Predicting Morbidity and Mortality in Asthma

Abstract & Commentary

Source: Magadle R, et al. The risk of hospitalization and near-fatal and fatal asthma in relation to the perception of dyspnea. Chest 2002;121:329-333.

The purpose of this study was to measure the perception of dyspnea (POD) in patients with asthma and to relate POD with life-threatening attacks within a 24-month period of follow-up. The authors hypothesized that low POD would identify patients at risk for fatal or near-fatal asthma attacks. Study subjects consisted of 113 patients with stable asthma referred to an outpatient asthma clinic by their primary physician. To measure POD, subjects breathed against a progressive load at one-minute intervals to achieve mouth pressures of 0, 5, 10, 20, and 30 cm H2O. The subjects rated the sensation of difficulty (SD) in breathing using a linear scale from 0 (none) to 10 (maximal). Normal POD was defined as a mean ± SD of 100 age and sex-matched normal subjects. Pre-bronchodilator morning peak expiratory flow rate (PEFR), daily regular treatment, and beta 2-agonist consumption were recorded in a diary for the first four weeks.

Compared to normal patients, 17 patients (15%) had a high POD, 67 patients (59%) had POD within the normal range, and 29 patients (26%) had a low POD. In the patients with low POD, there was a tendency for older age, higher female/male ratio, and a longer duration of disease. The mean daily beta 2-agonist consumption in the low-POD group was significantly lower (p < 0.01) than in the patients with high POD, although the mean PEFR was lower in the low-POD group. During the two years of follow-up, when compared to the normal-POD and high-POD groups, respectively, the patients in the low-POD group had statistically significantly more emergency department (ED) visits (p < 0.001 and p < 0.01), hospitalizations (p < 0.001 and p < 0.001), near-fatal asthma attacks (p < 0.001 and p < 0.001), and deaths (p < 0.001 and p < 0.001).

Commentary by Stephanie B. Abbuhl, MD, FACEP

The prevalence of asthma has increased dramatically during the past 30 years, now affecting almost 8% of the U.S. population. There are more than 550,000 deaths from asthma each year.1,2 Although predicting which patients will have fatal or near-fatal asthma attacks is likely to continue to involve multiple factors, this study suggests that reduced POD may be one of several factors that predispose patients to a life-threatening attack.

While this study is not without methodologic flaws, the conclusion appears sound and complements previous work done in 1994.3 In the 1994 study, patients with near-fatal asthma were compared to patients who had asthma of similar severity but no history of near-fatal attacks, and were found to have a decreased perception of dyspnea when breathing through tubes with increasing resistance. In a prospective design, the Magadle study has shown that reduced POD patients go on to have significantly more life- threatening episodes than normal- or high-POD patients.

The authors use their data to conclude that measurement of POD should be performed at least once in all asthma patients, to identify those at high risk for a fatal attack. Although one wonders if that would be feasible, the message for emergency physicians is more straight-forward. Reliance on a patient’s perception of the severity of his or her shortness of breath is fraught with difficulty and we need to continue to make treatment and admission decisions based on the National Institutes of Health guidelines, which include: peak flows; history of prior steroid use, ED visits, hospitalizations, and intubations; medication use over the course of the flare; medical or psychiatric comorbidity; access to medical care; home conditions, and other factors.4  

Dr. Abbuhl, Medical Director, Department of Emergency Medicine, The Hospital of the University of Pennsylvania; Associate Professor of Emergency Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA, is on the Editorial Board of Emergency Medicine Alert.

References

1. Busse WW. A 47-year-old woman with severe asthma. JAMA 2000;284:2225-2233.

2. Mannino DM, et al. Surveillance for asthma: United States, 1960-1995. Centers for Disease Control Surveillance Summary. MMWR Morb Mortal Wkly Rep 1998;47:1-27.

3. Kikuchi Y,et al. Chemosensitivity and perception of dyspnea in patients with a history of near-fatal asthma. N Engl J Med 1994;330:1329-1334.

4. National Asthma Education and Prevention Program. Expert panel report:Guidelines for the diagnosis and management of asthma. DHHS Pub. No. NIH 97-4051. Washington, DC; Dept. of Health and Human Services: 1997.