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Philadelphia, PA, 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: mcutaia{at}mail.med.upenn.edu
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 biology era.
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 5 6 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 be considered.
References
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