The Clinical Impact of New Long-Term Oxygen Therapy Technology
Patrick J Dunne MEd RRT FAARC
Introduction
Traditional Long-Term Oxygen Therapy Systems
Stationary Systems
Portable Systems
Oxygen-Conserving Technology
Titrating Patients to Oxygen-Conserving Devices
Limitations of Traditional Portable Systems
New Long-Term Oxygen Therapy Technology
Non-Delivery Long-Term Oxygen Therapy Systems
Portable Oxygen Concentrators
The Long-Term Oxygen Therapy Continuum
Oxygen as a Controller Medication
Optimum Long-Term Oxygen Therapy Dosing
Effect of Increased Respiratory Rate on Fraction of Inspired OxygenRole of the Respiratory Therapist With New Long-Term Oxygen Therapy
Technology
SummaryLong-term oxygen therapy (LTOT) improves survival for patients afflicted with severe chronic obstructive pulmonary disease and may also reduce the incidence of repeat hospitalization due to exacerbations.
When properly dosed and titrated, LTOT has also been shown to improve exercise tolerance, thereby
enhancing the overall health-related quality of life for this growing patient population. Equipment used
to provide LTOT is undergoing a radical transformation, with newer delivery devices offering a sharp
contrast to older, more traditional home oxygen equipment. This newer approach to providing LTOT—
commonly referred to as “non-delivery technology”—affords LTOT users unprecedented freedom,
since they are no longer dependent on home-care providers for repeat deliveries to replenish or replace
depleted oxygen contents. Instead, non-delivery LTOT equipment is self-sufficient and able to provide
all of the oxygen needed to meet both stationary and ambulatory requirements. However, several modelsof the newer LTOT equipment have certain operational and performance limitations. Accordingly, inorder to preclude unintended desaturation with newer LTOT devices, each patient must undergo anindividualized pulse-oximetry titration study by a knowledgeable and experienced respiratory therapist
to ensure optimum dosing under all conditions of use. Key words: long-term oxygen therapy, LTOT, chronic
obstructive pulmonary disease, COPD, oxygen-conserving technology, portable oxygen concentrator. [Respir
Care 2009;54(8):1100 –1111. © 2009 Daedalus Enterprises]

Patrick J Dunne MEd RRT FAARC is affiliated with HealthCare Productions, Fullerton, California.
Mr Dunne presented a version of this paper at the symposium COPD:
Empowering Respiratory Therapists to Make a Difference, at the 54th
International Respiratory Congress of the American Association for Respiratory Care, held December 13-16, 2008, in Anaheim, California. The

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symposium was made possible by an unrestricted educational grant from
Boehringer Ingelheim.
Mr Dunne has disclosed a relationship with SeQual Technologies.
Correspondence: Patrick J Dunne MEd RRT FAARC, HealthCare Productions, Sunny Hills Station, PO Box 5767, Fullerton CA 92838-9998.
E-mail: pjdunne@sbcglobal.net.

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THE CLINICAL IMPACT OF NEW LONG-TERM OXYGEN THERAPY TECHNOLOGY
Introduction
Long-term oxygen therapy (LTOT) is the administrationof low-flow supplemental oxygen that traditionally is administered at doses of 1– 4 L/min. When appropriately prescribedand correctly used, LTOT has been shown to improve survival in patients afflicted with severe chronic hypoxemia secondary to chronic obstructive pulmonary disease (COPD).1-5
Aside from minimizing the sequelae associated with untreatedchronic hypoxemia (eg, pulmonary hypertension, cor pulmonale, congestive heart failure), LTOT has also been shown toconfer a modest but definite enhancement in neuropsychological function in patients with longstanding hypoxemic
COPD.6-8 In terms of maximum benefit, studies have confirmed that continuous oxygen (ⱖ 15 h/d) is superior to intermittent or nocturnal LTOT.2 More recently, in a re-analysis of data from the landmark 1980 Nocturnal Oxygen
Therapy Trial, Petty and Bliss discovered that those subjects
using continuous LTOT who also reported high daily walking activity, seemed to derive maximum benefit over others(both nocturnal and continuous users) reporting low daily
walking activity.9
An economic benefit is likewise derived from LTOT. Effective treatment of chronic hypoxemia reduces exacerbations, which, more often than not, translate into costly andoften life-threatening re-hospitalizations.10 The value of
LTOT as a standard of care for severe chronic hypoxemia
is evidenced by its inclusion in the current Global Initiative for Chronic Obstructive Lung Disease (GOLD) Guidelines, an evidenced-based international document detailing
how COPD should be diagnosed, staged, managed, and,perhaps most importantly, prevented.11
The therapeutic objective of LTOT is to relieve chronic
hypoxemia. This is typically accomplished by the administration of a prescribed dose of supplemental oxygen administered via nasal cannula, although LTOT can also be administered via a transtracheal oxygen catheter.12,13 LTOT is
usually not administered via oxygen face masks, since thesedevices require a minimum flow rate of 8 L/min to reduce thelikelihood of rebreathing of exhaled CO2.14 The clinical goalof LTOT is to elevate the patient’s fraction of inspired oxygen (FIO2) such that the PaO2 is maintained ⱖ 60 mm Hg or,correspondingly, to maintain an arterial oxygen saturation
ⱖ 90%.15 When blood oxygen levels fall and remain precipitously below those values for a sustained period of time,
serious cardiovascular consequences are observed, most notably pulmonary hypertension with resultant right-heart failure.16 It has been suggested that the survival benefit observedwith sustained use of LTOT is related in part to the amelioration of pulmonary hypertension.17 It is estimated that there
are currently more than 1.3 million Americans receiving
LTOT.18 As the number of patients diagnosed with COPD is
expected to double in the next 7–10 years, the demand for
LTOT is certain to increase as well.19-21

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Traditional Long-Term Oxygen Therapy Systems
Stationary Systems
When LTOT is prescribed, it is intended to be used continuously. Most COPD patients spend the majority of theirtime in and around their home, where LTOT is traditionallyprovided using one of 2 types of large stationary system: astandard oxygen concentrator, or a liquid-oxygen (LOX) system.22 To facilitate movement in and about the home environment, patients can be connected to their stationary systemwith up to 50 feet of supply tubing. Should there be cause toambulate beyond that distance, either within the home or out
into the community, a portable oxygen device will be required if LTOT is to remain uninterrupted.
Oxygen concentrators, electrically powered devices weighing 35–50 pounds, employ air-separation technology and arecapable of delivering up to 6 L/min of concentrated oxygen(ⱖ 85%), although there are now several models of concentrators capable of providing up to 10 L/min. When properly
dosed, concentrated oxygen has proven to be more than sufficient to achieve the desired clinical goal of elevating andmaintaining the PaO2 ⱖ 60 mm Hg. Oxygen concentrators areeasy to operate and require minimal maintenance by the patient, although they do require an uninterrupted source ofhousehold electrical current. In that regard, sustained disruptions of electrical power, as experienced during severe weather
or other natural disasters, are problematic.
By contrast, the main component of a LOX stationary
system is a large base unit (referred to as a “dewar”), which
is a specially designed “thermos-type” container that stores
oxygen in its liquid state at ⫺273°F. Through controlled
evaporation, LOX is converted to United States Pharmacopoeia grade gaseous oxygen, which is in turn delivered to thepatient at the prescribed liter flow.22 However, as oxygen
contents are depleted, the dewar requires periodic refilling by
the home-care provider. Since the procurement, storage, andtransportation of LOX requires special equipment and compliance with additional regulatory requirements, these systems are not considered to be as cost-effective or as convenient as an oxygen concentrator. However, LOX systems dooffer one important advantage, most notably for those LTOT
patients who spend a large amount of time beyond the confines of their stationary system, as will be described shortly.
Figure 1 illustrates a standard oxygen concentrator and a
LOX stationary system.
Portable Systems
When patients must leave their home for a few hours(eg, to visit their physician or to shop for groceries), LTOT
should not be interrupted. Accordingly, as part of their
LTOT prescription, patients are also provided a small,portable oxygen-delivery system to complement their stationary system.22 As with stationary systems, there are also
2 traditional ways to provide portable LTOT.

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THE CLINICAL IMPACT OF NEW LONG-TERM OXYGEN THERAPY TECHNOLOGY

Fig. 1. Left: Standard oxygen concentrator. (Courtesy of Invacare,
Elyria, Ohio.) Right: Two liquid-oxygen (LOX) dewars. (Courtesy of
Caire Medical, Ball Ground, Georgia.)

The most common approach is the use of small, lightweight aluminum gaseous-oxygen cylinders (size M-6) thatare usually carried or, if need be, can easily be pulled on acart. However, with smaller cylinders, especially if they arelight enough to be carried, there is the tradeoff of limited
oxygen capacity. For instance, a patient with an LTOT prescription of 2 L/min will deplete an M-6 cylinder having a
total capacity of 164 L of gaseous oxygen in little more than
one hour. One way to extend the amount of time away fromthe stationary system would be to use a larger vessel, such as
an aluminum E cylinder having a capacity of 622 L of gaseous oxygen. At 2 L/min, a full E cylinder would last approximately 5 hours. However, an E cylinder with cart andregulator weighs in excess of 20 pounds, making this portablesystem unwieldy and extremely difficult to maneuver. This
contrasts sharply to the aforementioned M-6 cylinder, which,including regulator, weighs less than 5 pounds and is easily
carried.
The second option for providing traditional ambulatory
oxygen is to couple the aforementioned stationary LOX dewar with a smaller, portable LOX container that the patient
can refill from the stationary dewar prior to ambulation. In
the past this has been the main advantage of LOX systems,
especially for those patients who spend a great deal of the dayaway from home (ie, several hours a day on 2–3 or more days
per week). Since the home-care provider needs to refill thestationary LOX base unit approximately every 10 –14 days,
this traditional portable option is considered to be more costeffective for high ambulatory patients. However, many LTOT
patients, especially the very frail elderly, have difficulty refilling the portable LOX canister. Figure 2 illustrates a small
lightweight gaseous-oxygen cylinder with carrying case anda refillable portable LOX device.
Oxygen-Conserving Technology
A major drawback of both of the traditional continuousflow LTOT portable systems is the limited amount of time1102

the patients could be away from their stationary system. The
introduction of oxygen-conserving technology in the mid1980s for both gaseous oxygen and LOX portable systems
offered a creative solution.23 Rather than delivering oxygen
continuously, an oxygen-conserving device (OCD), which isan integral part of the oxygen regulator, dispenses oxygen
only intermittently. Instead of continuous flow, an OCD intermittently delivers a pre-set volume or bolus of oxygen,
which is measured in mL per breath. The bolus is delivered
in response to the patient’s inspiratory effort (or demand), as
detected through the nasal cannula. The bolus is delivered
during the first 60% of the patient’s inspiratory portion of thebreathing cycle.24-25 Hence, oxygen is not flowing—and thus
is not being wasted— during the remainder of each breathingcycle. Because the delivered dose of oxygen via intermittent
bolus is different from the physician’s continuous-flow prescription, a separate prescription is required whenever an OCD
is substituted.
OCDs allow patients to spend considerably more timeaway from the stationary system than continuous flow.
However, the actual length of time a particular cylinder or
LOX canister will last with an OCD is a function of:cylinder/canister size and capacity, the model of OCD
being used, and the patient’s respiratory rate.26
Titrating Patients to Oxygen-Conserving Devices
An important consideration when using any oxygen-conserving technology is to ensure that the delivered bolus ofoxygen is sufficient to maintain the same degree of oxygen
saturation that was attained with the physician’s original continuous-flow prescription. A common misperception is that anumerical setting on a particular OCD (eg, 1, 2, 3) is equivalent to the numerical settings on an oxygen flow meter. They
are not at all equivalent.27,28 The numerical settings on an
oxygen flow meter denote L/min of continuous flow, whereas

Fig. 2. Left: Standard portable gaseous-oxygen cylinder with oxygen-conserving device. (Courtesy of Western Medical, Westlilake, Ohio.) Right: Refillable portable liquid oxygen canister. (Courtesy of Caire Medical, Ball Ground, Georgia.)

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the numerical settings on an OCD indicate the relative sizesof the delivered boluses. Adding further confusion, a numerical setting of 2 on one particular model of OCD will delivera bolus of oxygen that may be larger or smaller than a settingof 2 on a model from a different manufacturer. Further, thebolus waveform will be different for each model. Unfortunately, product performance standardization is lacking andconfusion reigns.26
This gives rise to a major clinical concern that patients
may inadvertently be at risk for desaturation if an unsuspecting clinician simply sets the numerical setting on an OCD tothat of the continuous-flow prescription. For example, a patient with an LTOT prescription of 2 L/min may, in fact,
maintain adequate oxygenation when using a particular model
OCD set at 2 while resting in the sitting position, which could
only be ascertained via pulse oximetry. In this example, theOCD would be described as providing “functional” or “clinical” equivalency to the continuous-flow prescription, but only
under the condition of rest while in the sitting position. Should
this patient move to a different activity level, such as casual
walking or even structured exercise, then functional equivalency might be achieved only when the OCD is set at 3,
perhaps 4, or possibly never, again as could only be determined via pulse oximetry. Further, should a different modelof OCD be placed on this same patient under similar conditions, the numerical setting(s) used for the former OCD, in all
likelihood, would not necessarily provide the same degree ofoxygenation when selected on the replacement model.
The importance of the need to use pulse oximetry to individually titrate each individual when initially placed on an
OCD is underscored by recommendation 5 from the Sixth
Long-Term Oxygen Therapy Consensus Conference, held in
August 2005, which states, “All patients who are provided anintermittent-flow device (which is one category of oxygenconserving device) must be clinically evaluated and titrated
to the intermittent flow required by the specific device being
employed, in order to ensure optimal oxygen delivery for that
individual patient during rest and during routine activities ofdaily living.”29 This recommendation was later reaffirmed
and included in the August 2007 revised clinical practiceguideline for Oxygen Therapy in the Home or Alternate Site
Health Care Facility, developed and published by the American Association for Respiratory Care.30
Limitations of Traditional Portable Systems
While traditional portable LTOT systems employing OCD
technology have been used effectively for the past 3 decades,
one important issue remains: the amount of time a patient
may be away from their stationary system is limited. The
length of time of an excursion will be determined by theamount of oxygen contents (gaseous or liquid) contained in
the portable device, and the frequency of excursions will belimited by the available supply of oxygen contents in the

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home. Since one of the biggest fears LTOT patients have is“running out of oxygen,” ambulation is somewhat limitedwith traditional LTOT systems. Patients are always mindfulof the need to return home to their stationary system before
their portable supply is depleted. There are also issues associated with the continuing need to contact the home-careprovider to schedule home deliveries to obtain the neededrefills, and the anxiety of not knowing if the delivery will
occur in time for their next ambulatory excursion, planned orotherwise. The net effect is that spontaneous ambulation beyond the confines of the stationary system is not always
possible, and concerns over the availability of sufficient portable oxygen often becomes a disincentive to ambulation in
general.
Home oxygen providers are likewise dealing with theirown uncertainties regarding the need for frequent home deliveries to replenish depleted oxygen contents. Their concerns are driven in part by economic imperatives as well as
by newer clinical insights. In terms of economics, recent
Medicare policies and cuts in reimbursement levels for LTOT
equipment are cause for concern.31 Since one of the major
uncompensated costs that home oxygen providers encounteris repeat home deliveries to replace depleted contents, there is
growing concern that the frequency of such deliveries willneed to be further curtailed.
At the same time, there is growing evidence that patientswith COPD who perform a relatively high level of physicalactivity in their daily life on a sustained basis have a substantially reduced risk of readmission due to an exacerbation.32 It appears that regularly scheduled extended excursions out of the home into and around the community are not
only clinically advantageous, but add significantly to the overall quality of life for this patient population.33 Further, thescientific evidence of the clinical, psychological, and economic advantages of having COPD patients participate in aformal pulmonary rehabilitation program continues togrow.34-36 For many COPD patients, successful participation
in a pulmonary rehabilitation program entails the need for
ample portable oxygen, especially when structured walking
exercise is attempted.37 Any disruption to the unencumbered
access to unlimited portable oxygen quickly becomes a deterrent to subsequent participation. Fortunately, we are now
witnessing a veritable explosion of new technology for providing both stationary and ambulatory LTOT that contrasts
sharply with the older, more traditional equipment developed
and used during the late 20th century.
New Long-Term Oxygen Therapy Technology
Non-Delivery Long-Term Oxygen Therapy Systems
This newer, 21st-century LTOT technology has been described variously as “non-delivery” or “delivery-less,” due to1103

THE CLINICAL IMPACT OF NEW LONG-TERM OXYGEN THERAPY TECHNOLOGY
Portable Oxygen Concentrators

Fig. 3. Left: Concentrator that transfills a gaseous cylinder. (Courtesy of Invacare, Elyria, Ohio.) Right: Liquefier that transfills liquid
oxygen canister. (Inspired Technology, North Huntington,
Pennsylvania).

the fact that the home-care provider no longer has to makeperiodic home deliveries to replenish depleted gaseous or
LOX contents.27 A non-delivery LTOT device is self-sustaining— capable of producing ample oxygen to effectively provide for both stationary and ambulatory needs. This new
approach makes the LTOT user relatively self-sufficient interms of in-home use, ambulation (both within and outside of
the home), mobility, and overall lifestyle. Home oxygen providers are also finding that non-delivery LTOT technology
can be a very cost-effective alternative to the expense ofmaintaining traditional stationary and portable systems withrepeat home deliveries.
Concentrators That Transfill. Non-delivery systems areeither novel variations or scaled versions of traditional
oxygen concentrators. One approach is the use of a standard oxygen concentrator, which, when coupled with an
external pressure booster, can transfill a small, lightweightportable cylinder with pressurized concentrated oxygen.
One particular system goes even further and transfills asmall LOX-like canister with liquefied concentrated oxygen. Regardless of which of these novel transfilling approaches is used, patients are able to reuse the cylinder/
canister, which has an integral OCD, for their ambulatoryneeds. When they return home, it’s a simple matter ofattaching the empty cylinder/canister for refilling, and inseveral hours they are ready for their next excursion. However, this approach to non-delivery technology does haveits limitations. Since patients must return home each day,they are essentially tied to their home stationary unit. Further, these units are entirely too heavy to be transported
outside of the home. Figure 3 illustrates non-delivery systems that are able to provide in-home transfilling of gaseous-oxygen cylinders or LOX-type canisters.

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Portable oxygen concentrators (POCs) represent anothernon-delivery approach to providing LTOT. POCs are scaled
versions of standard concentrators, and there are 2 types:
POCs that can deliver oxygen only in the pulse-dose mode,and those capable of delivering oxygen in either the continuous-flow or pulse-dose mode. All POCs are lightweight,
user friendly, esthetically pleasing, and easily transportable. POCs can be powered by standard household alternating current, direct current (available in motor vehicles),or by a rechargeable battery. Thus, POCs afford LTOT
patients a heretofore unavailable luxury: the freedom to go
wherever they want, whenever they want, and however
they prefer to travel, including aboard commercial aircraft.38,39
Pulse-dose-only POCs are the lightest in weight (5–10 pounds), but the trade-off is a limitation on how muchtherapeutic oxygen (ie, ⱖ 85%) they are able to produce in
one minute’s time. The maximum oxygen production capabilities of existing pulse-dose POCs range from 480 mL/
min to 1,040 mL/min, thus limiting their operation topulse-dose delivery only, similar to what was described
previously with OCDs. However, while the OCDs wereintended to be used only during ambulation, pulse-doseonly POCs are increasingly being promoted as effective
for providing both stationary and ambulatory LTOT.
This raises important questions about the effectiveness andsafety of providing all LTOT via intermittent bolus delivery on a 24-hours-a-day, 7-days-a-week basis especiallysince the 2 landmark studies that demonstrated the survival benefit of LTOT used continuous flow delivery.2,3
Clearly, further research is needed to demonstrate that thesame outcomes can be attained using pulse-dose-only delivery devices. Figure 4 illustrates several POCs that can
only operate in the pulse-dose delivery mode.
A POC with higher oxygen production capabilities canoperate in either the continuous-flow mode (0.5–3 L/min)or in the pulse-dose mode during ambulation, to conserve
battery life. The more robust oxygen production capabilities of this non-delivery device (3,000 mL/min) offers
clinicians more options over pulse-dose-only POCs whenproviding LTOT on a 24-hours-a-day, 7-days-a-week basis. A POC with higher oxygen production capabilities isslightly heavier than pulse-dose-only POCs (17 pounds vs
5–10 pounds), and unlike certain pulse-dose POCs,
cannot be carried with a shoulder strap. However, it can beeasily lifted into and out of an automobile with an integral
handle and is easily pulled on a wheeled cart. Of interest
is a recent study that compared patients’ exercise capacity
when they carried their portable oxygen system or used awheeled cart.40 Patients performed significantly better on a
6-min walk test and had a better Borg score when theypulled their portable oxygen system than when they carried

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THE CLINICAL IMPACT OF NEW LONG-TERM OXYGEN THERAPY TECHNOLOGY

Fig. 4. Four models of pulse-dose-only portable oxygen concentrator. (Courtesy of (A) Respironics, Murrysville, Pennsylvania; (B) Invacare,
Elyria, Ohio; (C) Inogen, Goleta, California; and (D) AirSep, Buffalo, New York.)

the same system, suggesting that carrying a portable oxygen system might not be appropriate for all patients, regardless of the weight of the device. At this writing, there
is only one POC capable of operating in either the continuous-flow or pulse-dose mode (Fig. 5). No doubt as
non-delivery technology continues to evolve, we will see
further additions to this type of LTOT device.
Table 1 lists common operational and performance parameters of commonly available POCs.
The Long-Term Oxygen Therapy Continuum
As with traditional oxygen equipment, it is importantthat a non-delivery LTOT system, whatever the design,
provide ample protection from desaturation, regardless ofa patient’s type or intensity of activities of daily living.
One way to frame this important requirement is to think of
LTOT as a treatment intervention that must be effective
across a continuum of activities that each patient experiences throughout every day (personal communication,
Ron F Richard, SeQual Technologies, San Diego, California, April 2008). Individual oxygen requirements vary foreach patient as they move back and forth across the LTOT
continuum, as depicted in Figure 6.
At one end of the continuum we have sedentary use,
where the majority of daily LTOT use occurs. At this pointin the continuum, patients are typically at home, generally
resting and occasionally performing various, non-stressful
domiciliary activities of daily living such as personal hygiene, meal preparation, and possibly even light housekeeping. Systemic oxygen demand is at its lowest at thispoint on the continuum, and, accordingly, the amount of
supplemental oxygen required to ensure adequate saturation is likewise at its lowest.

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Fig. 5. This portable oxygen concentrator can operate in either
continuous-flow (0.5–3 L/min) or pulse-dose mode (settings 1– 6).
(Courtesy of SeQual Technologies, San Diego, California.)

However, when temporarily transitioning to the activity
portion of the continuum, there are a range of activities,
from casual walking to participation in structured pulmonary rehabilitation, that contribute to an increase in systemic oxygen demand. The increased oxygen demand is in
direct response to the intensity and frequency of activity
and often results in a concomitant increase in the patient’s
respiratory rate. Thus, any ambulatory LTOT device usedduring activity must be capable of providing sufficienttherapeutic oxygen to meet the higher systemic demands,
as well as responding to increased respiratory rates if arterial desaturation is to be avoided. When desaturation
does occur with a certain activity type or intensity, patientstypically cease performing that activity due to the distressof the accompanying dyspnea.
Oxygenation requirements during sleep may also be different from what is required during rest or activity. Although the neuro-chemical control of breathing during sleep

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THE CLINICAL IMPACT OF NEW LONG-TERM OXYGEN THERAPY TECHNOLOGY
Table 1.

Performance Characteristics of Several Models of Portable Oxygen Concentrator

Model

Company

Weight(lb)

Maximum
OxygenProduction(mL/min)Flow
Settings

Pulse
Settings

Maximum
Bolus Size(mL)

Maximum
FIO2 at20 breaths/min

FreeStyle
Inogen One
XPO2
EverGoEclipse 2

AirSep, Buffalo, New York
Inogen, Goleta, California
Invacare, Elyria, Ohio
Respironics, Murraysville, Pennsylvania
SeQual Technologies, San Diego, California

6
10
7
10
17

480
750
900
1,050
3,000

NA
NA
NA
NA
0.5–3.0 L/min

1–3
1–5
1–5
1–6
1–6

26
26
42
36
96

0.27 at setting 3
0.29 at setting 50.24 at setting 50.32 at setting 6
0.42 at setting 6

FIO2 ⫽ fraction of inspired oxygenNA ⫽ not available(Adapted from References 26 and 28.)is the same for COPD patients as it is for normal subjects,
there is diminished responsiveness and blunted sensitivity
with COPD.41,42 This leads to a higher incidence of nocturnal desaturation, especially in those patients with moreadvanced disease, who are prone to periods of transienthypoventilation with resultant alveolar gas-exchange dysfunction.43 Such episodes of desaturation, not unexpectedly, are most profound during periods of rapid-eyemovement (REM) sleep.44-46 To help mitigate nocturnal
desaturation in COPD patients receiving LTOT, in 1995
the American Thoracic Society promulgated guidelines
suggesting that the oxygen dose should be increased by
1 L/min over the regular prescription during periods ofextended exercise and sleep.47 A similar recommendation
appeared 15 years earlier in the Nocturnal Oxygen Therapy Trial.2 However, more recent studies cast doubt on
this recommendation when they were unable to show nocturnal desaturation was an absolute in every COPD patient using LTOT.48,49 Nonetheless, it is still good clinicalpractice to confirm that the prescribed dose for daytime
LTOT is sufficient to prevent exercise and/or sleep induced desaturation.
It should be noted that there is a subset of patients who,
in addition to COPD, also have obstructive sleep apnea
syndrome as a comorbid condition. The presence of bothconditions is now commonly referred to as overlap syndrome.50,51 Not surprisingly, the degree of nocturnal desaturation is even more profound in patients with overlap
syndrome, and in this patient population effective treat-ment must also include, in addition to LTOT, a nightly
regimen of positive-airway-pressure therapy.52
The last point on the LTOT continuum is altitude, essentially those instances where a decrease in atmospheric pressure results in a lower partial pressure of inspired oxygen.
The most common example of this would be patients whopermanently reside at a higher elevation (eg, Denver at 5,280ft), as well as those who occasionally travel to altitude in apersonal or commercial motor vehicle for business or pleasure. It would also include those COPD patients who takeadvantage of the new United States Department of Transportation policy requiring United States air carriers to permit
approved POCs to be brought aboard a commercial aircraft
for in-flight use.38,39 In each of the above situations, depending on the degree of chronic hypoxemia, there may be a needfor a higher dose of delivered oxygen than would otherwise
be the case at sea level, but this would need to be determinedon a case-by-case basis.
In summary, the systemic oxygen needs of patientsvary as they transition back and forth across the LTOT
continuum. It is therefore important that any non-delivery
device used to provide both stationary and ambulatory LTOT
be capable of providing sufficient concentrated oxygen in thedose required to protect the patient from desaturation.
Oxygen as a Controller Medication
Whether it is United States Pharmacopoeia grade, as ismost often found in institutional settings, or concentrated,

Fig. 6. The long-term oxygen therapy continuum. The primary clinical objective is to ensure adequate oxygenation/saturation (SpO2 ⱖ 90%)across the entire LTOT continuum at all times.

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as is largely used in home care, oxygen is a drug. Accordingly, the United States Food and Drug Administration,
regardless of care setting, requires that oxygen be dispensed only upon the written order of a licensed physician.
Additionally, state pharmacy boards likewise require thatthe storage, dispensing, and maintenance of oxygen equipment be controlled and do so by imposing strict personnel
requirements and facility standards for home-care providers. Clearly, it is the position of both the Food and Drug
Administration and state pharmacy boards that the unauthorized or inappropriate use of oxygen and oxygen-delivery equipment has the potential to result in real harm or
injury to the public.
LTOT is a controller medication, and in this respect isno different than any other inhaled medication prescribedto manage chronic respiratory symptoms of bronchoconstriction or airway inflammation. Physicians prescribe
LTOT to control the symptom of chronic hypoxemia.
The dosing of oxygen in the hospital setting for COPD
patients recovering from an exacerbation is well controlled and closely monitored. Specific therapeutic goals
are defined, with the goal of in-patient oxygen therapy toprevent tissue hypoxia and to preserve cellular oxygenation.15 Typically, the flow rate is adjusted to maintain a
PaO2 ⱖ 60 mm Hg or an arterial oxygen saturation ⱖ 90%.
The device setting is easily monitored by noting the setting
on the flow meter connected to the oxygen source. The
delivered dose of supplemental oxygen in turn elevates theFIO2, which ultimately determines the oxygen partial pressure in the alveolar gas-exchange areas. Since it is difficult
to measure with precision the actual inhaled FIO2, especially when using a low-flow oxygen-delivery system suchas a nasal cannula, the degree of arterial oxygen saturation
is most often used as a surrogate indicator.53,54 Accordingly, the liter flow is titrated up or down depending on thepatient’s response to therapy, as determined via pulse oximetry.
As the patient’s condition improves and preparations
are made for discharge, the decision to continue oxygen therapy is made based upon the severity of the disease state, and, most importantly, the degree of chronic
hypoxemia. Assuming the patient meets the requisite clinical and laboratory criteria, arrangements are made for
LTOT. The prescribed dose for LTOT is usually a reflection of the liter flow the patient received up to the time ofdischarge.

LTOT.24,26 In terms of physiologic response, the focus has
been on maintaining the PaO2 at or slightly above 60 mm Hg
or the arterial oxygen saturation at or slightly above 90%.15
Whether or not these physiologic values are optimally therapeutic has never been firmly established, leading one
preeminent pulmonary researcher to recently lament that,“we are remarkably casual in clinical practice about how
we assign supplemental oxygen dose.”54 However, theavailability of newer analytical technology, specificallythe latest generation of highly accurate and reliable portable pulse oximeters, provides a useful tool to determine
optimum dosing.
The actual targets for optimum arterial oxygen saturation levels for stable chronic hypoxemia remain to be empirically determined for each position on the LTOT continuum. However, a recent study evaluating the ability of
4 ambulatory oxygen systems to protect against exerciseinduced desaturation gives rise to an interesting “what if”
scenario.55 Subjects in that study (n ⫽ 39) were randomly
oxygenated for 5 min on each of the 4 devices being
evaluated before undergoing a 6-min walk test to assess
functional exercise capacity. While the reported mean prewalk saturation measured via pulse oximetry (SpO2) was
95%, the actual saturation values ranged from 88% to100%, indicating that while some of the subjects weresaturated to the high 90% range, others were saturated
only to levels at the lower end of the range (88 –90%).
While those authors did not specifically target a set prewalk saturation level, there did not appear to be any adverse effects for those subjects who did achieve a pre-walksaturation level well into the high 90% range. Of interestis that 44% of the subjects were unable to complete theentire 6-min walk test. The reported mean walking timewas 4.6 min, the mean post-walk SpO2 was 88% (range
70 –99%), and the mean pre-walk versus post-walk difference in oxygen saturation range was 6 ⫾ 4% to 7 ⫾ 5%.55
In essence, the data suggest that all four of the tested
devices failed equally in their ability to protect the subjects
from exercise-induced desaturation. One wonders what theresults of the study (distance walked relative to the level ofdesaturation) would have been had each of the subjects
been specifically titrated to a pre-walk saturation of 95–
96% on each of the 4 modalities tested and the stabilization period was for a minimum of 15 min, versus the 5 min
period used in the study? The validity of this conjecture
remains to be empirically determined.

Optimum Long-Term Oxygen Therapy Dosing

Effect of Increased Respiratory Rate on Fraction of
Inspired Oxygen

Regrettably, there is still no definitive data on what
constitutes the optimum dose for LTOT. For years, continuous flow has long been held to be the accepted standard, and, as such, 2 L/min was ordered (and is continuing
to be ordered) for the majority of patients starting

RESPIRATORY CARE • AUGUST 2009 VOL 54 NO 8

As mentioned, continuous-flow delivery has historically
been the accepted standard for low-flow supplemental oxygen therapy.24,26 When using LTOT equipment that provides continuous flow, the home-care provider (most often

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THE CLINICAL IMPACT OF NEW LONG-TERM OXYGEN THERAPY TECHNOLOGY
a respiratory therapist [RT]) sets the flow meter at theprescribed setting. In this scenario the set liter flow isreadily identifiable. However, a bench study that looked at
2 L/min oxygen flow and the effect of increased respiratory rate on oxygen concentration found that the measured
FIO2 dropped when the respiratory rate increased.56 The
prevailing explanation for this finding is that as the respiratory rate increases, the inspiratory time is shortened,
reducing the amount of oxygen inhaled per breath.26 Another possible contributing factor is that a decrease in inspiratory time might also result in a higher flow of inhaledambient air, causing further dilution of the FIO2.
As observed with continuous oxygen flow, when a patient is using a pulse-dose-only POC and their respiratory
rate increases, there is the possibility that the delivered
FIO2 will decrease. A more recent bench study compared
the relative FIO2 observed with oxygen flow at 2 L/min tothat obtained with 4 pulse-dose-only POCs (also set at 2)
at varying respiratory rates.57 Figure 7 demonstrates thedrop in the FIO2 observed with continuous flow (as reported in the aforementioned bench study), but also reveals a similar drop in the measured FIO2 in 3 of the 4pulse-dose-only POCs tested under conditions of increases
in the simulated respiratory rate. This finding suggests thatcertain pulse-dose-only POCs, due to their limited capacity for therapeutic oxygen production, may not always beable to maintain the purity of concentrated oxygen (ⱖ 85%)in the face of significant increases in the patient’s respiratory rate.
Another concern over the limited oxygen production capabilities of certain POCs is when these devices are usedaboard a commercial airliner where internal cabin pressure isequivalent to 8,000 –10,000 feet. Since the number of LTOT
patients using this mode of transportation is expected to increase substantially, it is important that any POC used during
air travel is able to protect the integrity of the FIO2 to maintainadequate oxygenation. Having the oxygen requirements of apatient exceed the therapeutic oxygen production capacity ofa particular model of POC (eg, as may happen with a low
dose pulse-only POC28) could result in suboptimal oxygen
dosing.
Since current lung simulators cannot accurately model
the complex interaction of physiology and respiratory mechanics that ultimately determines actual oxygen delivery,
the results of in-vitro studies do not universally translate towhat would be observed in vivo. However, bench studies
are useful to alert clinicians to issues that should not beignored, and in this particular case that would be the effectthat increases in the respiratory rate might have on theinhaled FIO2.
Regrettably, the lack of standardization that we saw
previously during the discussion of OCDs has carried overto POCs. For example, a selected numerical setting on thecontrol panel of a POC, while an indicator of the bolus size

1108

Fig. 7. Effect of breathing frequency on fraction of inspired oxygenwith continuous flow at 2 L/min, with 4 pulse-dose-only portable
oxygen concentrators at the numerical setting of 2. (Adapted from
Reference 57.)

does not specifically denote the actual bolus size in mL.
Instead, the home-care therapist must consult product literature to try to figure out the actual bolus size per numerical setting. Since it is the volume of the pulse dose,
not the pulse dose setting, that ultimately determines thetherapeutic dose (ie, the FIO2), in a perfect world eachnumerical setting on the control panel of all POCs would
depict the delivered bolus size of oxygen in mL.
The difficulty in quickly discerning the delivered doseat each numerical setting on a POC underscores the importance of having a titration study done by a knowledgeable and experienced clinician whenever an LTOT patientis first connected to a pulse-dose-only POC, or when acontinuous-flow POC is first being used in the pulse-dosedelivery mode. Subsequent reassessments should also be
considered to ensure that the selected pulse-dose settings
remain effective, especially once the patient has been using the newer device for several days following discharge
from an acute hospital stay. The frequency of such reassessments is best determined by the home-care therapist
and should be guided by the patient’s rate of recovery
from the exacerbation and their subsequent response to theselected settings as they transition back and forth acrossthe LTOT continuum.58
Role of the Respiratory Therapist With New LongTerm Oxygen Therapy Technology
One of the unfortunate legacies of home-care services in
the United States is that formal recognition of and reimbursement for RTs is lacking. This is due in large measure
to the fact that when the Medicare program was launchedin the mid-1960s, the profession itself was barely 20 years
old and only just beginning to establish itself as an important allied health profession. Over the past several de-

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THE CLINICAL IMPACT OF NEW LONG-TERM OXYGEN THERAPY TECHNOLOGY
cades, several attempts to redress this oversight have been,
regrettably, unsuccessful. Nonetheless, as part of its longstanding commitment to ensure timely access to quality
respiratory care services by those afflicted with chronic
respiratory conditions, the American Association for Respiratory Care continues its efforts to gain reasonable recognition and fair reimbursement for the contribution thatRTs render in all post-acute-care settings. Until such timethat these efforts are successful, the formidable costs associated with having RTs employed by home-care companies will continue to be recouped under payments received under the durable-medical-equipment benefit under
Medicare Part B.
The major challenge is that the Medicare durable-medical-equipment benefit reimburses home-care providers
only for the purchase or rental of prescribed medical equipment. In fact, Medicare manuals detailing eligibility andcoverage criteria for the Part B durable-medical-equipment benefit specifically state that services provided by an
RT are not reimbursable. However, over the last 30 years,
reimbursement rates for LTOT equipment were sufficientenough to allow most home-care providers to more thancover the costs associated with having RTs on staff. The
services and care that home-care RTs provided, while uncompensated directly, resulted in better utilization of allprescribed respiratory equipment, including the safe andeffective introduction of newer technology, most notably
in LTOT and devices used for the diagnosis and treatmentof sleep disorders.
Unfortunately, recent reductions in Medicare monthly
reimbursement rates for LTOT equipment, coupled with a
newly implemented 36-month payment cap, has reawakened longstanding concerns about the continued viabilityof RTs in home care.31 In some respects, while undertaken
to control escalating health-care expenditures and to takeadvantage of plummeting acquisition costs for standard
oxygen concentrators, various Medicare initiatives over
the years have, albeit unintentionally, reduced a prescribed
therapeutic intervention to commodity status. There is decidedly more emphasis on LTOT equipment at the expense of focusing instead on more important clinical andpatient outcomes.
This gives rise to a serious concern with respect to thegrowing demand for new, non-delivery LTOT technology,
which by all accounts will eventually become the way of
the future. Non-delivery LTOT technology, while clearly
offering great economic and clinical advantages to homecare providers, patients, and prescribers alike, is not completely free of unintended adverse consequences. If notproperly interfaced with each patient by a knowledgeable
and experienced clinician using pulse oximetry to confirm
oxygen saturation levels are therapeutic, the potential forserious under-treatment is real. Indeed, the benefits reported from the use of LTOT are observed only with the

RESPIRATORY CARE • AUGUST 2009 VOL 54 NO 8

successful and sustained correction of hypoxemia.59 Furthermore, the under-prescribing, under-utilization, andinadequate titration of LTOT has been identified as a significant risk factor for COPD exacerbations and exerciseinduced hypoxia.60,61 Accordingly, RTs, in spite of theeconomic hurdles faced by home-care providers, are essential for the safe and proper transition to non-delivery
LTOT technology, and, for that matter, for the continued
effective use of traditional LTOT equipment. One can only
hope that home-care providers continue to appreciate thevalue of having RTs on staff to provide the care and services the vulnerable COPD patient population requires for
optimum disease management.
At the same time, RTs in all care settings need to ensurethat COPD patients requiring LTOT have the equipmentthat best suits their respective needs, especially as theclinical value of scheduled ambulation and/or structured
exercise without concomitant oxygen desaturation continues to be reaffirmed. To that end, RTs in the home-caresetting must remain current with all of the latest LTOT
technology, inclusive of the operational and performancecapabilities (and limitations) of all available devices. For
their part, hospital-based therapists should spend time with
their home-care colleagues to keep abreast of the latest
LTOT technology and of which options are readily available. In turn, home-care therapists should regularly visit
their hospital colleagues to share information about successful outcomes observed when new LTOT technology isused optimally. Lastly, RT in all practice settings should
never pass on any opportunity to ensure that patients witha chronic respiratory disease remain adherent to all prescribed controller medications, including LTOT. The clinical and economic impact of non-adherence with prescribed
respiratory controller medications and devices is staggering and, in addition to recidivism, contributes to a substantial waste of precious health care resources.62
Summary
The availability of new, non-delivery LTOT technology
has ushered in a new era for COPD patients requiring
supplemental oxygen to manage chronic hypoxemia. Nondelivery technology represents a new paradigm for homecare providers, but the technology comes at a time when
there is still a huge installed base of traditional LTOT
equipment. Home-care providers are therefore faced witha real dilemma to try to maintain—in the face of continuing reimbursement cuts and caps—an existing process thatis heavily dependent on repeat and costly home deliveries
to replenish depleted oxygen contents, or to begin thetransition to the more patient-centric, cost-effective, nondelivery process. While the new non-delivery technology
certainly has its advantages, the higher capital acquisition
costs associated with any newer technology cannot be ig-

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THE CLINICAL IMPACT OF NEW LONG-TERM OXYGEN THERAPY TECHNOLOGY
nored. Each home-care provider will eventually have todetermine if non-delivery technology does indeed represent a viable, cost-effective option. If the answer is yes,then the next decision will be to determine which specifictechnology will provide the best clinical and economic
outcomes. Adding to the decision-making dilemma is thefact that patients themselves are now learning about nondelivery technology through other channels (eg, from fellow LTOT users or the Internet), and many prefer the
new-found freedom that comes with having a single, selfsustaining and easily transportable oxygen-delivery device.
Patients are now starting to request the newer technology
from their home-care providers, and sometimes the requests are brand-specific.
However, not every patient can be effectively oxygenated with every type of non-delivery device. Accordingly,
home-care providers deciding to transition to non-delivery
technology must carefully evaluate which system will provide the greatest flexibility to the largest number of theirpatients. This will require a careful review of the existing
devices, with special attention paid to the actual delivered
dose (whether in L/min or mL/breath) and degree of oxygenation provided by each device at each numerical setting.27,28 Again, in the words of one preeminent pulmonary
researcher, “It is good clinical practice to titrate oxygen
dose with the device the patient will be using, at rest,
during exercise, and during sleep.”54
Along these lines, instead of continuing to use the traditional prescription indicating so many L/min, the timing could
not be more opportune for prescribing physicians to henceforth consider writing orders for LTOT that would direct the“RT to titrate LTOT” to a specific saturation target.63 Such an
approach to prescribing LTOT would ensure that each patient
was properly interfaced with their oxygen equipment by anacknowledged expert and that the determined delivered dose(s)would be based upon each patient’s individual needs as dictated by their respective life-style and activities of daily living
across the entire LTOT continuum. Further, fulfilling a “titrate to saturate” prescription by way of a standing protocol
would be equally advantageous.64,65 RTs have long been using a protocol-directed approach to providing care in thehospital setting, and the time to extend this patient-centric
approach to the home-care setting could not be better.66 Moreover, this would be the same whether one is using the older
traditional systems or one of the newer non-delivery technologies. In either case, the goal should be the same: to ensurethat adequate oxygenation is provided at times and at all
points across the LTOT continuum. Our patients deserve no
less.
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