Daily duration of long-term oxygen therapy and risk of hospitalization in oxygen-dependent COPD patients

Figures & data

Table 1 Baseline characteristics

Characteristics	All patients with LTOT, N=2,249	Patients with prescribed LTOT duration 24 h/d or 15 h/d
		LTOT 24 h/d N=539 (24%)	LTOT 15 h/d N=1,231 (55%)	P-values
Age, years (SD)	74.7±8.2	75.0±8.1	74.7±8.2	0.57
Women, n (%)	1,328 (59)	283 (53)	767 (62)	<0.001
PaO2 air, kPa	6.5±0.9	6.3±0.9	6.6±0.8	<0.001
PaO2 oxygen, kPaa	8.7±1.1	8.6±1.1	8.7±1.1	0.006
PaCO2 air, kPa	6.3±1.2	6.2±1.3	6.2±1.2	0.90
PaCO2 oxygen, kPab	6.5±1.3	6.6±1.3	6.5±1.3	0.12
FEV1, Lc	0.84±0.48	0.89±0.54	0.83±0.45	0.10
FEV1, %pred	33.6±17.3	34.8±19.5	33.8±17.0	0.45
Prescribed oxygen dose, L/min	1.6±1.3	2.0±1.3	1.5±1.0	<0.001
Ever smoking, n (%)	2,106 (94)	478 (89)	1,110 (90)	0.35
BMI, kg/m^2d	24.0 (6.3)	24.0 (6.4)	23.9 (6.0)	0.80
WHO performance status, n (%)e
0	132 (6)	26 (5)	76 (6)	0.26
1	881 (39)	173 (32)	493 (40)	0.001
2	714 (32)	167 (31)	385 (31)	0.90
3	292 (13)	108 (20)	132 (11)	<0.001
4	31 (1)	11 (2)	14 (1)	0.14
Cardiovascular diagnoses, n (%)
0	755 (34)	158 (29)	428 (35)	0.03
1	823 (37)	203 (38)	433 (35)	0.32
2	449 (20)	113 (21)	242 (20)	0.53
≥3	222 (10)	65 (12)	128 (10)	0.30
Anxiety, n (%)	196 (9)	44 (8)	123 (10)	0.23
Renal failure, n (%)	97 (4)	28 (5)	57 (5)	0.60
Oral glucocorticoids, n (%)	1,375 (6)	327 (61)	731 (60)	0.61

Notes: Data presented as mean ± SD unless otherwise specified. Hospitalizations and diagnoses were assessed within the 4-year period before the start of LTOT.

a Missing data n=289.

b Missing data n=301.

c Missing data n=849.

d Missing data n=701.

e Missing data n=199.

Abbreviations: BMI, body mass index; FEV₁, forced expiratory volume in 1 second; LTOT, long-term oxygen therapy; PaCO₂, arterial blood gas tension of carbon dioxide; PaO₂, arterial blood gas tension of oxygen; SD, standard deviations; WHO, World Health Organization.

Table 2 Results from Fine–Gray regression of LTOT duration and hospitalizations

Characteristics	SHR (95% CI)	P-values
Oxygen duration 24 h/d	0.96 (0.84–1.08)	0.48
Age, per 1 year	1.00 (0.99–1.00)	0.19
Women	1.05 (0.92–1.19)	0.46
PaO2 air, per 1 kPa	0.99 (0.93–1.06)	0.80
PaCO2 air, per 1 kPa	0.66 (0.48–0.90)	0.01
FEV1, per 1 L	0.91 (0.76–1.08)	0.28
Prescribed oxygen dose, per 1 L/min	0.99 (0.94–1.05)	0.82
BMI, kg/m^2
<18.5	1.02 (0.86–1.21)	0.85
18.5–24.9	Ref
25.0–29.9	0.95 (0.82–1.11)	0.51
≥30.0	1.02 (0.84–1.23)	0.86
WHO performance status
0	Ref
1	1.07 (0.85–1.34)	0.58
2	1.11 (0.88–1.41)	0.38
3	0.97 (0.73–1.29)	0.83
4	0.52 (0.26–1.05)	0.07
Cardiovascular diagnoses
0	Ref
1	1.13 (0.99–1.28)	0.07
2	1.31 (1.11–1.54)	0.001
≥3	1.42 (1.16–1.75)	0.001
Anxiety	1.18 (0.97–1.43)	0.09
Renal failure	1.22 (0.94–1.58)	0.13
Oral glucocorticoids	1.39 (1.24–1.55)	<0.0001

Notes: Data from Fine–Gray analyses adjusted for baseline age, sex, oxygen dose (L/min), PaO₂ (air), baseline PaCO₂ (air), FEV₁, WHO performance status, BMI, treatment with oral glucocorticoids, and comorbid conditions including anxiety, renal failure, and number of cardiovascular diagnoses. An SHR above 1 indicates an increased risk for hospitalization.

Abbreviations: BMI, body mass index; FEV₁, forced expiratory volume in 1 second; LTOT, long-term oxygen therapy; PaCO₂, arterial blood gas tension of carbon dioxide; PaO₂, arterial blood gas tension of oxygen; Ref, reference; SHR, subdistribution hazard ratio; WHO, World Health Organization.

Figure 1 Cumulative incidence of first hospitalization in LTOT daily duration 24 h/d vs 15 h/d.

Note: Results from Fine–Gray analyses adjusted for baseline age, sex, oxygen dose (L/min), PaO₂ (air), baseline PaCO₂ (air), FEV₁, WHO performance status, body mass index, treatment with oral glucocorticoids, and comorbid conditions including anxiety, renal failure and number of cardiovascular diagnoses.

Abbreviations: FEV₁, forced expiratory volume in one second; LTOT, long-term oxygen therapy; PaCO₂, arterial blood gas tension of carbon dioxide; PaO₂, arterial blood gas tension of oxygen; SHR, subdistribution hazard ratio; WHO, World Health Organization.

Figure 2 All-cause and cause-specific hospitalizations in LTOT daily duration 24 h/d vs 15 h/d.

Note: Results from Fine–Gray analyses of LTOT 24 h/d vs 15 h/d adjusted for baseline age, sex, oxygen dose (L/min), PaO₂ (air), baseline PaCO₂ (air), FEV₁, WHO performance status, body mass index, treatment with oral glucocorticoids, and comorbid conditions including anxiety, renal failure and number of cardiovascular diagnoses.
Abbreviations: FEV₁, forced expiratory volume in one second; LTOT, long-term oxygen therapy; PaCO₂, arterial blood gas tension of carbon dioxide; PaO₂, arterial blood gas tension of oxygen; SHR, subdistribution hazard ratio; WHO, World Health Organization.