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Abstract Background: Level 4 sleep study with transcutaneous carbon dioxide (TcCO 2 ) monitoring is a simple, non-invasive method to investigate sleep-related hypoventilation. However, calibration drift in the TcCO 2 device weakens its reliability. Materials and Methods: We conducted a retrospective study of 61 patients from <1 to 20 years of age in our paediatric unit, who were assigned one of the two models of TcCO 2 machines (SenTec Digital Monitoring System and Tina Radiometer Copenhagen TCM4 Transcutaneous Blood Gas Monitor) for performing the Level 4 sleep study, using capillary blood gas carbon dioxide (pCO 2 ) level at the first and ninth hours as a reference. Results: For the 9-h sleep study, there was no change in the attachment site, membrane, or sensor. The TcCO 2 –pCO 2 difference at the ninth hour in the former model was 0.03 ± 0.61 kPa (0.26 ± 4.59 mm Hg), which was favourable in comparison to the latter (–0.45 ± 1.25 kPa or –3.38 ± 9.38 mm Hg), with P = 0.014; the TcCO 2 –pCO 2 difference between monitors A and B at the ninth hour compared to the first hour did not differ substantially from the former ( P = 0.160), but a statistically significant difference was noted in the latter model ( P = 0.037). Both findings indicated calibration drift and hence less accurate TcCO 2 readings in the latter model. Conclusion: In overnight extended use, calibration drift might affect the diagnosis and management of sleep-related hypoventilation.
Ng et al. (Mon,) studied this question.