Long-Term Oxygen Therapy Is Underutilized in COPD

PHILADELPHIA— For many COPD patients, prescriptions for and titration of long-term oxygen therapy (LTOT) fall short of therapeutic standards set forth by American Thoracic Society/European Respiratory Society guidelines, according to the results of a study presented at the American College of Chest Physicians 2008 Annual International Assembly. The guidelines state that therapy should be started if a patient’s oxygen saturation is 88% or lower at rest. During exertion, oxygen should be titrated to maintain oxygenation of more than 90%, according to the guidelines.

LTOT decreases mortality and may reduce the risk for exacerbations requiring hospitalization in patients with COPD, according to Jason McCarl, MD, of the Department of Medicine at the University of Colorado Health Sciences Center in Denver. However, Dr. McCarl and colleagues found that almost half of the patients enrolled in their study did not meet recommended targets for adequate oxygen therapy, despite clinical indications that adjustments were needed. They suggested that oxygen treatment is underprescribed and that additional guidelines are needed to determine oxygen titration during exercise.

The study included 511 COPD patients (mean age, 68) with stage 3 or 4 COPD as classified by Global Initiative for Chronic Obstructive Lung Disease (GOLD) criteria who were enrolled in an institutional review board–approved COPD trial. All were receiving treatment from various Colorado medical facilities, and all but 94 were on oxygen therapy. Twenty percent of participants were from rural areas, and the rest were urban residents; 21% of participants were smokers. Patients who smoked and were already on LTOT tended to have more pack-years than those who were not on oxygen therapy.

Oxygen saturation as measured by pulse oximetry (Spo₂) was assessed during rest and after a six-minute walk test. The researchers found that only 2% of those patients who were not on oxygen therapy had Spo₂ levels of 88% or less at rest, said Dr. McCarl. “This reflects that providers may be doing a good job of detecting hypoxia at rest in patients not on oxygen therapy.”

However, among the 98% of patients with adequate Spo₂ levels at rest, “we found that a large number of patients—42%—desaturated with exercise to an Spo₂ of 88% or less, effectively reflecting underprescription of oxygen therapy,” Dr. McCarl asserted.

Among those who were on oxygen therapy, only 8% had Spo₂ levels that were subtherapeutic at rest; however, they were not adequately titrated to 90%, Dr. McCarl pointed out. Of the 92% who were at therapeutic levels during rest, most (58%) became desaturated during exertion to Spo₂ levels of less than 90%.

In the entire cohort, 6.5% of patients were subtherapeutic at rest, and 54.4% were desaturated with exertion; as a whole, 57.1% of the cohort required some change of prescription or titration. He acknowledged that the study results may not be generalizable to other regions of the country, since Colorado is a high-altitude state.

Dr. McCarl highlighted the two landmark studies that demonstrated the positive impact of LTOT on mortality and formed the basis for the treatment guidelines. The Nocturnal Oxygen Therapy Trial in 1980 found that the relative risk for mortality in the control group that received nocturnal therapy only was 1.94 times that of the group treated with continuous oxygen therapy.

The Medical Research Council Working Party trial published in 1981, showed that COPD patients treated with oxygen therapy survived twice as long as those who received no therapy, but only after they had been on therapy for 500 days.

Dr. McCarl said the guidelines for oxygenation during exercise deserve more study and better recommendations for how to assess hypoxia. While studies show that oxygen therapy during exercise improves lung volume, self-reported quality of life, and length of exercise, he added, “we have no evidence that it might decrease mortality.”

—Kathlyn Stone

Suggested Reading
Medical Research Council Working Party. Long term domiciliary oxygen therapy in chronic hypoxic cor pulmonale complicating chronic bronchitis and emphysema. Lancet. 1981;1(8222):681-686.
Nocturnal Oxygen Therapy Trial Group. Continuous or nocturnal oxygen therapy in hypoxemic chronic obstructive lung disease: a clinical trial. Ann Intern Med. 1980;93(3):391-398.

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