Serial Measurements of Arterial Oxygen Tension are Associated with Mortality in COPD

Figures & data

Table 1. Baseline demographic-, clinical-, and physiological characteristics of COPD patients by survival status after five years

	Alive		Deceased		p*
n,% women	355	41.4%	64	32.3%	0.176
Age in years	62.6	(58.2–67.8)	69.3	(64.4–72.4)	<0.001
FEV1 in liter	1.5	(1.2–2.0)	1.2	(0.9–1.5)	<0.001
BMI in kg/m^2	25.5	(24.9–25.9)	23.8	(22.2–25.4)	0.02
Medical research council dyspnoea scale score ≥ 3	44	13.8%	18	30%	0.002
Six minutes walking distance in meter	450	(381–510)	336	(240–426)	<0.001
Updated BODE index in points	2	(1–3)	4	(3–5)	<0.001
Pack-years of smoking^†	34.5	(23.2–47.7)	47.2	(29.1–57.5)	0.003
Current smokers	160	45.1%	25	39%	0.363
Exacerbations last 12 months	0	(0–1)	0.5	(0.1)	0.154
Coronary heart disease^#	60	17.4%	21	32.8%	0.004
Charlson co-morbidity index	0	(0–1)	1	(0–2)	0.010

Data presented as n% or median (25th–75th percentiles).

*Kruskal Wallis thest for variables with skewed distributions, Chi square test for categorical variables. ^#Both with and without congestive heart failure.

^†One pack-year: the tobacco exposure equal to smoking 20 cigarettes a day for one year.

Figure 1. Boxplot of median arterial oxygen tension in study visit 1-7 by survival status.

Table 2. Distribution of arterial blood gases in kPa by survival status after five years

	Alive N = 355		Deceased N = 64		p^#
	Mean	SD	Mean	SD
PaO2 in kPa
First measurement	9.4	1.1	8.8	1.2	^***
Lowest measurement	8.6	1.0	8.2	1.1	^**
Last measurement	9.3	1.2	8.7	1.3	^***
PaCO2 in kPa
First measurement	5.3	0.5	5.5	0.7	^***
Highest measurement	5.6	0.5	5.7	0.7	*
Last measurement	5.3	0.5	5.5	0.8	*

Data presented as mean and standard deviation (SD).

^#Student´s t-test. *p < 0.05. ^**p < 0.01. ^***p < 0.001.

Figure 2. Boxplot of median arterial carbon dioxide tension in study visit 1-7 by survival status.

Table 3. Crude hazard ratios (HR) and 95% confidence intervals (CI) for all-cause mortality after five years by baseline demographic, clinical, and physiological characteristics from Cox proportional hazard models

HR	n = 64	95% CI	p
Males vs females	1.47	0.87–2.50	0.150
Age pr year increase	1.15	1.09–1.20	<0.001
PaO2 pr kPa increase	0.70	0.56–0.87	0.002
PaCO2 pr kPa increase	2.07	1.32–3.24	0.001
FEV1 pr liter increase	0.24	0.14–0.43	<0.001
GOLD stage with stage II as reference
III	2.53	1.40–4.63	0.002
IV	5.22	2.58–10.57	<0.001
MRC pr point increase	1.51	1.20–1.88	<0.001
BMI pr kg/m^2 increase	0.93	0.89–0.98	0.014
6MWD pr meter increase	0.99	0.99–0.99	<0.001
Updated BODE index pr point increase	1.47	1.32–1.65	<0.001
Pack-years^# of smoking pr pack-year increase	1.01	1.00–1.02	0.012
Coronary heart disease compared to no coronary heart disease	2.07	1.22–3.48	0.006
Charlson co-morbidity index pr point increase	1.54	1.22–1.94	<0.001

MRC: Medical research council dyspnoea scale. 6MWD: Six minutes walking distance. BMI: Body mass index. ^#One pack-year: the tobacco exposure equal to smoking 20 cigarettes a day for one year.

Table 4. Adjusted hazard ratios (HR) and 95% confidence intervals (CI) for all-cause mortality after five years with respect to first and repeated measurements of PaO₂ and PaCO₂

	Model 1^#				Model 2^##
	n		HR	95% CI	p	n	HR	95% CI	p
PaO2	First measurement pr kPa increase	64	0.65	0.53–0.81	^***	53	0.77	0.61–0.99	*
	Repeated measurements pr kPa increase	59	0.65	0.50–0.85	^**	49	0.73	0.55–0.97	*
PaCO2	First measurement pr kPa increase	64	2.21	1.41–3.45	^**	53	1.50	0.90–2.49	ns
	Repeated measurements pr kPa increase	59	2.14	1.25–3.68	^**	49	1.58	0.90–2.76	Ns

^#Adjusted for baseline age and sex. ## Adjusted for baseline age, sex, and updated BODE index at baseline. *p < 0.05. ^**p < 0.01.

ns: Not significant.

Table 5. Adjusted hazard ratios (HR) and 95% confidence intervals (CI) for all-cause mortality after five years with respect to variation in blood gas values expressed as slopes for PaO₂ and PaCO₂ (regressed linearily on time)

	HR^# n = 43	95% CI	p	HR^## n = 36	95% CI	p
	Increasing trend		Reference			Reference
PaO2	Stable/slightly decreasing trend	0.79	0.34–1.83	0.634	1.02	0.41–2.52	0.961
	Decreasing trend	2.69	1.31–5.52	0.007	4.16	1.76–9.84	0.001
	Decreasing trend		Reference			Reference
PaCO2	Stable	0.89	0.43–1.83	0.749	0.90	0.41–2.0	0.801
	Increasing trend	1.12	0.53–2.38	0.773	0.80	0.34–1.86	0.599

^#Adjusted for baseline age, sex, and baseline corresponding blood gas value.

^##Adjusted for baseline age, sex, the updated BODE index, and baseline corresponding blood gas value.