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Portable oxygen delivery and oxygen conserving devices

Portable oxygen delivery and oxygen conserving devices
Literature review current through: Jan 2024.
This topic last updated: May 12, 2023.

INTRODUCTION — Patients with chronic lung disease and other conditions who require long-term oxygen therapy are often mobile outside of the home and need access to a portable supply of oxygen to maintain a normal lifestyle. For patients with advanced lung disease who require long-term supplemental oxygen, exertional breathlessness, hypoxemia, and lack of energy are compounded by the increased demand of carrying or dragging portable oxygen equipment when they are away from home.

Portable oxygen sources can be heavy, cumbersome, and limited in the duration of oxygen supply, so oxygen conserving devices have been introduced as a means of making oxygen therapy more efficient, more portable, and less intrusive [1,2].

This review will compare traditional, continuous flow oxygen delivery by nasal cannula with a variety of oxygen conserving devices. The indications for long-term supplemental oxygen, the use of oxygen in hypercapnic patients, and issues regarding oxygen therapy during air travel are discussed separately. (See "Long-term supplemental oxygen therapy" and "The evaluation, diagnosis, and treatment of the adult patient with acute hypercapnic respiratory failure" and "Evaluation of patients for supplemental oxygen during air travel".)

OXYGEN DELIVERY DEVICES — A variety of devices are available for oxygen delivery, such as nasal cannulas, reservoir cannulas, and transtracheal catheters. Each method has unique features that recommend for or against its use in the individual patient (table 1 and table 2).

Continuous flow nasal cannula — Continuous flow oxygen delivery through nasal cannula is the usual prescription for long-term oxygen delivery in hypoxemic patients and, thus, is the standard against which all oxygen-conserving techniques should be compared [2].

An important consideration for patients who are hypoxemic at rest is that their oxygen demands increase, sometimes abruptly, with exertion such as during activities of daily living, walking, and climbing stairs. As a result, higher oxygen flows are often necessary during exertion. Flow can be increased incrementally in response to increasing demand, but nasal cannulas have an upper limit of approximately 10 to 15 L/minute. Engineering technologies are making portable high-flow delivery possible for those individuals requiring high-flow supplemental oxygen. (See 'Future innovations' below.)

While continuous flow delivery via the nasal cannula is widely used for long-term supplemental oxygen, continuous flow is inefficient, as only a small percentage of the oxygen delivered to the nose actually reaches the alveoli. Oxygen flowing through the standard nasal cannula is nearly 100 percent pure. However, the patient actually receives a blend of pure oxygen and room air, as atmospheric air (20.9 percent oxygen) is entrained with the oxygen [3,4]. The resultant inspiratory oxygen concentrations of standard nasal cannula flow settings are approximated in the figure (figure 1).

Assuming the most effective oxygen delivery occurs in the first 200 millisecond of inspiration, the fraction of inspired oxygen (FiO2) can be calculated and expressed as a percentage (table 1). For example, the typical flow setting of 2 L/minute would raise the FiO2 to about 27 to 28 percent. This is a small amount of oxygen enrichment; however, it adequately corrects hypoxemia in most patients during rest, particularly those with chronic obstructive pulmonary disease (COPD) [4].

Nasal cannulas are generally well-tolerated, although device-related pressure injuries can develop on the ears and nostrils in some patients.

Delivery methods to improve oxygen conservation — Unlike oxygen supply in the hospital, oxygen supply in the home can be limited. Oxygen cylinders have limited storage and oxygen concentrators tend to have limited flow ranges. This is particularly true when the flow requirements reach beyond 6 L/minute. Certain types of oxygen delivery methods may enable patients with high-flow requirements to live at home and maintain adequate oxygen saturation (table 2).

Some additional considerations include:

Reservoir cannulas are the simplest, least expensive, and easiest for patients to convert from standard cannulas, but they are considered obtrusive for some patients.

Pulsed demand oxygen delivery devices. These devices deliver oxygen at the beginning of inhalation targeting the portion of inhalation that reaches the alveoli where gas exchange takes place.

The efficiency of these systems is expressed as the ratio of oxygen flow required by continuous flow delivery to the flow required by the conserver to achieve equivalent oxygen saturation, as expressed in the equation.

Efficiency = Continuous flow ÷ flow to conserving device (at equivalent saturation)

Transtracheal oxygen, in which oxygen was delivered directly into the trachea through a small opening in the neck, was a method previously used for oxygen conservation. Using this method, continuously flowing oxygen was stored in the upper airways and trachea toward the end of exhalation and could be delivered during early inhalation along with supply oxygen, bypassing a portion of the dead space of the upper airways. Disadvantages included the need for a minor surgical procedure, a tendency to form mucus balls at the catheter tip, and the need for significant patient training on the device. Although it excelled cosmetically and was highly effective for some patients, supplies have been discontinued by the manufacturer and the system is no longer available.

RESERVOIR CANNULAS — Reservoir cannulas function by storing oxygen in the reservoir space during exhalation, making that oxygen available as a bolus upon the onset of the next inhalation. Oxygen is conserved because the patient breathes a higher concentration of oxygen without increasing flow from the oxygen tank or concentrator. Reservoir cannulas increase the percent of oxygen in the oxygen/air that the patient inhales over that delivered by standard nasal cannula and usually enable a reduction in the oxygen flow setting of approximately 25 to 50 percent while maintaining the same pulse oxygen saturation.

Reservoir cannulas can help decrease the flow rate needed for patients on low-flow oxygen, but they are more commonly used to provide a higher concentration of oxygen to patients who require a flow rate of oxygen 4 L/minute or higher.

Reservoir cannulas are available in three configurations:

A mustache configuration (Oxymizer), in which the reservoir is located directly beneath the nose (figure 2) [5,6]. While some patients find this configuration more comfortable than the pendant, it is more noticeable on the face, causing some patients to reject it.

A pendant configuration (Oxymizer Pendant) utilizes an in-line plastic reservoir that rests on the anterior chest (picture 1) [7]. The pendant configuration is less noticeable than the moustache, although more noticeable than a standard nasal cannula.

The fluidic mustache reservoir cannula is designed to operate at flow rates from 1 to 16 L/minute. Thus, it is both a conserving device and a high-flow device. As an example, a patient using oxygen 20 L/minute (fraction of inspired oxygen [FiO2] of 80 percent) on high-flow oxygen may achieve equivalent oxygen saturation at 10 L/minute with the fluidic reservoir cannula (picture 2). Thus they may be able to be discharged from the hospital on a 10 L/minute oxygen concentrator.

In the first two reservoir cannulas, a thin, compliant membrane in the reservoir is pushed forward during exhalation, creating a chamber between the membrane and the posterior wall (figure 2). The continuously flowing oxygen fills the reservoir during most of exhalation. When ready to inhale, the patient receives the stored oxygen along with the continuously flowing supply oxygen. The fluidic reservoir does not have an inner membrane, but otherwise functions similarly. These reservoir cannulas are simple, reliable, inexpensive, and disposable. All three devices are partial rebreathing systems. As some of the patient's warmed expired air with elevated moisture is stored for the next breath, the relative humidity of the inhaled oxygen is increased. This is particularly true with the mustache configuration in which the reservoir is warmed by contact with the upper lip.

The efficacy of reservoir cannulas compared with standard nasal cannula delivery is shown in the figure (figure 3) [5,7-12]. Oxygen supplied at 0.5 L/minute via the reservoir cannulas achieves equivalent saturation to continuous flow at 2 L/minute. Similarly, 1 and 2 L/minute reservoir settings are equivalent to 3 and 4 L/minute continuous flow, respectively. Thus, the efficacy of reservoir cannulas ranges between 2:1 and 4:1.

For patients requiring higher oxygen flows, reservoir cannulas can improve oxygen supply delivered from an oxygen concentrator or low-flow portable oxygen system [13]. For reservoir cannulas, add approximately 2 L/minute to continuous flow settings. For example, a reservoir cannula setting of 4 L/minute is equivalent to 6 L/minute by continuous flow.

Studies performed during exercise and sleep generally yield results consistent with resting values, albeit with some variation [10,11,14].

DEMAND OXYGEN PULSE DEVICES — Demand oxygen pulse devices were developed to conserve oxygen flow and improve patient mobility outside of the home. These devices have small reservoirs that supply a metered amount of oxygen only during inspiration, thus extending oxygen availability and portable tank life. Different technological features have been used to optimize the size of the oxygen bolus and the delivery efficiency.

How demand oxygen pulse devices work — The patient's inspiratory flow through the nasal cannula or transtracheal catheter is detected as a pressure swing (figure 4). The valve then opens and delivers a short pulse of nearly 100 percent oxygen. The aim is to discharge the pulse of oxygen during the earliest part of inhalation, when it can participate in alveolar gas exchange [15-17].

The reason that oxygen is provided early during the inspiratory cycle is explained in the model of inspiration shown in the figure (figure 5) [3,18]. Assuming a tidal volume of 450 mL, the first gas to reach the alveoli is the 150 mL of oxygen-poor gas (end expiratory gas) already occupying the airways. This is followed by 300 mL of inspired room air expected to reach the alveoli. The final 150 mL of inspired gas is destined to fill the airways at the end of inspiration, never reaching the alveoli (becoming the anatomic dead space gas). Thus, only the middle 300 mL of inhaled gas reaches the alveoli to enrich alveolar air with supplemental oxygen. The figure shows that airflow slows at the end of inspiration, so that dead space inspiration occupies a disproportionate 50 percent of inspiratory time (figure 6).

One study demonstrated that nasal oxygen delivered incrementally earlier in inhalation progressively increased oxygen saturation (figure 7) [19]. Consequently, oxygen delivery should occur within the first 0.5 second of inspiration, prior to the last 150 mL of inspired air, as oxygen delivered beyond this time will not participate fully in alveolar gas exchange and will preferentially occupy anatomic dead space.

Types of devices — Pulsing devices are available as stand-alone modules or integrated into a liquid oxygen system, compressed gas system, or portable oxygen concentrator (POC) [2]. Importantly, there is no industry standard with regard to the numeric settings on different pulsing devices, so that a setting of "2," for example, on one device does not generalize to any other pulsing system at that same setting and may not equate to oxygen delivery on 2 L/minute on a continuous flow device.

Settings for oxygen delivery are adjusted in some devices by varying the length of the oxygen pulse. Other devices deliver an early pulse each time they discharge, avoiding lengthening of the pulse into the dead space portion of inhalation. Examples of demand oxygen pulse devices include the following: Chad-Oxymatic, Devilbiss-PD-1000, Helios, Invacare-Venture, Nellcor PB-CR50, Respironics e-POD, EasyPulse, Bonsai, Evolution, Evolution Motion, Smart Dose, Air Sep, Drive, Victor, Medline and Impulse, among others, and all the portable oxygen concentrators include demand oxygen conserving devices.

An addition to portable oxygen delivery is the noninvasive open ventilator (NIOV) device, which is a 1 pound wearable augmentation ventilator attached to a portable oxygen cylinder with a nasal pillow interface (picture 3). Connected to a pressurized oxygen source, it delivers 50 to 250 mL boluses. In a study of subjects with chronic obstructive pulmonary disease (COPD), the NIOV increased oxygenation, reduced dyspnea on exertion, and enabled a higher exercise work rate compared with breathing room air, supplemental oxygen via nasal cannula, and NIOV without supplemental oxygen [20].

Some devices require a battery and others are pneumatically driven. The pneumatic devices are less expensive and weigh less, but are less likely to sense the very beginning of inhalation, resulting in a delay in oxygen delivery pulse. The batteries on the electronic devices may last from three hours to one month, depending on the electronic circuitry. Pneumatically driven units do not require batteries.

Variability in oxygenation — In research studies, demand oxygen pulse devices perform well relative to continuous flow delivery [15,21-24]. However, these devices may fail to adequately oxygenate some patients (figure 8). This limitation can sometimes be prevented by modifying the device to deliver a larger pulse during the earliest part of inhalation or using a higher oxygen flow setting [25,26]. Because of the variability among devices and patient needs, it is always advisable to evaluate each patient during rest and exertion to assure adequate oxygen saturation via the device being prescribed. Generally, a prescription for an oxygen conserving device should include a request that the therapist supplying the device assess the patient's oximetry at rest and during exertion/activity.

In a study that compared four different oxygen conserving devices with continuous flow oxygen at 2 L/minute in patients with COPD, the devices varied in terms of the oxygen delivered, the pulse oxygen saturation achieved, and the exercise ability of the patients [27]. Breath-by-breath output was variable for all devices in terms of activation of the pulse and bolus size.

A cross-over study compared two oxygen conserving systems, demand oxygen pulse and a pendant reservoir cannula (picture 1), with standard nasal cannula during a six-minute walk test in patients with COPD or interstitial lung disease (ILD) [28]. The target pulse oxygen saturation (SpO2 ≥90 percent) was achieved by all devices in approximately 80 percent of patients with the exception of the demand oxygen pulse system, which was inadequate in nearly 40 percent of patients with ILD. The pendant reservoir cannula was the most effective device used for oxygenating patients with ILD under exercise conditions.

In general, the efficacy of a particular oxygen conserving device is maintained during exercise and sleep [22-25]. However, as noted above, the performance of these devices should be assessed in individual patients under the various conditions of use [29]. As a safety feature, some devices have a feature in which they automatically revert to continuous flow if they fail to detect a breath in 20 to 30 seconds, but this feature uses more battery current.

Prescribing pulse oxygen devices — In general, an oxygen conserving device should be considered for patients who would benefit from a longer lasting supply of oxygen or a lighter weight system (to improve mobility). This would include virtually all patients who are ambulatory and wish to maintain an active lifestyle. Also, patients who live a long distance from their home medical equipment supplier need a wider variety of options, due to the practical limitation of less frequent home deliveries. As the efficacy of oxygen delivery improves through use of oxygen conserving devices, the duration of time that the cylinder can provide oxygen is extended (figure 9).

Each conserving device has inherent advantages and disadvantages that should be understood by the clinician and patient. The choice between systems often requires compromise.

The demand oxygen pulse devices generally improve the efficiency of both nasal and transtracheal delivery. These devices have enabled the development of integrative systems that maximize oxygen delivery. However, they make audible pulses that may be distracting, and mechanical failure, albeit rare, is possible. Some pulsing devices fail to oxygenate patients adequately during exertion [26,27].

Each patient's respiratory pattern, respiratory rate, inspiratory flow rate, and tidal volume, can affect conserver performance. Thus, it is advisable to assess oxygenation by pulse oximetry or an arterial blood gas to determine the actual liter-flow setting prescription for the patient's various levels of rest and exertion. For patients in the United States, Medicare requires that patients be tested at rest and during exertion while using the proposed oxygen conserving device and at the proposed level of supplemental oxygen [29].

PORTABLE OXYGEN SYSTEMS — A variety of portable oxygen systems are available for patients to go beyond the limits of a stationary oxygen delivery system with 50 feet of tubing. For patients who are ambulatory, the oxygen delivery system should weigh less than 10 pounds (4.5 kg), deliver oxygen at 2 L/minute for ≥4 to 6 hours, and be easily carried by the patient. This 10 pounds limit is high enough to encompass a number of portable oxygen concentrators (POC) and also several portable gas, concentrator, and liquid systems that typically weigh less than 5 pounds. The lightweight units should be provided for patients who are highly mobile and active, consistent with the principles of pulmonary rehabilitation.

Lightweight compressed gas cylinders — The total weight of an oxygen system consists of the cylinder, regulator, and the oxygen conserving device. Composite cylinders are manufactured from aluminum liners and strengthened by carbon fiber in an epoxy resin matrix. Fiber-wrapped aluminum cylinders are lighter and store more oxygen than steel cylinders. While they accept higher pound-force per square inch (psi) up to 3000 psi, they are usually pressurized to 2000 to 2500 psi. They are carried in a bag rather than a cart, but are also much more expensive, limiting widespread use.

Liquid oxygen systems — Liquid oxygen does not require a high pressure container for oxygen storage; rather, a thermos-like device called a Dewar Flask is used. One liquid liter of liquid oxygen expands to nearly 1000 liters of gaseous oxygen deliverable to the patient. Liquid oxygen also offers safe and easy transfer (known as transfilling) of oxygen to an ambulatory unit from a main storage device or certain types of oxygen concentrators.

The lightweight flasks can be combined with an integrated demand oxygen pulse device or reservoir cannula. A portable liquid oxygen flask with an integrated oxygen conserving device provides some of the smallest and most portable systems (weighing about 3.5 pounds or 1.6 kg).

Oxygen pulsing devices have expanded the delivery life of the smallest liquid oxygen cylinders. Some of these compressed demand oxygen pulse systems that weigh less than 1.8 kg compare favorably to standard 4.3 kg liquid systems that have similar delivery life. The Helios Plus, for example, weighs 1.6 kg and at a setting of 2 L/minute lasts up to 22 hours between refills, thus providing the dual advantages of portability and transfillability. If a patient needs oxygen flow for longer, access to a liquid oxygen reservoir to transfill their Helios system is necessary.

Despite their high efficiency, liquid oxygen systems have certain disadvantages. With liquid oxygen, some oxygen typically bleeds off to the atmosphere when the device is not in operation, so the tanks may not last as long as expected. Additionally, liquid oxygen systems may freeze up and thus, the patient needs to be educated about these problems and have backup plans established until oxygen delivery can be restored. The main storage tanks need to be delivered to the home on a regular basis, so transportation costs can become important.

Portable oxygen concentrators — Portable oxygen concentrators (POC) have become much more common and have essentially replaced liquid oxygen systems. POCs make use of improved battery technology and size and power of pumps and motors to provide lightweight, battery-powered oxygen concentration. POCs are smaller than oxygen concentrators designed for home use, and POCs are battery operated instead of being continuously plugged into an electrical socket. Examples of POCs include Eclipse, EverGo, FreeStyle, Inogen, and XPO2 with battery lives ranging from 2.5 to 8 hours. Additional batteries can further extend the time that a patient can depend on the oxygen supply from a POC. POCs vary in the oxygen flow that they can provide and in whether they supply continuous or pulsed demand oxygen flow.

The weight and size of oxygen concentrators is partly determined by the oxygen requirement of the patient to meet a target pulse oxygen saturation (SpO2). While a standard oxygen concentrator weighs 16 to 23 kg (35 to 50 pounds), several POCs have been developed that weigh between 2.3 and 8.2 kg (5 and 18 pounds). As they generally deliver oxygen via pulsing, there could be a lack of delivery during sleep if the patient resorts to mouth breathing and does not trigger the pulse [29,30].

Using an oxygen conserving device in conjunction with the concentrator enables adequate oxygen delivery at lower flows, thus relieving some of the limitations. Most POCs have an integrated conserver, which may not be ideal for patients who require a higher flow rate, but some larger units provide continuous flow oxygen delivery options. The smaller units weigh about 2.3 to 3.2 kg (5 to 7 pounds), while the larger units that have continuous flow settings may weigh 7.2 to 8.2 kg (16 to 18 pounds).

Prescribing portable oxygen systems — The oxygen system provided to patients is often determined by their insurance and medical supply company. Nonetheless, it is helpful to know the main differences between the systems. Home oxygen prescriptions should specify whether the patient is ambulatory (ambulatory systems should weigh less than 10 pounds and last at least four hours), what their oxygen requirement is at rest and with exertion, how many hours a week they expect to be away from their stationary system, and whether they should be assessed for use of an oxygen conserving device or a POC. The prescription of long-term oxygen is discussed separately. (See "Long-term supplemental oxygen therapy".)

The most commonly dispensed portable system for home use is an E cylinder designated to serve in the event of power failure or for infrequent portable use. The aluminum E cylinder with regulator and cart weighs about 6 kg (13 pounds) and lasts about 5 hours at 2 L/minute or 2.5 hours at 4 L/minute. With an oxygen conserving device at setting 2, the oxygen may last two to seven times longer.

Patients often find that the E cylinder is cumbersome and that smaller tanks that can be carried allow for increased time away from home.

Other options and considerations for supplying portable oxygen include the following:

The sizes of portable oxygen cylinders vary from M-2 (42L) to M-6 (165L) to the larger D (425L) to E cylinders (680 L). Even larger cylinder sizes up to H cylinder are not considered portable.

Some stationary oxygen concentrators can refill portable compressed oxygen cylinders. Examples of these systems are the Venture HomeFill Compressor and the DeVilbiss i-Fill Oxygen Station.

The home oxygen provider can deliver compressed gas cylinders.

A standard oxygen concentrator can be used at home with a portable oxygen concentrator (POC) for use when away from home. (See 'Portable oxygen concentrators' above.)

AIR TRAVEL — POCs are the only devices approved by the US Federal Aviation Administration for air travel [31,32]. Other countries and their airlines may have different requirements.

There are as many as 23 brands of FAA approved POCs are allowable by airlines. It is always a good idea to check with the airline well before a flight (eg, two weeks) if the patient is going to take a POC.

As battery power is needed for oxygen production, patients typically need to bring enough batteries for one and one-half times the anticipated duration of travel. When considering the weight and size of the POC aboard aircraft, battery life must be considered since smaller units may require extra batteries, which add to the weight, for the same number of hours of oxygen [33].

The ability of POCs to provide adequate oxygen delivery to patients at aircraft altitudes pressurized to the equivalent of 8000 feet has been assumed but not fully studied. The partial pressure of oxygen is decreased at altitude due to reduced barometric pressure. The effect on POC output may not be the same as normobaric oxygen tent with 15 percent oxygen (comparable to the partial pressure of oxygen at 8000 feet). One study addressing this issue found three of four POCs were able to concentrate oxygen under hypobaric hypoxic conditions although they produced a slightly lower oxygen concentration than at sea level [34]. They also found that the conditions of a hypoxemia simulation test (normobaric 15 percent oxygen) did not fully correspond to the hypobaric conditions.

There is a possibility that miniaturized POCs may not be able to maintain adequate oxygenation aboard long flights. It would be reasonable to bring a finger pulse oximeter on-board to assure an adequate pulse oxygen saturation (SpO2).

The evaluation of patients for in-flight oxygen is described separately. (See "Evaluation of patients for supplemental oxygen during air travel", section on 'Arranging for portable oxygen during flight'.)

FUTURE INNOVATIONS — Experimental innovations that may compensate for the difficulty with oxygenation during exercise are under study. One device senses the onset of activity and automatically increases oxygen delivery volume to a higher level to meet the patient's metabolic demands [25,35]. The exercise delivery volume continues for 50 seconds following discontinuation of activity and then reverts to the resting volume [35]. These devices meet the patient's oxygen requirements during rest and exertion and also conserve oxygen. Several devices that auto-adapt to rest and activity have been developed, including closed-loop devices (eg, AccuO2, FreeO2) that use measured SpO2 to titrate oxygen flow to achieve a target SpO2. When compared with continuous flow and a standard oxygen conserving device, the AccuO2 maintains SpO2 and improves the overall efficiency of oxygen delivery [36]. Compared with continuous flow, the FreeO2 device maintains exertional SpO2, improves exertional endurance, and does not increase postexertional carbon dioxide retention [37].

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Supplemental oxygen".)

SUMMARY AND RECOMMENDATIONS

Oxygen conserving devices offer greater versatility, portability, and cost savings for patients using oxygen systems. They all involve trade-offs on cost, weight, portability, cosmesis, availability, and efficiency (table 2). (See 'Introduction' above.)

Each patient who is considered for an oxygen conserving device should have their oxygen saturation (oximetry) tested, using the device being prescribed, during wakeful rest, usual levels of exertion/activity, and perhaps during sleep to ensure an adequate oxygen prescription. (See 'Demand oxygen pulse devices' above and 'Prescribing pulse oxygen devices' above.)

Some patients who are active away from their stationary system prefer to use a lightweight liquid oxygen system combined with an oxygen pulsing device to maximize ease of portability and duration of oxygen supply. However, liquid oxygen is not always available. A portable oxygen concentrator (POC) with an oxygen conserving device is a more available alternative. Newer POCs have a more extensive battery life, but POCs may be limited in meeting the needs of patients with higher flow requirements. (See 'Prescribing portable oxygen systems' above.)

For patients who require high-flow oxygen (ie, 4 L/minute or greater), a reservoir device, either a mustache cannula or pendant cannula, may be prescribed. Patients who do not require high-flow oxygen, but who wish to prolong their oxygen supply by lowering the flow rate, may also utilize a reservoir device. Reservoir cannulas may be worn at rest, during sleep, and with activity, although comfort and cosmetic issues may impact their use. (See 'Reservoir cannulas' above.)

As oxygen requirements increase (eg, in patients with idiopathic pulmonary fibrosis, pulmonary hypertension), demand oxygen pulse devices may not achieve adequate arterial oxygenation, particularly during exertion. Continuous flow is then necessary, with the setting adjusted to achieve adequate saturations at rest and with exertion. Reservoir cannulas may enable improved oxygen delivery without increasing the liter flow. (See 'Demand oxygen pulse devices' above and 'Reservoir cannulas' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Brian L Tiep, MD (deceased), who contributed to earlier versions of this topic review.

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References

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