COPD and cognitive impairment: the role of hypoxemia and oxygen therapy

Abstract

Background: several studies have shown an association between chronic obstructive pulmonary disease (COPD) and cognitive impairment. These studies have been limited by methodological issues such as diagnostic uncertainty, cross-sectional design, small sample size, or lack of appropriate referent group. This study aimed to elucidate the association between COPD and the risk of cognitive impairment compared to referent subjects without COPD. In patients with established COPD, we evaluated the impact of disease severity and impairment of respiratory physiology on cognitive impairment and the potential mitigating role of oxygen therapy.

Methods: we used the Function, Living, Outcomes and Work (FLOW) cohort study of adults with COPD (n = 1202) and referent subjects matched by age, sex, and race (n = 302) to study the potential risk factors for cognitive impairment among subjects with COPD. Cognitive impairment was defined as a Mini-Mental State Exam score of <24 points. Disease severity was using Forced Expiratory Volume in one second (FEV(1)); the validated COPD Severity Score; and the BMI (Body Mass Index), Obstruction, Dyspnea, Exercise Capacity (BODE) Index. Multivariable analysis was used to control for confounding by age, sex, race, educational attainment, and cigarette smoking.

Results: COPD was associated with a substantive risk of cognitive impairment compared to referent subjects (odds ratio [OR] 2.42; 95% confidence interval [CI] 1.043-6.64). Among COPD patients, none of the COPD severity measures were associated with the risk of cognitive impairment (P > 0.20 in all cases). Low baseline oxygen saturation was related to increased risk of cognitive impairment (OR for oxygen saturation ≤88% (OR 5.45; 95% CI 1.014-29.2; P = 0.048). Conversely, regular use of supplemental oxygen therapy decreased the risk for cognitive impairment (OR 0.14; 95% CI 0.07-0.27; P < 0.0001).

Conclusion: COPD is a major risk factor for cognitive impairment. Among patients with COPD, hypoxemia is a major contributor and regular use of home oxygen is protective. Health care providers should consider screening their COPD patients for cognitive impairment.

Keywords: chronic obstructive pulmonary disease.

Figure 1

Relationship between resting oxygen saturation and the risk of cognitive impairment. Oxygen saturation was measured using pulse oximetry. The LOWESS (locally weighted regression scatter plot smoother) procedure was used to graphically depict the relationship between oxygen saturation and the logit (ie, log odds) of cognitive impairment. This method fitted a flexible smoothed curve that did not impose a linear relationship.