Transcutaneous Pco2 monitoring in critically ill adults: Clinical evaluation of a new sensor*

Accuracy of Transcutaneous Carbon Dioxide Measurement During Transcatheter Aortic Valve Replacement Under Monitored Anesthesia Care: A Prospective Observational Study

Background Transcutaneous carbon dioxide tension (PtcCO2) measurement is a promising alternative to arterial carbon dioxide tension (PaCO2) measurement. PaCO2 measurement is invasive and intermittent, whereas PtcCO2 measurement is non-invasive and continuous. However, previous studies evaluating PtcCO2measurements did not include patients undergoing transcatheter aortic valve replacement (TAVR), who experience anticipated hemodynamic changes, particularly before and after valve placement. Therefore, we investigated whether PtcCO2 measurement could provide an alternative to PaCO2 measurement during transfemoral TAVR under monitored anesthesia care (MAC) with local anesthesia. Methodology We conducted a prospective observational study. We included all consecutive patients with severe aortic stenosis who were scheduled to undergo a transfemoral TAVR under MAC at our institution from November 1, 2020, to April 30, 2021. During the procedures, PaCO2 and PtcCO2 were concurrently monitored six times as a reference standard and index test, respectively. PtcCO2 was monitored continuously using a non-invasive earlobe sensor. The agreement between PtcCO2 and PaCO2 measurements was assessed using the Bland-Altman method, and the 95% limits of agreement were calculated. Based on previous studies, we determined that 95% limits of agreement of ±6.0 mmHg would be clinically acceptable to define PtcCO2 as an alternative to PaCO2. Results We obtained 88 measurement pairs from 15 patients. The lower and upper 95% limits of agreement between the PtcCO2 and PaCO2 measurements were -4.22 mmHg and 6.56 mmHg, respectively. Conclusions During TAVR under MAC with local anesthesia, PtcCO2 measurement could not provide a viable alternative to PaCO2 measurement to reduce high PaCO2 events. This study focused on comparing intraoperative periods before and after valve implantation. Therefore, further investigation is warranted to assess the impact of various factors, including the prosthetic valve type and the hemodynamic effects of balloon aortic valvuloplasty, on PtcCO2 measurement in TAVR.

Skin temperature influence on transcutaneous carbon dioxide (CO2) conductivity and skin blood flow in healthy human subjects at the arm and wrist

Objective: present transcutaneous carbon dioxide (CO2)-tcpCO2-monitors suffer from limitations which hamper their widespread use, and call for a new tcpCO2 measurement technique. However, the progress in this area is hindered by the lack of knowledge in transcutaneous CO2 diffusion. To address this knowledge gap, this study focuses on investigating the influence of skin temperature on two key skin properties: CO2 permeability and skin blood flow. Methods: a monocentric prospective exploratory study including 40 healthy adults was undertaken. Each subject experienced a 90 min visit split into five 18 min sessions at different skin temperatures-Non-Heated (NH), 35, 38, 41, and 44°C. At each temperature, custom sensors measured transcutaneous CO2 conductivity and exhalation rate at the arm and wrist, while Laser Doppler Flowmetry (LDF) assessed skin blood flow at the arm. Results: the three studied metrics sharply increased with rising skin temperature. Mean values increased from the NH situation up to 44°C from 4.03 up to 8.88 and from 2.94 up to 8.11 m·s-1 for skin conductivity, and from 80.4 up to 177.5 and from 58.7 up to 162.3 cm3·m-2·h-1 for exhalation rate at the arm and wrist, respectively. Likewise, skin blood flow increased elevenfold for the same temperature increase. Of note, all metrics already augmented significantly in the 35-38°C skin temperature range, which may be reached without active heating-i.e. only using a warm clothing. Conclusion: these results are extremely encouraging for the development of next-generation tcpCO2 sensors. Indeed, the moderate increase (× 2) in skin conductivity from NH to 44°C tends to indicate that heating the skin is not critical from a response time point of view, i.e. little to no skin heating would only result in a doubled sensor response time in the worst case, compared to a maximal heating at 44°C. Crucially, a skin temperature within the 35-38°C range already sharply increases the skin blood flow, suggesting that tcpCO2 correlates well with the arterial paCO2 even at such low skin temperatures. These two conclusions further strengthen the viability of non-heated tcpCO2 sensors, thereby paving the way for the development of wearable transcutaneous capnometers.

Limitations of transcutaneous carbon dioxide monitoring in apneic oxygenation

BACKGROUND

High-flow nasal oxygenation is increasingly used during sedation procedures and general anesthesia in apneic patients. Transcutaneous CO2 (ptcCO2)-monitoring is used to monitor hypercapnia. This study investigated ptcCO2-monitoring during apneic oxygenation.

METHODS

We included 100 patients scheduled for elective surgery under general anesthesia in this secondary analysis of a randomized controlled trial. Before surgery, we collected ptcCO2 measured by TCM4 and TCM5 monitors and arterial blood gas (ABG) measurements every two minutes during 15 minutes of apnea. Bland-Altman plots analyzed agreement between measurement slopes; linear mixed models estimated the different measuring method effect, and outlined differences in slope and offset between transcutaneous and arterial CO2 partial pressures.

RESULTS

Bland-Altman plots showed a bias in slope (95% confidence intervals) between ABG and TCM4-measurements of 0.05mmHg/min (-0.05 to 0.15), and limits of agreement were -0.88mmHg/min (-1.06 to -0.70) and 0.98mmHg/min (0.81 to 1.16). Bias between ABG and TCM5 was -0.14mmHg/min (-0.23 to -0.04), and limits of agreement were -0.98mmHg/min (-1.14 to -0.83) and 0.71mmHg/min (0.55 to 0.87). A linear mixed model (predicting the CO2-values) showed an offset between arterial and transcutaneous measurements of TCM4 (-15.2mmHg, 95%CI: -16.3 to -14.2) and TCM5 (-19.1mmHg, -20.1 to -18.0). Differences between the two transcutaneous measurements were statistically significant.

CONCLUSIONS

Substantial differences were found between the two transcutaneous measurement systems, and between them and ABG. Transcutaneous CO2 monitoring cannot replace arterial CO2-monitoring during apneic oxygenation. In clinical settings with rapidly changing CO2-values, arterial blood gas measurements are needed to reliably assess the CO2-partial pressure in blood.

TRIAL REGISTRATION

ClinicalTrials.gov (NCT03478774).

A Patient-Ready Wearable Transcutaneous CO2 Sensor

Continuously monitoring transcutaneous CO₂ partial pressure is of crucial importance in the diagnosis and treatment of respiratory and cardiac diseases. Despite significant progress in the development of CO₂ sensors, their implementation as portable or wearable devices for real-time monitoring remains under-explored. Here, we report on the creation of a wearable prototype device for transcutaneous CO₂ monitoring based on quantifying the fluorescence of a highly breathable CO₂-sensing film. The developed materials are based on a fluorescent pH indicator (8-hydroxy-1,3,6-pyrenetrisulfonic acid trisodium salt or HPTS) embedded into hydrophobic polymer matrices. The film’s fluorescence is highly sensitive to changes in CO₂ partial pressure in the physiological range, as well as photostable and insensitive to humidity. The device and medical-grade films are based on our prior work on transcutaneous oxygen-sensing technology, which has been extensively validated clinically.

Monitoring of carbon dioxide in ventilated neonates: a prospective observational study

OBJECTIVE

To assess the reliability, accuracy and precision of distal end-tidal capnography (detCO₂) in neonates compared with transcutaneous (tcCO₂) carbon dioxide measurements.

DESIGN

Observational, prospective clinical study.

SETTING

Neonatal intensive care unit at Medical University of Vienna.

PARTICIPANTS

Conventionally ventilated neonates with a body weight between 1000 g and 3000 g.

INTERVENTION

End-tidal partial pressure of CO₂ was measured in distal position using the separate lumen of a double-lumen endotracheal tube connected to an external side-stream capnometer. Three consecutive detCO₂ and tcCO₂ values were recorded simultaneously and compared with simultaneous arterialised partial pressure of CO₂ (paCO₂) measurements in each patient.

MAIN OUTCOME MEASURES

Reliability, accuracy and precision of detCO₂ and tcCO₂ measurements compared with paCO₂ in neonates.

RESULTS

Twenty-five neonates were included with a median (range) weight at enrolment of 1410 (1010-2980) g, from which 81 simultaneous measurements of detCO₂, tcCO₂ and paCO₂ were obtained. The mean (SD) of paCO₂, detCO₂ and tcCO₂ was 45.0 (8.6) mmHg, 42.4 (8.4) mmHg and 50.4 (20.4) mmHg, respectively. The intraclass correlation between paCO₂ and detCO₂ and between paCO₂ and tcCO₂ reached 0.80 (95% CI 0.71 to 0.87, p<0.001) and 0.59 (95% CI 0.43 to 0.72, p<0.001), respectively. In the Bland-Altman analysis, bias and precision of detCO₂ with respect to paCO₂ amounted to -2.68 mmHg and 10.62 mmHg (95% CI 8.49 to 14.51), respectively. Bias and precision of tcCO₂ with respect to paCO₂ amounted to 5.39 mmHg and 17.22 mmHg (95% CI 13.21 to 23.34), respectively.

CONCLUSION

DetCO₂ had better reliability, accuracy and precision with paCO₂ than tcCO₂ in ventilated neonates without severe lung diseas.

TRIAL REGISTRATION NUMBER

NCT03758313.

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.

Prehospital management of a non-intubated inhalation injury patient using transcutaneous monitoring of carbon dioxide

A 46-year-old man experienced facial burns due to a fire in his house. In the prehospital setting, suspecting inhalation injury and carbon monoxide poisoning, an emergency physician decided to bring him to the hospital for carbon dioxide (CO₂) monitoring without endotracheal intubation for approximately 20 min because of less severe respiratory distress. On the way to the hospital, the patient's end-tidal CO₂ monitoring ranged from 19 to 30 mm Hg, and transcutaneous carbon dioxide (TcPCO₂) remained between 50 and 55 mm Hg. On arrival at the hospital, PaCO₂ showed 51.6 mm Hg. Endotracheal intubation using a bronchoscope was performed in the emergency room, and inhalation injury was observed. He was extubated on day 5 and discharged on day 10. In the prehospital setting, TcPCO₂ monitoring is useful for initial management of non-intubated inhalation injury patients even with high concentration oxygen.

Evaluation of Mathematical Arterialization of Venous Blood in Intensive Care and Pulmonary Ward Patients

BACKGROUND

Arterial blood gases are important when assessing acute or critically ill patients. Capillary blood and mathematical arterialization of venous blood have been proposed as alternative methods, eliminating pain and complications of arterial puncture.

OBJECTIVES

This study compares the arterial samples, arterialized venous samples, and capillary samples in ICU and pulmonary ward patients.

METHOD

Ninety-one adult patients with respiratory failure were included in the analysis. Arterial, peripheral venous, and mathematically arterialized venous samples were compared in all patients using Bland-Altman analysis, with capillary samples included in 36 patients.

RESULTS

Overall for pH and PCO2, arterialized venous values, and in the subset of 36 patients, capillary values, compared well to arterial values and were within the pre-defined clinically acceptable differences (pH ± 0.05 and PCO2 ± 0.88 kPa). For PO2, arterialized or capillary values describe arterial with similar precision (PO2 arterialized -0.03, LoA -1.48 to 1.42 kPa and PO2 capillary 0.82, LoA -1.36 to 3 kPa), with capillary values underestimating arterial.

CONCLUSIONS

Mathematical arterialization functions well in a range of patients in an ICU and ward outside the country of development of the method. Furthermore, accuracy and precision are similar to capillary blood samples. When considering a replacement for arterial sampling in ward patients, using capillary sampling or mathematical arterialization should depend on logistic ease of implementation and use rather than improved measurements of using either technique.

Review on Biomedical Sensors, Technologies and Algorithms for Diagnosis of Sleep Disordered Breathing: Comprehensive Survey

This paper provides a comprehensive review of available technologies for measurements of vital physiology related parameters that cause sleep disordered breathing (SDB). SDB is a chronic disease that may lead to several health problems and increase the risk of high blood pressure and even heart attack. Therefore, the diagnosis of SDB at an early stage is very important. The essential primary step before diagnosis is measurement. Vital health parameters related to SBD might be measured through invasive or non-invasive methods. Nowadays, with respect to increase in aging population, improvement in home health management systems is needed more than even a decade ago. Moreover, traditional health parameter measurement techniques such as polysomnography are not comfortable and introduce additional costs to the consumers. Therefore, in modern advanced self-health management devices, electronics and communication science are combined to provide appliances that can be used for SDB diagnosis, by monitoring a patient's physiological parameters with more comfort and accuracy. Additionally, development in machine learning algorithms provides accurate methods of analysing measured signals. This paper provides a comprehensive review of measurement approaches, data transmission, and communication networks, alongside machine learning algorithms for sleep stage classification, to diagnose SDB.

Evaluating a novel formula for noninvasive estimation of arterial carbon dioxide during post-resuscitation care

BACKGROUND

Controlling arterial carbon dioxide is paramount in mechanically ventilated patients, and an accurate and continuous noninvasive monitoring method would optimize management in dynamic situations. In this study, we validated and further refined formulas for estimating partial pressure of carbon dioxide with respiratory gas and pulse oximetry data in mechanically ventilated cardiac arrest patients.

METHODS

A total of 4741 data sets were collected retrospectively from 233 resuscitated patients undergoing therapeutic hypothermia. The original formula used to analyze the data is PaCO₂ -est1 = PETCO₂  + k[(PIO₂  - PETCO₂ ) - PaO₂ ]. To achieve better accuracy, we further modified the formula to PaCO₂ -est2 = k₁ *PETCO₂  + k₂ *(PIO₂  - PETCO₂ ) + k₃ *(100-SpO₂ ). The coefficients were determined by identifying the minimal difference between the measured and calculated arterial carbon dioxide values in a development set. The accuracy of these two methods was compared with the estimation of the partial pressure of carbon dioxide using end-tidal carbon dioxide.

RESULTS

With PaCO₂ -est1, the mean difference between the partial pressure of carbon dioxide, and the estimated carbon dioxide was 0.08 kPa (SE ±0.003); with PaCO₂ -est2 the difference was 0.036 kPa (SE ±0.009). The mean difference between the partial pressure of carbon dioxide and end-tidal carbon dioxide was 0.72 kPa (SE ±0.01). In a mixed linear model, there was a significant difference between the estimation using end-tidal carbon dioxide and PaCO₂ -est1 (P < .001) and PaCO₂ -est2 (P < .001) respectively.

CONCLUSIONS

This novel formula appears to provide an accurate, continuous, and noninvasive estimation of arterial carbon dioxide.

Measuring hemoglobin spectra: searching for carbamino-hemoglobin

SIGNIFICANCE

The arterial carbon dioxide (CO2) partial pressure PaCO2 is a clinically relevant variable. However, its measurement requires arterial blood sampling or bulky and expensive transcutaneous PtcCO2 meters. While the spectrophotometric determination of hemoglobin species-such as oxy-hemoglobin (O2Hb) and deoxy-hemoglobin (HHb)-allowed for the development of pulse oximetry, the measurement of CO2 blood content with minimal discomfort has not been addressed yet.

AIM

Characterizing human carbamino-hemoglobin (CO2Hb) absorption spectrum, which is missing from the literature. Providing the theoretical background that will allow for transcutaneous, noninvasive PaCO2 measurements.

APPROACH

A tonometry-based approach was used to obtain gas-equilibrated, lysed, diluted human blood. Equilibration was performed with both CO2, dinitrogen (N2), and ambient air. Spectrophotometric measurements were carried out on the 235- to 1000-nm range. A theoretical background was also derived from that of pulse oximetry.

RESULTS

The absorption spectra of both CO2Hb and HHb were extremely close and comparable with that of state-of-the-art HHb. The above-mentioned theoretical background led to an estimated relative error above 30% on the measured amount of CO2Hb in a subject's blood. Auxiliary measurements revealed that the use of ethylene diamine tetraacetic acid did not interfere with spectrophotometric measurements, whereas sodium metabisulfite did.

CONCLUSIONS

CO2Hb absorption spectrum was measured for the first time. Such spectrum being close to that of HHb, the use of a theoretical background based on pulse oximetry theory for noninvasive PaCO2 measurement seems extremely challenging.

Comparison of arterial CO2 estimation by end-tidal and transcutaneous CO2 measurements in intubated children and variability with subject related factors

Transcutaneous PCO₂ (P_TCCO₂) and end-tidal PCO₂ (P_ETCO₂) measurement methods serve as alternatives to arterial PCO₂ (PaCO₂), providing continuous non-invasive monitoring. The objective of this study was to evaluate the P_TCCO₂ and P_ETCO₂ methods with actual PaCO₂ levels, and to assess the variability of measurements in relation to subject-related factors, such as skin and subcutaneous adipose tissue thickness and presence of pulmonary diseases. P_TCCO₂, P_ETCO₂ and PaCO₂ were measured at the same time in intubated pediatric subjects. Subjects' demographic characteristics, clinical features, laboratory parameters, skin and subcutaneous adipose tissue thickness were identified. The study was carried out on 102 subjects with a total of 1118 values for each method. In patients with non-pulmonary disease, the mean difference between P_TCCO₂ and PaCO₂ was - 0.29 mmHg (± 6.05), while it was 0.44 mmHg (± 6.83) bias between P_ETCO₂ and PaCO₂. In those with pulmonary diseases, the mean difference between P_TCCO₂ and PaCO₂ was - 1.27 mmHg (± 8.32), while it was - 4.65 mmHg (± 9.01) between P_ETCO₂ and PaCO₂. Multiple linear regression demonstrated that increased subcutaneous adipose tissue thickness, core body temperature and inotropic index were related with higher P_TCCO₂ values relative to the actual PCO₂ values. Other factors, such as skin tissue thickness, presence of pulmonary disease, measurement location and measurement times were non-significant. The P_TCCO₂ method has higher reliability than the P_ETCO₂ method, and P_TCCO₂ measurements are not influenced by most subject-related factors; however, core body temperature, inotropic index and subcutaneous adipose tissue thickness can lead to significant differences in PCO₂ measurement.

Arterial and transcutaneous variability and agreement between multiple successive measurements of carbon dioxide in patients with chronic obstructive lung disease

PURPOSE

This study evaluates agreement between carbon dioxide measured arterial (PaCO₂) and transcutaneous (PtcCO₂) over time, by repeated successive measures, taking into consideration the inherent variability of arterial measurements.

METHODS AND RESULTS

11 patients receiving LTOT, with severe to very severe COPD in a stable phase were studied. Repeated arterial blood samples were drawn and PtcCO₂ measured simultaneously at the ear lobe. Bland-Altman analysis was used to evaluate 95 % limits of agreement (LoA). 194 paired samples were analysed. Following correction for bias, the difference between PaCO₂ and PtCO₂ during dynamic conditions was 0.02 kPa and LoA 0.94 to -0.90 kPa while 29 % of PtCO₂ measurements were outside the range of variability for arterial measurements.

CONCLUSION

PtcCO₂ corrected for intra-patient bias provide reasonable description of PaCO₂ values within but not outside steady state conditions. Our results suggest that PtcCO₂ is a valuable method for monitoring in chronic rather than acute conditions when bias can be removed.

Evaluation of time courses of agreement between minutely obtained transcutaneous blood gas data and the gold standard arterial data from spontaneously breathing Asian adults, and various subgroup analyses

BACKGROUND

Usual clinical practice for arterial blood gas analysis (BGA) in conscious patients involves a one-time arterial puncture to be performed after a resting period of 20-30 min. The aim of this study was to evaluate the use of transcutaneous BGA for estimating this gold standard arterial BGA.

METHODS

Spontaneously breathing Asian adults (healthy volunteers and respiratory patients) were enrolled (n = 295). Transcutaneous PO₂ (PtcO₂) and PCO₂ (PtcCO₂) were monitored using a transcutaneous monitor (TCM4, Radiometer Medical AsP, Denmark) with sensors placed on the chest, forearm, earlobe or forehead. Transcutaneous BGA at 1-min intervals was compared with arterial BGA at 30 min. Reasonable steps to find severe hypercapnia with PaCO₂ > 50 mmHg were evaluated.

RESULTS

Sensors on the chest and forearm were equally preferred and used because of small biases (n = 272). The average PCO₂ bias was close to 0 mmHg at 4 min, and was almost constant (4-5 mmHg) with PtcCO₂ being higher than PaCO₂ at ≥8 min. The limit of agreement for PCO₂ narrowed over time: ± 13.6 mmHg at 4 min, ± 7.5 mmHg at 12-13 min, and ± 6.3 mmHg at 30 min. The limit of agreement for PO₂ also narrowed over time (± 23.1 mmHg at 30 min). Subgroup analyses showed that the PaCO₂ and PaO₂ levels, gender, and younger age significantly affected the biases. All hypercapnia subjects with PaCO₂ > 50 mmHg (n = 13) showed PtcCO₂ ≥ 50 mmHg for until 12 min.

CONCLUSIONS

Although PtcCO₂ is useful, it cannot completely replace PaCO₂ because PCO₂ occasionally showed large bias. On the other hand, the prediction of PaO₂ using PtcO₂ was unrealistic in Asian adults. PtcCO₂ ≥ 50 mmHg for until 12 min can be used as a screening tool for severe hypercapnia with PaCO₂ > 50 mmHg.

Application of P(jv-a) CO2 in monitoring cerebral oxygen supply-demand balance in injured brain

Transcranial Doppler sonography (TCD) assayed cerebral blood flow (CBF) may vary between different intracranial pathologies. Blood gas analysis of the jugular bulb provides a novel way to estimate the global relationship between CBF and oxygen metabolism. In this study, 25 patients with brain trauma, spontaneous intracerebral hemorrhage, and acute cerebral infarction were recruited. Jugular venous oxygen saturation (SjvO₂) increased significantly at different time points after hyperventilation (p < 0.05). A negative correlation between the partial pressure of CO₂ between jugular venous bulb and radial artery blood (P(jv-a)CO₂) and CBF could be observed in acute brain injury and spontaneous intracerebral hemorrhage groups, while P(jv-a)CO₂ and CBF show positive correlation in acute cerebral infarction group. Our results suggest that serial P(jv-a)CO₂ analysis combing with SjvO₂ can be utilized to monitor the change of CBF for patients undergoing craniocerebral surgery.

Transcutaneous PCO2 monitoring in critically ill patients: update and perspectives

The physiology of venous and tissue CO₂ monitoring has a long and well-established physiological background, leading to the technological development of different tissue capnometric devices, such as transcutaneous capnometry monitoring (TCM). To outline briefly, measuring transcutaneous PCO₂ (tcPCO₂) depends on at least three main phenomena: (I) the production of CO₂ by tissues (VCO₂), (II) the removal of CO₂ from the tissues by perfusion (wash-out phenomenon), and (III) the reference value of CO₂ at tissue inlet represented by arterial CO₂ content (approximated by arterial PCO₂, or artPCO₂). For this reason, there are, at present, roughly two clinical uses for tcPCO₂ measurement: a respiratory approach where tcPCO₂ is likely to estimate and non-invasively track artPCO₂; and a hemodynamic under-estimate use where tcPCO₂ can reflect tissue perfusion, summarized by a so-called "tc-art PCO₂ gap". Recent research shows that these two uses are not incompatible and could be combined. The spectrum of indications and validation studies in ICUs is summarized in this review to give a survey of the potential applications of TCM in critically ill patients, focusing mainly on its potential (micro)circulatory monitoring contribution. We strongly believe that the greatest benefit of measuring tcPCO₂ is not to only to estimate artPCO₂, but also to quantify the gap between these two values, which can then help clinicians continuously and noninvasively assess both respiratory and hemodynamic failures in critically ill patients.

Regional capnometry to evaluate the adequacy of tissue perfusion

Tissue hypoperfusion is a major cause of morbidity and mortality in critically ill patients but cannot always be detected by measuring standard whole-body hemodynamic and oxygen-related parameters (e.g., blood pressure, cardiac output, and central venous oxygen saturation). Preclinical and clinical studies have demonstrated that low-flow states are consistently associated with large increases in venous and tissue PCO₂. Monitoring regional PCO₂ with gastric tonometry (PgCO₂) is known to have independent prognostic value for predicting postoperative complications and mortality. The PgCO₂ gap might also be of value as a treatment target (endpoint) in critically ill patients. However, this tool has several limitations and has not yet been developed commercially, thus restricting its use. Regional capnography with sublingual and transcutaneous sensors might be an alternative noninvasive option for evaluating the adequacy of tissue perfusion in critically ill patients. However, further studies are needed to determine whether or not this monitoring technique is of value-particularly as an endpoint for guiding resuscitation. Bladder PCO₂, has only been evaluated in animal studies, and so remains to be validated in patients.

Change in capnogram waveform is associated with bronchodilator response and asthma control in children

BACKGROUND

Airway hyper-reactivity, inflammation and remodeling contribute to inhomogeneity of ventilation-perfusion ratio VA·/Q· in asthma. Short-term variations in V.A/Q· can cause changes in expired capnographic indices.

OBJECTIVES

To measure acute changes in the phase 3 slope of the volumetric capnogram after β2-agonist inhalation (ΔSIII), for comparison with airway response based on FEV1 (ΔFEV1), and asthma control.

SUBJECTS AND METHODS

After ethical approval and informed consent, 72 children aged 6-18 y, followed up for asthma underwent spirometry and capnography before and after β-agonist inhalation through a spacer, using a side-stream rapid infrared analyzer. Asthma control was assessed using the GINA questionnaire.

RESULTS

Children with positive reversibility tests (defined as ΔFEV1>12%) had a significantly higher ΔSIII (m ± SE: 87.4 ± 41.4) versus those with negative tests (31.3 ± 14.0%, P = 0.001). Uncontrolled asthma was associated with a significantly larger ΔSIII (103.4 ± 64.0%, n = 7) compared to partly controlled (52.0 ± 26.1, n = 24; P = 0.009) and controlled asthma (30.8 ± 16.3, n = 41; P = 0.003). Neither Bohr dead space nor ΔFEV1 were different between asthma control groups.

CONCLUSIONS

ΔSIII was significantly larger in children with positive response to β2-agonist, and in uncontrolled asthmatics. To our knowledge these are the first data on exhaled CO₂ phase III volumetric slope change and asthma control. The observed ΔSIII could be due to an increased ventilation of inhomogeneous peripheral lung units, and merits further evaluation as a potential phenotypic biomarker in asthma.

Estimation of Arterial Carbon Dioxide Based on End-Tidal Gas Pressure and Oxygen Saturation

Arterial blood gas (ABG) analysis is the traditional method for measuring the partial pressure of carbon dioxide. In mechanically ventilated patients a continuous noninvasive monitoring of carbon dioxide would obviously be attractive. In the current study, we present a novel formula for noninvasive estimation of arterial carbon dioxide. Eighty-one datasets were collected from 19 anesthetized and mechanically ventilated pigs. Eleven animals were mechanically ventilated without interventions. In the remaining eight pigs the partial pressure of carbon dioxide was manipulated. The new formula (Formula 1) is PaCO₂ = PETCO₂ + k(PETO₂ − PaO₂) where PaO₂ was calculated from the oxygen saturation. We tested the agreements of this novel formula and compared it to a traditional method using the baseline PaCO₂ − ETCO₂ gap added to subsequently measured, end-tidal carbon dioxide levels (Formula 2). The mean difference between PaCO₂ and calculated carbon dioxide (Formula 1) was 0.16 kPa (±SE 1.17). The mean difference between PaCO₂ and carbon dioxide with Formula 2 was 0.66 kPa (±SE 0.18). With a mixed linear model excluding cases with cardiorespiratory collapse, there was a significant difference between formulae (p < 0.001), as well as significant interaction between formulae and time (p < 0.001). In this preliminary animal study, this novel formula appears to have a reasonable agreement with PaCO₂ values measured with ABG analysis, but needs further validation in human 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).

Continuous non-invasive PCO2 monitoring in weaning patients: Transcutaneous is advantageous over end-tidal PCO2

BACKGROUND AND OBJECTIVE

Continuous partial pressure of carbon dioxide (PCO₂ ) assessment is essential for the success of mechanical ventilation (MV). Non-invasive end-tidal PCO₂ (PetCO₂ ) and transcutaneous PCO₂ (PtcCO₂ ) measurements serve as alternatives to the gold standard arterial PCO₂ (PaCO₂ ) method, but their eligibility in critical care is unclear.

METHODS

The present study therefore performed methodological comparisons of PaCO₂ versus PetCO₂ and PtcCO₂ , respectively, in weaning patients receiving invasive MV via tracheal cannulas. PetCO₂ and PtcCO₂ were recorded continuously, while PaCO₂ was analysed at baseline, and after 30 and 60 min. Using the Bland-Altman analysis, a clinically acceptable range was defined as a mean difference of ±4 mm Hg between PaCO₂ and non-invasive strategies.

RESULTS

A total of 60 patients (COPD (n = 30) and non-COPD (n = 30)) completed the protocol. Mean PCO₂ values were 42.4 ± 8.6 mm Hg (PaCO₂ ), 36.5 ± 7.5 mm Hg (PetCO₂ ) and 41.7 ± 8.7 mm Hg (PtcCO₂ ). Mean differences between PtcCO₂ and PaCO₂ were -0.7 ± 3.6 mm Hg (95% CI: -1.6/0.3 mm Hg; 95% limits of agreement: -7.8 to 6.4 mm Hg), and between PetCO₂ and PaCO₂ -5.9 ± 5.3 mm Hg (95% CI: -7.2/-4.5 mm Hg; 95% limits of agreement: -16.2 to 4.5 mm Hg). Underestimation of PaCO₂ by PetCO₂ was most pronounced in COPD patients.

CONCLUSION

Our data therefore support PtcCO₂ as a suitable means for monitoring PCO₂ in patients undergoing invasive MV. This is in contrast to PetCO₂ , which clearly underestimated PaCO₂ , especially in patients with COPD.

Can transcutaneous carbon dioxide pressure be a surrogate of blood gas samples for spontaneously breathing emergency patients? The ERNESTO experience

BACKGROUND

It is known that the arterial carbon dioxide pressure (PaCO2) is useful for emergency physicians to assess the severity of dyspnoeic spontaneously breathing patients. Transcutaneous carbon dioxide pressure (PtcCO2) measurements could be a non-invasive alternative to PaCO2 measurements obtained by blood gas samples, as suggested in previous studies. This study evaluates the reliability of a new device in the emergency department (ED).

METHODS

We prospectively included patients presenting to the ED with respiratory distress who were breathing spontaneously or under non-invasive ventilation. We simultaneously performed arterial blood gas measurements and measurement of PtcCO2 using a sensor placed either on the forearm or the side of the chest and connected to the TCM4 CombiM device. The agreement between PaCO2 and PtcCO2 was assessed using the Bland-Altman method.

RESULTS

Sixty-seven spontaneously breathing patients were prospectively included (mean age 70 years, 52% men) and 64 first measurements of PtcCO2 (out of 67) were analysed out of the 97 performed. Nineteen patients (28%) had pneumonia, 19 (28%) had acute heart failure and 19 (28%) had an exacerbation of chronic obstructive pulmonary disease. Mean PaCO2 was 49 mm Hg (range 22-103). The mean difference between PaCO2 and PtcCO2 was 9 mm Hg (range -47 to +54) with 95% limits of agreement of -21.8 mm Hg and 39.7 mm Hg. Only 36.3% of the measurement differences were within 5 mm Hg.

CONCLUSIONS

Our results show that PtcCO2 measured by the TCM4 device could not replace PaCO2 obtained by arterial blood gas analysis.

Erratum: Concordance and limits between transcutaneous and arterial carbon dioxide pressure in emergency department patients with acute respiratory failure: a single-center, prospective, and observational study

Abstract

After publication of this article (Scand J Trauma Resusc Emerg Med 23:40, 2015), it came to light that an earlier version had been published in error. This erratum contains the correct version of the article, which incorporates revisions made in response to reviewer comments. Additionally, one of the authors was inadvertently omitted from the author list. This author, Justin Yan, has been included in the corrected author list above.

Background

Transcutaneous CO₂ (PtCO₂) is a continuous and non-invasive measure recommended by scientific societies in the management of respiratory distress. The objective of this study was to evaluate the correlation between PtCO₂ and arterial partial pressure of CO₂ (PaCO₂) by arterial blood gas analysis in emergency patients with dyspnoea, and to determine the factors that interfere with this correlation.

Methods

From January to June 2014, all adult patients admitted to the RR with dyspnoea during business hours were included in the study if arterial blood gas measurements were indicated. A sensor measuring the PtCO₂ was attached to the ear lobe of the patient before the gas analysis. Anamnesis, clinical and laboratory parameters were identified.

Results

Ninety patients with dyspnoea were included (104 pairs of measurements). The median (IQR) age was 79 years (69 – 85). The correlation between PtCO₂ and PaCO₂ was R² =.83 (p<.001) but became lower for values of PaCO₂ above 60 mm Hg. The mean bias (± SD) between the two methods of measurement (Bland-Altman analysis) was −1.4 mm Hg (± 7.7) with limits of agreement from −16.4 to 13.7 mm Hg. In univariate analysis, PaO₂ interfered with this correlation. After multivariate analysis, temperature (OR = 3.01; 95 % CIs [1.16, 7.80]) and PaO₂ (OR = 1.22; 95 % CIs [1.02, 1.47]) significantly interfered with this correlation.

Conclusions

There is a significant correlation between PaCO₂ and PtCO₂ values for patients admitted to the emergency department for acute respiratory failure. One limiting factor to routine use of PtCO₂ measurements in the emergency department is the presence of hyperthermia.

Evaluation of transcutaneous and end-tidal carbon dioxide levels during inhalation sedation in volunteers

Measurement of end-tidal carbon dioxide (PETCO2) is useful because of its noninvasiveness, continuity, and response time when sudden changes in ventilation occur during inhalation sedation. We compared the accuracy of PETCO2 using a nasal mask and nasal cannula with the accuracy of transcutaneous carbon dioxide (TC-CO2) and determined which method is more useful during inhalation sedation in volunteers. We used a modified nasal mask (MNM) and modified nasal cannula (MNC) for measurement of PETCO2. The capnometer measured PETCO2 in the gas expired from the nasal cavity by means of two devices. The volunteers received supplemental O2 by means of each device at a flow rate of 6 L/min. After the volunteers lay quietly for 5 min with a supply of 100 % O2, they received supplemental N2O by means of each device at concentrations of 10, 20, and 25 % for 5 min and 30 % for 25 min. The correlation coefficient was poorer in the MNM than in the MNC, and the mean difference between TC-CO2 and PETCO2 in the MNM was greater than that in the MNC. The difference between the TC-CO2 and PETCO2 ranged from 3 to 6 mmHg in the MNM and from 2 to 5 mmHg in the MNC. The difference between two variables against the TC-CO2 and the CO2 waveforms obtained by means of the two devices were within the clinically acceptable range. Our two devices can provide continuous monitoring of PETCO2 with a supply of N2O/O2 in patients undergoing inhalation sedation.

Concordance and limits between transcutaneous and arterial carbon dioxide pressure in emergency department patients with acute respiratory failure: a single-center prospective observational study

Introduction

Transcutaneous CO ₂ (PtCO ₂) is a continuous and non-invasive measure recommended by scientific societies in the management of respiratory distress. The objective of this study is to evaluate the correlation between PtCO ₂ and blood pressure of CO ₂ (PaCO ₂) by blood gas analysis in emergency patients with dyspnoea and to determine the factors that interfere in this correlation.

Methods

From January to June 2014, all patients admitted to resuscitation room of the emergency department targeted for arterial blood gases were included prospectively. A sensor measuring the PtCO ₂ was attached to the ear lobe of the patient before the gas analysis. Anamnesis, clinical and laboratory parameters were identified.

Results

90 patients with dyspnoea were included (with 104 pairs of measurements), the median age was 79 years [69-85]. The correlation between PtCO ₂ and PaCO ₂ was R ²= 0.83 (p <0.001) but became lower for values of PaCO ₂>60 mm Hg. The mean bias (±SD) between the two methods of measurement (Bland-Altman analysis) was -1.4 mm Hg (±7.7) with limits of agreement of -16.4 to 13.7 mm Hg. In univariate analysis, PaO ₂ interfered in this correlation. After multivariate analysis, the temperature (OR = 3.01, 95% CI = 1.16-7.09) and the PaO ₂ (OR = 1.22, 95% CI = 1.02-1.47) were found to be significant.

Conclusions

In patients admitted in emergency unit for acute respiratory failure, there is a significant correlation between PaCO ₂ and PtCO ₂, mainly for values below 60 mm Hg. The two limiting factors of use are hyperthermia and users training.

The noninvasive carbon dioxide gradient (NICO2G) during hemorrhagic shock

Hemorrhagic shock (HS) is a setting in which both pulmonary and cutaneous perfusion may be impaired. The goals of this study were to evaluate the relationship between end-tidal (etCO2), transcutaneous (tPCO2), arterial carbon dioxide (PaCO2) and lactate during lethal HS and to assess the effect of progressive HS on those variables and on a new variable, the noninvasive CO2 gradient ([NICO2G] or the difference between tPCO2 and etCO2). Ten consciously sedated swine were hemorrhaged, by means of a computerized exponential protocol, of up to 80% estimated blood volume for 20 min. End-tidal carbon dioxide, tPCO2, PaCO2, and lactate measurements were taken at baseline and every 5 min thereafter, that is, after 25%, 44%, and 62% total blood volume hemorrhage (TBVH) and at cardiac arrest. Cardiac arrest occurred on average at 67% TBVH. Data were analyzed by linear regression and one-way repeated-measures analysis of variance and are presented as means ± SD. Forty-nine paired measurements were made. There was no overall relationship between NICO2 variables and PaCO2: PaCO2 vs. tPCO2 (r2 = 0.002, P = 0.78); PaCO2 vs. etCO2 (r2 = 0.0002, P = 0.93). Rather, NICO2G increased at each level of blood loss: 4.0 ± 24.9 at baseline, 6.3 ± 35.7 at 25% TBVH, 25.0 ± 37.6 at 44% TBVH, 55.0 ± 33.9 at 62% TBVH, and 70.0 ± 33.2 at cardiac arrest (P < 0.05). Similarly, tPCO2 increased and etCO2 decreased at each level. Linear regression of NICO2G and lactate showed a better correlation than was observed for the other two variables: NICO2G, r2 = 0.58; tPCO2, r2 = 0.46; etCO2, r2 = 0.26. During HS, NICO2 monitors lose accuracy for approximating the PaCO2 but gain usefulness as hemodynamic monitors. Also, by combining data from two different organ systems, NICO2G demonstrated improved correlation with lactate than did either etCO2 or tPCO2 alone.

Analysis of mean transcutaneous capnography in consecutive patients undergoing polysomnography

Transcutaneous capnography is a noninvasive method useful for analysis of the behavioral tendency of transcutaneous CO₂pressure (PtcCO₂) in patients undergoing polysomnography, to evaluate respiratory sleep disorders.

OBJECTIVE

Determine normative PtcCO₂values in normal patients undergoing polysomnography.

METHOD

One hundred seventy-nine patients who underwent polysomnography with simultaneous PtcCO₂measurement were assessed by means of a transcutaneous capnograph (TCM4 series from Radiomiter).

RESULTS

The group classified as normal (N=53) presented a apnea/hypopnea index (AHI) <5 events/per hour of sleep and their age groups varied between 7 and 76 years of age.

CONCLUSION

Global mean values of PtcCO₂in the normal group had a Gaussian distribution that varied between 33.1 and 50.0 mmHg (SD 4,363). Such findings allowed the establishment of normative PtcCO₂values for normal individuals.

Monitoring CO2 in shock states

The primary end point when treating acute shock is to restore blood circulation, mainly by reaching macrocirculatory parameters. However, even if global haemodynamic goals can be achieved, microcirculatory perfusion may remain impaired, leading to cellular hypoxia and organ damage. Interestingly, few methods are currently available to measure the adequacy of organ blood flow and tissue oxygenation. The rise in tissue partial pressure of carbon dioxide (CO2) has been observed when tissue perfusion is decreased. In this regard, tissue partial pressure of CO2 has been proposed as an early and reliable marker of tissue hypoxia even if the mechanisms of tissue partial pressure in CO2 rise during hypoperfusion remain unclear. Several technologies allow the estimation of CO2 content from different body sites: vascular, tissular (in hollow organs, mucosal or cutaneous), and airway. These tools remain poorly evaluated, and some are used but are not widely used in clinical practice. The present review clarifies the physiology of increasing tissue CO2 during hypoperfusion and underlines the specificities of the different technologies that allow bedside estimation of tissue CO2 content.

Carbon dioxide monitoring during laparoscopic-assisted bariatric surgery in severely obese patients: transcutaneous versus end-tidal techniques

Various factors including severe obesity or increases in intra-abdominal pressure during laparoscopy can lead to inaccuracies in end-tidal carbon dioxide (PETCO2) monitoring. The current study prospectively compares ET and transcutaneous (TC) CO2 monitoring in severely obese adolescents and young adults during laparoscopic-assisted bariatric surgery. Carbon dioxide was measured with both ET and TC devices during insufflation and laparoscopic bariatric surgery. The differences between each measure (PETCO2 and TC-CO2) and the PaCO2 were compared using a non-paired t test, Fisher's exact test, and a Bland-Altman analysis. The study cohort included 25 adolescents with a mean body mass index of 50.2 kg/m2 undergoing laparoscopic bariatric surgery. There was no difference in the absolute difference between the TC-CO2 and PaCO2 (3.2±3.0 mmHg) and the absolute difference between the PETCO2 and PaCO2 (3.7±2.5 mmHg). The bias and precision were 0.3 and 4.3 mmHg for TC monitoring versus PaCO2 and 3.2 and 3.2 mmHg for ET monitoring versus PaCO2. In the young severely obese population both TC and PETCO2 monitoring can be used to effectively estimate PaCO2. The correlation of PaCO2 to TC-CO2 is good, and similar to the correlation of PaCO2 to PETCO2. In this population, both of these non-invasive measures of PaCO2 can be used to monitor ventilation and minimize arterial blood gas sampling.

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.

Impact of low filter resistances on subjective and physiological responses to filtering facepiece respirators

Ten subjects underwent treadmill exercise at 5.6 km/h over one hour while wearing each of three identical appearing, cup-shaped, prototype filtering facepiece respirators that differed only in their filter resistances (3 mm, 6 mm, and 9 mm H2O pressure drop). There were no statistically significant differences between filtering facepiece respirators with respect to impact on physiological parameters (i.e., heart rate, respiratory rate, oxygen saturation, transcutaneous carbon dioxide levels, tympanic membrane temperature), pulmonary function variables (i.e., tidal volume, respiratory rate, volume of carbon dioxide production, oxygen consumption, or ventilation), and subjective ratings (i.e., exertion, thermal comfort, inspiratory effort, expiratory effort and overall breathing comfort). The nominal filter resistances of the prototype filtering facepiece respirators correspond to airflow resistances ranging from 2.1 - 6.6 mm H2O/L/s which are less than, or minimally equivalent to, previously reported values for the normal threshold for detection of inspiratory breathing resistance (6 - 7.6 mm H2O/L/sec). Therefore, filtering facepiece respirators with filter resistances at, or below, this level may not impact the wearer differently physiologically or subjectively from those with filter resistances only slightly above this threshold at low-moderate work rates over one hour.

[Nocturnal monitoring of home non-invasive ventilation: Contribution of simple tools such as pulse-oximetry, capnography, built-in ventilator software and autonomic markers of sleep fragmentation]

Complex respiratory events, which may have a detrimental effect on both quality of sleep and control of nocturnal hypoventilation, occur during sleep in patients treated by non-invasive ventilation (NIV). Among these events are patient-ventilator asynchrony, increases in upper airway resistance with or without increased respiratory drive, and leaks. Detection of these events is important in order to select the most appropriate ventilator settings and interface. Simple tools can provide important information when monitoring NIV. Pulse-oximetry is important to ensure that an adequate SpO2 is provided, and to detect either prolonged or short and recurrent desaturations. However, the specificity of pulse-oximetry tracings under NIV is low. Transcutaneous capnography discriminates between hypoxemia related to V/Q mismatch and hypoventilation, documents correction of nocturnal hypoventilation, and may detect ventilator-induced hyperventilation, a possible cause for central apnea/hypopnea and glottic closure. Data provided by ventilator software helps the clinician by estimating ventilation, tidal volume, leaks, rate of inspiratory or expiratory triggering by the patient, although further validation of these signals by independent studies is indicated. Finally, autonomic markers of sympathetic tone using signals such as pulse wave amplitude of the pulse-oximetry signal can provide reliable information of sleep fragmentation.

Comparison of transcutaneous, arterial and end-tidal measurements of carbon dioxide during laparoscopic cholecystectomy in patients with chronic obstructive pulmonary disease

OBJECTIVE

Transcutaneous, arterial and end-tidal measurements of carbon dioxide were compared in patients (American Society of Anesthesiology physical status classes II and III) with chronic obstructive pulmonary disease (COPD) who underwent laparoscopic cholecystectomy with carbon dioxide insufflation.

METHODS

General anaesthesia was performed in all patients. The Sentec(®) system was used for transcutaneous monitoring of the partial pressure of carbon dioxide (TcPCO(2)). TcPCO(2) and arterial partial pressure of carbon dioxide (PaCO(2)) were recorded preoperatively, after induction of anaesthesia, during insufflation and postoperatively; end-tidal carbon dioxide (ETCO(2)) was recorded after induction and during insufflation.

RESULTS

PaCO(2) increased during insufflation and reached a maximum at extubation. It declined within 20 min postoperatively but did not return to preoperative levels during this time. TcPCO(2) levels followed a similar pattern. ETCO(2) was significantly lower than PaCO(2) after induction and during insufflation.

CONCLUSION

TcPCO(2) was a valid and practical measurement compared with ETCO(2). In patients with COPD undergoing laparoscopic cholecystectomy, TcPCO(2) and ETCO(2) could be used instead of arterial blood gas sampling.

Pulmonary and heart rate responses to wearing N95 filtering facepiece respirators

BACKGROUND

Filtering facepiece respirators are the most common respirator worn by US health care and industrial workers, yet little is known on the physiologic impact of wearing this protective equipment.

METHODS

Twenty young, healthy subjects exercised on a treadmill at a low-moderate (5.6 km/h) work rate while wearing 4 different models of N95 filtering facepiece respirators for 1 hour each, 2 models of which were equipped with exhalation valves, while being monitored for physiologic variables.

RESULTS

Compared with controls, respirator use was associated with mean 1 hour increases in heart rate (range, 5.7-10.6 beats per minute, P < .001), respiratory rate (range, 1.4-2.4 breaths per minute, P < .05), and transcutaneous carbon dioxide (range, 1.7-3.0 mm Hg, P < .001). No significant differences in oxygen saturation between controls and respirators were noted (P > .05).

CONCLUSION

The pulmonary and heart rate responses to wearing a filtering facepiece respirator for 1 hour at a low-moderate work rate are relatively small and should generally be well tolerated by healthy persons.

Monitoring in the intensive care

In critical care, the monitoring is essential to the daily care of ICU patients, as the optimization of patient's hemodynamic, ventilation, temperature, nutrition, and metabolism is the key to improve patients' survival. Indeed, the decisive endpoint is the supply of oxygen to tissues according to their metabolic needs in order to fuel mitochondrial respiration and, therefore, life. In this sense, both oxygenation and perfusion must be monitored in the implementation of any resuscitation strategy. The emerging concept has been the enhancement of macrocirculation through sequential optimization of heart function and then judging the adequacy of perfusion/oxygenation on specific parameters in a strategy which was aptly coined “goal directed therapy.” On the other hand, the maintenance of normal temperature is critical and should be regularly monitored. Regarding respiratory monitoring of ventilated ICU patients, it includes serial assessment of gas exchange, of respiratory system mechanics, and of patients' readiness for liberation from invasive positive pressure ventilation. Also, the monitoring of nutritional and metabolic care should allow controlling nutrients delivery, adequation between energy needs and delivery, and blood glucose. The present paper will describe the physiological basis, interpretation of, and clinical use of the major endpoints of perfusion/oxygenation adequacy and of temperature, respiratory, nutritional, and metabolic monitorings.

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

BACKGROUND

Non-invasive measurement of oxygenation is a routine procedure in clinical practice, but transcutaneous monitoring of PCO(2)(PtCO(2)) is used much less than expected.

METHODS

The aim of our study was to analyze the value of a commercially available combined SpO(2)/PtCO(2) monitor (TOSCA-Linde Medical System, Basel, Switzerland) in adult non-invasive ventilated patients with acute respiratory failure. Eighty critically ill adult patients, requiring arterial blood sample gas analyses, underwent SpO(2) and PtCO(2) measurements (10 min after the probe was attached to an earlobe) simultaneously with arterial blood sampling. The level of agreement between PaCO(2) - PtCO(2) and SaO(2) - SpO(2)was assessed by Bland-Altman analyses.

RESULTS

Both, SaO(2) from blood gas analysis and SpO(2) from the transcutaneous monitor, and PaCO(2) and PtCO(2) were equally useful. No measurements were outside of the acceptable clinical range of agreement of ± 7.5 mmHg.

CONCLUSIONS

The accuracy of estimation of the TOSCA transcutaneous electrode (compared with the "gold standard" blood sample gas analysis) was generally good. Moreover, TOSCA presents the advantage of the possibility of continuous non-invasive measurement. The level of agreement of the two methods of measurement allows us to state that the TOSCA sensor is useful in routine monitoring of adults admitted to an intermediate respiratory unit and undergoing non-invasive ventilation.

Use of a combined SpO₂/PtcCO₂ sensor in the delivery room

Arterial oxygen saturation (SaO₂) and partial arterial pressure of carbon dioxide (PaCO₂) are important respiratory parameters in critically ill neonates. A sensor combining a pulse oximeter with the Stow-Severinghaus electrode, required for the measurement of peripheral oxygen saturation (SpO₂) and transcutaneous partial pressure of carbon dioxide (PtcCO₂), respectively, has been recently used in neonatal clinical practice (TOSCA^500ÒRadiometer). We evaluated TOSCA usability and reliability in the delivery room (DR), throughout three different periods, on term, late-preterm, and preterm neonates. During the first period (period A), 30 healthy term neonates were simultaneously monitored with both TOSCA and a MASIMO pulse oximeter. During the second period (period B), 10 healthy late-preterm neonates were monitored with both TOSCA and a transcutaneous device measuring PtcCO₂ (TINA^Ò TCM3, Radiometer). During the third period (period C), 15 preterm neonates were monitored with TOSCA and MASIMO after birth, during stabilization, and during transport to the neonatal intensive care unit (NICU). Blood gas analyses were performed to compare transcutaneous and blood gas values. TOSCA resulted easily and safely usable in the DR, allowing reliable noninvasive SaO₂ estimation. Since PtcCO₂ measurements with TOSCA required at least 10 min to be stable and reliable, this parameter was not useful during the early resuscitation immediately after birth. Moreover, PtcCO₂ levels were less precise if compared to the conventional transcutaneous monitoring. However, PtcCO₂ measurement by TOSCA was useful as trend-monitoring after stabilization and during transport to NICU.

Concordance between transcutaneous and arterial measurements of carbon dioxide in an ED

BACKGROUND

Transcutaneous carbon dioxide pressure (PtcCO(2)) has been suggested as a noninvasive surrogate of arterial carbon dioxide pressure (PaCO(2)). Our study evaluates the reliability of this method in spontaneously breathing patients in an emergency department.

PATIENTS AND METHODS

A prospective, observational study was performed in nonintubated dyspneic patients who required measurement of arterial blood gases. Simultaneously and blindly to the physicians in charge, PtcCO(2) was measured using a TOSCA 500 monitor (Radiometer, Villeurbanne, France). Agreement between PaCO(2) and PtcCO(2) was assessed using the Bland-Altman method.

RESULTS

Forty-eight patients (mean age, 65 years) were included, and 50 measurements were done. Eleven (23%) had acute heart failure; 10 (21%), pneumonia; 7 (15%), acute asthma; and 7 (15%), exacerbation of chronic obstructive pulmonary disease. Median PaCO(2) was 42 mm Hg (range, 17-109). Mean difference between PaCO(2) and PtcCO(2) was 1 mm Hg with 95% limits of agreement of -3.4 to +5.6 mm Hg. All measurement differences were within 5 mm Hg, and 32 (64%) were within 2 mm Hg.

CONCLUSION

Transcutaneous carbon dioxide pressure accurately predicts PaCO(2) in spontaneously breathing patients.

Transcutaneous monitor approximates PaCO(2) but not PaO(2) in anesthetized rabbits

OBJECTIVE

To compare the accuracy of transcutaneous (tc) to arterial partial pressure of carbon dioxide (PaCO(2) ) and partial pressure of oxygen (PaO(2) ) in anesthetized rabbits.

STUDY DESIGN

Prospective, randomized, experimental study.

ANIMALS

Eight healthy adult female New Zealand white rabbits weighing 4.05± 0.30 kg.

METHODS

Isoflurane anesthetized rabbits received six treatments in random order; PaCO(2) <35, 35-45, and >45 mmHg and PaO(2)  < 80, 100-200, >200 mmHg. Arterial and transcutaneous measurements were taken after 15 minutes of stabilization at each condition. Linear regression, correlation and Bland-Altman analysis were performed to compare PtcCO(2) to PaCO(2) and PtcO(2) to PaO(2) .

RESULTS

Over a range of measured PaCO(2) values from 21 to 67 mmHg (n=24) mean bias for PtcCO(2) was -1 mmHg and the 95% limits of agreement were -7 to 5 mmHg. The correlation between PtcCO(2) and PaCO(2) was strong with R(2) value of 0.9454. Over the entire range of measured PaO(2) values (46-508 mmHg) mean bias for PtcO(2) was -61 mmHg and the 95% limits of agreement were -226 to 104 mmHg. Correlation was poor with R(2) =0.5969. Comparing PtcO(2) to PaO(2) over a narrower range [PaO(2) < 150 mmHg (n=13)] improved the correlation, with an R(2) value of 0.8518, mean bias of -7 mmHg and 95% limits of agreement from -33 to 19 mmHg.

CONCLUSIONS AND CLINICAL RELEVANCE

In healthy anesthetized rabbits, PtcCO(2) closely approximated PaCO(2) . In contrast PtcO(2) underestimated PaO(2) , particularly at high values. The PtcCO(2) sensor may be a useful noninvasive way to assess adequacy of ventilation in anesthetized rabbits.