Dr. Cutaia is from the Pulmonary Section, VA Medical Center, University of Pennsylvania.
Correspondence to: Michael Cutaia, MD, FCCP, Woodland and University Ave, Research Service, Philadelphia, PA 19104; e-mail: email@example.com
The life-preserving benefits of long-term oxygen
therapy (LTOT) were established nearly 2 decades ago.1–2
One cannot overemphasize the fact that LTOT is the only treatment that
has a positive impact on mortality in COPD patients. Pulmonologists are
well versed in the benefits of LTOT, and recognize the importance of
identifying hypoxemic patients and instituting LTOT. The criteria for
implementation of LTOT are well defined. Therefore, it is somewhat
surprising that there has been little interest in building on the
findings of the original studies that documented the survival benefit
of LTOT. Acceptance of LTOT has lead to a complacency that there is
nothing more to learn on this topic, especially in the molecular
The limitations of the original studies on LTOT are not widely
appreciated. Some very interesting questions remain unanswered. The
answers could have a major impact on the effectiveness of LTOT. For
example, the original studies provided little insight into the
frequency and magnitude of hypoxemia in COPD patients in the outpatient
setting. Oximetry was not widely available, and arterial blood samples
were drawn at infrequent intervals in the hospital or clinic setting.
The article by Plywaczewski et al (March 2000)3 is a good
example of the renewed interest in questions related to gaps in
knowledge about adequate oxygenation in the outpatient setting. This
report is the latest work from these authors focused on nocturnal
oxygen desaturation in COPD patients. The results provide new data
relevant to an unresolved issue: the frequency and magnitude of
nocturnal oxygen desaturation in these patients. This study
demonstrates a higher frequency of nocturnal desaturation than in prior
work, suggesting that we may be underestimating the frequency and
magnitude of nocturnal desaturation. Although this work does not
completely resolve this issue, the results provide additional support
for the American Thoracic Society recommendation that clinicians
increase the liter flow of oxygen during sleep in COPD patients to
avoid nocturnal desaturation.
Other reports indicate that unanswered questions concerning LTOT
are beginning to receive more careful scrutiny. Several studies
demonstrated that the frequency and magnitude of hypoxemia in COPD
patients in the outpatient setting is greater than anyone previously
realized.4–7 These studies herald the emergence of
a new field, the monitoring of oxygen saturation (and other physiologic
variables?) in the outpatient setting, set in motion by earlier
work.8–9 This is an interesting development, because this
approach should provide a more accurate picture of the temporal profile
of oxygen saturation (or desaturation!) while patients with advanced
lung disease are engaged in activities of daily living. This approach
is linked to the continued improvement in monitoring equipment that
will facilitate the assessment of physiologic variables in the
outpatient setting. Outpatient monitoring could eventually replace the
current type of evaluation for LTOT, which does not reflect patient
activity outside of the hospital or clinic.
Why is this important? Our goal is still to reduce the morbidity and
mortality in patients with COPD. Defining the temporal profile of
oxygen saturation during activities of daily living may enable us to
optimize LTOT beyond the level in the original studies.1–2
This is certainly relevant to the issue of nocturnal desaturation
highlighted by Plywaczewski et al.3 A challenging
long-term objective will be to demonstrate that optimizing LTOT with
outpatient monitoring leads to improved outcomes in patients with
advanced lung disease. Can we achieve even better survival rates than
in the original studies on LTOT using data derived from outpatient
monitoring? This is not an unreasonable hypothesis in view of findings
of one study that untreated exercise-induced hypoxemia worsens survival
in COPD.10 Increased life expectancy in the general
population will lead into an increase in the numbers of patients
surviving beyond age 70 with chronic diseases, like COPD. Therefore,
reducing the morbidity and mortality in patients with advanced lung
disease will take on added significance. Developing new ways to
optimize LTOT fits well with these objectives. This is the broader
context in which the results of Plywaczewski et al3 should
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