Abstract & Commentary
Synopsis: Asthmatic patients with low POD had a 10-fold increased risk of emergency department visits, hospitalizations, near-fatal asthma attacks, and deaths when compared to patients in the normal POD group.
Source: Magadle R, et al. Chest. 2002;121:329-333.
To prevent deaths from asthma, it is important to identify patients who may be at risk of a fatal attack. Large variations in perception of respiratory symptoms may be observed from one asthmatic patient to another.1 Reduced perception of dyspnea (POD) may result in a delay in instituting appropriate therapy and, thus, constitute a risk factor for severe exacerbations of asthma. By measuring POD, it may be possible to identify this subset of patients who are at risk for near fatal and fatal attacks allowing more aggressive management in these patients.
Patients (n = 113) attending an outpatient clinic had their POD measured using the Borg scale while breathing against a resistive load. Patients were followed up at 3-month intervals for a total of 8 visits and all hospitalizations, near fatal, and fatal attacks were recorded. Near fatal attacks were defined as attacks of asthma requiring treatment with mechanical ventilation or resulting in unconsciousness and severe respiratory failure. The reference standard was established by measuring POD in 100 age-and-sex matched controls. Normal POD was defined as the mean ± 1 standard deviation. Patients maintained a record of their prebronchodilator morning peak expiratory flow rates, b2 agonist use, and use of their other regular asthma medications including inhaled corticosteroids, theophylline, and oral corticosteroids for the first 4 weeks.
There were 67 (59%) patients with a normal POD, 17 patients (15%) with a high POD, and 29 patients (26%) with a low POD. Patients with low POD tended to be older (42 ± 5.4 years vs 39 ± 4.8 years, and 32 ± 4.9 years in the normal and high POD groups), and were more likely to be female (62% vs 45% vs 59%). The duration of asthma was longer in the low POD group when compared to patients in the normal POD and high POD group (21 ± 5 years vs 15 ± 4.6 years vs 12 ± 4.1 years, respectively). Severe asthma was present in 8 of 29 (27.5%) patients in the low POD group compared to 10 of 67 (14.9%) patients in the normal POD group and 4 of 17 (23.5%) in the high POD group. Patients in the low POD group had more emergency department visits than the normal and high POD groups (32 vs 8 vs 14 respectively; P < 0.01), were hospitalized more frequently (22 vs 4 vs 3; P < 0.001), had more incidents of near-fatal asthma (13 vs 2 vs 1; P < 0.001), and more deaths (6 vs 1 vs 0; P < 0.001).
Comment by David Ost, MD, & Najma Usmani, MD
Despite advances in our understanding and treatment of asthma, mortality from asthma continues to rise, unlike mortality from other common treatable conditions.2 To prevent death from asthma, it is important to identify the subset of patients who are most at risk for a fatal attack. It has been shown that such patients may have a decreased hypoxic response accompanied by a blunted POD.3 As shown in this study, low POD is associated with adverse events. Though Magadle and colleagues recommend measuring POD at least once in asthmatic patients, the test is not available in routine practice and is done mostly in a research setting. Unfortunately, a history of near fatal attack that requires hospitalization and mechanical ventilation is the strongest single predictor of subsequent death from asthma.4 Though POD cannot be measured routinely in this subset of patients, it may be that some of these patients have low POD contributing to their poor outcomes. Aggressive objective measures of disease activity such as daily peak flow recording, education on warning symptoms, and patient management plans may be of use in this setting.
Dr. Ost, Assistant Professor of Medicine, NYU School of Medicine, Director of Interventional Pulmonology, Division of Pulmonary and Critical Care Medicine, Northshore University Hospital, Manhasset, NY, is Associate Editor of Internal Medicine Alert. Dr. Usmani is a Fellow in Pulmonary and Critical Care Medicine, North Shore University Hospital and Nassau University Medical Center, Manhasset, NY.
References
1. Barnes PJ. Thorax. 1992;47:408-409.
2. Sly RM. Ann Allergy. 1992;69:81-84.
3. KikuchiY, et al. N Engl J Med. 1994;330:1329-1334.
4. Rea HH, et al. Thorax. 1986;41:833-839.
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