Understanding Early Predictors of Mortality in COPD

A recent study from Sweden sought to understand the most important predictors of death for patients with chronic obstructive pulmonary disease (COPD) by general, respiratory, and cardiac causes of death.

While different measures have been proposed to predict mortality in patients with COPD (both single factors and composite measures) the authors, writing in International Journal of Chronic Obstructive Pulmonary Diseases, said they wanted to analyze the relative importance of each component, as advanced COPD disease is a leading cause of death worldwide. COPD death rates rose by 11.6% from 1990 to 2015.

Several factors have been linked to COPD mortality, such as dyspnea; dyspnea has been shown to be a better predictor of 5-year survival than percentage of predicted forced expiratory volume in 1 second (FEV₁). Other factors include comorbidities, body mass index (BMI), exercise capacity, COPD exacerbations, biomarkers, and other factors.

Predictive indices include the BODE, which is a composite measure of 4 factors of COPD severity—BMI, Obstruction, Dyspnea, and Exercise Capacity. Other predictive tools include DOSE (Dyspnea, Obstruction, Smoking, and Exacerbations) and ADO (Age, Dyspnea, and Obstruction).

In this study, researchers merged the Swedish Respiratory Tract Register (SRTR) and the Swedish Cause of Death Register to identify patients with respiratory, cardiac, and other causes of death. Three univariable and multivariable Cox proportional hazards regression analyses were conducted for different causes of death, with time from first registration to either death or a fixed end date as dependent variable. Independent variables included demographics, respiration, and comorbidities.

Results showed that patients with cardiac causes of death had a significantly shorter time between diagnosis and death, and between diagnosis and first registration, compared with those who died of respiratory causes. The mean time between first registration and death for these patients was 1.6 (1.1) years.

In univariable analyses, more women with COPD died from respiratory causes than from cardiac ones. Compared with patients dying from lung cancer, patients dying from respiratory causes were older, had lower FEV₁, lower saturation, more exacerbations, and more hospital admissions.

Respiratory variables were largely consistent predictors of mortality for all-cause, respiratory, and cardiac deaths.

Older age and low FEV₁ predicted mortality in all models. BMI and dyspnea remained significant in analyses of all causes and respiratory causes of death, whereas low saturation and presence of heart diseases were predictors of all causes and cardiac causes of death.

COPD exacerbations predicted death from respiratory causes.

In the Cox proportional hazard model, mortality for patients with all causes of death was predicted by (all P < .002 to P < .001):

• Older age (hazard ratio [HR], 1.79; 95% CI, 1.41-2.27)
• Lower percentage of FEV₁ (HR, 0.99; 95% CI, 0.98-0.99)
• Lower saturation (HR, 0.92; 95% CI, 0.86-0.97)
• Worse dyspnea (HR 1.48; 95% CI, 1.26-1.74)

In addition, less exercise (HR, 0.91; 95% CI, 0.85-0.98) and heart disease (HR, 1.53; 95% CI, 1.06-2.19) were also significant predictors (both P < .05).

By respiratory cause of death, mortality was also predicted by older age and lower FEV₁, in addition to:

• Worse dyspnea (HR, 2.05; 95% CI,1.45-2.90)
• Higher number of exacerbations (HR, 1.27; 95% CI, 1.11-1.45); (P < .001 in all comparisons).

By cardiac cause of death, mortality was predicted by older age and lower FEV₁ as well as

• Lower saturation (HR, 0.82; 95% CI, 0.76, 0.89) (P < .001)
• Presence of heart disease at first registration (HR, 2.06; 95% CI 1.13-3.73) (P < .05).

The researchers highlighted their findings that lung obstruction predicted mortality in all models and dyspnea in 2 models. Cardiac comorbidity bodes poorly for COPD prognosis and requires treatment by a multidisciplinary team, they added.

Reference

Henoch I, Ekberg-Jansson A, Löfdahl CG, Strang P. Early predictors of mortality in patients with COPD, in relation to respiratory and non-respiratory causes of death: A national register study. Int J Chron Obstruct Pulmon Dis. Published online June 25, 2020. doi: 10.2147/COPD.S252709