A rate-based transcutaneous CO2 sensor for noninvasive respiration monitoring

Recent Technologies for Transcutaneous Oxygen and Carbon Dioxide Monitoring

The measurement of partial pressures of oxygen (O2) and carbon dioxide (CO2) is fundamental for evaluating a patient's conditions in clinical practice. There are many ways to retrieve O2/CO2 partial pressures and concentrations. Arterial blood gas (ABG) analysis is the gold standard technique for such a purpose, but it is invasive, intermittent, and potentially painful. Among all the alternative methods for gas monitoring, non-invasive transcutaneous O2 and CO2 monitoring has been emerging since the 1970s, being able to overcome the main drawbacks of ABG analysis. Clark and Severinghaus electrodes enabled the breakthrough for transcutaneous O2 and CO2 monitoring, respectively, and in the last twenty years, many innovations have been introduced as alternatives to overcome their limitations. This review reports the most recent solutions for transcutaneous O2 and CO2 monitoring, with a particular consideration for wearable measurement systems. Luminescence-based electronic paramagnetic resonance and photoacoustic sensors are investigated. Optical sensors appear to be the most promising, giving fast and accurate measurements without the need for frequent calibrations and being suitable for integration into wearable measurement systems.

Modeling and Evaluation of a Rate-Based Transcutaneous Blood Gas Monitor

OBJECTIVE

Current methods for transcutaneous blood gas monitoring (TBM) - a common health monitoring method in neonatal care - comes with a suite of challenges like limited attachment opportunities, and risks of infections from burning and tearing of the skin, which limits its use. This study presents a novel system and method for rate-based transcutaneous CO2 measurements with a soft, unheated skin-interface that can address many of these problems. Additionally, a theoretical model for the gas transport from the blood to the system's sensor is derived.

METHODS

By simulating CO2 advection and diffusion through the cutaneous microvasculature and epidermis to the system's skin interface, the effect of a wide range of physiological properties on the measurement has been modeled. Following these simulations, a theoretical model for the relationship between the measured CO2 concentration and that in the blood was derived and compared to empirical data.

RESULTS

Applying the model on measured blood gas levels, even when the theory was based solely on the simulations, produced blood CO2 concentrations within ∼35% of empirical measurements from a state-of-the-art device. Further calibration of the framework, also using the empirical data, yielded an output with a Pearson correlation of 0.84 between the two methods.

CONCLUSION

Compared to the state-of-the-art device the proposed system measured the partial CO2 pressure in the blood with an average deviation of 0.04 kPa and 1.97σ of ±1.1 kPa. However, the model indicated that this performance could be hampered by different skin properties.

SIGNIFICANCE

Given its soft and gentle skin interface and lack of heating, the proposed system could significantly decrease health risks like, burns, tears, and pain, currently associated with TBM on premature neonates.

Physiological effects of N95 respirators on rescuers during cardiopulmonary resuscitation

Objectives

There is a lack of evidence in the medical literature reporting the physiological stress imposed by the wearing of N95 respirators during cardiopulmonary resuscitation (CPR) in healthcare providers. The aim of this study is to monitor the changes in hemodynamics and blood gas profiles in rescuers during the performance of CPR while wearing N95 respirators.

Methods

Thirty-two healthy healthcare workers performed standard CPR on manikins, each participant conducted 2 min of chest compression followed by 2 min of rest for 3 cycles. A non-invasive blood gas measuring device via a fingertip detector was used to collect arterial blood gas and hemodynamic data. Student t-test was used for comparison of various physiologic parameters before and after each session of chest compression.

Results

There were no significant differences in arterial blood gas profiles including partial pressure of arterial carbon dioxide and partial pressure of arterial oxygen before and after each session of chest compression (p > 0.05 for all). Heart rate and cardiac output were significantly higher after CPR (p < 0.05 for all), but no significant changes were found on blood pressure.

Conclusions

Our data suggest that healthcare providers wearing N95 respirators during provision of CPR in a short period of time does not cause any significant abnormalities in blood gas profiles and blood pressure. This may provide evidence to reassure the safe use of N95 respirator during performance of CPR.

Dynamic Modeling of Carbon Dioxide Transport through the Skin Using a Capnometry Wristband

The development of a capnometry wristband is of great interest for monitoring patients at home. We consider a new architecture in which a non-dispersive infrared (NDIR) optical measurement is located close to the skin surface and is combined with an open chamber principle with a continuous circulation of air flow in the collection cell. We propose a model for the temporal dynamics of the carbon dioxide exchange between the blood and the gas channel inside the device. The transport of carbon dioxide is modeled by convection-diffusion equations. We consider four compartments: blood, skin, the measurement cell and the collection cell. We introduce the state-space equations and the associated transition matrix associated with a Markovian model. We define an augmented system by combining a first-order autoregressive model describing the supply of carbon dioxide concentration in the blood compartment and its inertial resistance to change. We propose to use a Kalman filter to estimate the carbon dioxide concentration in the blood vessels recursively over time and thus monitor arterial carbon dioxide blood pressure in real time. Four performance factors with respect to the dynamic quantification of the CO₂ blood concentration are considered, and a simulation is carried out based on data from a previous clinical study. These demonstrate the feasibility of such a technological concept.

Noninvasive carbon dioxide monitoring in pediatric patients undergoing laparoscopic surgery: transcutaneous vs. end-tidal techniques

PURPOSE

The present study aimed to investigate the correlation between transcutaneous carbon dioxide partial pressure (PtcCO₂) and arterial carbon dioxide pressure (PaCO₂) and the accuracy of PtcCO₂ in predicting PaCO₂ during laparoscopic surgery in pediatric patients.

METHODS

Children aged 2-8 years with American Society of Anesthesiologists (ASA) class I or II who underwent laparoscopic surgery under general anesthesia were selected. After anesthesia induction and tracheal intubation, PtcCO₂ was monitored, and radial arterial catheterization was performed for continuous pressure measurement. PaCO₂, PtcCO₂, and end-tidal carbon dioxide partial pressure (PetCO₂) were measured before pneumoperitoneum, and 30, 60, and 90 min after pneumoperitoneum, respectively. The correlation and agreement between PtcCO₂ and PaCO₂, PetCO₂, and PaCO₂ were evaluated.

RESULTS

A total of 32 patients were eventually enrolled in this study, resulting in 128 datasets. The linear regression equations were: PtcCO₂ = 7.89 + 0.82 × PaCO₂ (r² = 0.70, P < 0.01); PetCO₂ = 9.87 + 0.64 × PaCO₂ (r² = 0.69, P < 0.01). The 95% limits of agreement (LOA) of PtcCO₂ - PaCO₂ average was 0.66 ± 4.92 mmHg, and the 95% LOA of PetCO₂ - PaCO₂ average was -4.4 ± 4.86 mmHg. A difference of ≤ 5 mmHg was noted between PtcCO₂ and PaCO₂ in 122/128 samples and between PetCO₂ and PaCO₂ in 81/128 samples (P < 0.01).

CONCLUSION

In pediatric laparoscopic surgery, a close correlation was established between PtcCO₂ and PaCO₂. Compared to PetCO₂, PtcCO₂ can estimate PaCO₂ accurately and could be used as an auxiliary monitoring indicator to optimize anesthesia management for laparoscopic surgery in children; however, it is not a substitute for PetCO₂.

REGISTRATION NUMBER OF CHINESE CLINICAL TRIAL REGISTRY

ChiCTR2100043636.

A novel approach to noninvasive monitoring of dissolved carbon dioxide in small-scale cell culture processes

Disposable small-scale vessels are commonly used in cell culture studies in academia as well as early stages of bioprocess development. These types of research are crucial for our understanding about cells and bioprocesses as they provide important information regarding different parameters affecting cells. Dissolved carbon dioxide (DCO₂) is one main parameter affecting cell metabolism. It is also an indicator of cell culture well-being. Despite CO₂ being a critical process parameter, there is a lack of appropriate monitoring system for CO₂ in small-scale vessels. Here, we present a membrane-based noninvasive method for measuring DCO₂ in cell culture medium. The idea was achieved by modifying a T-flask and replacing a small area of it with CO₂ permeable silicone membrane. In the proposed method, the concentration of CO₂ dissolved in the cell culture medium is determined by measuring the initial diffusion rate of CO₂ through a silicone membrane attached to the bottom wall of the T-flask. The measurement method was validated previously, and the efficacy of the noninvasive method was evaluated by growing E.coli, Pichia pastoris, and CHO cells in the proposed prototype. The results obtained from this method were verified with other quantitative data obtained from the process such as optical density (OD), cell density, dissolved oxygen (DO) and pH. The results show that the proposed membrane-based method is an effective way for completely noninvasive monitoring of DCO₂ in small-scale cell culture processes. Additional diffusing species such as oxygen could also be measured using the same approach.

Carbon Dioxide Sensing-Biomedical Applications to Human Subjects

Carbon dioxide (CO2) monitoring in human subjects is of crucial importance in medical practice. Transcutaneous monitors based on the Stow-Severinghaus electrode make a good alternative to the painful and risky arterial "blood gases" sampling. Yet, such monitors are not only expensive, but also bulky and continuously drifting, requiring frequent recalibrations by trained medical staff. Aiming at finding alternatives, the full panel of CO2 measurement techniques is thoroughly reviewed. The physicochemical working principle of each sensing technique is given, as well as some typical merit criteria, advantages, and drawbacks. An overview of the main CO2 monitoring methods and sites routinely used in clinical practice is also provided, revealing their constraints and specificities. The reviewed CO2 sensing techniques are then evaluated in view of the latter clinical constraints and transcutaneous sensing coupled to a dye-based fluorescence CO2 sensing seems to offer the best potential for the development of a future non-invasive clinical CO2 monitor.

What do masks mask? A study on transdermal CO2 monitoring

Medical professionals have complained of extreme discomfort and fatigue from continuous wearing of N95 respirators (N95) overlaid with surgical masks (SM) and face shields (FS) during COVID-19 pandemic. However, there are no reports on the effect of face coverings on transdermal CO₂ (TrCO₂) levels (a measure of blood CO₂) during moderate activity. In this study, real-time monitoring of TrCO₂, heart rate and skin surface temperature was conducted for six subjects aged 20-59 years with and without wearing personal protective equipment (PPE). We initially studied the effect of wearing PPE (N95+SM+FS) at rest. Then, the effect of moderate stepping/walking activity (120 steps per minute for 60 min) while wearing PPE was evaluated. In addition, we investigated the effect of exercising intensity with different masks. We observed a significant difference (p < 0.0001) in TrCO₂ levels between without and with PPE during moderate exercise, but not while resting. TrCO₂ levels were correlated to exercise intensity independently with masking condition and breathability of masks. For the first time, we present data showing that a properly fitting N95 worn along with SM and FS consistently leads to elevated TrCO₂ under moderate exertion, which could contribute to fatigue over long-term use.

Transdermal sensing: in-situ non-invasive techniques for monitoring of human biochemical status

Improving life expectancy necessitates prevention and early diagnosis of any disease state based on active self-monitoring of symptoms and longitudinal biochemical profiling. Non-invasive and continuous measurement of molecular biomarkers that reflect metabolism and health must however be established to realize this plan. Human samples non-invasively obtained via the skin are suitable in this context for in-situ biochemical monitoring. We present a brief classification of transdermal sampling in aqueous and gaseous phases and then introduce a new generation of transdermal monitoring devices for rapid and accurate assessment of important parameters. Finally, we have summarized the diversity of body-wide skin characteristics that have possible effects for transdermal sampling. Because of its passive nature, in-situ biochemical monitoring via transdermal sampling will potentially lead to a greater understanding of important biochemical markers and their temporal variation.

Wearable Transcutaneous CO2 Monitor Based on Miniaturized Nondispersive Infrared Sensor

Transcutaneous oxygen and carbon dioxide provide the status of pulmonary gas exchange and are of importance in diagnosis and management of respiratory diseases. Though significant progress has been made in oximetry, not much has been explored in developing wearable technologies for continuous monitoring of transcutaneous carbon dioxide. This research reports the development of a truly wearable sensor for continuous monitoring of transcutaneous carbon dioxide using miniaturized nondispersive infrared sensor augmented by hydrophobic membrane to address the humidity interference. The wearable transcutaneous CO₂ monitor shows well-behaved response curve to humid CO₂ with linear response to CO₂ concentration. The profile of transcutaneous CO₂ monitored by the wearable device correlates well with the end-tidal CO₂ trend in human test. The feasibility of the wearable device for passive and unobstructed tracking of transcutaneous CO₂ in free-living conditions has also been demonstrated in field test. The wearable transcutaneous CO₂ monitoring technology developed in this research can be widely used in remote assessment of pulmonary gas exchange efficiency for patients with respiratory diseases, such as COVID-19, sleep apnea, and chronic obstructive pulmonary disease (COPD).

Respiratory Monitoring: Current State of the Art and Future Roads

In this article, we present current methodologies, available technologies, and demands for monitoring various respiratory parameters. We discuss the importance of noninvasive techniques for remote and continuous monitoring and challenges involved in the current "smart and connected health" era. We conducted an extensive literature review on the medical significance of monitoring respiratory vital parameters, along with the current methods and solutions with their respective advantages and disadvantages. We discuss the challenges of developing a noninvasive, wearable, wireless system that continuously monitors respiration parameters and opportunities in the field and then determines the requirements of a state-of-the-art system. Noninvasive techniques provide a significant amount of medical information for a continuous patient monitoring system. Contact methods offer more advantages than non-contact methods; however, reducing the size and power of contact methods is critical for enabling a wearable, wireless medical monitoring system. Continuous and accurate remote monitoring, along with other physiological data, can help caregivers improve the quality of care and allow patients greater freedom outside the hospital. Such monitoring systems could lead to highly tailored treatment plans, shorten patient stays at medical facilities, and reduce the cost of treatment.

Continuous Noninvasive Carbon Dioxide Monitoring in Neonates: From Theory to Standard of Care

Ventilatory support may affect the short- and long-term neurologic and respiratory morbidities of preterm infants. Ongoing monitoring of oxygenation and ventilation and control of adequate levels of oxygen, pressures, and volumes can decrease the incidence of such adverse outcomes. Use of pulse oximetry became a standard of care for titrating oxygen delivery, but continuous noninvasive monitoring of carbon dioxide (CO₂) is not routinely used in NICUs. Continuous monitoring of CO₂ level may be crucial because hypocarbia and hypercarbia in extremely preterm infants are associated with lung and brain morbidities, specifically bronchopulmonary dysplasia, intraventricular hemorrhage, and cystic periventricular leukomalacia. It is shown that continuous monitoring of CO₂ levels helps in maintaining stable CO₂ values within an accepted target range. Continuous monitoring of CO₂ levels can be used in the delivery room, during transport, and in infants receiving invasive or noninvasive respiratory support in the NICU. It is logical to hypothesize that this will result in better outcome for extremely preterm infants. In this article, we review the different noninvasive CO₂ monitoring alternatives and devices, their advantages and disadvantages, and the available clinical data supporting or negating their use as a standard of care in NICUs.

Wearable Health Devices-Vital Sign Monitoring, Systems and Technologies

Wearable Health Devices (WHDs) are increasingly helping people to better monitor their health status both at an activity/fitness level for self-health tracking and at a medical level providing more data to clinicians with a potential for earlier diagnostic and guidance of treatment. The technology revolution in the miniaturization of electronic devices is enabling to design more reliable and adaptable wearables, contributing for a world-wide change in the health monitoring approach. In this paper we review important aspects in the WHDs area, listing the state-of-the-art of wearable vital signs sensing technologies plus their system architectures and specifications. A focus on vital signs acquired by WHDs is made: first a discussion about the most important vital signs for health assessment using WHDs is presented and then for each vital sign a description is made concerning its origin and effect on heath, monitoring needs, acquisition methods and WHDs and recent scientific developments on the area (electrocardiogram, heart rate, blood pressure, respiration rate, blood oxygen saturation, blood glucose, skin perspiration, capnography, body temperature, motion evaluation, cardiac implantable devices and ambient parameters). A general WHDs system architecture is presented based on the state-of-the-art. After a global review of WHDs, we zoom in into cardiovascular WHDs, analysing commercial devices and their applicability versus quality, extending this subject to smart t-shirts for medical purposes. Furthermore we present a resumed evolution of these devices based on the prototypes developed along the years. Finally we discuss likely market trends and future challenges for the emerging WHDs area.

Development and characterization of a point-of care rate-based transcutaneous respiratory status monitor

Blood gas measurements provide vital clinical information in critical care. The current "gold standard" for blood gas measurements involves obtaining blood samples, which can be painful and can lead to bleeding, thrombus formation, or infection. Mass transfer equilibrium-based transcutaneous blood gas monitors have been used since the 1970s, but they require heating the skin to ≥42 °C to speed up the transcutaneous gas diffusion. Thus, these devices have a potential risk for skin burns. Here we report a new generation of noninvasive device for respiratory status assessment. Instead of waiting for mass transfer equilibrium, the blood gas levels are monitored by measuring the transcutaneous diffusion rate, which is proportional to blood gas concentration. The startup time of this device is almost independent of skin temperature, so the measurement can be made at any body temperature. The test results show that this device can track the blood gas levels quickly even at normal body temperature.