Background: We compared the accuracy and practicability of a new combined ear sensor device measuring pulse oximetry and transcutaneous carbon dioxide tension. Methods: Validation studies were done by comparing the results of the combined sensor with arterial blood gas measurements. In an observational part, monitoring data were obtained from 25 patients undergoing colonoscopy, sedated with midazolam and alfentanil and from 8 patients without sedation. Results: There was an excellent correlation between the oxygen saturation and carbon dioxide tension measurements comparing the combined sensor with arterial blood gas analysis (R 0.96 and 0.93, respectively). A mean rise in transcutaneous carbon dioxide tension of 7.6 mm Hg was detectable during sedation with midazolam/alfentanil and of 2.3 mm Hg without sedation. Conclusion: Combined POX/PcCO₂ monitoring at the ear lobe is a novel approach to improve patient safety during sedation and may be helpful in preventing an unintentional slide into a state of deep sedation with impairment of ventilation.

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