COMMENTARY

Supplemental Oxygen Has Limited Powers

Aaron B. Holley, MD

Disclosures

May 02, 2018

Over 1 million Medicare recipients with chronic obstructive pulmonary disease (COPD) are prescribed oxygen at an annual cost of $2 billion.[1] I routinely see staff pulmonologists and pulmonary clinics investing time and energy securing oxygen prescriptions for patients. Pulmonary fellows at the academic medical center where I work screen patients for hypoxia with 6-minute walk testing and overnight oximetry. What important health outcomes are achieved after devoting considerable labor to screening for hypoxia and prescribing oxygen?

A recent review article[2] provides a sobering answer. We do not achieve much.

To be clear, there is widespread agreement that oxygen therapy for COPD patients with resting hypoxia reduces mortality. The two studies[3,4] supporting this benefit are old and small, but they were randomized and found a large absolute risk reduction with a number needed to treat (NNT) of 5-6. It is tough to alter the disease course for patients with COPD, so an NNT of 5-6 is very attractive. Beyond these two studies, though, oxygen runs into trouble as a proven therapy.

A randomized trial[5] cast doubt on the utility of ambulatory oxygen for patients who desaturate with activity. Previous studies found inconsistent improvements in exercise capacity, dyspnea, and quality of life.[1] This recent review article[2] cites a meta-analysis published in 2014[6] that found statistical benefits in dyspnea and fatigue scores that were not clinically significant. The authors concluded that there is insufficient evidence to support prescribing ambulatory oxygen to patients with isolated, exertional hypoxia.[2]

Data for nocturnal oxygen therapy are also limited. This review article[2] notes that the prevalence of nocturnal hypoxia is anywhere from 27%-70% among COPD patients depending on the definition used. The "American" definition, endorsed by the Centers for Medicare & Medicaid Services (CMS), is a pulse oximetry reading ≤88% for ≥5 nonconsecutive minutes.[7] One study[8] found a prevalence of 27% for COPD patients who did not qualify for 24/7 oxygen therapy. However, given that studies in patients (aged >60 years) without COPD show a median oxygen nadir of 88-89%,[9,10] it is likely that substantial numbers of elderly COPD patients would meet CMS criteria for nocturnal hypoxia.

As for evidence for efficacy, there is not much. Three small, randomized trials failed to find a benefit from nocturnal oxygen.[2] Luckily, a large, multicenter, randomized trial is being conducted to determine the effects from nocturnal oxygen.[11] Until it is completed, the authors of this review argue against screening or providing oxygen for isolated, nocturnal hypoxia.[2]

Adherence to oxygen is also a problem, with different studies citing rates from 45% to 70%.[2] Unfortunately, adherence is not routinely monitored, and prescription and reimbursement are not dependent on proven use. Because the symptomatic benefits from supplementing patients with isolated nocturnal or exertional hypoxia are so inconsistent, it is likely that patients prescribed nocturnal and ambulatory oxygen are particularly noncompliant.

In summary, supplemental oxygen reduces mortality for patients with resting hypoxia. Beyond that, the benefits are less certain. It stands to reason that patients who use ambulatory oxygen to improve exercise capacity and increase activity levels could benefit. I have had some patients say that they feel better using nocturnal oxygen. That said, the results are inconsistent. Given the high prevalence of nocturnal and exertional hypoxia, the cost of therapy, and problems with adherence, expenditures are high and cost-efficacy is poor. It is refreshing to read that the authors of this review recommend against screening and treating isolated nocturnal or exertional hypoxia. Until better evidence is available, we need to change clinical practice and stop ordering so much oxygen.

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