted with room air, and the degree of dilution depends on the inspiratory flows. They include:
This is the most common oxygen delivery system, used for patients with mild low oxygen in the body. It delivers oxygen through the nose and can be set to deliver between one and six litres per minute. Nasal cannula are commonly used in domiciliary oxygen devices such as oxygen concentrators. Problems experienced when using a nasal cannula include dry airways.
Simple face mask
A simple face mask can be set to deliver between five and 10 litres per minute and is indicated when the patient requires a moderate amount of oxygen. It fits over the mouth and nose and has side exhalation ports through which the patient’s exhaled carbon dioxide escapes. Humidified air may be added if the oxygen concentration is causing dry airways. Eating and drinking can be difficult with the mask on – and it may feel claustrophobic for some patients.
A non-rebreather mask is a low-flow device that helps deliver oxygen in emergency situations. It consists of a face mask connected to a reservoir bag filled with a high concentration of oxygen. The reservoir bag is connected to an oxygen tank. The mask covers the patient’s nose and mouth and is useful in a severe oxygen shortage.
Unlike the non-rebreather mask, there is no one-way valve between the rebreather mask and the reservoir bag. A rebreather mask saves one third of a person's exhaled air in the reservoir bag, while the rest of the air gets out via side ports covered with a one-way valve. This allows the patient to rebreathe some of the carbon dioxide, which acts as a way to stimulate breathing.
This type of face mask allows exact measurement of the oxygen delivered to a patient by regulating the flow of oxygen. The mask provides oxygen at flow rates that are lower than the patient’s inspiratory demands so that when the patient's inspiratory flow exceeds the gas flow rate from the mask, room air is entrained.
High-flow oxygen delivery systems, such as high-flow nasal cannula, provide higher oxygen flows. The inspiratory oxygen fraction is stable and is not affected by the patient’s type of breathing.
High-flow nasal cannula (HFNC)
The use of heated and humidified oxygen administered through an HFNC has become increasingly popular in treating patients of all ages with acute respiratory failure. An HFNC is more than just a standard nasal cannula cranked up to extremely high flow rates; it takes gas and can heat it to 37°C with a 100% relative humidity and deliver 0.21 to 1.00% fi02 at flow rates of up to 60 litres per minute. The flow rate and amount of air the patient breathes can be independently titrated (measured and adjusted) based on the patient’s flow and amount of oxygen required. The air on the high-flow nasal cannula is heated to body temperature, as compared to the one on the low-flow system, where the body needs to warm it up to body temperature.