The effect of 50% oxygen on PtCO2 in patients with stable COPD, bronchiectasis, and neuromuscular disease or kyphoscoliosis: randomised cross-over trials

Table 3 Transcutaneous carbon dioxide outcomes

	Neuromuscular disease/ Kyphoscoliosis N = 20^a	Bronchiectasis N = 24^a	COPD N = 24^a
Change in PtCO₂on placement of mask^b Mean (SD), mmHg
Intervention 1	1.8 (2.8)	1.3 (1.7)	1.3 (1.4)^f
Intervention 2	1.3 (1.1)^d	2.0 (1.4)^f	1.8 (1.4)^f
PtCO₂during air and oxygen interventions Mean (SD), mmHg
Oxygen T = 0	39.4 (4.2)^d	38.5 (2.6)	37.0 (3.2)^f
Oxygen T = 30	40.3 (4.1)^d	39.6 (2.8)^e	38.8 (3.5)^f
Air T = 0	40.2 (5.6)	38.6 (2.7)^f	37.3 (3.5)^f
Air T = 30	39.7 (3.6)^c	38.9 (2.9)^f	37.7 (3.3)^f
Mixed linear model estimates^g(95% CI), mmHg
Change at 30 min, oxygen minus air	0.2 (− 0.4 to 0.9) P = 0.40	0.5 (− 0.2 to 1.2) P = 0.18	1.3 (0.7 to 1.8) P < 0.001
Change over duration of intervention, oxygen minus air^h	−0.07 (− 0.40 to 0.27) P = 0.70	0.4 (0.08 to 0.7) P = 0.012	1.3 (1.0 to 1.5) P < 0.001

Air Air intervention, COPD Chronic obstructive pulmonary disease, Oxygen Oxygen intervention, PtCO₂ Transcutaneous partial pressure of carbon dioxide, T = 0 Value taken at Time 0 min (i.e. following mask stabilisation and prior to start of intervention), T = 30 Value taken at Time 30 min
^aUnless otherwise stated
^bChange is PtCO₂ at T = 0 minus last recorded PtCO₂ value prior to placement of mask
^cN = 17
^dN = 18
^eN = 22
^fN = 23
^g Mixed linear model values represent oxygen minus air change from T = 0
^hIncorporated values are from T = 10, 20 and 30 min. The interaction between each time point (10, 20 and 30 min) was not significantly different, see Online Supplement for P values. N values for PtCO₂ at each time point during the study were as follows:
Neuromuscular/Kyphoscoliosis study oxygen intervention/washout: n = 18 at T = 0 to T = 50, n = 17 at T = 60
Neuromuscular/Kyphoscoliosis study air intervention/washout: n = 20 at T = 0, n = 19 at T = 10, n = 18 at T = 20 and n = 17 at all other time points
Bronchiectasis study oxygen intervention/washout: n = 24 at T = 0 and T = 10, n = 23 at T = 20, n = 22 at all other time points
Bronchiectasis study air intervention/washout: n = 23 at T = 0 to T = 50 and n = 23 at T = 60
COPD oxygen and air interventions/washouts: n = 23 at all time points
See Online Supplement for further N value details

ISSN: 1471-2466