PURPOSE: To determine whether capillary blood gas carbon dioxide values can substitute for arterial sampling to calibrate transcutaneous carbon dioxide during polysomnography. METHODS: Participants underwent capillary (arterialized earlobe) and blood gas (radial artery) sampling at polysomnography commencement (Evening) and end (Morning). Participant and scientist sample preference, and participant pain were recorded. The transcutaneous offset from the corresponding arterial/capillary sample, and the transcutaneous electrode drift over the night were determined. RESULTS: Seventy-five people consented and 44 had complete paired timepoint data. Both the capillary and arterial carbon dioxide values were higher than the transcutaneous (capillary evening mean -0.9 ± standard deviation 2.8, capillary morning -2.5 ± 3.9, arterial evening -3.7 ± 2.7, arterial morning -5.6 ± 3.8 mmHg). Capillary and arterial measures were comparable for assessing transcutaneous carbon dioxide drift (mean difference -0.3 mmHg (95% confidence interval -1.3, 0.7). The failure rate for both techniques was equivalent. Patients and scientists both preferred the capillary method. CONCLUSION: Capillary blood gas sampling of carbon dioxide levels from the earlobe is feasible. Capillary sampling provides a comparable measure of transcutaneous carbon dioxide drift, but not absolute offset, during polysomnography to that observed with radial arterial sampling. Importantly, patients prefer the capillary technique as it is less painful.
Sheers et al. (Wed,) studied this question.