Hypoxemia occurs frequently in patients with advanced lung disease (obstructive and restrictive), cancer, and specific heart disease processes. When the condition is detected, the primary goals are to address the underlying pathophysiology and to correct hypoxemia with supplemental oxygen. As the patient’s care progresses from acute intervention, and the long-term need for supplemental oxygen is determined, the next decision focuses on the best oxygen delivery devices and configurations to prescribe. The clinician must address patient needs, costs, mobility, ease of use, access, time in ambulation per day, and other important life-preserving/enhancing considerations.

Presently, oxygen can be provided using several technologic approaches for both stationary and portable applications that may or may not include oxygen-conserving devices to enhance their efficacy. Perhaps the first major consideration is the oxygen flow setting required to achieve target oxygen saturation. Numerous options are available for patients who require flow settings up to 4 LPM. Options are more limited for patients requiring high-flow oxygen. In choosing a system, the clinician must consider distance from the supplier, mobility, home environment, health care assistance or lack thereof, patient preference, reimbursement, and other patient-centered needs. In today’s climate, most individuals who require 24-hour-per-day oxygen elect either concentrators or liquid oxygen systems. Each has advantages and disadvantages coupled mainly with a cost factor to the supplier; and, for the patient with a concentrator, the cost of electricity is a factor also. If Medicare is the third-party payor, its reimbursement criteria provide a stationary system at a fixed cost with a cap, regardless of the system specified, and if a portable system is ordered and justified, a small additional reimbursement is allowed.1

While a primary indication for supplemental oxygen is to correct hypoxemia, other considerations are focused on reducing functional disability, improving quality of life, enhancing mobility, and ensuring that oxygen is provided continually 24 hours per day, as prescribed. The NOTT and MRC trials have collectively documented the positive effects of continuous supplemental oxygen administration, eg, improved survival.2,3 New and emerging data suggest that supplemental oxygen may be reparative for lung tissue and other associated vascular processes.4,5 Thus, technologies that make supplemental oxygen easier to use, more efficient, and more reliable are highly desirable and will enable ease of ambulation and prevent tissue hypoxia throughout the day.

Oxygen systems have been improved in two ways: oxygen delivery to the patient has been rendered more efficient, and oxygen storage or production sources have been made smaller and lighter. By coupling these advantages, truly lightweight portable systems are now in common use by patients. The overall benefit is that our patients can be active and participate in life—consistent with the principles of pulmonary rehabilitation.

Portable Oxygen/Oxygen-Conserving Nasal Cannulas

Portable oxygen delivery has evolved during the past 25 years. Oxygen-conserving technologies were developed to extend cylinder life in order for patients to carry smaller cylinders for a greater number of hours per day. Smaller oxygen systems allow patients greater mobility to get out of the house, ambulate, and participate in life. Based on the physiology of breathing and considering that up to five sixths of the oxygen supplied with a standard flow nasal cannula is wasted to the environment,6 reservoir conserving nasal cannulas were developed. The first had a mustache configuration; this was followed by a pendant above the chest wall. Each device uses a movable membrane to form a storage chamber during exhalation and draws upon that stored oxygen during the next inhalation. Thus, reservoir cannulas store oxygen that is normally wasted during exhalation, making a bolus of almost 100% oxygen available during the first part of the following inspiration, when it is most likely to contribute to gas exchange. The overall benefit is that the oxygen flow setting can be turned down and the patient can still achieve adequate arterial oxygenation.

This technology has the unique advantage that it can be utilized with almost any oxygen system to maximize the efficiency and capability of oxygen delivery. We have previously compared Sao2 levels between a pendant-style cannula and a standard nasal cannula in COPD patients with hypoxemia on exercise.7 Similar Sao2 levels were achieved with the pendant cannula at one-third the oxygen flow rate when compared to the Sao2 values using a standard nasal cannula at similar exercise workloads. Additionally, we have demonstrated significant oxygen savings for the mustache-style conserving cannula compared to the standard nasal cannula.8 Also, the same advantage enables patients with high-flow requirements to be adequately oxygenated. Oxygen flows of 10 LPM or more have become alternatives to high-flow masks and high-flow nasal oxygen.

Portable Oxygen/Pulse–Demand Oxygen Delivery

Oxygen-conserving technologies migrated to the electronic age with the introduction of demand oxygen delivery systems. These devices sense the beginning of inspiration and immediately deliver an oxygen bolus. The first devices consisted of an electronic transducer coupled with a solenoid valve. Later, pneumatic sensing and delivery became available. The first devices were extremely sensitive to the beginning of inhalation and delivered a very short and effective oxygen bolus during the first few milliseconds of inspiration. Because they gave their most efficient oxygen shot every time they delivered a pulse, they were designed to deliver on every fourth, third, second, and every breath to correspond to continuous flow at 1, 2, 3, and 4 LPM, respectively. As valve technology improved, these devices could be designed to deliver on every breath and still maintain high efficiency compared with continuous flow. Later, pneumatically sensing and delivery devices became available. They are not as efficient as electronic devices; but they are lighter, because they do not require batteries.

One limitation of the conserving technologies and oxygen therapy in general is that patients must change their oxygen setting for rest and exercise. It is believed that most patients forget to adjust the oxygen setting to exertion when they get up and to return it to the resting setting when they sit down. This either wastes oxygen or does not meet the patient’s oxygen needs during exertion. Thus, a new electronic conserving device was developed to vary the amount of oxygen delivered in response to their activity level. The device is programmed by the physician or therapist for both rest and activity to maintain appropriate delivery. This might be the first oxygen delivery technology to respond to the patient’s physiological requirements. Several attempts have been made to develop closed loop systems guided by the patient’s oxygen saturation, but none are presently available.

Transtracheal Oxygen Delivery

Transtracheal catheters were first introduced by Heimlich9,10 and have been further improved and refined.11-13 Transtracheal catheters deliver oxygen via a surgically placed hole in the neck. Hence, the decision to deliver oxygen in this manner requires several considerations on the part of the patient and clinician. First, minor surgery is required to place the catheter, and thus, a very small potential for complications exists. Second, the catheter requires some ongoing inspection and care on the part of the patient. The catheter should be checked daily for potential failure, breakage, and restricted flow. If these are suspected, the catheter can be replaced. Mucus can plug the catheter, and the patient must be willing and able to clean and troubleshoot the catheter when required. These concerns aside, transtracheal catheters offer patients a high-quality delivery system that is hidden from sight and provides significant oxygen savings as compared to standard nasal cannula. Additionally, transtracheal catheters can be coupled to pulsed-flow devices to further improve their efficacy.14 Because transtracheal oxygen delivery bypasses the upper airway, questions concerning humidification have been raised, given the possibility of mucous plugging or mucous ball formation on the end of the catheter. Studies have demonstrated that at flows of less than 4 LPM via nasal cannula, humidification is generally not necessary.15 However, for transtracheal delivery especially at high flow, humidification is recommended.

Portable Oxygen/New Storage and Delivery Devices

Smaller Lighter Cylinders. Oxygen-cylinder technology has also improved. Heavy steel and aluminum cylinders are now being replaced with lighter aluminum-wrap and carbon fiber composite cylinders. Coupled with oxygen-conserving devices, smaller overall systems weighing less than 5 pounds are now in common use. Patients can be out and about for hours before changing or refilling cylinders.

Oxygen Concentrators That Refill Portable Cylinders. Oxygen concentrators that transfill portable oxygen cylinders have been developed. This transfilling capability is available as a stand-alone device or integrated into the concentrator. A compressor pressurizes the oxygen in the portable cylinder to 2,000 psi through a patient-friendly fail-safe high-pressure connector. The patient now has the ability to have continuous supplies of portable oxygen. Transfilling concentrators have been shown to be reliable, safe, and cost-effective and can provide stationary and portable oxygen simultaneously. Patient acceptance has been high. This system is especially suited for patients who reside long distances from the supplier, as it obviates the necessity for regular deliveries to the home. Accordingly, it also reduces cost to the supplier.

Liquid Oxygen Systems. Portable liquid systems were introduced to address the limited storage of compressed gas oxygen. Liquid oxygen is a very efficient means for storing large quantities of oxygen in a small space; 1 liquid liter stores nearly 860 gaseous liters of oxygen. Liquid transfilling is easier and faster than gas transfilling. When this technology is coupled to an oxygen-conserving device, the benefits of small storage volume and weight and efficient delivery to the patient collaborate to produce the lightest weight and longer-lasting systems.

Portable Oxygen Concentrators. The above two solutions did not address all aspects of portability for some patients. Thus, portable oxygen concentrators were introduced to deliver supplemental oxygen for long periods while traveling and using a variety of energy sources (battery and DC and AC current). Most of these devices weigh more than their gas and liquid counterparts, but they afford the patient the freedom to travel extended distances as long as a suitable power source is available. Battery power and weight limitations significantly restrict delivery volumes of portable concentrators, although when configured with oxygen-conserving technologies, their efficiency is enhanced and battery life extended. As battery technologies advance, the utility of portable concentrators will increase.

General Considerations/Recommendations

Portable oxygen systems are designed to be small, lightweight, easy to use, more cosmetically acceptable, durable, and efficacious at maintaining the patient’s oxygen saturation. Other considerations are also important. Since oxygen is reimbursed by Medicare based on liter flow, it is typically within the purview of the oxygen supplier to decide which system to provide to the patient. Therefore, cost drivers and market share contribute significantly to development and innovations of systems. With these concerns addressed, the providers will then make their choices with regard to which technologies to embrace, dispense, and support. System efficacy for a particular patient cohort, reliability, patient ease of use, location of the vendor, availability of technical support and parts, longevity of systems, costs and reimbursement, etc are each considered.

Once a system is selected, it is important that patients be evaluated using their systems. The systems should be evaluated under a variety of conditions and the results documented. For example, resting delivery rates to achieve desired oxygen saturation should be established for the selected device and configuration. Next, the devices should be evaluated during activities of daily living or exercise. The precise setting for each of these should be documented and patients instructed on how to vary the settings and why. Patients should also receive high-quality instruction regarding trouble-shooting and routine maintenance of the devices dispensed. Additional instruction should be offered so that the patients understand and follow all safety guidelines and know how to plan for emergency situations. For example, they should understand what they should do if their portable liquid system freezes up, or their pulsed system fails to operate. By ensuring that the patients and their supportive families completely understand and in turn are able to demonstrate what they have learned, potentially disastrous situations can be avoided.


Portable oxygen systems continue to evolve and become more therapeutic in design. The challenge for the future is to provide greater oxygen savings by maximizing efficacy of delivery, miniaturizing systems, and finding better ways to meet the physiological requirements of our patients. We also need to take into account the patient’s living style and the cost of providing an appropriate oxygen system. It is incumbent on the clinician and the home medical equipment supplier to make sure that the patient is adequately oxygenated via a system that is reliable and easy to use. Costs and other market forces are part of this clinically oriented landscape. As the overhead of doing their business rises at the same time reimbursement rates diminish, home oxygen suppliers must be able to purchase and maintain this equipment at an affordable cost. It is helpful to consider the physician, therapist, home care provider, and patient as a health care team.

Rick Carter, PhD, MBA, is professor and chair, Department of Health, Exercise and Sport Sciences; James S. Williams, PhD, is associate professor, Department of Health, Exercise and Sport Sciences, and adjunct associate professor of physiology, Texas Tech University, Lubbock. Brian Tiep, MD, is medical director, Respiratory Disease Management Institute, Monrovia, Calif, and director of pulmonary rehabilitation at City of Hope Medical Center, Duarte, Calif. For further information, contact [email protected].


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