An 85-year-old man with long-standing chronic obstructive pulmonary disease (COPD) has a witnessed aspiration event while undergoing an outpatient procedure requiring conscious sedation. He is admitted to the hospital for observation overnight. The next morning, he feels well, but his oxygen saturation dips to 85% with ambulation. He reports this is not new for him, but he vehemently does not want supplemental oxygen.
Patients with COPD and severe resting hypoxemia – arterial oxygen partial pressure less than or equal to 55 mm Hg or peripheral capillary oxygen saturation (SpO2) less than or equal to 88% – commonly are prescribed supplemental oxygen. The evidence supporting this practice is limited to two small trials from the 1970s that showed a survival benefit of long-term oxygen therapy (LTOT) in this population,1,2 but these trials may not be generalizable to patients today.
For patients with COPD and mild to moderate resting hypoxemia (SpO2, 89%-93%) or patients with exercise-induced hypoxemia, LTOT has not been shown to improve survival, although it may improve symptoms of dyspnea, exercise tolerance, and other patient reported outcomes. Given the costs, risks, and burdens associated with LTOT, a high-quality clinical trial assessing the effects of LTOT on clinically meaningful outcomes, such as survival or hospitalization, in patients with COPD and moderate hypoxemia has been long overdue.
Overview of the data
The utility of long-term treatment with supplemental oxygen in patients with stable COPD and moderate resting or exercise-induced desaturation was examined by the Long-Term Oxygen Treatment Trial () Research Group. Results were published in the New England Journal of Medicine in October 2016 in the article, “A Randomized Trial of Long-Term Oxygen for COPD with Moderate Desaturation.”3
The study was initially designed to test whether the use of supplemental oxygen would lead to longer time until death as compared with no supplemental oxygen in the subgroup of COPD patients with stable disease and moderate resting desaturation (defined as resting SpO2 of 89%-93%). However, because of an enrollment of only 34 patients after 7 months, the trial was redesigned to include exercise-induced desaturation (defined as SpO2 of greater than or equal to 80% for at least 5 minutes, and less than 90% for at least 10 seconds, on a 6-minute walk test) and the secondary outcome of all-cause hospitalization. Hospitalization for any cause was combined with mortality into a new composite primary outcome.
This study was a randomized, controlled trial which enrolled patients at a total of 14 regional clinical centers and their associated sites for a total of 42 centers in the United States. The experimental arm consisted of a long term supplemental oxygen group, and the control group did not receive long term supplemental oxygen. Patients were assigned to groups in a 1:1 ratio and the study was not blinded. Patients with moderate resting desaturation were prescribed 24 hour oxygen at 2 L/min, and patients with moderate exercise-induced desaturation were prescribed oxygen at 2 L/min during exercise and sleep only. The primary outcome was a composite outcome of time until death or time until first hospitalization for any cause. There were multiple secondary outcomes, including incidence of COPD exacerbation, incidence of severe resting desaturation and severe exercise-induced desaturation, quality of life, sleep quality, depression and anxiety, adherence to regimen, 6-minute walk distance, spirometric measurements, risk of cardiovascular disease, and neurocognitive function.
Data were gathered via yearly visits, biannual telephone interviews, and questionnaires mailed at 4 months and 16 months. Adherence was assessed by inquiring about oxygen use every 4 months. If patients in the supplemental oxygen group used stationary oxygen concentrators, logs of meter readings were kept as well. The necessary final sample size was calculated using a time to composite event survival model with the use of the log-rank test statistic.
A total of 738 patients were enrolled in the trial between January 2009 and September 2015 and were followed for 1-6 years. A total of 97% of participants had at least 1 year of follow-up. Out of the 738 randomized patients, 133 (18%) had only resting desaturations, 319 (43%) had only exercise-induced desaturations, and 286 (39%) had both resting and exercise-induced desaturations. Baseline characteristics including age, sex, race, smoking status, quality of life scores, resting SpO2, and nadir SpO2 during the 6-minute walk test were similar between the two groups. The only significant difference noted by the authors between the two groups was a lower BODE (body mass index, airflow obstruction, dyspnea, and exercise) index, which was lower in the group with no supplemental oxygen.
In the time-to-event analysis, there was no significant difference between the two groups in the time to death or first hospitalization (hazard ratio, 0.94; 95% confidence interval, 0.79-1.12; P = .52). There were no significant differences in the rates of all hospitalizations (rate ratio, 1.01; 95% CI, 0.91-1.13), COPD exacerbations (RR 1.08; 95% CI, 0.98-1.19), and COPD related hospitalizations (RR, 0.99; 95% CI, 0.83-1.17). There were also no differences between the experimental and control groups in quality of life, lung function, and 6-minute walk distance. There were no significant differences in the subgroups classified by desaturation profile, sex, race, nadir SpO2 during the 6-minute walk test, and forced expiratory volume in 1 second.
The findings in this study show that, in the subgroup of chronic obstructive pulmonary disease patients with stable COPD and moderate resting or exercise-induced desaturation, supplemental oxygen did not affect the time to death or first hospitalization, time to death, time to first hospitalization, time to first COPD exacerbation, time to first hospitalization for a COPD exacerbation, rate of all hospitalizations, rate of all COPD exacerbations, or changes in metrics surrounding quality of life, anxiety/depression, or functional status. This supports earlier studies that demonstrated that long-term treatment with oxygen does not result in longer survival than does no long-term treatment with oxygen in patients with COPD and resting SpO2 of more than 88%.
The results of this study are a departure from previous studies that had shown improved mortality in patients with COPD and severe desaturation who were treated with LTOT. The authors hypothesized that this may have been caused by physiological effects of oxygen saturation on pulmonary vasoconstriction, release of mediators, and ventilator drive, which occur at an O2 saturation of 88% or less and may be more significant in patients with chronic hypoxemia. This trial also contrasted previous studies that had shown that oxygen therapy may reduce dyspnea in COPD patients with mild or no hypoxia because the LOTT trial showed no improvement in quality of life, anxiety, and depression measures in patients treated with long-term oxygen as compared with those treated with no oxygen.
Some limitations of the study included the absence of highly symptomatic patients or patients who the providers believed were too ill to participate, the effect of the unblinded nature of the study on outcomes that were patient reported, the lack of assessment of immediate effects of oxygen on exercise performance or symptoms, possible variability in amount of oxygen delivered, and the fact that patients may have overestimated their oxygen use.
In patients with stable COPD and moderate resting or exercise induced desaturation, long-term supplemental oxygen did not provide any benefit in regard to time until death or first hospitalization or any of the other measured outcomes.