Hypercapnia in Advanced Chronic Obstructive Pulmonary Disease: A Secondary Analysis of the National Emphysema Treatment Trial
Anne M. Mathews, Nicholas G. Wysham, Jichun Xie, Xiaodi Qin, Coral X. Giovacchini, Magnus Ekström, Neil R. MacIntyre
Abstract
RATIONALE: ) production, increased dead space ventilation, and the complex interactions of deranged respiratory system mechanics, inspiratory muscle overload and the ventilatory control center in the brainstem. However, these factors have not previously been systematically analyzed in a large, well-characterized population of severe COPD patients. METHODS: based on consensus of the investigators and literature review. Stepwise variable selection yielded 10 statistically significant associations in multivariate regression. RESULTS: A total of 1419 patients with severe COPD were included in the analysis; mean age 66.4 years (standard deviation 6.3), 38% females, and 422 (29.7%) had baseline hypercapnia. Key variables associated with hypercapnia were low resting partial pressure of oxygen in blood, low minute ventilation (Ve), high volume of exhaled carbon dioxide, low forced expiratory volume in 1 second, high residual volume, lower % emphysema on chest computed tomography, use of oxygen, low ventilatory reserve (high Ve/maximal voluntary ventilation), and not being at high altitude. Low diffusing capacity for carbon monoxide showed a positive association with hypercapnia in univariate analysis but a negative correlation in multivariate analysis. Measures of dyspnea and quality of life did not associate with degree of hypercapnia in multivariable analysis. CONCLUSION: production, and a reduced ventilatory capability. Hypercapnia is less impacted by gas exchange abnormalities or the presence of emphysema.