The Risk of Hospitalization and Near-Fatal and Fatal Asthma in Relation to the Perception of Dyspnea

Rasmi Magadle, MD, Noa Berar-Yanay, MD and Paltiel Weiner, MD

Disclosures

CHEST. 2002;121(2) 

In This Article

Abstract and Introduction

Background. A life-threatening asthma attack is still of major concern. One of the main goals in treating patients with asthma is identification of the patients at risk of having these attacks. It has been shown that patients who have a near-fatal asthma attack have a blunted perception of dyspnea (POD). The purpose of this study is to measure the POD in patients with asthma, and to relate POD to life-threatening attacks within a 24-month follow-up period.
Methods. The POD was scored using the Borg scale during breathing against a progressive load at 1-min intervals, in order to achieve mouth pressure up to 30 cm H2O, in 113 consecutive asthmatic patients with stable asthma attending an outpatient clinic. All patients were invited to regular follow-up every 3 months for up to 24 months, and all hospitalizations and near-fatal and fatal asthma attacks were recorded. The prebronchodilator morning peak expiratory flow rate (PEFR), daily regular treatment, and beta 2-agonist consumption were recorded in a diary card for the first 4 weeks.
Results. Seventeen patients (15%) had high POD compared to the normal subjects, 67 patients (59%) had POD within the normal range, and 29 patients (26%) had lower-than-normal POD. In the patients with low POD, there was a tendency for higher age, higher female/male ratio, and a longer duration of disease. The rate of severe asthma was higher in the low-POD group than in the normal-POD group, but did not differ from the rate in the high-POD group. The mean daily beta 2-agonist consumption in the patients with low POD 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 2 years of follow-up, the patients in the low-POD group had statistically significantly more emergency department (ED) visits, hospitalizations, near-fatal asthma attacks, and deaths compared to the normal-POD and high-POD groups.
Conclusions. Approximately 26% of the referral subjects with asthma had low POD when compared to healthy matched subjects. Patients with low POD had statistically significantly more ED visits, hospitalizations, near-fatal asthma attacks, and deaths during the follow-up period. Reduced POD may predispose patients to a life-threatening attack.

From 1.1 to 7.0% of patients with asthma die from an asthma attack.[1,2,3] It is hard to predict which asthma patients will have a fatal or near-fatal asthma attack. In both fatal and near-fatal asthma, there is a female predominance,[4,5] history of frequent hospital admissions and emergency department (ED) visits,[6] noncompliance,[7] psychosocial abnormalities,[8] and socioeconomic factors linked to poverty.[9] In addition, Kikuchi et al[10] reported in 1994 a significantly decreased response to inspiration against resistance and to hypoxic hypercapnia in 11 patients with nearfatal asthma. This observation that most patients with near-fatal asthma have blunted perception of dyspnea (POD) suggests that a dysfunction in these defense mechanisms may play a role in near-fatal asthma.

Fatal or near-fatal asthma is undoubtedly severe asthma, but it may not have been manifested in poor lung function or in terms of disturbing the patient very much, leading to consultation with a doctor. In the Barcelona soybean epidemic,[11] patients with near-fatal asthma had fewer symptoms and had attended EDs significantly less than asthmatic patients who did not have near-fatal asthma.

The prognosis of patients with near-fatal asthma is not good. The in-hospital mortality rate is 16.5% in patients who require mechanical ventilation, and an additional 14% of patients die during the following period.[12] We hypothesized that assessment of the POD in patients with asthma will identify patients at risk of having fatal or near-fatal asthma attacks.

Materials and Methods One hundred thirteen patients with stable asthma attending an outpatient clinic (54 male and 59 female patients) were recruited for the study. Our outpatient clinic receives only patients who are referred by their primary physician, and therefore may have more complicated conditions than patients with asthma alone. All patients satisfied the American Thoracic Society definition of asthma, with symptoms of episodic wheezing, coughing, and shortness of breath responding to bronchodilators, and reversible airflow obstruction documented in at least one previous pulmonary function study.[13] Their characteristics are summarized in Table 1. All patients were tested at baseline and were followed up for at least 24 months. The severity of asthma was defined according to spirometric values.[14] Patients with a history of near-fatal asthma attacks were excluded from the study, because these patients are known to have an excessive risk for further fatal or near-fatal attacks. Near-fatal attacks were defined as attacks of asthma requiring treatment with mechanical ventilation or resulting in unconsciousness and severe respiratory failure.

All patients were invited to have regular follow-up every 3 months and were required to be compliant with the recording of prebronchodilator morning peak expiratory flow rates (PEFRs), daily regular treatment, and beta 2-agonist consumption on a diary card for the first 4 weeks. The study protocol was approved by the institutional ethics committee, and informed consent was obtained from all the subjects.

Spirometry
FVC and FEV1 were measured three times on a computerized spirometer (Compact; Vitalograph; Buckingham England), and the best trial is reported.

POD
The sensation of dyspnea was measured while the subject breathed through a device similar to that proposed by Nickerson and Keens.[15] Subjects inhaled through a two-way valve (Hans- Rudolph; Kansas City, MO), the inspiratory port of which was connected to a chamber and plunger to which weights could be added externally. The subjects breathed against a progressive load at 1-min intervals, in order to achieve mouth pressures of 0 (no load), 5, 10, 20, and 30 cm H2O. After breathing for 1 min at each level of threshold load, in a protocol similar to the one previously described by Kikuchi and coworkers,[10] with resistive loads, using a method recently published by Larson and associates[16] with the same device as ours, using threshold loads, the subjects rated the sensation of difficulty in breathing (dyspnea) using the modified Borg scale.[17] This is a linear scale of numbers ranking the magnitude of difficulty in breathing, ranging from 0 (none) to 10 (maximal).

Data Analysis
Normal POD was defined as mean ± 1 SD of 100 age- and sex-matched normal subjects. Comparisons of dyspnea score and follow-up hospital visits were carried out using the two-way repeated-measures analysis of variance.

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