An Overview of Home Oxygen Delivery Devices and Prescribing Practices

James K. Stoller, M.D., M.S.
Jean Wall Bennett Professor of Medicine
Cleveland Clinic Lerner College of Medicine
Chairman, Education Institute
Head, Cleveland Clinic Respiratory Therapy

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Abstract Home oxygen is used commonly, is costly, and consumes many resources in Canada and the United States. Because a variety of oxygen delivery and oxygen-conserving devices are available, optimal prescribing requires solid understanding of these devices and of strategies for their clinical use by respiratory clinicians. At the same time, a review of current prescribing practices suggests opportunities to standardize practice and to improve. In the hope of enhancing clinical care of patients using home oxygen, this paper reviews available features and relative advantages and disadvantages of oxygen delivery devices: compressed gas, liquid oxygen, and oxygen concentrators. Oxygen conserving devices – reservoir devices, transtracheal oxygen, and demand-pulse systems – are then reviewed. Finally, current practices of prescribing home oxygen are reviewed, highlighting a great degree of variation within and across countries.

 

INTRODUCTION

Consider ing that oxygen use is increasingly common and costs the United States Medicare system more than $2 billion (1), understanding oxygen devices is important to optimize the delivery and use of oxygen. This brief paper will first review the types of home oxygen delivery devices that are currently available and their relative advantages and disadvantages, as well as the types of oxygen-conserving devices and how they perform in patients at rest, with activity, and during sleep. Attention then turns to current practices of prescribing oxygen and to strategies to improve prescribing oxygen. Finally, several recommendations regarding the use and prescription of oxygen that derive from prior oxygen consensus conferences and guidelines are reviewed. As with the issue of oxygen in general, many gaps in current knowledge about devices and prescribing exist and the discussion will identify opportunities to clarify fundamental but unanswered questions. Also, enhanced awareness should permit improved clinical care for individual patients and more rational use of oxygen for society.

Oxygen Delivery Devices

Three general types of oxygen delivery systems are available: compressed gas, liquid oxygen, and oxygen concentrators (2, 3). As reviewed in Table 1, each type of delivery device offers advantages and has drawbacks. For example, compressed gas cylinders are relatively inexpensive, are available in a spectrum of tank sizes (from A to H cylinders), and can provide an F_IO₂ of 1.0 (2). On the other hand, some compressed gas cylinders are heavy (e.g., steel H cylinders may weigh 135 pounds), bulky, and provide oxygen for generally shorter durations than other delivery systems. Also the regulators may be difficult to change.

Liquid oxygen systems offer the advantages of longer use (because a volume of liquid oxygen can provide a large volume of gas [i.e., 1 square foot of liquid oxygen can supply 24,335 liters of oxygen]), the ability to provide an F_IO₂ of 1.0, and a spectrum of vessel sizes, but carry the disadvantages of increased expense related to delivery costs and the associated services required, evaporative loss, and risk of thermal burns in transfilling smaller portable vessels from larger dewar vessels.

Finally, oxygen concentrators are self-sufficient once delivered, can be transfilled (with high pressure concentrators) to smaller, portable vessels, and are now available as portable systems (some of which are permitted by the United States Federal Aviation Administration on commercial airplanes [4]). However, concentrators show a drop in the delivered F_IO₂ with increasing liter flow rates and cause the associated costs of electricity use that are born by the patient; this cost is approximately $20-$30/month. Overall, although the choice of a delivery system is often influenced by regional factors (i.e., which local durable medical equipment companies are available to the patient and what equipment they offer, the prescribing physician’s level of awareness of various systems and their relative individual advantages for their patients), optimal prescribing of oxygen should consider the informed patient’s choice based on lifestyle issues and the likelihood of adhering to a carefully considered oxygen prescription.

Table 1. Features of Available Oxygen Delivery Systems*

Delivery System	Advantages	Disadvantages
Compressed gas	• Inexpensive    • More widely available in less developed parts of the world • Range of cylinder sizes available (e.g., A to H) • Can provide 100% oxygen • Available in lighter aluminum and epoxy matrix cylinders	• Some cylinders are heavy (e.g., steel H cylinders) • Some cylinders are unsightly • Shorter duration of available oxygen (e.g., H cylinder provides 2 L/min for maximum of 57 hours, 33 minutes (vs. > 11 days for a liquid reservoir) • Bulky, requiring storage space in the patient’s home • Difficult to change regulators • Risk that the cylinder would become a projectile if the stem breaks
Liquid oxygen	• Small liquid volume provide much gas (i.e., 1 square foot of liquid oxygen provides 24,255 liters of gas) • Long duration supply (home reservoir holds 40 liters and can provide 2 L/m in flow for > 11 days) • Portable vessels can be transfilled from large reservoirs • Can provide 100% oxygen over a range of flows	• Expensive to provide (requires regular delivery, trucks, etc.), making liquid oxygen less available in costattentive settings • Evaporative loss (0.055 pounds/ hour or 40-55 liters/hour loss) • Transfilling technique can be challenging and risks thermal burns
Oxygen concentrator	• No home delivery needed • Self-sufficient system • Range of devices from stationary home devices to portable devices, many of which are now permitted aboard commercial airliners by the Federal Aviation Administration • High-pressure concentrators are available that can transfill portable tanks	• FIO2 decreases as flow rate increases (to <0.90 at > 5 L/min) and is less than 1.0 • Use of home concentrators requires electricity and incurs a cost (~$300/year) which is not reimbursed by Medicare
*All oxygen delivery systems pose the risk of combustion of oxygen near open flames.

Oxygen-Conserving Devices

Because a major goal in providing oxygen is to enhance the patient’s functional status and freedom from lifestyle constraints in using supplemental oxygen and because both compressed gas and liquid oxygen delivery systems are limited by the finite amount of oxygen available in the vessel, oxygen-conserving devices have been developed to extend the available use time by optimizing and conserving the delivery of oxygen (5-14). Three main types of conserving devices are available: reservoir devices, transtracheal oxygen, and demand-pulse oxygen delivery devices. Currently, available reservoir devices include the Oxymizer cannula and the Oxymizer Pendant Chad Therapeutics, Naples, FL [Figure 1{6-8}). Though different, both devices share the design feature of frontloading the delivery of high fraction oxygen to the airway on the patient’s inspiration because oxygen is stored in special chambers in the cannula or in the tubing of the Pendant. Like all oxygen-conserving devices, the efficiency of the reservoir devices can be described by the so-called efficacy ratio, which represents the ratio of liter flow rates of the conserving device to continuous flow nasal cannula needed to provide the same degree of oxygen saturation for the patient (6, 7, 9). For example, an efficacy ratio of 4 means that the patient achieves the same saturation value on 0.5 L/ minute using the conserving device as on 2 L/minute using continuous flow oxygen provided through nasal cannula. Efficacy ratios for the three types of conserving devices vary, and may be as high as 7. The higher the efficacy ratio, the more efficient the conserving device, the longer the time available to use oxygen, and the greater the associated savings. Reservoir devices generally achieve efficacy ratios of 2 to 4 (6-8). While available studies of their performance during activity and sleep are sparse, the few available studies suggest that the performance of reservoir systems during exercise is good and that saturations achieved during sleep achieved are lower than those obtained using continuous flow with nasal cannula, though the clinical significance of the differences remain unclear (9, 10).

Figure 1. Reservoir Devices: The Oxymizer Cannula (A) and the Oxymizer Pendant (B)

Oxymizer Cannula (A)	Oxymizer Pendant (B)
From www.deltaoxygensystems.com

 

Transtracheal oxygen (11, 12) involves the placement of a catheter through the neck into the trachea and can achieve better oxygenation than nasal cannula because high concentrations of oxygen can collect in the trachea for inspiration. Though transtracheal oxygen offers many benefits, including a better cosmetic appearance, the need for an invasive placement procedure, significant motivation and manual dexterity to regularly clean and replace the catheter, and the risk, albeit small, of serious and even life-threatening complications, has resulted in limited adoption by physicians and patients (11, 12).

Demand pulsed oxygen-conserving devices represent the third available oxygen-conserving system and offer three different approaches (5, 6, 13, 14): demand systems that are triggered by the patient’s inspiration and provide flow throughout the inspiratory cycle, turning off with exhalation; pulsed dose systems that deliver a small bolus of pure oxygen for a brief interval at the very onset of inspiration (ideally within the first 0.5 second), and hybrid systems that provide both a pulse at the onset of inspiration and a continuous flow through the remainder of inspiration. Considering that there are no standard manufacturers’ specifications for the demand-pulse systems, the flow profiles of various available devices differ greatly, with the consequence that the delivered F_IO₂ of various devices vary greatly as the patient’s respiratory rate changes. For example, in a comparison of 18 different demand-pulse devices (11 pulse devices and 7 demand flow devices) by Bliss et al. (13), the delivered F_IO₂ varied widely at respiratory rates of 15 breaths/minute (from 0.30 to 0.46) and 30 breaths/minute (from 0.27 – 0.37).

As with the performance of reservoir devices during activity and sleep, studies of the performance of the pulse-demand devices with exercise and sleep are sparse (5-7, 14). Available studies suggest that the ability of different devices to maintain equivalent oxygen saturation values differ widely and that a minority of studied patients show markedly worsened oxygenation with the demand-pulse devices compared with continuous flow oxygen through nasal cannula. The result is that ideal use of such conserving devices requires individual patient assessment with the specific device that the patient is using under the clinical conditions of use (i.e., at rest, with exercise, and during sleep [15-17]). Regrettably, available data and experience suggest that practice often differs from this ideal. This challenge is compounded by uncertainty regarding the need and benefits of supplemental oxygen use that is confined to exercise and sleep only (18, 19).

Prescribing Practices for Home Oxygen

Knowledge gaps regard the performance of oxygenconserving devices as well as prescribing and monitoring oxygen for patients (20-22). Table 2 outlines the sequence of steps in recognizing a patient’s need for supplemental oxygen and then prescribing and monitoring supplemental oxygen use. Importantly, available guidelines suggest that patients’ oxygen needs should be assessed at rest, with activity, and during sleep (20, 23, 24), with some discretion given to the clinician as to how adjustments of liter flow requirements should be made during sleep. Specific oxygen saturation targets are offered. For example, the American Thoracic Society COPD guidelines (20) suggest the oxygen prescription should target an oxygen saturation of 90% in all states and, for sleep, oxygen should either be directly titrated (as with nocturnal oximetry to guide adjustment of prescribed liter flow rates) or increased by 1 L/min for sleep over the patient’s resting flow rate (Table 3).

Table 2. Steps in Prescribing Homegoing Supplemental Oxygen Therapy

1. Assess room air oxygenation (by pulse oximetry or arterial blood gas) 2. Determine the need for supplemental oxygen 3. Write an oxygen prescription   a. Determine and specify the type of delivery system and the durable medical equipment (DME) supplier   b. Determine and specify settings (flow rates [for a continuous flow system] or settings on an       oxygen-conserving device) at rest, during activity, and with sleep   c. Determine and specify whether an oxygen-conserving device will be used 4. Complete the required forms (i.e., United States CMS Form 484 [Certification of Medical Necessity]) 5. The Durable Medical Equipment company supplies the oxygen 6. Re-certify at one year as required by United States Medicare 7. Re-assess the need for oxygen and required settings at physician discretion

Despite some agreement across countries regarding the specific indications for prescribing supplemental oxygen at rest and the specific oxygenation targets (e.g., a resting room air PaO2 of 55 mmHg or less), observations suggest wide variability in clinicians’ adherence to the target saturation criteria as well as wide variation in how oxygen is actually prescribed (21-24). For example, Ringbaek et al. (22) showed that although guidelines across seven countries (United States, Australia, England, Sweden, Poland, Spain, France, and Denmark) uniformly recommended a criterion of P_aO₂ of < 55 mmHg as the indication for prescribing supplemental oxygen at rest, adherence by clinicians in those countries was as low as 30%. Similarly, in a survey (21) of 100 practicing pulmonologists from seven countries (United States, Canada, Brazil, the Netherlands, France, Italy, and Spain), wide variation in practices regarding both the saturation targets for oxygen titration studies and the methods for prescribing oxygen flow rates at rest, during sleep, and with activity was demonstrated. For example, in the United States, 19% of respondents to a survey reported an oxygen saturation target for supplemental oxygen of <90%, 71% reported a target of 90-91% saturations, and 10% reported a target >91% saturation (20). Similarly, recommendations from official pulmonary/critical care societies from Australia/New Zealand (23), the United States (20), and the United Kingdom (24) regarding the recommended frequency of reassessing patients’ needs for supplemental oxygen vary greatly.

Beyond knowledge gaps related to practice and adherence variation among clinicians in prescribing oxygen, another challenge is healthcare providers’ inadequate knowledge about basic aspects of prescribing oxygen, delivery systems, and monitoring systems (25-27). Several opportunities to enhance healthcare providers’ knowledge are evident. For example, because misallocation of respiratory care services in general and oxygen in particular is so frequent (28), many observers suggest that inadequate knowledge of the monitoring systems (e.g., oximetry [27]) and of treatments (e.g., oxygen delivery devices, conserving systems, etc. [25,26])contribute to misallocation. More specifically regarding knowledge of prescribing oxygen, Mbamalu et al. (26) reported that only 2% of senior British house officers correctly answered all 4 straightforward questions regarding how to prescribe and monitor supplemental oxygen. Similarly, inadequate knowledge of the principles and use of pulse oximetry has also been reported (27). That inadequate knowledge and / or time to educate patients contributes to suboptimal use of oxygen has been suggested by the recent findings of Arnold et al. (29); they reported that 92.6% of surveyed British patients on long-term oxygen therapy did not recall receiving any information from their providers regarding how to use their oxygen systems.

The considerable disconnect between guideline recommendations for optimal practice and the actual practice of prescribing and monitoring oxygen invites measures to enhance prescribing and monitoring of supplemental oxygen. Several strategies enjoy current support, though others are undoubtedly yet to be developed. Substantial evidence, including concordant randomized controlled trials (30, 31), shows that empowering respiratory therapists (RTs) to implement respiratory therapy protocols can lessen misallocation, preserve clinical outcomes, and lessen cost. For prescribing oxygen, Guyatt et al. (32) reported the results of a randomized controlled clinical trial which compared oxygen utilization when patients were either re-assessed for oxygen use according to usual physician-directed care vs. when RTs reassessed after oxygen was initially prescribed. At 1 year, significantly fewer patients still required supplemental oxygen in the RT-supervised group than with usual physician-directed care (43% vs. 59%, p < 0.001) with a trend towards lower associated net cost (by $38/year). While this cost decrease failed to satisfy statistical significance criteria, the decrease remains administratively quite significant. Similarly, Chaney et al. (33) reported that an oxygen therapy clinic staffed by an RT (who conducted oxygen titration studies at rest and with activity) and overseen by a pulmonologist was associated with frequent discontinuation of unneeded supplemental oxygen. Specifically, rates at which patients using supplemental oxygen were able to be appropriately discontinued from its use were as high as 50.5% for those for whom oxygen was initiated on discharge from a recent hospitalization but still 31.6% for those being evaluated after prior longstanding supplemental oxygen use.

Table 3. Indications for Prescribing Home Long-term Oxygen Therapy (LTOT) According to the American Thoracic Society

Pa,O2 mmHg	Sa,O2 %	LTOT indication	Main results
<55	<88	Absolute	None
55-59	89	Relative with qualifier	“P” pulmonale, polycythemia >55% History of oedema
>60	>90	None except with qualifier	Excersice desaturation Sleep desaturation not corrected by CPAP Lung disease with severe dyspnea responding to O2
Pa,O2: arterial oxygen tension: arterial oxygen saturation; Right heart failure; CPAP: continuous positive airways pressure; O2: oxygen

In summary, a review of existing oxygen delivery devices and conserving systems indicates that a variety of devices and systems are available but that basic questions regarding their use remain (1). As examples of unanswered questions, what are the benefits and indications for supplemental oxygen during exercise and sleep (1, 18, 19) and, if there is clear benefit, what are the optimal treatment targets (e.g., percent saturation values, etc.)? Do differences between the available oxygen-conserving devices regarding delivery strategies and flow profiles matter clinically and, if so, which strategy and/or devices should be recommended? How can healthcare providers be better prepared to optimally prescribe supplemental oxygen and what specific tactics are best suited to offer patients individually optimized care?

While we struggle with these larger technical, clinical, and healthcare system challenges and uncertainties, it is also appropriate to register some takeaway conclusions that have been the subject of prior oxygen consensus conferences and guidelines (15, 16, 34) but for which implementation and clinical practice lags. Importantly, as has been discussed in the 5th and 6th Long-term Oxygen Therapy Conference proceedings (15, 34), oxygen should be prescribed with the intent of optimizing the patient’s functional status and ability to engage in as full activity as possible. To do so, based on current, albeit inadequate knowledge and pending results of forthcoming trials like the NIH-sponsored Long-term Oxygen Treatment Trial (18), oxygen should be titrated during activity and sleep to assure adequate saturation and activity. Patients for whom oxygen has been recently prescribed should be evaluated within 90 days regarding the ongoing need for supplemental oxygen. Should the physiologic need for supplemental oxygen not persist, the oxygen should be discontinued. Finally, clinicians must be mindful of what has been called the “fallacy of equivalence,” i.e., that numeric settings on oxygen-conserving devices are equivalent to liter flow rates using continuous flow (17). Because numeric settings on conserving devices are neither standard across devices nor in any way equivalent to continuous flow rates (5,17), patients using such oxygen-conserving systems must be tested and titrated regarding the adequacy of their oxygen prescription using the actual delivery and conserving device they are using at home. In the office setting, this requires asking patients to bring their ambulatory systems with them on office follow-up visits so that titrating studies can be performed with their own equipment.

The hope is that future research will both identify ways to enhance compliance with currently understood optimal practice and will answer remaining questions that interfere with optimal care today.

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