Categories of Oxygen Therapy: Low-Flow vs High-Flow Systems
Apr 20, 2023
Oxygen therapy is a treatment where the patient is provided with extra oxygen to breathe. Also called supplemental oxygen, it is provided to people whose bodies are incapable of taking in the required amount of oxygen.
Oxygen therapy is an important topic for Anesthesia. Read this blog post till the end and ace your NEET PG preparation.
Categories of Oxygen Therapy
Depending on this, there are two categories of oxygen therapy.
Low-flowoxygen therapy
High-flowoxygen therapy
These therapies are being given because the patient is not able to maintain their saturation in the natural atmosphere. Oxygen therapy is therefore given to the patient if their O2 saturation is low due to any kind of illness or injury, be it at a cellular or a bigger level. It is administered at a concentration of pressure greater than that found in the atmosphere.
Low Flow System Vs High Flow System
Low flow system/ Variable performance
High flow system/ Fixed performance
Contribute partially to inspired gases FiO2 is dependent of TV, RR
Delivers Specific and constant % of O2
Eg.
Nasal Cannula
Simple mask / Hudson mask
Non rebreakable mask
Partial rebreaking Mask
Eg.
Venturi mask
High flow nasal cannula
Low Flow System
Nasal Cannula
Used in low to medium concentration of O2 (22-44%)
Amount delivered-
1 l/min – 24%
2 l/min -28%
3 l/min – 32%
4 l/min – 36%
5 l/min – 40%
6 l/min – 44%
This device is used for providing preliminary oxygen to the patient. These can deliver oxygen with a concentration of 22 to 44%.
When these are attached to the flow metre which is connected to the central pipeline supply of an ICU or cylinders and is turned on at 1L per minute, these deliver oxygen of about 24%. Atmospheric oxygen is from 20 to 21%. When the concentration of oxygen is increased, it leads to an increase in the concentration of FiO2. This device can only deliver up to 6L per minute. Every litre corresponds to its subsequent FiO2. This device is not beneficial for a capacity of > 6 litres.
Advantages
Patients are able to talk and eat with O2 support when using a nasal cannula. A nasal cannula can be used in home settings.
Disadvantages
It may cause irritation of nasal and pharyngeal mucosa. If the flow is given for more than 6L, the FiO2 may vary.
Face Mask
It is a simple O2 mask. There are partial rebreather masks and non rebreather masks. These face masks are used when the oxygen requirement of the patient increases. These have a flow rate of 6 to 10 litres per minute. These supply 35 to 60% O2.
Advantages
An increased delivery of oxygen can be made but for a shorter duration due to damage to the skin surface from the mask.
Disadvantages
Tight seals are required, which can make many patients feel claustrophobic. There lies a potential for skin breaching. It can be uncomfortable for the patient while eating or talking.
Partial Rebreathing Mask
This consists of a mask and a reservoir bag. The bag should be inflated all the time during inspiration and expiration to avoid any rebreathing. The flow rate is from 6 to 8 L per minute, with the FiO2 being at 80%.
Advantage
The patient can inhale room air through the opening of the oxygen supply is cut.
Disadvantage
This device has a tight seal which can be uncomfortable for patients.
Non-Breathing Mask
These are instruments through which oxygen with a concentration of 95 to 100% (0.9 -1% FiO2) is delivered. This oxygen percentage is the maximum among all instruments. The flow rate is 10 to 15 L/m in this case.
Advantage
These instruments deliver the highest possible oxygen concentration for patients suffering from severe hypoxemia.
Disadvantage
This instrument is not good for long-term oxygen use. It can cause suffocation. It is expensive.
Fixed-Performance Devices
If the patient’s tidal volume or respiratory rate is not normal, fixed performance devices provide the accurate volume of oxygen to the patient.
Venturi Mask
Oxygen is delivered at a concentration of 24 to 60% with the help of a Venturi Mask. The flow rate is 4 to 15 litres per minute. A constant amount is delivered through this mask which is not dependent on the respiratory rate and the tidal volume of the patient. Colour coding is done on these masks, according to which they deliver a specific percentage of oxygen to the patient.
Colour Flowrate
Oxygen Concentration
Blue
2L - 24%
White
4L - 28%
Yellow
6L - 35%
Red
8L - 40%
Green
12L - 60%
Advantage
A very precise concentration of oxygen is provided. It does not dry out the mucosa and does not cause irritation.
Disadvantage
It might be uncomfortable. It might cause skin irritation.
High-Flow Nasal Cannula (HFNC)
These have humidifiers, heated tubes, a nasal cannula, and an oxygen blender.
Advantage
There is Peak End Expiratory Pressure (PEEP). At the end of respiration, the alveoli collapse. And in order to avoid a complete collapse, Peak End Expiratory pressure has to be present. There is the delivery of constant FiO2 at 100%. These decrease the anatomical dead space and provide the maximum amount of oxygen possible to the patient.
PEEP (peak end expiratory pressure)
To avoid the collapse of alveoli PEEP is needed in these devices. The patient can inhale the air in the room till the time the oxygen supply is replenished.
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