Oxygen therapy may be administered in several ways, using several different types of devices. Oxygen therapy may be needed on an emergency basis in an acute setting or on a long-term basis in the home management of chronic illness. Increasing the amount of oxygen supplied to the lungs can benefit the patient by making more oxygen available to the various bodily tissues.
In most oxygen delivery devices, the oxygen is first passed through a pressure regulator, which controls the pressure of the oxygen as it moves from an oxygen cylinder (or other source) to a lower pressure. Once at this lower pressure, the flow of oxygen is controlled by a flowmeter and measured in litres per minute (lpm). Typically, the flowmeter range for the delivery of medical oxygen is between 0 and 15 lpm, although the rate can be as high as 25 lpm in some units. Many flowmeters are based on a design referred to as the “thorpe tube” style that can be set to “flush,” which can be useful in the emergency setting.
The atmospheric content of oxygen within room air is only 21%. Although this amount is adequate for healthy individuals, those with certain diseases can benefit from an increased oxygen fraction in the gas they breathe, which will increase the oxygen content of their blood. For most of these diseases, increasing the oxygen fraction to around 30% to 35% is enough to make a significant difference to the blood oxygen level. This supplementary level of oxygen can be achieved using a nasal cannula, a thin tube with an individual nozzle for each nostril. This can provide oxygen at a low flow rate of 0.25 to 6.00 lpm, to achieve an oxygen level of 24% to 40%.
For oxygen at greater concentrations, various face masks can be used. This includes the simple face mask, which can deliver oxygen at 5 to 15 lpm flow, to achieve an oxygen level between 28% and 50%; the Venturi mask which can provide oxygen to the trachea at concentrations of up to 40%; and a partial re-breathing mask which is similar to a simple mask but includes a reservoir bag and can deliver 40% to 70% oxygen at 5 to 15 lpm.
For patients who require 100% oxygen, several devices are available, the most common of which is the non-breather mask or reservoir mask. This is based on a similar design to the re-breathing mask but a number of valves line the device to stop air that has been exhaled returning to the bag. This device achieves a minimum flow of 10 lpm and the fraction of inspired oxygen achieved is between 60% and 80%. Air or oxygen that has been warmed or humidified can also be administered via nasal cannula so that the patient can still talk, eat and drink while they undergo therapy.
For patients who are unable to breathe independently, positive pressure may be needed to force air into their lungs. Systems used to deliver this therapy vary in complexity but essentially, they provide artificial respiration.
Reviewed by Sally Robertson, BSc