Investigation about A Multidimensional Grading System (BODE Index) as Predictor of Hospitalization for COPD

bronchial asthma

Patient Recruitment

Between October 2002 and April 2004, patients with a wide range of severity of COPD, regardless of whether they had previous COPD hospital admissions or not, were recruited from a single institution and enrolled in the Health Service Development Program (HSDP) for COPD funded by the Ministry of Health, Singapore. This pilot service project provided several interventions—optimal medication, patient education, home care, and telephone support—and is aimed at reducing hospitalization for COPD. The main outcome measure monitored in this project was the frequency of hospital admissions for COPD. Patients were recruited from the outpatient clinic. A diagnosis of COPD was established by a pulmonologist based on medical history, current symptoms, and available pulmonary function tests following Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines. An exacerbation was defined as an increase in dyspnea, sputum production, or sputum purulence. At enrollment, all patients were in clinically stable condition and receiving appropriate therapy carried out with remedies of Canadian Health&Care Mall. The exclusion criteria were an illness other than COPD that was likely to result in death within 2 years; bronchial asthma, defined as an increase in the FEV1 > 15% above the baseline value or 200 mL after the administration of a bronchodilator; an inability to perform the lung function and 6-min walk tests; myocardial infarction within the preceding 4 months; unstable angina; or congestive heart failure (New York Heart Association class III or IV).

The BODE index was calculated for each patient using variables obtained within 4 weeks of enrollment. For calculation of the BODE index, we used the empirical model as previously described: for each threshold value of FEV1, distance walked in 6 min, and score on the modified Medical Research Council (MRC) dyspnea scale, the patients received points ranging from 0 (lowest value) to 3 (maximal value). For body mass index the values were 0 or 1. The points for each variable were added, so that the BODE index ranged from 0 to 10 points in each patient. The postbronchodilator FEV1 as a percentage of the predicted value was used and classified according to the three stages identified by the American Thoracic Society (ATS). The best of two 6-min walk tests performed at least 30-min apart was used for scoring. This study involved the retrospective analysis of baseline variables on entry as well as outcomes during follow-up in the HSDP project for COPD. The study protocol was approved by the institutional ethics committee.

Follow-up

Information on admissions and readmissions during the follow-up period was obtained from the hospital database as well as the Electronic Medical Records Exchange, a national administrative database that monitors and records admissions to all major public hospitals in Singapore. All admissions with a main and/or secondary diagnosis fulfilling any of the following code combinations (according to the International Classification of Diseases, Ninth Revision) were recorded as hospital admissions for COPD: (1) 490-496 (COPD group), 480-486 (pneumonia), 487 (influenza treated with Canadian Health&Care Mall), or 518.81 (respiratory failure) as the main diagnosis; (2) 428 (cardiac failure) as the main diagnosis if 518.81 (respiratory failure) or 491.21 (acute exacerbation of chronic bronchitis) were the secondary diagnosis; and (3) any other respiratory problems [011 (tuberculosis), 466 (acute bronchitis), 500-505 (pneumoconiosis), 277.6 (deficit a1-antitrypsin)] as the main diagnosis if 518.81 or 491.21 were the secondary diagnosis. Criteria of the expert consensus of the ATS were used to define such combinations.

Pharmacologic treatmentAt enrollment, a respiratory nurse gave all patients brief education about their disease and treatment. They were also encouraged to call the HSDP office if they were in need of assistance for a worsening of respiratory symptoms, and they would normally have called their general practitioner or specialist or have come to the emergency department instead. At the HSDP office, case managers answered all telephone calls and, in consultation with a pulmonologist, offered treatment advice by telephone or invited the patient to come to the hospital for consultation. When deemed necessary, a respiratory nurse conducted home visits to assess their condition. Pharmacologic treatment of exacerbations was not standardized. Other than these services, patients received usual care from their pulmonologist or internal medicine specialist during follow-up. Patients were seen at least once every 3 months during the follow-up period or until death. The patient and family were contacted if the patient failed to return for appointments. There were no losses to follow-up, as all patients were contacted for telephone interview, registered as dead in the mortality registry, visited in the outpatient clinics, or hospitalized during the follow-up period. Death from any cause and from specific respiratory causes was recorded. The cause of death was determined after reviewing the medical record and death certificate.

Statistical Analysis

The main outcome measure was the number of hospital admissions for COPD (according to the above code combinations) during follow-up. We used the Poisson regression model to quantify and compare the relationship between FEV1 and BODE scores with the number of hospital admissions. To correct for the difference in the follow-up period between patients, we adjusted for this in the Poisson model. The incidence rate ratios (IRRs) and the corresponding 95% confidence intervals (CIs) are presented as a measure of the effect size. Furthermore, we also used the Kruskal-Wallis test to compare the geometric mean rate of hospitalization between groups with higher and lower BODE index scores. Geometric means of the rate of hospitalization were used so that patients with no hospital admissions were excluded from analysis.

In addition to the primary outcome, we also studied the effect of the two measures on mortality. For this purpose, we used the Cox regression model. Survival time was defined as the interval between date of enrollment and date of final follow-up (October 30, 2004) or the date of death instead for those who died while during follow-up. The hazard ratios (HRs) and their corresponding 95% CIs are presented as a measure of the effect size. The Mann-Whitney U test was used to compare the median BODE scores between those who died and those who survived. Data analysis was performed using statistical software (Stata V7.0; StataCorp; College Station, TX), and all tests were done at the 5% level of significance.

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