The electrochemical approach with CO₂ electrodes is the gold standard for the measurement of transcutaneous CO₂ (PtCO₂), but it requires the continuous re-calibration of the electrodes, the remembranization of the measuring sensors, specialized personnel, patient cooperation, and a still position during the measurement. We present a wearable device for PtCO₂ measurement with an optical approach.

The new device first measures the environmental CO₂, then brings the skin temperature to 42°C, and finally measures the actual PtCO₂. 30 subjects (20 men, mean age 27.2±7.0) were enrolled to validate the new device against a gold standard PtCO₂ monitor. The protocol consisted in a rebreathing maneuver test with the following steps: 10 minutes of normal breathing, 2 minutes of rebreathing in a 2L bag, and 12 minutes of normal breathing to go back to the baseline.

A statistically significant difference between the distributions of the PtCO₂ values of the new device before and after the rebreathing (p?0.001) confirms that the stimulus was detected. The response time delays of the gold standard and the new device were both in the order of minutes. The individual PtCO₂ increase and the slope of the increase after the rebreathing were comparable between the two devices. However, the gold standard device goes back to the baseline after the end of the stimulus, while the new device saturates.

This work demonstrates the technical feasibility of a wearable device to measure PtCO₂ based on an optical sensor. Possible clinical applications are in the detection of rapid PtCO₂ changes, like patients with chronic obstructive pulmonary disease (COPD), pulmonary hypertension and severe acute asthma.