<P> A nasal cannula (NC) is a thin tube with two small nozzles that protrude into the patient's nostrils . It can only comfortably provide oxygen at low flow rates, 2--6 litres per minute (LPM), delivering a concentration of 24--40% . </P> <P> There are also a number of face mask options, such as the simple face mask, often used at between 5 and 8 LPM, with a concentration of oxygen to the patient of between 28% and 50% . This is closely related to the more controlled air - entrainment masks, also known as Venturi masks, which can accurately deliver a predetermined oxygen concentration to the trachea up to 40% . </P> <P> In some instances, a partial rebreathing mask can be used, which is based on a simple mask, but featuring a reservoir bag, which increases the provided oxygen concentration to 40--70% oxygen at 5--15 LPM . </P> <P> Non-rebreather masks draw oxygen from attached reservoir bags, with one - way valves that direct exhaled air out of the mask . When properly fitted and used at flow rates of 8--10 LPM or higher, they deliver close to 100% oxygen . This type of mask is indicated for acute medical emergencies . </P>

What is the purpose and method of oxygen administration