Identifying the predictors of asthma-related death

October 23, 2008

Death caused by asthma is not traditionally thought to be especially common, but it is important to note that asthma often plays a contributing and probably unrecognized role even if it is not often listed as the cause of death on a death certificate. Because early response to asthma exacerbations can make a crucial difference, it is important to develop patient action plans in the outpatient setting well before an attack occurs. However, since busy clinicians must prioritize their educational efforts, identifying who is most at risk for death from asthma is all the more important.

What are the most significant risk factors for asthma mortality?

Death caused by asthma is not traditionally thought to be especially common, but it is important to note that asthma often plays a contributing and probably unrecognized role even if it is not often listed as the cause of death on a death certificate. Because early response to asthma exacerbations can make a crucial difference, it is important to develop patient action plans in the outpatient setting well before an attack occurs. However, since busy clinicians must prioritize their educational efforts, identifying who is most at risk for death from asthma is all the more important.

Aside from the more general risk factors of age, education, and socioeconomic status, more specific factors must be kept in mind when treating patients with asthma. The first and most intuitive risk factor is the severity of asthma, but there is controversy about how to best gauge this. This uncertainty stems from the fact that there are few prospective studies on asthma mortality; thus, few studies show that one measure of asthma severity is better than another in predicting death. Forced expiratory volume in 1 second (FEV1) and peak flow are each predictive of death, with a 25% drop in FEV1 (as a percentage of the predicted value) conferring about a 2-fold higher risk of all-cause mortality in patients with asthma.1

Even in the absence of spirometric information, however, severity as assessed by dyspnea, asthma medication use, and previous asthma-related hospitalizations or intubations provides good insight into the risk of death. An asthma severity score developed at the University of California at San Francisco incorporates these items and has been shown prospectively to be predictive of death.2,3 The staging system used in the Global Initiative on Asthma guidelines appears reasonable to use as a measure of severity, but it specifically has not been shown to predict death.4

Another important risk factor is tobacco use. Although we typically think of chronic obstructive pulmonary disease in connection with smoking and obstructive lung disease, patients with asthma smoke at approximately the same rates as the general population, and smoking significantly increases their risk of death.5 I emphasize this because cross-sectional studies have suggested that tobacco smoking may decrease the risk of asthma,6 and it is not uncommon for patients to insist that their asthma symptoms developed after they stopped smoking.7

However, better research has demonstrated that smoking worsens asthma.8,9 In fact, the observation of higher rates of death in former smokers is explained by the "healthy smoker" effect, whereby patients who are sicker tend to quit smoking because they are sicker, thus leaving the healthier patients behind. When taking into account this general health effect, we see that quitting tobacco reduces the risk of death from asthma.

Finally, race must be mentioned as a possible risk factor. However, the evidence here is murky. Most studies on race as a risk factor have been retrospective and have not been able to adjust for socioeconomic status or health care access.10 These retrospective studies have shown that asthma mortality rates for African Americans are about 5-fold higher than in other racial groups. However, African Americans were not at increased risk for longer-term death in one population of insured adults who were hospitalized for asthma and survived to discharge.2 Although the jury is still out on this question, it appears reasonable for now to focus on such factors as socioeconomic status, health literacy, social support, and insurance status rather than on race specifically in deciding who is most at risk for asthma-related death.

References:

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