Chronic airways obstruction leading to chronic hypoxemic respiratory failure: an estimate of the size and trend of the problem in Canada.

Abstract

Chronic airways obstruction is a common cause of morbidity and mortality in Canada. It may progress to hypoxic respiratory failure and then to death. Only a few studies of the prevalence of chronic airways obstruction have been reported from Canada, but a number of studies have been reported from the United States and the United Kingdom, countries with similar socioeconomic conditions and ethnic compositions to those in Canada. The prevalence of chronic airflow limitation in these studies averages 9.3%. In each study, tobacco smoke exposure is the most prominent etiologic agent. Other contributing factors identified in the studies are air pollution, occupational exposure, respiratory infections and childhood respiratory illness. Endogenous modifiers of these risk factors demonstrated in the published studies include age, elevated peripheral blood leukocyte count and familial factors. Although epidemiologic studies have been able to identify the prevalence of functional impairment associated with chronic airways obstruction, risk factors associated with its development and modifiers of these risk factors, it is not possible to determine the prevalence of severe chronic airways obstruction resulting in hypoxemic respiratory failure. An estimate of this prevalence has been calculated based on certain assumptions. It was assumed that patients dying of chronic airways obstruction were likely, in a high proportion of cases, to have hypoxemic respiratory failure. It has been demonstrated that only one-half of all patients dying of chronic airways obstruction are correctly designated on death certificates. It was assumed, conservatively, that the median survival of patients with hypoxemic respiratory failure is two years. From these assumptions, it was estimated that the prevalence of hypoxemic respiratory failure in 1986 in Canada was 100 per 100,000 population. This is higher than the present rate of oxygen therapy, indicating that some patients currently eligible for this treatment may not be receiving it.