Changes in transcutaneous PCO2 with sleep in normal subjects and in patients with chronic respiratory diseases

In order to establish the normal range for increase in transcutaneous PCO2 (PtcCO2) during sleep, 33 healthy volunteers were investigated with the Hewlett Packard capnometer 47210A option A10. PtcCO2 was on average 46 mmHg (6.1 kPa) when the subjects were awake. The highest recorded level during sleep was, on average, 52 mmHg (6.9 kPa). The mean maximal increase was thus 6 mm Hg (0.8 kPa) or 13% of awake PtcCO2. Measurements were also performed in 15 patients with interstitial lung disease, 23 patients with chronic obstructive pulmonary disease, 10 patients with scoliosis and in 21 patients with obstructive sleep apnoea syndrome. The mean maximal increase in PtcCO2 with sleep was essentially the same in all groups, except in the scoliosis patients who showed an increase of 11 mmHg (1.5 kPa) (21% of awake PtcCO2); this was significantly more than in any other group. There was a positive relationship (r = 0.67, p less than 0.05) between arterial PCO2 and the increase in PtcCO2 in the scoliotics but not in the other groups.