Nasal Cannula and Venturi Mask

Overview

There are several ways of classifying oxygen delivery systems : 

• Low flow (nasal cannula, Hudson mask) 
• Fixed performance (Venturi mask) 
• Devices with an oxygen reservoir (non-rebreather mask) 
• High flow (high flow nasal oxygen) 

Below are some of the devices we will cover in this week’s learning along with their associated FiO₂: 

Nasal Cannula and Venturi Mask

Dr Keith Ip (Clinical Teaching Fellow)

Nasal Cannula 

A nasal cannula is a low-flow, variable performance device and achieves a FiO₂ or inspired oxygen concentration of 0.24-0.28. They are widely used throughout the hospital. 

It has several advantages. It is well tolerated, and the patient can eat and drink while having the cannula in place. 

The disadvantages are that they are low flow and thus only useful in patients who are mildly hypoxic, as the flow will poorly match the PIFR in respiratory distress. Not only that, it can dry the secretions and mucosa of the nasal cavity and cause nasal septal erosion (particularly with prolonged use). Lastly, as the oxygen is delivered nasally, it is contraindicated in those with a nasal obstruction. 

An example of a nasal cannula in use is shown below:

Source: Image From: https://www.pexels.com/photo/a-bald-man-with-nasal-cannula-6010880/ By : Tima Miroshnichenko-6010880

Venturi 

The Venturi mask is a fixed-performance oxygen delivery device. It is also known as a high air flow oxygen enrichment (HAFOE) mask. 

It achieves a constant FiO₂ by combining a high gas delivery rate with a moderately large mask reservoir. The Venturi masks make use of the Bernoulli principle to entrain a fixed amount of air. The final FiO₂ will depend on the flow going into the mask and the size of the nozzle which will affect the amount of entrained air. 

Different masks have different colour codes and require different flow rates of oxygen.  

The Venturi system is advantageous as it provides a fixed concentration of inspired oxygen. This is useful in pathological processes such as COPD, when careful titration of oxygen is important. Overzealous administration of oxygen may result in worsening of respiratory failure in susceptible patients who are dependent on their ‘hypoxic drive.’ This can worsen carbon dioxide retention leading to an impairment of consciousness. (Remember your learning of Type 2 Respiratory Failure in Week 2: The Pump?)

The disadvantages are, that as it is a mask, it covers the nose and mouth and impairs eating and drinking. It also poorly matches PIFR in patients in respiratory distress. 

Below is an image of the Venturi Mask set-up along with some of the other mask nozzles available to create the desired oxygen concentration. Note how the nozzles have an indication of the oxygen flow required to create the required concentration. 

Source: Images taken by Dr Keith Ip

Click next to move on to Hudson Masks and Non-Rebreather Masks