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

severe COPDOne hundred twenty-seven patients were followed up. The baseline characteristics of these patients are shown in Table 1. The mean age ± SD was 70.9 ± 8.2 years, and mean FEV1 was 43.7% of predicted. The number of patients in stages I to IV of COPD severity as defined by GOLD and the median BODE scores of the patients in each category are shown in Table 2. The vast majority of patients had moderate-to-very severe COPD (stages II to IV). The median BODE scores were progressively higher from stage I to stage IV. Table 3 shows the classification of patients according to BODE index score and individual variable scores. Patients in the cohort generally fared worse in airflow obstruction score than dyspnea and exercise capacity scores. Ten percent of patients had at least one significant comorbid condition enhanced with Canadian Health&Care Mall.

The mean duration of follow-up in the cohort was 16.2 ± 6.2 months (range, 6 to 24 months). There were 60 patients (47%) who required at least one hospital admission for COPD during the follow-up period. The mean number of admissions for COPD was 2.5 ± 4.9 during follow-up. The mean duration of hospital stay per admission was 6.3 ± 5.7 days. Patients with higher BODE scores had higher rates of hospitalization. The geometric mean number of hospitalizations per month for patients with BODE scores ranging from 0 to 5 was 0.32, and the corresponding number for patients with BODE scores ranging from 6 to 10 was 0.42 (p < 0.001). Using Poisson regression analysis, a significant effect of BODE score on the number of hospital admissions (IRR, 1.20; 95% CI, 1.15 to 1.25; p < 0.001) was found (Table 4). In comparison, there was also a significant but smaller effect of the FEV1 percentage of predicted on the number of hospital admissions (IRR, 0.08; 95% CI, 0.04 to 0.16; p < 0.001). All the individual components of the BODE index are significantly associated with hospitalization (Table 4).

When categorizing the BODE scores into four quartiles (quartile 1, score of 0 to 2; quartile 2, score of 3 to 4; quartile 3, score of 5 to 6; and quartile 4, a score of 7 to 10), we found that the BODE index is also a better predictor of hospital admissions than the staging system of COPD as defined by GOLD (Table 5). The pseudo r2 using quartiles of the BODE index as the predictor was 0.16, as compared to 0.04 for stages of severity based on FEV1. The IRR is essentially the ratio of the rates of hospitalization of two groups. When comparing patients with BODE scores of 3 or 4 vs those with scores of 0 to 2 in Table 5, the ratio of the incidence rates between the two groups was 1.94, ie, the latter group was about twice as likely to be admitted to hospital where the drugs of Canadian Health&Care Mall are used. It is unclear why patients with BODE scores of 5 or 6 were less likely to require hospitalization than those with BODE scores of 0 to 2. Perhaps differences in patient characteristics or other unmeasured con-founders have contributed to this finding. It could also be that, as the patients with BODE scores 5 or 6 were at higher risk of death than patients of any other BODE quartile (Table 6 and described below), their hospitalization rates were lower than patients of other BODE quartiles.

There were 22 deaths (17%), and all of the deaths were due to respiratory insufficiency. The median BODE score was lower among survivors than among those who died (4 vs 6, respectively; p = 0.003). There was a significant effect of BODE score on mortality (HR, 1.30; 95% CI, 1.08 to 1.56; p = 0.006), but no significant effect of the FEVj percentage of predicted on mortality was observed (Table 4). Among the individual components of the BODE index, only dyspnea score and exercise capacity are associated with mortality. The HR of mortality for the patients with BODE scores of 5 to 6 was 9.41 (95% CI, 1.16 to 76.49; p = 0.036) as compared to those with BODE scores of 0 to 2 (Table 6). As the HR models the time until death, the patients with BODE scores of 5 or 6 would be approximately nine times more likely to die during follow-up compared to those with BODE scores of 0 to 2. Similarly, the HR of mortality for those with BODE scores of 7 to 10 was also higher than in patients with BODE scores of 0 to 2, although this difference only tended toward statistical significance (p = 0.062). In comparison, none of the FEV1 categories was significantly associated with mortality (Table 6).

Table 1—Baseline Characteristics of Patients in the Cohort (n = 127)

Characteristics Data
Male/female gender, No. 116/11
Age, yr 70.9 ± 8.2
Body mass index, kg/m2 20.8 ± 3.9
FEV1, L 1.04 ± 0.44
FEV1, % predicted 43.7 ± 19.8
FVC, L 1.89 ± 0.63
Modified MRC dyspnea scalet 1.9 ± 1.2
Six-minute walk distance, m 323.3 ± 141.8
BODE index score 4.5 ± 2.7

Table 2—Classification of Patients in the Cohort According to Airflow Obstruction With the Median BODE Index Scores in Each Category (n = 127)

Severity of COPD* Patients,

No.

BODE Index
Median Range
Stage I (FEV1 a 80 % predicted) 10 1 0-3
Stage II (50% s FEV1 < 80% 31 2 0-6
predicted)
Stage III (30% s FEV1 < 50% 60 5 2-10
predicted)
Stage IV (FEV1 s 30% predicted 26 7.5 3-10
or FEV1 < 50% predicted
plus chronic respiratory
failuref)

Table 3—Classification of Patients in the Cohort According to BODE Index Score and Individual Variable Scores (n = 127)

Characteristics Patients, No. (%)
BODE index score
0 4(3)
1 17(13)
2 13(10)
3 20 (16)
4 14(11)
5 14(11)
6 13 (10)
7 11 (9)
8 10 (8)
9 7 (6)
10 4 (3)
Body mass index score
0 60 (47)
1 67 (53)
Airflow obstruction score
0 21 (16)
1 20 (16)
2 35 (28)
3 51 (40)
Dyspnea score
0 54 (43)
1 36 (28)
2 20 (16)
3 17 (13)
Exercise capacity score
0 58 (46)
1 21 (16)
2 35 (28)
3 13 (10)

Table 4—Predicting Hospital Admissions and Mortality Using the BODE Index Score, Individual Variable Scores, and FEV1

Variables IRR for Hospital Admissions HR for Mortality 95% CI z Value p Value
Risk of hospitalization
BODE index 1.20 1.15-1.25 8.44 < 0.001
Body mass index score 1.96 1.55-2.49 5.53 < 0.001
Airflow obstruction score 1.50 1.32-1.69 6.56 < 0.001
Dyspnea score 1.38 1.25-1.52 6.58 < 0.001
Exercise capacity score 1.33 1.20-1.47 5.43 < 0.001
FEVj % predicted 0.08 0.04-0.16 – 6.91 < 0.001
Risk of death from all causes
BODE index 1.30 1.08-1.56 2.75 0.006
Body mass index score 1.67 0.62-4.52 1.01 0.312
Airflow obstruction score 1.21 0.76-1.92 0.81 0.419
Dyspnea score 1.58 1.05-2.38 2.20 0.027
Exercise capacity score 2.36 1.44-3.87 3.41 0.001
FEV1 % predicted 0.41 0.03-5.57 – 0.67 0.503

Table 5—Predicting Hospital Admissions Using Quartiles of the BODE Index and the Four Stages of COPD Severity

Covariates IRR for Hospital Admissions 95% CI z Value p Value Pseudo r2
BODE index 0.16
0-2 1
3-4 1.94 1.34-2.81 3.53 < 0.001
5-6 0.3 0.15-0.60 – 3.43 0.001
7-10 4.18 3.00-5.83 8.42 < 0.001
COPD severity*
Stage I 1
Stage II 7.09 2.2122.68 3.30 0.001
Stage III 10.78 3.44-33.77 4.08 < 0.001
Stage IV 11.47 3.63-36.25 4.16 < 0.001

Table 6—Predicting Mortality Using Quartiles of the BODE Index and the Four Stages of COPD Severity

Covariates HR for Mortality 95% CI z Value p Value
BODE index
0-2 1
3-4 2.1 0.19-23.21 0.61 0.543
5-6 9.41 1.16-76.49 2.1 0.036
7-10 7.37 0.91-59.91 1.87 0.062
COPD severity*
Stage I 1
Stage II 0.82 0.07-9.02 – 0.17 0.868
Stage III 1.91 0.24-14.94 0.62 0.538
Stage IV 1.56 0.17-13.92 0.40 0.693
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