Predictors of 30- and 90-Day COPD Exacerbation Readmission: A Prospective Cohort Study

Figures & data

Table 1 Characteristics of the Index Admission Between Those with and without 30-Day Readmission. Variables Measured at the Admission Assessment

Characteristics	All Patients (n=82)	Patients Readmitted Within 30 Days (n=31)	Patients Who Were Not Readmitted Within 30 Days (n=51)	P value
Male	40 (49%)	18 (58%)	22 (43%)	0.19
Female	42 (51%)	13 (42%)	29 (57%)
Age (years)	71 ± 10.4	71 ± 10	71.4 ± 11	0.85
BMI (kg/m2)	24 (20–29)	23 (20–28)	25 (19–30)	0.59
Current smoker	24 (29%)	7 (23%)	17 (33%)	0.30
Ex-smoker	58 (71%)	24 (77%)	34 (67%)
Smoking history (Pack Years)	42 (29–56)	42 (27–63)	42 (29–54)	0.50
Living alone at home	39 (48%)	16 (52%)	23 (46%)	0.60
FEV1 (L)	0.90 ± 0.34	0.90 ± 0.35	0.85 ± 0.34	0.60
FEV1%	34.3 ± 12.4	34 ± 11	35 ± 13	0.67
FVC (L)	2.2 ± 2.3	2.2 (1.7–2.5)	1.4 (2–2.4)	0.22
FVC %	61 ± 16.7	61 ±17	61±16.6	0.98
FEV1/FVC (%)	43.5 ± 11	42 ± 11	44 ± 11	0.56
IC (L)	1.3 (1–1.8)	1.40 (1–1.7)	1.20 (1–2)	0.77
PIFR (L/min)	60 (50–85)	50 (40–60)	80 (55–90)	0.001
∆Xrs5Hz at upright position [cmH2O/(L/s)]	2.1 (0.4–5.1)	1.7 (0.2–4.7))	2.2 (0.50–5)	0.60
FL% at upright position	20 (0–91)	20 (0–90)	2- (0–93)	0.98
∆Xrs5Hz at supine position [cmH2O/(L/s)]	3 (0.9–7)	2.6 (1.7–8)	3 (0.8–7)	0.73
FL% at Supine position	50 (12–100)	40 (27–90)	60 (7–100)	0.92
Rrs5Hz at upright position [cmH2O/(L/s)]	4.7 (3.2–6.2)	4.8 (3–6.3)	4.8 (3.45–6.2)	0.53
Rrs5Hz at supine position [cmH2O/(L/s)]	5.3 (3.7–7.2)	5.5 (3.5–6.6)	5.7 (3.8–7.4)	0.58
Number of Exacerbations (within past 12 months)	2 (1–4)	3 (2–5)	2 (1–4)	0.01
Number of hospitalised exacerbations (<12 months)	2 (1–3)	2 (1–4)	1 (0–2)	0.006
Pulmonary rehabilitation (<12 months)	28 (34%)	13 (42%)	15 (29%)	0.24
Flu Vaccination (<12 months)	60 (73%)	24 (77%)	36 (71%)	0.50
Pneumonia Vaccination (<10 years)	26 (32%)	13 (42%)	13 (26%)	0.12
DECAF Score	2 (1–2)	1.7 ± 1	1.6 ± 0.9	0.70
ICS	50 (61%)	21 (68%)	29 (57%)	0.32
LAMA	35 (43%)	15 (49%)	20 (39%)	0.41
LABA	4 (5%)	2 (7%)	2 (4%)	0.60
Length of stay in days	7 (4–10.3)	8 (5–14)	6 (4–10)	0.03
CAT Score	31 (27.7–34)	31 (28–36)	32 (27–33)	0.50
mMRC	4 (3.7–4)	4 (3–4)	4 (4–4)	0.80
Frailty (REFS)	10 (9–12.2)	12 (11–14)	10 (8–11)	0.001
Depression (HADS)	11 (7–14)	12 (8–14)	9.5 (6–13)	0.02
Anxiety (HADS)	9 (6.7–11)	10 (7–11)	9 (6–11)	0.33
WBC (10^9/L)	10.6 (7.9–14.5)	10.5 (7–14)	10.7 (9–15)	0.50
Eosinophils (10^9/L)	0.07 (0.02–0.24)	0.07 (0.03–0.4)	0.06 (0.01–0.2)	0.30
Neutrophils (10^9/L)	8 (5.1–11.6)	7.3 (5–10.4)	8.2 (6–12.3)	0.24
CRP (mg/L)	20 (6–62)	30 (4–75)	19 (7.4–5.5)	0.80
eGFR mL/min	85 (65–90)	90 (66–90)	78 (60–90)	0.25
Charlson Comorbidity Index	4.3 ± 1.6	4.4 ± 1.6	4.2 ± 1.5	0.71
Systemic hypertension	32 (39%)	12 (39%)	20 (40%)	0.10
Hyperlipidaemia	11 (13%)	6 (55%)	5 (45%)	0.22
Atrial Fibrillation	19 (23%)	6 (19%)	13 (26%)	0.52
Heart failure	13 (16%)	6 (19%)	7 (14%)	0.50
Chronic kidney disease	13 (16%)	5 (16%)	8 (16%)	0.95
Home oxygen	7 (9%)	2 (6.5%)	5 (10%)	0.60
Home NIV	7 (9%)	2 (6.5%)	5 (10%)	0.60

Note: Data are presented as n (%), mean ±SD or median (IQR).

Abbreviations: BMI, body mass index; CAT, COPD Assessment Test; CRP, C-reactive protein; DECAF, Dyspnoea, Eosinopenia, Consolidation, Acidaemia and Atrial Fibrillation; eGFR, estimated glomerular filtration rate; HAD, Hospital Anxiety and Depression Scale; ICS, inhaled corticosteroid; LABA, long-acting β-agonist; LAMA, long-acting muscarinic antagonist; mMRC, modified Medical Research Council dyspnoea scale; REFS, Reported Edmonton Frail Scale; WBC, white blood cell; NIV, noninvasive ventilation.

Figure 1 Consort diagram.

Table 2 Changes from Admission to Discharge Between Those with 30 Days Readmission and Those with No 30 Days Readmission

Outcomes	Patients with 30-Day Readmission (n= 31)				Patients with No 30-Day Readmission (n=51)				P value*
	Admission	Discharge	Median Difference	P value	Admission	Discharge	Median Difference	P value
∆Xrs5Hz at upright position [cmH2O/(L/s)]	1.7 (0.2, 4.7)	2.6 (0.4, 5)	0.2 (−2.4, 2.2)	0.98	2.2 (0.50, 5)	2.8 (1, 5.6)	0.1 (−0.5, 1.4)	0.41	0.74
FL% at upright position	38 (0, 91)	34 (0, 100)	0 (−24, 9.3)	0.77	26 (0, 100)	59 (0, 91)	0 (−9, 11)	0.30	0.50
∆Xrs5Hz at supine position [cmH2O/(L/s)]	2.6 (1.7, 8)	4.7 (1.3, 7.5)	0.2 (−2.37, 2.22)	0.87	3 (0.8, 7)	3 (1.3, 7.4)	0.2 (−1.2, 1.5)	0.52	0.88
FL% at Supine position	40 (27, 90)	48 (7, 100)	0.4 (−31, 20)	0.91	60 (2,100)	50 (2,100)	0 (−15, 11)	0.85	0.90
Rrs5Hz at upright position [cmH2O/(L/s)]	4.7 (3, 6)	4.9 (3, 6)	0.1 (−0.9, 0.7)	0.92	5 (4, 6)	5 (4, 6)	0.2 (−0.5, 1)	0.27	0.58
Rrs5Hz at Supine position [cmH2O/(L/s)]	5.5 (3.5, 7)	5 (4, 6.5)	−0.4 (−0.9, 1)	0.53	5.7 (4, 7)	5.9 (4.7, 8)	0.05 (−0.6, 1.4)	0.19	0.19
PIFR (L/min)	50 (40, 60)	50 (45, 55)	5 (−10, 8.5)	0.65	80 (55, 90)	95 (70, 110)	12.5 (5, 20)	0.001	0.001
IC (L)	1.3 (1, 1.7)	1.4 (0.9, 1.7)	0.05 (−0.18, 0.5)	0.38	1.2 (1.0, 1.8)	1.3 (1.1, 1.6)	0.06 (−0.06, 0.2)	0.05	0.87
mMRC	4 (3, 4)	3 (2, 4)	−1 (−1, 0)	0.001	4 (4, 4)	3 (2, 3)	−1 (−1, 0)	0.001	0.21
CAT score	31 (28, 36)	23 (17, 28)	−8 (−12, −3)	0.001	32 (27, 33)	19 (15, 22)	−11 (−14, −7)	0.001	0.01
WBC (10^9/L)	10.5 (7, 14)	8.4 (7, 11.4)	−0.6 (−4.8, 0.6)	0.03	10.7 (9, 15)	10 (8, 12)	−1.4 (−3.7, 1.1)	0.004	0.85
Eosinophils (10^9/L)	0.07 (0.03, 0.4)	0.14 (0.05, 0.2)	0 (−0.17, 0.09)	0.55	0.06 (0.01, 0.20)	0.12 (0.03, 0.30)	0.03 (−0.04, 0.18)	0.05	0.08
Neutrophils (10^9/L)	7.3 (5, 10.4)	6 (5, 8)	−0.7 (−4.2, 0.3)	0.03	8.2 (6, 12.3)	7 (5, 8)	−2 (−5, 0.7)	0.001	0.46
CRP (mg/L)	30 (4, 75)	15 (3, 41)	−3 (−57, 1)	0.02	19 (7.4, 5.5)	9 (4, 22)	−8 (−34, 1.5)	0.001	0.60
eGFR mL/min	90 (66, 90)	90 (78, 90)	0 (−1, 9)	0.28	78 (60, 90)	90 (66, 90)	0 (0, 9)	0.02	0.31

Notes: *Data are presented as median IQR; *P value= difference between the groups with and without readmission.

Abbreviations: EFL, expiratory flow limitation; ∆Xrs_5Hz, within breath reactance at 5 Hz; FL%, flow limitation percentage; Rrs_5Hz, resistance at 5 HZ; CAT, COPD Assessment Test; CRP, C-reactive protein; eGFR, estimated glomerular filtration rate; FEV₁%, predicted forced expiratory volume in 1 second; FEV₁/FVC, calculated ratio between both measurements; IC, inspiratory capacity; mMRC, modified Medical Research Council dyspnoea scale; PIFR, peak inspiratory flow rate; WBC, white blood cell.

Table 3 Predictors of Readmission Within 30 Days of Index COPD Exacerbation Hospitalisation

Risk Factor	OR	95% CI	P value	AUC (95% CI)	P value
Univariate analysis
Number of Exacerbations (<12 months)	1.27	1.03–1.60	0.027	0.66 (0.54–0.78)	0.01
Number of hospitalised exacerbations (<12 months)	1.39	1.05–1.80	0.021	0.67 (0.55–0.79)	0.008
CAT at discharge	1.14	1.04–1.24	0.004	0.68 (0.55–0.81)	0.006
Frailty Score	1.72	1.32–2.29	<0.001	0.81 (0.71–90)	<0.001
Depression	1.12	1.01–1.24	0.038	0.65 (0.53–0.77)	0.02
PIFR at admission (L/min)	0.94	0.92–0.97	<0.001	0.77 (0.67–0.88)	<0.001
PIFR at discharge (L/min)	0.93	0.90–0.96	<0.001	0.86 (0.78–0.95)	<0.001
Length of stay (days)	1.08	1.01–1.16	0.034	0.64 (0.52–0.76)	0.03
Change in PIFR (L/min)	0.93	0.89–0.97	0.001	0.66 (0.53–0.78)	0.02
Change in CAT	1.12	1.02–1.22	0.019	0.76 (0.65–0.87)	<0.001
Multivariable analysis
Frailty score	1.31	0.96–1.80	0.08
PIFR at discharge (L/min)	0.94	0.91–0.97	<0.001
CAT at discharge	1.01	0.91–1.13	0.77

Abbreviations: AUC, area under curve; CAT, COPD Assessment Test; FEV1%, predicted forced expiratory volume in 1 second; PIFR, peak inspiratory flow rate; OR, odd ratio; CI, confidence interval.

Figure 2 Receiver Operating Characteristic (ROC) curve of predictors for COPD exacerbation readmission within 30 days. (A) ROC of peak inspiratory flow rate (PIFR) at discharge. (B) ROC of Frailty score. (C) ROC of COPD Assessment Test (CAT) score at discharge. (D) ROC of combined variables (PIFR at discharge, Frailty score and CAT score at discharge).

Table 4 Sensitivity, Specificity, PPV and NPV of the PIFR and Frailty to Predict 30 Days Readmission Following COPD Exacerbation (AUC>0.80)

Predictor	Cut-Off	Sensitivity	Specificity	PPV	NPV
PIFR at discharge (L/min)	62.5	82%	83%	70%	91%
	54	58%	90%	78%	77%
	82.5	90%	67%	64%	91%
Frailty Score	10.5	81%	73%	46%	70%
	12.5	45%	90%	50%	66%
	9.5	93%	44%	45%	79%

Abbreviations: PIFR, peak inspiratory flow rate; PPV, positive predictive value; NPV, negative predictive value.

Table 5 Predictors of Readmission Within 90 Days of Index Hospitalisation

Risk Factor	OR	95% CI	P value	AUC (95% CI)	P value
Univariate analysis
Number of Exacerbations (<12 months)	1.44	1.11–1.87	0.005	0.72 (0.61–0.84)	0.001
Number of hospitalised exacerbations (<12 months)	1.57	1.13–2.18	0.007	0.71 (0.59–0.83)	0.001
CAT at discharge	1.16	1.06–1.28	0.002	0.72 (0.61–0.83)	0.001
Frailty Score	1.65	1.27–2.13	<0.001	0.78 (0.67–0.88)	<0.001
Depression	1.14	1.02–1.27	0.013	0.67 (0.55–0.79)	0.007
PIFR at admission (L/min)	0.94	0.92–0.97	<0.001	0.81 (0.71–0.90)	<0.001
PIFR at discharge (L/min)	0.93	0.91–0.96	<0.001	0.86 (0.77–0.95)	<0.001
Length of stay (days)	1.03	0.96–1.10	0.37	0.55 (0.43–0.68)	0.38
Change in PIFR (L/min)	0.94	0.91–0.98	0.002	0.73 (0.60–0.84)	0.001
Change in CAT	1.05	0.96–1.16	0.25	0.76 (0.65–0.87)	<0.001
Flow Limited in supine position at discharge (Yes vs No)	3.02	1.17–7.83	0.022	0.63 (0.51–0.76)	0.04
BMI (kg/m2)	0.94	0.89–0.99	0.031	0.65 (0.53–0.77)	0.02
Multivariable analysis
Frailty score	1.17	0.85–1.61	0.32
PIFR at discharge (L/min)	0.95	0.92–97	0.001
CAT at discharge	1.05	0.92–1.19	0.44
Exacerbations (<12 months)	1.36	0.95–1.95	0.76

Abbreviations: AUC, area under curve; CAT, COPD Assessment Test; FEV1%, predicted forced expiratory volume in 1 second; PIFR, peak inspiratory flow rate; OR, odd ratio; CI, confidence interval.

Table 6 Sensitivity, Specificity, PPV and NPV of the Best Predictor for 90-Day Readmission

Predictor	Cut-Off	Sensitivity	Specificity	PPV	NPV
PIFR at discharge (L/min)	72.5	78%	88%	77.5%	64%
	92.5	89%	67%	75%	77%
	77.5	78%	92%	76%	65%

Abbreviations: PIFR, peak inspiratory flow rate; PPV, positive predictive value; NPV, negative predictive value.