Open Journal of Respi ratory Diseases, 2011, 1, 14-18
doi:10.4236/ojrd.2011.12002 Published Online November 2011 (
Copyright © 2011 SciRes. OJRD
Ambulatory Oxygen in Chronic Obstructive Pulmonary
Kah Yee Tham1,2, Devanand Anantham2
1Department of Internal Medicine, Singapore Gen eral Hospital, Singapore
2Department of Respiratory and Critical Care Medicine, Singapore General Hospital, Singapore
E-mail: anantham.devanand@
Received September 8, 2011; revised October 2, 2011; accepted October 20, 2011
Ambulatory oxygen has been shown to improve pulmonary hemodynamics and reduce dynamic hyperinfla-
tion in patients with Chronic Obstructive Pulmonary Disease. Therefore, it is hypothesized to be of benefit in
patients with either exertional desaturation or dyspnoea. There is evidence of short-term improvements in
exercise distance, exercise time, breathlessness, oxygen saturation and minute ventilation. However, longer
term studies only identified improvements in oxygenation and minute ventilation. The benefits were even
more limited in patients with no resting hypoxemia. The role in improving exercise training in pulmonary
rehabilitation by increasing exercise time and reducing dyspnoea was marginal and no improvements were
detected in walking distance or quality of life. Practical considerations make compliance with ambulatory
oxygen therapy a major issue with the weight of oxygen and social unacceptability the most often quoted
problems. The evidence for any benefit of ambulatory oxygen is therefore limited despite the theoretical
Keywords: Ambulatory Oxygen, Pulmonary Rehabilitation, Long-Term Oxygen Therapy, Chronic
Obstructive Pulmonary Disease (COPD)
1. Introduction
Since the 1980s, long-term oxygen therapy has been a
non-surgical intervention proven to improve survival in
Chronic Obstructive Pulmonary Disease(COPD) patients
with severe resting hypoxemia. Treatment requiring 15
hours of oxygen has been shown to reduce mortality
[1,2]. This forms the basis of standardized guidelines for
the prescription and maintenance of home oxygen ther-
apy. Long-term oxygen therapy may, however, be detri-
mental to patients’ quality of life and hinder efforts at
rehabilitation by rendering them homebound and con-
nected to stationary oxygen concentrators that require
direct wall currents for operation. It is postulated that
ambulatory oxygen may contribute to the survival by
enabling physical conditioning through improved mobi-
lity [3].
Exertional desaturation and dyspnoea portend a poorer
morality prognosis. [4-6]. In a prospective study of 579
patients, exercise de-saturation of more than 4% to a
saturation level of less than 90% conferred a 2.63 mor-
tality risk in COPD patients [7]. The mechanisms behind
exertional hypoxemia include ventilation perfusion mis-
match, shunting and limitations in diffusion capacity [8].
Supplemental oxygen may delay diaphragmatic muscle
fatigue and reduce lactic acidosis [9]. Oxygen has also
been shown to have a beneficial effect on pulmonary
hemodynamics by reducing the increase in pulmonary
artery pressure and pulmonary wedge pressures that is
experienced in exercise by patients with moderate to
severe COPD [10].
Dynamic hyperinflation has also been demonstrated as
a cause of exercise intolerance in COPD. A reduction in
inspiratory capacity by 0.37 ± 0.39 liters in these patients
during exercise showed a positive correlation with de-
creased maximum tidal volume attained during peak ex-
ercise (r = 0.79, p < 0.0005) [11]. The reduction of peak
tidal volume in response to increased ventilatory demand
contributes to exercise intolerance in COPD even in the
absence of exertional desaturation [11]. Hyperoxia via
supplemental oxygen is believed to reduce this ventila-
tory demand and reduce hyperinflation [12].
Currently there are no evidence-based guidelines for
the prescription of ambulatory oxygen. To address this
knowledge gap, this comprehensive review was carried
out using a literature search through internet based re-
search portal OvidSP and PubMed using the search terms:
“ambulatory oxygen”, “portable oxygen”, “rehabilita-
tion” and “oxygen”, “air travel”. A search for relevant
meta-analyses of randomized controlled trials and sys-
temic reviews via The Cochrane Library was also per-
2. Use of Ambulatory Oxygen
2.1. Patients Already on Domiciliary Long-Term
Oxygen Therapy
Long term oxygen therapy via an oxygen concentrator or
cylinder can potentially limit mobility, debilitate function
and risk deconditioning. There are meta-analysis data
showing short-term benefit of ambulatory oxygen in
COPD [13]. These data involve 31 studies consisting of
534 patients aged 47 to 73 with predominantly moderate
to severe airflow obstruction and a mean resting arterial
oxygenation of 52 mm to 85 mm Hg. Both maximal, as
well as, endurance exercise testing were performed. The
primary outcome of exercise capacity as measured by
exercise distance in endurance testing improved by 18.86
meters (95% confidence interval CI was 13.11 to 24.61
meters, n = 238) with oxygen therapy. Similarly, exercise
time increased by 2.71 minutes (95% CI, 1.96 minutes to
3.46 minutes, n = 77). In maximal exercise testing, am-
bulatory oxygen increased exercise distance by 32 meters
(95% CI, 20.61 meters to 43.38 meters, n = 70) and ex-
ercise time by 1.06 minutes (95% CI, 0.67 minutes to
1.46 minutes, n = 50).
Secondary outcomes such as breathlessness, oxygen
saturation and minute ventilation were not directly com-
pared because of the dependence of exercise perform-
ance and instead were compared at isotime i.e. the time
at which the group without oxygen ended the test. In
endurance testing, oxygen reduced breathlessness by
1.15 points on the Borg scale (95% CI, –1.65 Borg points
to –0.66 Borg points, n = 44); improved oxygen satura-
tion by 8.36% (95% CI, 5.08% to 11.64%, n = 29) and
reduced minute ventilation by 3.58 liters/minute (95% CI,
–4.85 liters/min to –2.31 liters/min, n = 52). Similar
findings were found on maximal exercise testing with
improvements in oxygen saturation of 7.82% (95% CI,
4.89% to 10.74%, n = 31) and reductions in minute ven-
tilation of 3.26 liters/minute (95% CI, –4.33 liters/minute
to –2.19 liters/minute).
Although another systematic review [13] with studies
of low heterogeneity provides evidence for the short-
term improvements of ambulatory oxygen on exercise
capacity in COPD, it is questionable if these statistically
significant improvements are really clinically significant.
The limitation in benefit achieved from supplemental
oxygen may be due to the fact that COPD patients reach
a ventilatory ceiling limit beyond which further im-
provements cannot be achieved with hyperoxia alone [9].
Furthermore, these studies do not provide guidance on
what target oxygen saturation to dose titrate supplemen-
tal oxygen nor inform us of the long-term impact of this
Another systemic review involving 2 randomized con-
trolled trials examined the longer-term effects of ambu-
latory oxygen on patients with COPD [14] and demon-
strated a statistically significant reduction in minute ven-
tilation during maximal exercise (weighted mean differ-
ence –11 liters/minute; 95% CI –17.53 liters/minute to
–4.47 liters/minute; p < 0.00097) and increased PaO2 at
rest (weighted mean difference 17 mmHg; 95% CI 9.13
mmHg to 24.87 mmHg) after 12 weeks. There were mo-
dest but statistically insignificant improvements in Borg
dyspnoea scores, distance walked and quality of life on
the Chronic Respiratory Disease Questionnaire.
2.2. Patients with Exercise Desaturation or
Ambulatory oxygen can improve exercise performance
by reducing dynamic hyperinflation as deduced by a
dose ranging study on non-hypoxaemic COPD patients
compared to healthy subjects [15]. Significant reduc-
tions in minute ventilation, end-expiratory lung volume
and respiratory rate with supplemental oxygen were
found. Improved endurance time negatively co-related
with end-expiratory lung volume (r = 0.48, p = 0.002)
and dyspnoea rating correlated with reductions in
respiratory rate at isotime. These benefits are seen in
dose dependent increments of oxygen flow rates and
oxygen fractions up to 50%.
Multiple small, single assessment studies have shown
acute improvements in exercise tolerance, maximal ex-
ercise capacity and breathlessness (measured by Borg
scores) in COPD patients on ambulatory oxygen. Oxy-
gen increased exercise distance by 32 meters and signi-
ficantly increased exercise time by 1.06 minutes. Dy-
spnoea improved by –1.16 Borg units [10]. 68% showed
a 54 meter improvement in 6-minute-walk and 56% had
clinically significant improvements in Chronic Respira-
tory Questionnaire [16]. Similarly, in a double-blind
randomized controlled trial of 11 patients with severe
COPD and exercise desaturation, the use of ambulatory
oxygen prevented hypoxemia; improved the distance
walked during 6-minut-walk test by 22%, and reduced
the level of dyspnoea by an average of 2.09 units [17].
However, such acute responses to hyperoxia have not
Copyright © 2011 SciRes. OJRD
been found to be directly predictive of long-term exerse
enhancements or quality of life [18,19].
Other recent studies have found no benefit of ambu-
latory oxygen over intranasal air in improving the extent
of exertional dyspnoea or quality of life in patients with
COPD. Results from a parallel, double-blinded, ran-
domized controlled study [12], involving 139 patients,
showed no significant differences between the ambu-
latory oxygen group versus placebo air in dyspnoea as
measured by either the Transitional Dyspnoea Index or
the Chronic Respiratory Disease Questionnaire; func-
tional outcomes as measured by the 6-minute-walk,
outings time or pedometer count; or health-related qual-
ity of life over 12 weeks. However, at baseline there was
an improvement in 6-minute-walk distance in oxygen
treated group by 10.7 ± 38.7 meters. The degree of exer-
cise desaturation was also not predictive of therapeutic
outcome [10,19]. These findings suggest that although
oxygen supplementation may improve short term exer-
cise tolerance, longer term benefits may depend on op-
timizing other factors that influence functional ability
such as cardiovascular and muscle capacity. In another
retrospective review of more than 400 patients with
emphysema and exercise-induced hypoxemia over 8
years, no significant difference in survival was seen
between the groups receiving continuous or intermittent
oxygen [6].
The lack of standardized criteria in the definition of
exercise desaturation continues to challenge research in
establishing the effect of ambulatory oxygen on patients
who develop hypoxemia on exertion. There are some
proposals that recommend that ambulatory oxygen be
prescribed to patients who demonstrate desaturation of
4% to an oxygen saturation of less than 90% on exer-
tion [20,21]. The Long-term Oxygen Treatment Trial
[LOTT] is an on-going multi-centre randomized con-
trolled trial that aims to study the survival benefit of
long-term domiciliary oxygen in 2 groups of COPD pa-
tients-a group with moderate hypoxemia (arterial satura-
tion of 56 to 65 mmHg at rest) and a group with exercise
desaturation. However, that study is unlikely to address
many of the issues in this controversial area [22].
2.3. Role in Pulmonary Rehabilitation
Pulmonary rehabilitation in COPD patients has shown
improvements in quality of life, exercise capacity and
perception of dypsnoea [23]. If the benefits of exercise
training lie in the duration and intensity of training; it
was hypothesized that with supplemental oxygen, these
patients could train longer. COPD patients with exerti-
onal desaturation area subgroup that may particularly
benefit. In a meta-analysis of 2 randomized controlled
trials comparing the use of ambulatory oxygen over pla-
cebo air in pulmonary rehabilitation, significant improve-
ments were seen in exercise time (weighted mean dif-
ference 2.68 minutes; 95% CI 0.07 minutes to 5.28 mi-
nutes), as well as a reduction in Borg dyspnoea scores by
a mean of –1.22 units (95% CI –2.39 to –0.06) [24]. No
significant differences were seen in exercise outcomes,
shuttle walk distance or health-related quality of life.
Wadell and colleagues demonstrated improved exer-
cise performance (increased distance in 6-minute walk
test by 14%), but there were no significant differences in
exercise training effects between supplemental oxygen
and air at the end of the rehabilitation period [25]. Simi-
larly, Garrod et al. demonstrated improvement in dysp-
noea scores by –1.46 units (95% CI –2.72 to 0.19) in
patients with severe COPD on ambulatory oxygen com-
pared to placebo room air, but there were no significant
differences in other outcome measures such as shuttle
walk test, Chronic Respiratory Disease Questionnaire,
Hospital Anxiety and Depression Scale and London
Chest Activity of Daily Living Scale [9]. There have
been no studies to prove survival benefit in the use of
supplemental oxygen in pulmonary rehabilitation. No
recommendations have been made regarding the use of
supplemental oxygen as an adjunct to pulmonary reha-
bilitation to improve survival [23]. Incidentally, there is
also no evidence of any detrimental effects of supple-
mental oxygen during pulmonary rehabilitation.
3. Practical Considerations
Despite the relief of symptoms and acute improvement in
exercise capacity, compliance to prescribed ambulatory
oxygen is less than 50% [16,26] A qualitative study of 27
patients with COPD revealed several barriers to the use
of ambulatory oxygen [27]. Patients listed weight of cy-
linder (92.5%), lack of patient education and perceived
benefits (92.5%), embarrassment of being seen with an
oxygen canister (77.8%) and lack of a carer (96.3%) as
reasons as to why they were not compliant with their pre-
scribed ambulatory oxygen [27]. Up to 50% of patients
report difficulties with their oxygen cylinders because of
poor portability or problems with the regulators [12].
Patients felt that despite the relatively lighter weight of
an ambulatory oxygen system, it still contributed to their
exertional dyspnoea and had a negative impact on their
mobility. Comfort and costs were also other reasons cited
by patients. Furthermore, relatively higher flow rates (6
liters/minute) may be needed in ambulatory oxygen
therapy compared to domiciliary oxygen in order to alle-
viate exertional symptoms [12]. These higher flow sys-
tems may dry the upper airways and require more fre-
uent refilling (Table 1). q
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Copyright © 2011 SciRes. OJRD
Table 1. Practical considerations in the prescription of ambulatory oxygen.
Factors Implications
Weight of cylinder 1). Increased exertional dyspnoea
2). Poor portability
Oxygen flow rates 1). Higher flow rates increase discomfort
2). More frequent refilling required (leading to increased cost)
Limited capacity of canister 1). More frequent refilling required (leading to increased cost)
Embarrassment 1). Non-compliance
Lack of patient education
Lack of perceived benefits
Lack of carer
1). Confusion over proper usage, duration of therapy
2). Non-compliance
3). Decreased community ambulation
Costs 1). Increased economic burden
Other Storage and handling 1). Fire hazard
2). Frostbite from liquid O2 during refilling
4. Conclusions
The aim of ambulatory oxygen remains the relief of
symptoms and the freedom to participate in activities of
daily living without being debilitated by symptoms. The
future calls for the development of more economical,
highly portable and more efficient devices suitable for
daily use. The benefits are not clearly defined, largely
due to underpowered studies and lack of a standardized
ethodology. There appears to be some role in acute re-
lief of exertional dyspnoea and improved exercise ca-
pacity. However, short-term improvements in exercise
testing may not necessarily lead to improved functional
capacity in activities of daily living. Furthermore, no
long term or survival benefit has been shown in the
usage of ambulatory oxygen in patients with COPD.
Patients also need to be fully engaged in their manage-
ment and multiple practical limitations addressed before
ambulatory oxygen is considered. Therefore, physicians
should be extremely circumspect in the prescription of
ambulatory oxygen. It should only be offered on a
case-by-case basis to motivated and symptomatic pa-
tients after medical therapy with bronchodilators as
well as inhaled steroids have been optimized and pul-
monary rehabilitation has been completed. Patients who
are hypercapneic at rest may also require blood gas
analysis after initiating oxygen to exclude possibility of
deterioration [12]. All cases should also be carefully
monitored for clear evidence of symptomatic improve-
ment before there is any commitment to long term
therapy. More data on the efficacy of ambulatory domi-
ciliary oxygen and to identify sub-groups who will
clearly benefit are needed before definitive recommen-
dations can be made.
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