Implementation Techniques for Transcutaneous Carbon Dioxide Monitoring: Approaches for Wearable Smart Health Applications.

Wearable smart health applications aim to continuously monitor critical physiological parameters without disrupting patients' daily activities, such as giving a blood sample for lab analysis. For example, the partial pressure of arterial carbon dioxide, the critical indicator of ventilation efficacy reflecting the respiratory and acid-base status of the human body, is measured invasively from the arteries. Therefore, it can momentarily be monitored in a clinical setting when the arterial blood sample is taken. Although a noninvasive surrogate method for estimating the partial pressure of arterial carbon dioxide exists (i.e., transcutaneous carbon dioxide monitoring), it is primarily limited to intensive care units and comes in the form of a large bedside device. Nevertheless, recent advancements in the luminescence sensing field have enabled a promising technology that can be incorporated into a wearable device for the continuous and remote monitoring of ventilation efficacy. In this review, we examine existing and nascent techniques for sensing transcutaneous carbon dioxide and highlight novel wearable transcutaneous carbon dioxide monitors by comparing their performance with the traditional bedside counterparts. We also discuss future directions of transcutaneous carbon dioxide monitoring in next-generation smart health applications.

A Transcutaneous Carbon Dioxide Monitor Based on Time-Domain Dual Lifetime Referencing.

The partial pressure of arterial carbon dioxide plays a critical role in assessing the acid-base and respiratory status of the human body. Typically, this measurement is invasive and can only be taken momentarily when an arterial blood sample is drawn. Transcutaneous monitoring is a noninvasive surrogate method that provides a continuous measure of arterial carbon dioxide. Unfortunately, current technology is limited to bedside instruments mainly used in intensive care units. We developed a first-of-its-kind miniaturized transcutaneous carbon dioxide monitor that utilizes a luminescence sensing film and a time-domain dual lifetime referencing method. Gas cell experiments confirmed the monitor's ability to accurately identify changes in the partial pressure of carbon dioxide within the clinically significant range. Compared to the luminescence intensity-based technique, the time-domain dual lifetime referencing method is less prone to measurement errors caused by changes in excitation strength, reducing the maximum error from  âˆ¼ 40% to  âˆ¼ 3% and resulting in more reliable readings. Additionally, we analyzed the sensing film by investigating its behavior under various confounding factors and its susceptibility to measurement drift. Finally, a human subject test demonstrated the effectiveness of the applied method in detecting even slight changes in transcutaneous carbon dioxide, as small as  âˆ¼ 0.7%, during hyperventilation. The prototype, which consumes 30.1 mW of power, is a wearable wristband with compact dimensions of 37 mm× 32 mm.

An Infra-Red-Based Prototype for a Miniaturized Transcutaneous Carbon Dioxide Monitor.

New types of miniaturized biomedical devices transform contemporary diagnostic and therapeutic techniques in medicine. This evolution has demonstrated exceptional promise in providing infrastructures for enabling precision health by creating diverse sensing modalities. To this end, this paper presents a prototype for transcutaneous carbon dioxide monitoring to diversify the measurable critical parameters for human health. Transcutaneous carbon dioxide monitoring is a noninvasive, surrogate method of assessing the partial pressure of carbon dioxide in the blood. The partial pressure of carbon dioxide is a vital index that can help understand momentarily changing ventilation trends. Therefore, it needs to be reported continuously to monitor the ventilatory status of critically ill patients. The proposed prototype employs an infrared LED as the excitation source. The infrared emission, which decreases in response to an increasing carbon dioxide concentration, is applied to a thermopile sensor that can detect the infrared intensity variations precisely. We have measured the changes in the partial pressure of carbon dioxide in the range of 0-120 mmHg, which covers humans' typical values, 35-45 mmHg. The prototype occupies an area of 25 cm2 (50 mm × 50 mm) and consumes 85 mW power.