Evaluation of a transcutaneous carbon dioxide monitor in patients with acute respiratory failure

Optical sensors for transdermal biomarker detection: A review

This review has explored optical sensors and their important role in non-invasive transdermal biomarker detection. While electrochemical sensors have been thoroughly studied for biomarker tracking, optical sensors present a compelling alternative due to their high sensitivity and selectivity, multiplex capabilities, cost-efficiency, and small form factor. This review examines the latest advancements in optical sensing technologies for transdermal biomarker detection, such as colorimetry, fluorescence, surface plasmon resonance (SPR), fiber optics, photonic crystals, and Raman spectroscopy. These technologies have been applied in the analysis of biomarkers present in sweat and skin gases, which are essential for non-invasive health monitoring. Furthermore, the review has discussed the challenges and future perspectives of optical sensors in in transdermal biomarker detection. The analysis of various sensor types and their applications highlights the transformative potential of optical sensors in enhancing disease diagnostics and promoting proactive health management.

Transcutaneous Carbon Dioxide Monitoring More Accurately Detects Hypercapnia than End-Tidal Carbon Dioxide Monitoring during Non-Intubated Video-Assisted Thoracic Surgery: A Retrospective Cohort Study

Transcutaneous carbon dioxide (PtcCO₂) monitoring is known to be effective at estimating the arterial partial pressure of carbon dioxide (PaCO₂) in patients with sedation-induced respiratory depression. We aimed to investigate the accuracy of PtcCO₂ monitoring to measure PaCO₂ and its sensitivity to detect hypercapnia (PaCO₂ > 60 mmHg) compared to nasal end-tidal carbon dioxide (PetCO₂) monitoring during non-intubated video-assisted thoracoscopic surgery (VATS). This retrospective study included patients undergoing non-intubated VATS from December 2019 to May 2021. Datasets of PetCO₂, PtcCO₂, and PaCO₂ measured simultaneously were extracted from patient records. Overall, 111 datasets of CO₂ monitoring during one-lung ventilation (OLV) were collected from 43 patients. PtcCO₂ had higher sensitivity and predictive power for hypercapnia during OLV than PetCO₂ (84.6% vs. 15.4%, p < 0.001; area under the receiver operating characteristic curve; 0.912 vs. 0.776, p = 0.002). Moreover, PtcCO₂ was more in agreement with PaCO₂ than PetCO₂, indicated by a lower bias (bias ± standard deviation; -1.6 ± 6.5 mmHg vs. 14.3 ± 8.4 mmHg, p < 0.001) and narrower limit of agreement (-14.3-11.2 mmHg vs. -2.2-30.7 mmHg). These results suggest that concurrent PtcCO₂ monitoring allows anesthesiologists to provide safer respiratory management for patients undergoing non-intubated VATS.

Nocturnal hypercapnia with daytime normocapnia in patients with advanced pulmonary arterial hypertension awaiting lung transplantation

BACKGROUND

Pulmonary arterial hypertension (PAH) is frequently complicated by sleep disordered breathing (SDB), and previous studies have largely focused on hypoxemic SDB. Even though nocturnal hypercapnia was shown to exacerbate pulmonary hypertension, the clinical significance of nocturnal hypercapnia among PAH patients has been scarcely investigated.

METHOD

Seventeen patients with PAH were identified from 246 consecutive patients referred to Kyoto University Hospital for the evaluation of lung transplant registration from January 2010 to December 2017. Included in this study were 13 patients whose nocturnal transcutaneous carbon dioxide partial pressure (PtcCO2) monitoring data were available. Nocturnal hypercapnia was diagnosed according to the guidelines of the American Academy of Sleep Medicine. Associations of nocturnal PtcCO2 measurements with clinical features, the findings of right heart catheterization and pulmonary function parameters were evaluated.

RESULTS

Nocturnal hypercapnia was diagnosed in six patients (46.2%), while no patient had daytime hypercapnia. Of note, nocturnal hypercapnia was found for 5 out of 6 patients with idiopathic PAH (83.3%). Mean nocturnal PtcCO2 levels correlated negatively with the percentage of predicted total lung capacity (TLC), and positively with cardiac output and cardiac index.

CONCLUSION

Nocturnal hypercapnia was prevalent among advanced PAH patients who were waiting for lung transplantation, and associated with %TLC. Nocturnal hypercapnia was associated with the increase in cardiac output, which might potentially worsen pulmonary hypertension especially during sleep. Further studies are needed to investigate hemodynamics during sleep and to clarify whether nocturnal hypercapnia can be a therapeutic target for PAH patients.

Estimating Arterial Partial Pressure of Carbon Dioxide in Ventilated Patients: How Valid Are Surrogate Measures?

The arterial partial pressure of carbon dioxide (Pa_CO2) is an important parameter in critically ill, mechanically ventilated patients. To limit invasive procedures or for more continuous monitoring of Pa_CO2, clinicians often rely on venous blood gases, capnography, or transcutaneous monitoring. Each of these has advantages and limitations. Central venous Pco₂ allows accurate estimation of Pa_CO2, differing from it by an amount described by the Fick principle. As long as cardiac output is relatively normal, central venous Pco₂ exceeds the arterial value by approximately 4 mm Hg. In contrast, peripheral venous Pco₂ is a poor predictor of Pa_CO2, and we do not recommend using peripheral venous Pco₂ in this manner. Capnography offers measurement of the end-tidal Pco₂ (Pet_CO2), a value that is close to Pa_CO2 when the lung is healthy. It has the advantage of being noninvasive and continuously available. In mechanically ventilated patients with lung disease, however, Pet_CO2 often differs from Pa_CO2, sometimes by a large degree, often seriously underestimating the arterial value. Dependence of Pet_CO2 on alveolar dead space and ventilator expiratory time limits its value to predict Pa_CO2. When lung function or ventilator settings change, Pet_CO2 and Pa_CO2 can vary in different directions, producing further uncertainty. Transcutaneous Pco₂ measurement has become practical and reliable. It is promising for judging steady state values for Pa_CO2 unless there is overt vasoconstriction of the skin. Moreover, it can be useful in conditions where capnography fails (high-frequency ventilation) or where arterial blood gas analysis is burdensome (clinic or home management of mechanical ventilation).

How should we monitor patients with acute respiratory failure treated with noninvasive ventilation?

Noninvasive ventilation (NIV) is currently one of the most commonly used support methods in hypoxaemic and hypercapnic acute respiratory failure (ARF). With advancing technology and increasing experience, not only are indications for NIV getting broader, but more severe patients are treated with NIV. Depending on disease type and clinical status, NIV can be applied both in the general ward and in high-dependency/intensive care unit settings with different environmental opportunities. However, it is important to remember that patients with ARF are always very fragile with possible high mortality risk. The delay in recognition of unresponsiveness to NIV, progression of respiratory failure or new-onset complications may result in devastating and fatal outcomes. Therefore, it is crucial to understand that timely action taken according to monitoring variables is one of the key elements for NIV success. The purpose of this review is to outline basic and advanced monitoring techniques for NIV during an ARF episode.

Transcutaneous carbon-dioxide partial pressure trends during six-minute walk test in patients with very severe COPD

BACKGROUND

Transcutaneous carbon-dioxide partial-pressure (T_CPCO₂) can be reliably measured and may be of clinical relevance in COPD. Changes in T_CPCO₂ and exercise-induced hypercapnia (EIH) during six-minute walk test (6MWT) need further investigation. We aimed (1) to define patterns of T_CPCO₂ trends during 6MWT and (2) to study determinants of CO2-retention and EIH.

METHODS

Sixty-two COPD patients (age: 63±8years, FEV1: 33±10%pred.) were recruited and T_CPCO2 was recorded by SenTec digital-monitoring-system during 6MWT.

RESULTS

Half of patients (50%) exhibited CO₂-retention (T_CPCO₂[Δ]>4mmHg); 26% preserved and 24% reduced T_CPCO₂. Nineteen (31%) patients presented EIH (T_CPCO₂>45mmHg). EIH was associated to higher baseline-P_CCO₂, worse FEV1, lower inspiratory-pressures, underweight/normal BMI, and pre-walk dyspnea. Stronger determinants of CO₂-retention were FEV1 and pre-walk dyspnea, whereas baseline-P_CCO₂ and pre-walk dyspnea better predict EIH.

CONCLUSIONS

PCO₂ response to 6MWT is highly heterogeneous; however, very low FEV1 and elevated baseline-P_CCO₂ together with pre-walk dyspnea increase the risk for CO₂-retention and EIH. Overweight-BMI seems to carry a protective effect against EIH in very severe COPD.

Noninvasive carbon dioxide monitoring in a porcine model of acute lung injury due to smoke inhalation and burns

In critically ill intubated patients, assessment of adequacy of ventilation relies on measuring partial pressure of arterial carbon dioxide (PaCO2), which requires invasive arterial blood gas analysis. Alternative noninvasive technologies include transcutaneous CO2 (tPCO2) and end-tidal CO2 (EtCO2) monitoring. We evaluated accuracy of tPCO2 and EtCO2 monitoring in a porcine model of acute lung injury (ALI) due to smoke inhalation and burns. Eight anesthetized Yorkshire pigs underwent mechanical ventilation, wood-bark smoke inhalation injury, and 40% total body surface area thermal injury. tPCO2 was measured with a SenTec system (SenTec AG, Therwil, Switzerland) and EtCO2 with a Capnostream-20 (Oridion Medical, Jerusalem, Israel). These values were compared with PaCO2 measurements from an arterial blood gas analyzer. Paired measurements of EtCO2-PaCO2 (n = 276) and tPCO2-PaCO2 (n = 250) were recorded in the PaCO2 range of 25 to 85 mmHg. Overlapping data sets were analyzed based on respiratory and hemodynamic status of animals. Acute lung injury was defined as PaO2/FIO2 ≤ 300 mmHg; hemodynamic instability was defined as mean arterial pressure ≤ 60 mmHg. Before ALI, EtCO2 demonstrated moderate correlation with PaCO2 (R = 0.45; P < 0.0001), which deteriorated after onset of ALI (R = 0.12; P < 0.0001). Before ALI, tPCO2 demonstrated moderate correlation (R = 0.51, P < 0.0001), which was sustained after onset of ALI (R = 0.78; P < 0.0001). During hemodynamic stability, EtCO2 demonstrated moderate correlation with PaCO2 (R = 0.44; P < 0.0001). During hemodynamic instability, EtCO2 did not correlate with PaCO2 (R = 0.03; P = 0.29). tPCO2 monitoring demonstrated strong correlation with PaCO2 during hemodynamic stability (R = 0.80, P < 0.0001), which deteriorated under hemodynamically unstable conditions (R = 0.39; P < 0.0001). Noninvasive carbon dioxide monitors are acceptable for monitoring trends in PaCO2 under conditions of hemodynamic and pulmonary stability. Under unstable conditions, reevaluation of patient status and increased caution in the interpretation of results are required.