Short-Term Oxygen Therapy Outcomes in COPD

Rationale

Short-term oxygen therapy (STOT) is often prescribed to allow patients with chronic obstructive pulmonary disease (COPD) to be discharged safely from hospital following an acute illness. This practice is widely accepted without being based on evidence.

Purpose

Our objective was to describe the characteristics and outcomes of patients with COPD who received STOT.

Patients and Methods

The study was a secondary analysis of the INOX trial, a 4-year randomised trial of nocturnal oxygen in COPD. The trial indicated that nocturnal oxygen has no significant effect on survival or progression to LTOT, allowing our merging of patients who received nocturnal oxygen and those who received placebo into a single cohort to study the predictors and outcomes of STOT regardless of the treatment received during the trial.

Results

Among the 243 participants in the trial, 60 required STOT on at least one occasion during follow-up. Patients requiring STOT had more severe dyspnoea and lung function impairment, and lower PaO₂ at baseline than those who did not. STOT was associated with subsequent LTOT requirement (hazard ratio [HR]: 4.59; 95% confidence interval [CI]: 2.98–7.07) and mortality (HR: 1.93; 95% CI: 1.15–3.24). The association between STOT and mortality was confounded by age, disease severity and comorbidities. Periods of STOT of more than one month and/or repeated prescriptions of STOT increased the probability of progression to LTOT (OR: 5.07; 95% CI: 1.48–18.8).

Conclusion

Following an acute respiratory illness in COPD, persistent hypoxaemia requiring STOT is a marker of disease progression towards the requirement for LTOT.

Randomized Trial of Nocturnal Oxygen in Chronic Obstructive Pulmonary Disease

BACKGROUND

Long-term oxygen therapy improves survival in patients with chronic obstructive pulmonary disease (COPD) and chronic severe daytime hypoxemia. However, the efficacy of oxygen therapy for the management of isolated nocturnal hypoxemia is uncertain.

METHODS

We designed this double-blind, placebo-controlled, randomized trial to determine, in patients with COPD who have nocturnal arterial oxygen desaturation without qualifying for long-term oxygen therapy, whether nocturnal oxygen provided for a period of 3 to 4 years would decrease mortality or the worsening of disease such that patients meet current specifications for long-term oxygen therapy. Patients with an oxygen saturation of less than 90% for at least 30% of the recording time on nocturnal oximetry were assigned, in a 1:1 ratio, to receive either nocturnal oxygen or ambient air from a sham concentrator (placebo). The primary outcome was a composite of death from any cause or a requirement for long-term oxygen therapy as defined by the Nocturnal Oxygen Therapy Trial (NOTT) criteria in the intention-to-treat population.

RESULTS

Recruitment was stopped prematurely because of recruitment and retention difficulties after 243 patients, of a projected 600, had undergone randomization at 28 centers. At 3 years of follow-up, 39.0% of the patients assigned to nocturnal oxygen (48 of 123) and 42.0% of those assigned to placebo (50 of 119) met the NOTT-defined criteria for long-term oxygen therapy or had died (difference, -3.0 percentage points; 95% confidence interval, -15.1 to 9.1).

CONCLUSIONS

Our underpowered trial provides no indication that nocturnal oxygen has a positive or negative effect on survival or progression to long-term oxygen therapy in patients with COPD. (Funded by the Canadian Institutes of Health Research; INOX ClinicalTrials.gov number, NCT01044628.).

Influence of a single antigenic challenge on the pattern of airway response to exercise in asthma

We studied 14 atopic subjects with mild asthma (six men and eight females) to document whether allergen exposure can change the pattern of response to exercise. Each had an exercise test at 80% of the VO2 max for six minutes before (exercise 1) and 48 hours (exercise 2) after an allergen inhalation test (AIT). FEV1 was measured at regular intervals up to eight hours after each challenge. On the day following AIT, spontaneous changes in FEV1 were measured for eight hours (control day). Airway responsiveness (AR) to histamine was measured at the beginning of the study, then 24 hours after AIT and at the end of the 2nd exercise. Mean early fall in FEV1 after exercise 1, AIT and exercise 2 were, 24.9 +/- 3.2%, 24.5 +/- 2.2%, and 27.6 +/- 3.8%, respectively. Airway responsiveness to histamine was increased at 32 and 56 hours post-AIT with a mean PC20 (SEM) of 0.50 (0.40, 0.62) and 0.93 (0.74, 1.17) mg/mL compared with 1.87 (1.33, 2.61) at baseline (P less than .05). Allergen inhalation test induced an isolated early asthmatic response (EAR) in four subjects, an equivocal response (late fall in FEV1: 5% to 15%) in four and a definite late asthmatic response (LAR) in six. No subject had a LAR before the AIT but two with a LAR after allergen exposure developed a late response to exercise after the AIT. This last was only partly explained by an increased diurnal variation of expiratory flows.(ABSTRACT TRUNCATED AT 250 WORDS)

Perception of breathlessness during bronchoconstriction induced by antigen, exercise, and histamine challenges

Perception of breathlessness was studied in eight patients with mild, stable asthma after a histamine and exercise challenge performed before and 24 and 48 hours respectively after an antigen challenge. FEV1 and perception of breathlessness, evaluated by Borg's 10 point category scale, were measured after each administration of doubling antigen or histamine concentrations to achieve a greater than 20% fall in FEV1, and after six minutes of steady state exercise at 80% of maximal oxygen consumption (VO2max). The geometric mean provocative concentration of histamine causing a 20% fall in FEV1 (PC20) fell from 1.67 mg/ml before antigen challenge to 0.52 mg/ml 24 hours after the challenge. The median maximal % fall in FEV1 with exercise was 24.9% (range 10.5-40.5%) before and 30.6% (range 13.8-52.3%) 48 hours after antigen challenge. The median maximum % fall in FEV1 after antigen inhalation was 20.1% (range 13.3-35.2%) within the first hour; only two subjects had a late fall in FEV1 (23% and 58%). The median (range) of Borg scores obtained when FEV1 was reduced by 20% did not differ significantly for the three types of acute challenges: 1.25 (0.5-2.5) and 1.0 (0.5-3.0) after histamine tests, 1.0 (0.5-4.1) and 1.55 (0.5-2.0) after exercise, and 1.5 (0-3.0) after antigen challenge. In the two subjects who had a late response to antigen the Borg score was reduced for the same % fall in FEV1 as with the early response. It is concluded that the perception of breathlessness does not differ appreciably during the early response to histamine, antigen exposure, or exercise, but that it is reduced during the late asthmatic response. It was not influenced by previous antigen exposure, despite an increase in airway responsiveness.