Another Cherished Clinical Dogma Bites the Dust

Abstract & Commentary

By Barbara Phillips, MD, MSPH, Professor of Medicine, University of Kentucky; Director, Sleep Disorders Center, Samaritan Hospital, Lexington. Dr. Phillips reports no financial relationship to this field of study.

Synopsis: Ambulatory oxygen probably should not be routinely prescribed for patients with COPD who do not have a stable, resting arterial PaO2 less than 55 mm Hg.

Source: Nonoyama M, et al. Effect of Oxygen on Health Quality of Life in Patients with Chronic Obstructive Pulmonary Disease with Transient Exertional Hypoxemia. Am J Respir Crit Care Med. 2007;176:343-349.

This study evaluated the effect of ambulatory (portable) oxygen on quality of life and exercise tolerance in patients with COPD. To be eligible for inclusion in this study, patients had to have COPD with dyspnea that limited daily activities, no significant comorbidities, a resting arterial saturation (Sa02) of > 88%, and an exercise (walking) oxygen saturation of 88% or less. From 178 potential COPD patients, the authors were able to recruit 38 who met the study requirements, but only 27 actually completed the entire trial. The authors describe the protocol as "individual (N-of-1) randomized controlled trials (RCT's)." Each patient underwent 3 testing periods of 4 weeks each. In each 4-week testing period, ambulatory oxygen was used for 2 weeks, and placebo (air) was used for 2 weeks; oxygen and air were applied in random order. The outcome variables were Chronic Respiratory Questionnaire (CRQ)1, the St. George's Respiratory Questionnaire2, and a home five-minute-walk test at the end of each period. A positive response was a CRQ dyspnea score greater (less dyspnea) on oxygen than placebo during all three treatment periods, with a difference of 0.5 inches for at least two of the testing periods. Oxygen significantly increased the five-minute-walk test (427 vs 412 steps, p = 0.04). Among the whole group, neither the CRQ nor the St. George's Respiratory Questionnaire showed any statistical or clinical differences between oxygen and placebo. The authors concluded that the general application of long-term ambulatory oxygen therapy for patients with COPD who do not "qualify" for continuous oxygen (eg, who don't have a resting Sa02 of 88% or less) cannot be supported. There are a few individuals who might benefit (in this study, it was 2 out of 27), and they may be identifiable by N-of-1 RCTs such as were used in this study.

Commentary

On any given day in our Pulmonary Clinic, you can see patients with COPD shuffling down the hall, wearing pulse oximeters and accompanied by a nurse or respiratory therapist. The purpose of this activity is to "qualify" folks with COPD who do not otherwise meet insurance criteria for oxygen therapy for ambulatory oxygen. Current Centers for Medicare and Medicaid (CMS) criteria for payment for long term oxygen therapy (LTOT) are based on the documented mortality benefits for patients with resting hypoxemia (Sa02 < 88%, Pa02 <55 mm Hg)3, but many clinicians prescribe oxygen for patients who desaturate with exercise, and insurance will generally cover ambulatory oxygen for this indication if the desaturation is documented. The current study suggests that a very small minority of COPD patients will experience improved quality of life with this approach; only 2 of the eventual cohort met this study's definition of "responder." In trying to apply this finding to the COPD population at large, I believe it is probably most appropriate to use 178 as the denominator (the number who were screened for this study), which suggests that fewer than one in a hundred COPD'ers whose resting Sa02's are above 88% will benefit from chronic ambulatory oxygen.

One result of this study is that CMS will likely set up a much more arduous "qualification" hurdle for payment for ambulatory oxygen, perhaps based on oxygen trials at home. It makes good fiscal and humanitarian sense to more strictly control the flow of oxygen (so to speak). In 2002, total U.S. Medicare costs for home oxygen therapy was $2.2 billion4, and oxygen is associated not only with cost but with inconvenience for the patient. The authors of this paper note that, "One approach to this issue is to restrict oxygen use to patients who show benefit in an N-of-1 RCT. Adopting such an approach would require including the cost of conducting such trials with the costs associated with ambulatory oxygen. The many home-based assessments in this trial increased its costs to an estimated U.S. $1,400.00 ... However, this cost is still considerably less than the cost of providing long-term ambulatory oxygen for patients who do not benefit from it."

In the accompanying editorial5, Drs. Bradley Drummond and Robert Wise note, "The authors conclude that only a small proportion of patients with mild resting hypoxemia and exercise desaturation receive an important benefit from home oxygen. Implicit in this conclusion is the assumption that patients were in fact mobile and active during the study period. After all, an intervention designed to improve dyspnea will have no effect if the patient is not involved in activities that induce dyspnea. ... Essentially, patients used portable oxygen approximately 40 minutes per day, raising question as to their level of dyspnea-inducing activities." Drummond and Wise encourage further research of the effects of oxygen combined with exercise training before throwing in the towel on ambulatory oxygen.

The bottom line is that the routine prescription or "qualification" of ambulatory oxygen for patients with COPD will probably decrease substantially in the near future. Does that mean we should stop prescribing it altogether? I hope not, especially since the odds are much poorer than one in a hundred that patients will benefit from lots of things we do in clinics (and especially in ICU's!!) every day, and because someday that one in a hundred could be you or your mother. But we will need to think more critically about when to consider someone a candidate for ambulatory oxygen, and probably should consider coupling the use of ambulatory oxygen with a structured or formal plan for exercise.

References

1. Guyatt GH, et al. A measure of quality of life for clinical trials in chronic lung disease. Thorax. 1987;42:773–778.

2. Jones PW, et al. A self-complete measure of health status for chronic airflow limitation: the St. George's Respiratory Questionnaire. Am Rev Respir Dis. 1992;145:1321–1327.

3. Crockett Aj, et al. Domiciliary oxygen for chronic obstructive pulmonary disease. Cochrane Database Syst Rev 2005;4;CD001744.

4. Office of Research Development and Information. Health care industry market update: home health. Baltimore, MD: Centers for Medicare and Medicaid Services; 2003.

5. Drummond MB, et al. Oxygen Therapy in COPD: What Do We Know? Am J Respir Crit Care Med. 2007;176:321-322.