Recent papers have shown that amongst practicing trainee doctors and nurses there is a lack of knowledge about oxygen therapy devices and their correct use. There are also many false beliefs with the result that many patients on general wards are incorrectly treated. This article cover the main types of device commonly used for delivering oxygen therapy which enable clinicians to comply with guidelines published worldwide. Such as the British thoracic society guidelines and the American Association for respiratory care guideline.
We can now look at how these devices work, when and how they are used, features of the devices and precautions associated with their use. We hope this will increase the level of knowledge in this important discipline.
The devices for delivery of oxygen can be divided into two groups depending on whether they deliver a proportion or all the patient’s ventilator each requirement.
Variable oxygen concentration devices also known as low flow devices deliver oxygen that flows lower than the patient’s inspiratory requirements. So additional room air is also breathed in.
Fixed oxygen concentration devices also known as high flow devices deliver flows that meet the patient’s total inspiratory requirements.
Firstly, let’s look at variable oxygen concentration devices and the various device options that are available.
Nasal cannula are one of the most common ways of delivering oxygen therapy. A nasal cannulae consists of two soft prongs attached to the oxygen supply tubing. First, attach the oxygen tubing to the oxygen flow meter and set the flow rate to the appropriate flow for the patient. The prongs are inserted into the patient’s nares. The tubing is looped over the patient’s ears and the toggle is adjusted to ensure a good fit. Oxygen flows from the cannulae into the patient’s nasopharynx which acts as an anatomic reservoir. Nasal cannulae are available with different prong shapes and a lightweight and generally comfortable. Oxygen can be administered at 6 liters per minute or less and flow rates of 4 liters per minute or less. Do not need to be humidified. Nasal cannulae can also be used at very low flow rates with children and mouth breathers can benefit from this device. Patients are able to eat, drink and speak whilst receiving oxygen therapy. However, the use of a nasal cannulae requires the upper airway to be free of obstruction. Nasal cannula are contraindicated in patients with nasal obstruction. For example, nasal polyps. The concentration of oxygen received by the patient will vary as previously mentioned. However, oxygen flows of 1 to 6 liters per minute will deliver up to 44 percent of oxygen to most adult patients.
There are various sizes available for adults, paediatric and neonates. And a variety of prong shapes are also available to suit varying circumstances. Straight prongs are the original design and these are still the most frequently used in hospitals. Curved prongs are designed to direct the flow of oxygen posteriorly rather than upward towards the frontal sinuses. Flared prongs have an increased diameter towards the tip. This has the effect of slowing down the gas as it enters the nose making it more comfortable for the patient. Curved and flared prongs combine the best features of the two options releasing oxygen more slowly and away from the frontal sinuses.
Nasal cannulae can be surprised with ear guards which can benefit long-term users of nasal cannulae by preventing sores on and around the ears nasal cannulae are also available which allows sampling of exhaled carbon dioxide in non-intubated patients and the inter surgical devices with this feature called sentry nasal cannulae. These devices are suitable for patients undergoing conscious sedation where a spirit or depression needs to be monitored. The Sentry nasal cannula is fitted to the patient in the same manner as a conventional nasal cannulae. A monitoring line is then attached and connected to the capnograph. The Sentry nasal cannulae allows delivery of oxygen through one nasal prong and the sampling of exhaled gas through the other prong. The end tidal co2 values are comparable to those achieved with intubated patients.
Now we can look at medium concentration oxygen masks which provide another option for the delivery of low flow oxygen therapy. These may be used for concentrations higher than those that can be achieved with nasal cannulae or when the nares are unavailable. These masks are available in adult and pediatric sizes.
The arrows demonstrate the manner in which gases are inhaled and exhaled by the patient. The red arrows represent the oxygen delivered to the mask, the orange arrows represent ambient air which is drawn in through the mask vents as the patient inhales and the blue arrows represent exhalation.
The concentration of oxygen received by the patient will vary.
However, as a guideline a flow rate of five to eight liters per minute will deliver concentrations between 35 and 50 percent oxygen to most adult patients.
One end of the oxygen tube is attached to the spigot on the mask and the other to the oxygen flow meter. The flow meter is set to give the prescribed oxygen concentration. The mask is then fitted over the patient’s nose and mouth and the elastic tightened to give a secure and comfortable fit. The elastic historically has been secured over the years. However new generation into surgical eco light oxygen masks can also be secured under the ears to avoid the occurrence of pressure sores. It is important to use a mask which obtains a good seal on the patient’s nose to prevent oxygen entering the eyes. A poorly fitting mask can expose the eye to a high flow of dry oxygen which can result in exposure keratoplasty which then may lead to corneal perforation. Caution must be taken when using these masks to ensure that the flow is at least 5 liters per minute to wash carbon dioxide out of the mask and prevent re breathing. Aspiration of vomitus is also more likely when a mask is in place.
Medium concentration masks such as the inter surgical sentry masks are also available which feature the ability to measure and tidal co2. This is beneficial for patients undergoing conscious sedation where respiratory depression should be monitored. A monitoring line can be attached to the mask with a lower lock connector and the other end is attached to a cap NE graph.
The final variable concentration oxygen mask we are looking at is the high concentration mask also known as the non-rebreathing mask. And is usually used when high concentrations of oxygen are required. For example, with the critically ill or unstable patient. The patient breathes from the mask and the inspiratory valve opens so that oxygen is taken from the reservoir bag. The patient breathes out through the expiratory valve. Ideally the patient does not breathe any room air. However, the fit of the mask and the patient’s breathing pattern will affect the amount of room air entrained and the oxygen concentration delivered. Limitations of the mask fit associated with older mask designs. Meant that high concentration oxygen masks delivered up to 80 percent oxygen with flows set between 10 and 15 liters per minute.
The improved fit achieved with the new generation into Surgical eco light masks minimizes the amount of air that is entrained through the sides of the mask. And hence concentrations approaching 90 percent oxygen can be delivered to the patient where flows are set between 10 and 15 meters per minute.
This improved performance however makes it necessary to include masks safety valves. In the event of the oxygen supply failing and the reservoir bag emptying, the safety valves will open allowing air to enter the mask and the patient is still able to breathe. When using the high concentration oxygen mask, first attach the oxygen tubing to the oxygen flow meter and set the flow rate to 15 liters per minute. Include the inspiratory valve being careful not to damage the valve and allow the reservoir bag to fill. Squeeze the reservoir bag to test the patency of the valve between the reservoir bag and the mask. if the reservoir will not empty, discard the mask, choose another and test again. Refill the reservoir bag and place the mask on the patient’s face obtaining a tight but comfortable fit. Adjust the oxygen flow rate so that the bag deflates by no more than one-third at the end of inspiration. When a mask is in place be aware that aspiration of vomitus is more likely. An additional feature found in some high concentration oxygen masks is the resipe check breathing indicator. Respiratory rate should be recorded in anyone requiring oxygen therapy and yet it is often inaccurately estimated and poorly recorded. The recipe check features a Bow contained in a clear plastic tube which acts as a visual indicator of respiratory rate. The flow of oxygen into the mask pushes the ball to the top of the tube.
The negative pressure generated by the patient’s inspiratory effort pulls the ball to the bottom of the tube giving an instant visual notification of each breath taken.
Now let’s look at the fixed oxygen concentration devices also known as high flow devices. These provide sufficient flow of gas to meet all the patients minute ventilation requirements. Firstly, why would you use a fixed oxygen concentration device? These devices might be more appropriate for patients with chronic lung disease and co2 retention whose ventilation is dependent on hypoxic drive. This is an over emphasized condition where the usual stimulus for respiration which is the maintenance normal co2 levels is lost due to chronically high carbon dioxide levels. Respiration is then driven by hypoxia. If high concentrations of oxygen are given to these patients and their pio2 increases this hypoxic respiratory drive can be lost. Hyperventilation may occur and the co2 will become very high causing coma and possibly death. A high-flow device in which the oxygen concentration can be carefully controlled and guided by blood gas measurements is more appropriate for these patients. The inspired oxygen concentration is determined by the design of the device and not by the patient’s rate and depth of breathing. This is because venturi devices accurately deliver predetermined oxygen concentrations but flows too high enough to meet the inspiratory flow rates of most adult patients. The gas flow to the patient is increased by in training air into the device using the venturi effect. Accurate oxygen concentrations are delivered by the mixing of entrained air and oxygen. Masks are available with interchangeable, color-coded, venturi valves for different oxygen concentrations. For example, 35%. When using a venturi mask, select a venturi valve of the prescribed oxygen concentration and attach it to the mask. Attach one end of the oxygen tubing to the valve spigot and the other end to the oxygen flow meter. Set the flow meter to the flow indicated on the valve. Place the mask over the patient’s nose and mouth to obtain a secure and comfortable fit. It is important to be aware that oxygen requirements above 40% the valve may not generate enough total flow to meet high inspiratory demands.
There is also a widespread misconception that the oxygen concentration varies with the oxygen flow rate. If the oxygen flow rate is increased, the total flow to the patient is increased but the oxygen concentration stays the same. For example, the recommended flow rate for a 35% of venturi valve is 8 liters per minute. This delivers to the patient a flow rate of 45 liters per minute and an oxygen concentration of 35 percent. Increasing the flow rate to 10 liters per minute, increases the total flow to the patient but the oxygen concentration delivered remains at 35 percent. Fixed venturi valves can also be incorporated into oxygen recovery t-piece kits. The most popular is the 40 percent valve. These are used to provide spontaneously breathing intubated patients with supplementary oxygen during transport and in the recovery room. Attach one end of the oxygen tubing to the valve spigot and the other end to the oxygen flow meter and set the flow meter to the flow indicated on the valve. Connect the T-piece to the 15-millimeter connector of the tracheal tube or supraglottic airway device. A disadvantage of fixed concentration venturi valves is that in order to change the concentration delivered to the patient it is necessary to change the valve. This can be overcome by using an adjustable venturi valve. With an adjustable venturi valve, the rotation of the sleeve increases or decreases the size of the air entrainment window. This in turn changes the oxygen concentration. This means that the same valve can deliver a wide range of concentrations. As the valve does not have to be replaced, each time the prescribed oxygen concentration changes. The changes can be made quickly. It also means that different valves do not have to be held in stock by the hospital. The Celente adjustable venturi can be set to concentrations between 26 and 50% and incorporates a twist lock mechanism to prevent inadvertent concentration changes. As with a fixed valve attach one end of the oxygen tubing to the valve spigot and the other end to the oxygen flow meter. To select the desired oxygen concentration, ensure the range selector sleeve is in the appropriate position. If the desired concentration is between 26 and 35 percent then ensure the oxygen range selector is set 26 to 35. If the desired concentration is between 40 and 50%, rotate the oxygen concentration selector to 35% and then pull and rotate the oxygen range selector to select the 40 to 50 range. Select the desired oxygen setting by rotating the oxygen concentration selector. Set the oxygen flow meter to the flow indicated adjacent to the oxygen concentration.
The inter surgical eco light range of masks represent a new development in oxygen therapy devices and address many of the limitations found in earlier designs. The materials used have a significantly lower impact on the environment. Into surgical eco light oxygen masks have a lightweight design incorporating a soft face seal which provides a high level of patient comfort. Mask seal to the contours of different face shapes to maximize delivery of oxygen to the patient and prevent oxygen from entering the eyes. In to surgical eco light oxygen masks have also been designed to address tissue viability requirements by reducing the risk of pressure sores developing.
The final section covers the different types of humidifier that deliver cool humidification. Finkle hunt in clinical practice in respiratory care describe the two most commonly used devices in this category as follows. “a humidifier is a device that adds molecular water to gas whereas a nebulizer produces an aerosol or suspension of particles in gas” bubble humidifiers use the bubble through humidification process to bring dry oxygen gas to ambient levels of humidity. The gas is directed into the water bottle where it is broken up into small bubbles. These gain humidity as they rise to the surface of the water. The absolute humidity of the gas varies with flow rate, water temperature, bottle size and volume of water in the bottle. Bubble humidifiers are most commonly used with low-flow devices such as nasal cannulae and medium concentration oxygen masks. Some models incorporate a pressure relief valve designed to prevent excessive pressures building up in the bottle should the oxygen tubing become occluded operation of the relief valve may also activate an audible warning. Drawing the attention of the user to this problem. The head of the bubble humidifier may also incorporate a universal screw thread. This permits the use of a bottle which can be refilled with sterile water or the use of some prefilled sterile water bottles. The flow meter should be attached to an appropriate oxygen supply. Fill the bottle with sterile water using an aseptic technique and fit to the humidifier head or fit a prefilled sterile water bottle. The humidifier should then be attached to the flow meter. To test the pressure relief valve, adjust the flow meter to four liters per minute and occlude the outlet. Verify that the relief valve operates within five seconds. Reset the oxygen flow meter to the appropriate flow for the patient. Attach the oxygen tubing to the bubble humidifier and the delivery device and fit to the patient.
The other method of delivering cold humidification is by using a humidifier nebulizer. Humidifier nebulizers use the venturi principle to create a low-pressure area at the end of a tube. The other end of the tube extends into a bottle containing sterile water. Water is drawn up the tube and is broken into an aerosol of small droplets by the oxygen stream. This same low-pressure area also entrained air from the atmosphere to dilute the oxygen to the desired level. The air oxygen mixture containing the water droplets then passes to the patient. Humidifier nebulizers can deliver between 24 and 50 milligrams of water per liter of gas depending on the flow setting. Humidifier nebulizers are most commonly used with devices such as aerosol and tracheostomy masks. It is important that these devices operate as quietly as possible to ensure a comfortable environment for the patient. They should also conform to the international standards to ensure that the oxygen concentrations are delivered accurately. Some devices for example the Aqua mist are fitted with a tamper proof control to prevent inadvertent changes to oxygen concentrations. As with Bubble humidifiers the head of the aqua mist nebulizer humidifier incorporates a universal screw thread. This permits the use of a bottle which can be refilled with sterile water or the use of some prefilled sterile water bottles. The flow meter should be attached to an appropriate oxygen supply. Fill the bottle with sterile water using an aseptic technique and fit to the humidifier head. A humidifier nebulizer should then be attached to the flow meter. Attach 22-millimeter flex tube to the outlet of the humidifier nebulizer. It is important to position the tubing so that the lowest point is below the patient. And to regularly drain any condensate to prevent any condensed water from running into the patient or occluding the Flex tube. Attach the aerosol mask and then adjust the oxygen concentration to the required level, set the flow meter to provide the required total flow to the patient. The inter surgical aqua mist makes this simple by indicating the appropriate flow above each oxygen setting. Then fit the delivery device to the patient. An aerosol mask should be placed over the patient’s nose and mouth and the elastic is adjusted to give a secure and comfortable fit. When using a tracheostomy mask the mask is positioned over the patient’s tracheostomy site and secured in place using an adjustable elastic strap around the patient’s neck. There is no international standard for flow meter connections and they can vary by country and manufacturer. The aqua flow and aqua mist both incorporate a DISS oxygen connection which is the most common type. Flowmeter adapters are available to fit other types of flow meter for example the m12. These devices should not be used in ventilator circuits as the air entrainment port will introduce a leak into the system. These devices should also only be filled with sterile fluids that have changed every day. Any residual fluid should be drained from the bottle and discarded before refilling.
To summarize, we have looked at many different oxygen therapy devices including variable oxygen concentration devices, fixed oxygen concentration devices and humidification devices. We hope this has helped improve your understanding in this important discipline.
While the information contained within this article was considered correct at the time of production, it in no way qualifies anyone to undertake any medical activity.
EasyOxygen can accept no responsibility for the medical practices of persons who directly or indirectly reference this programme.
Credit to Intersurgical U.K