PtcCO2 Measurements Research Articles

Prospective, observational study investigating the level of agreement between transcutaneous and invasive carbon dioxide measurements in critically ill emergency department patients

BackgroundTranscutaneous carbon dioxide (Ptcco2) measurement is a non-invasive surrogate marker for arterial carbon dioxide (Paco2), which requires invasive arterial blood sampling. Use of Ptcco2 has been examined in different clinical...

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

Transcutaneous PCO2 (PTCCO2) and end-tidal PCO2 (PETCO2) measurement methods serve as alternatives to arterial PCO2 (PaCO2), providing continuous non-invasive monitoring. The objective of this study was to evaluate the PTCCO2 and PETCO2 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. PTCCO2, PETCO2 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 PTCCO2 and PaCO2 was − 0.29 mmHg (± 6.05), while it was 0.44 mmHg (± 6.83) bias between PETCO2 and PaCO2. In those with pulmonary diseases, the mean difference between PTCCO2 and PaCO2 was − 1.27 mmHg (± 8.32), while it was − 4.65 mmHg (± 9.01) between PETCO2 and PaCO2. Multiple linear regression demonstrated that increased subcutaneous adipose tissue thickness, core body temperature and inotropic index were related with higher PTCCO2 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 PTCCO2 method has higher reliability than the PETCO2 method, and PTCCO2 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.

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

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. 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. 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. 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.

Abstract P-607: MAY TRANSCUTANEOUS PCO2 (PtcCO2) MEASUREMENT BE GOLD STANDARD NON-INVASIVE METHOD IN MECHANICALLY VENTILATED PATIENTS? DO PATIENT RELATED FACTORS INFLUENCE THE RELIABILITY OF MEASUREMENTS?

Aims & Objectives: The current gold standard method for measurement of partial carbon dioxide pressure (PCO2) is arterial blood gas (ABG) analysis. However ABG is an invasive method and does not provide continuous monitoring. Transcutaneous PCO2 (PtcCO2) and end-tidal PCO2 (PetCO2) measurements serve as alternatives to arterial PCO2 (PaCO2) method and provide continuous monitoring. Transcutaneous carbon dioxide monitor measures CO2 which diffused from capillary lumen to the membrane of the monitor found on skin by heat induced vasodilatation. The objective of this study is to evaluate the correlation between PtcCO2 and PetCO2 methods with the gold standard ABG analysis. We also aimed to assess the variability of PtcCO2 measurements with patient related factors including age, weight, sex, laboratory findings, skin and subcutaneous fat tissue thickness and also different disease spectrum like pulmonary and non pulmonary causes. Methods Non-invasive PetCO2 and transcutaneous PtcCO2 measurements and invasive ABG analysis were measured in intubated patients admitted to Istanbul Medeniyet University Hospital pediatric intensive care unit (PICU). The results were recorded after sensor fixation at three locations and compared with ABG analysis measured similtanously. Patient demographic characteristics, clinical and laboratory parameters, skin and subcutaneous tissue thickness were identified. Results There was more potent correlation between PtcCO2 and ABG compared to PetCO2. (p<0,001). Neither sensor location nor patient related factors causes statistically significant differences on results. Conclusions When compared with PetCO2 method, PtcCO2 measurement can be used more reliably as a noninvasive method. Providing a continuous monitoring and to not be affected by patient related factors make PtcCO2 method more advantagable.

Validity of transcutaneous PCO2 in monitoring chronic hypoventilation treated with non-invasive ventilation

BackgroundNon-invasive ventilation (NIV) is an efficient treatment for patients with chronic hypercapnic respiratory failure (CRF), but requires regular monitoring to detect both diurnal and nocturnal residual hypercapnia.The present study was designed to determine 1) whether transcutaneous PCO2 (PtcCO2) is a valid tool for monitoring PaCO2 in this group of patients, and 2) if overnight instrumental drift of the PtcCO2 sensor is clinically significant. MethodsSixty-seven patients with CRF on long term NIV were included. Arterial blood gases (ABG) were sampled from the radial artery during PtcCO2 measurement. PtcCO2 was recorded 2 min after ABG sampling. Instrumental drift was tested by measuring a gas of known CO2 concentration after auto-calibration of the sensor in the evening, and on the following morning. FindingsPaCO2 values ranged from 3·97 kPa to 9.0 kPa. Thirty-six (53%) patients were hypercapnic. Correlation between PaCO2 and PtcCO2 was highly significant (r2 = 0.9, p < 0.0001), Bias (d) and SD of bias (s) were 0.23 kPa and 0.28 kPa respectively, with a minor underestimation of PaCO2. Limits of agreement (d ± 2s) were; −0.32; 0.79 kPa. None of the paired values of PaCO2/PtcCO2 had a difference exceeding 1 kPa. The mean drift of PtcCO2 was 0.14 ± 0.54 kPa/8 h (p = 0.04; 95% CI: 0.01–0.27). InterpretationWith the device tested, in stable patients under NIV-treatment for CRF, PtcCO2 accurately reflects PaCO2. PtcCO2 can be used to monitor CO2 overnight during NIV without any clinically significant drift. Trial registration N°NCT01845233.

Can Transcutaneous CO2 Tension Be Used to Calculate Ventilatory Dead Space? A Pilot Study.

Dead space fraction (V d/V t) measurement performed using volumetric capnography requires arterial blood gas (ABG) sampling to estimate the partial pressure of carbon dioxide (PaCO2). In recent years, transcutaneous capnography (PtcCO2) has emerged as a noninvasive method of estimating PaCO2. We hypothesized that PtcCO2 can be used as a substitute for PaCO2 in the calculation of V d/V t. In this prospective pilot comparison study, 30 consecutive postcardiac surgery mechanically ventilated patients had V d/V t calculated separately using volumetric capnography by substituting PtcCO2 for PaCO2. The mean V d/V t calculated using PaCO2 and PtcCO2 was 0.48 ± 0.09 and 0.53 ± 0.08, respectively, with a strong positive correlation between the two methods of calculation (Pearson's correlation = 0.87, p < 0.05). Bland-Altman analysis showed a mean difference of −0.05 (95% CI: −0.01 to −0.09) between the two methods. PtcCO2 measurements can provide a noninvasive means to measure V d/V t, thus accessing important physiologic information and prognostic assessment in patients receiving mechanical ventilation.

Transcutaneous PtcCO2 measurement in combination with arterial blood gas analysis provides superior accuracy and reliability in ICU patients

Hyper or hypoventilation may have serious clinical consequences in critically ill patients and should be generally avoided, especially in neurosurgical patients. Therefore, monitoring of carbon dioxide partial pressure by intermittent arterial blood gas analysis (PaCO2) has become standard in intensive care units (ICUs). However, several additional methods are available to determine PCO2 including end-tidal (PETCO2) and transcutaneous (PTCCO2) measurements. The aim of this study was to compare the accuracy and reliability of different methods to determine PCO2 in mechanically ventilated patients on ICU. After approval of the local ethics committee PCO2 was determined in n=32 ICU consecutive patients requiring mechanical ventilation: (1) arterial PaCO2 blood gas analysis with Radiometer ABL 625 (ABL; gold standard), (2) arterial PaCO2 analysis with Immediate Response Mobile Analyzer (IRMA), (3) end-tidal PETCO2 by a Propaq 106 EL monitor and (4) transcutaneous PTCCO2 determination by a Tina TCM4. Bland-Altman method was used for statistical analysis; p<0.05 was considered statistically significant. Statistical analysis revealed good correlation between PaCO2 by IRMA and ABL (R2=0.766; p<0.01) as well as between PTCCO2 and ABL (R2=0.619; p<0.01), whereas correlation between PETCO2 and ABL was weaker (R2=0.405; p<0.01). Bland-Altman analysis revealed a bias and precision of 2.0±3.7mmHg for the IRMA, 2.2±5.7mmHg for transcutaneous, and -5.5±5.6mmHg for end-tidal measurement. Arterial CO2 partial pressure by IRMA (PaCO2) and PTCCO2 provided greater accuracy compared to the reference measurement (ABL) than the end-tidal CO2 measurements in critically ill in mechanically ventilated patients patients.

Superiority of transcutaneous CO2 over end-tidal CO2 measurement for monitoring respiratory failure in nonintubated patients: A pilot study

PurposeArterial blood gas measurement is frequently performed in critically ill patients to diagnose and monitor acute respiratory failure. At a given metabolic rate, carbon dioxide partial pressure (Paco2) is entirely determined by CO2 elimination through ventilation. Transcutaneous partial pressure of carbon dioxide (PtcCO2) monitoring permits a noninvasive and continuous estimation of arterial CO2 tension (Paco2). The accuracy of PtcCO2, however, has not been well studied.To assess the accuracy of different CO2 monitoring methods, we compared PtcCO2 and end-tidal CO2 concentration (EtCO2) to Paco2 measurements in nonintubated intensive care unit (ICU) patients with acute respiratory failure. MethodsDuring a 2-month period, we conducted a prospective observational cohort study in 25 consecutive nonintubated and spontaneously breathing patients admitted to our ICU. Arterial blood gases were measured at study inclusion, 30, 60, and 120 minutes later. At each sampling time, EtCO2 was continuously monitored using a Philips Smart Capnoline Plus, and PtcCO2 was measured using was measured using SenTec device. The aim of the study was to assess agreement between PtcCO2 and Paco2 and between EtCO2 and Paco2 in nonintubated ICU patients with acute respiratory failure. Bland-Altman techniques and Pearson correlation coefficients were used. The differences over time (at 30, 60, and 120 minutes) between Paco2 and EtCO2 and between PtcCO2 and Paco2 were evaluated using 1-way analysis of variance. ResultsTranscutaneous partial pressure of carbon dioxide and Paco2 were well correlated (R = 0.97), whereas the correlation between EtCO2 and Paco2 was poor (R = 0.62) probably due to the presence of an alveolar dead space in a few patients, most notably in the group with chronic obstructive pulmonary disease. The difference over time remained stable for both Paco2 vs EtCO2 (analysis of variance; P = .88) and Paco2 vs PtcCO2 (P = .93). ConclusionWe found large differences between EtCO2 and Paco2 in spontaneously breathing nonintubated ICU patients admitted for acute respiratory failure. Our study argues against the use of EtCO2 monitoring in such patients but raises the possibility that PtcCO2 measurement may provide reasonable estimates of Paco2.

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. Determine normative PtcCO₂values in normal patients undergoing polysomnography. One hundred seventy-nine patients who underwent polysomnography with simultaneous PtcCO₂measurement were assessed by means of a transcutaneous capnograph (TCM4 series from Radiomiter). 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. 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.

Transcutaneous monitoring of partial pressure of carbon dioxide during endoscopic retrograde cholangiopancreatography using a double‐balloon endoscope with carbon dioxide insufflation under conscious sedation

A double-balloon (DB) endoscope can be selectively inserted into the afferent loop to carry out endoscopic retrograde cholangiopancreatography (ERCP) in patients with surgically altered anatomy, allowing various types of endoscopic treatments for pancreaticobiliary diseases to be successfully carried out. In order to make such a lengthy procedure more comfortable and safe, sedatives and carbon dioxide (CO2 ) insufflation are widely used for gastrointestinal endoscopy. However, these techniques can increase the risk of CO2 retention. Recently, a new sensor for transcutaneous measurement of partial pressure of carbon dioxide (PCO2 ) has been introduced. The aim of the present study was to evaluate the changes in transcutaneous PCO2 (PtcCO2 ) during DB-ERCP with CO2 insufflation under conscious sedation and assess any complications related to sedation and CO2 insufflation. A total of 312 patients underwent DB-ERCP with CO2 insufflation at our hospital between March 2009 and December 2012. The patients were moderately sedated using midazolam with or without pentazocine. PtcCO2 was measured by a non-invasive sensor throughout DB-ERCP in all patients. The mean peak PtcCO2 during the procedure was significantly higher than the mean PtcCO2 value before and after DB-ERCP. Body mass index, procedure time and dose of pentazocine were significantly higher in the CO2 retention group (peak PtcCO2 ≥ 50 mmHg). CO2 narcosis was observed in one case. DB-ERCP with CO2 insufflation under conscious sedation might have the potential to increase the risk of CO2 retention. Hence, non-invasive and continuous PtcCO2 measurement is useful for early detection of hypercapnia.

Combined Use of Transcutaneous and End-Tidal Measures of Carbon Dioxide to Predict PCO2 during General Anaesthesia in Adults

Background: The aim of the present study was to integrate PtcCO2 and PetCO2 models to improve the accuracy and precision of PCO2 measurements. Methods: 26 ASA physical status I-III postoperative patients recovering from general anesthesia after surgery were selected for investigation. The carbon dioxide partial pressure (PCO2) levels were determined six times during the anesthesia of each patient by using arterial blood gas analysis (PaCO2), end-tidal (PetCO2) and transcutaneous (PtcCO2) measurements. This study tested the hypothesis that combining PetCO2 and PtcCO2 measurements by a regression function, namely Pet_tcCO2, will improve PCO2 measurements during sedation. The Bland-Altman method was used for the statistical analysis, and a p<0.05 was considered statistically significant. Results: A total of 156 data sets (i.e., PaCO2, PetCO2, and PtcCO2) were obtained from 26 patients (63 ± 17 years old; 18 males, 8 females). The mean PaCO2 was 44.3 ± 3.88 mm Hg. The mean PetCO2 was 38.9 ± 4.01 mm Hg. The mean PtcCO2 level was 46.1 ± 3.95 mm Hg. The average PtcCO2-PaCO2 difference was 3.8 ± 1.85 mm Hg. The average PetCO2-PaCO2 difference was -3.9 ± 1.95 mm Hg. When the value of Pet_tcCO2 were combined, the fit equation was Pet_tcCO2=7.24+0.36 × PetCO2+0.46 × PtcCO2, R2= .66, p<0.001. The average Pet_tcCO2-PaCO2 difference was 2.1 ± 1.25 mm Hg. Conclusions: The combined use of transcutaneous and end-tidal methods could help improve the accuracy and precision of PCO2 measurements. Pet_tcCO2 approach of combining PetCO2 and PtcCO2 techniques could be a new technology for PCO2 measurement in spontaneously breathing patients have no serious lung disease.

Accuracy and Precision of Three Different Methods to Determine Pco2 (Paco2 vs. Petco2 vs. Ptcco2) During Interhospital Ground Transport of Critically Ill and Ventilated Adults

Interhospital transportation of critically ill and mechanically ventilated patients represents a common, yet difficult problem. Three different methods to determine Pco2 during transport are available: arterial blood gas analysis (Paco2), end-tidal (Petco2) and transcutaneous (Ptcco2) measurement. The aim of the present study is to analyze accuracy and precision of those different methods simultaneously in critically ill and ventilated adults during interhospital transport. Patients scheduled for interhospital transport were investigated after approval of the local ethics committee in the prospective study. Pco2 was determined five times in each patient during the transport simultaneously by (1) arterial blood gas analysis (Paco2[Immediate Response Mobile Analyzer, IRMA]), (2) end-tidal (Petco2), and (3) transcutaneous (Ptcco2) measurements. The results were compared with an in-hospital reference measurement performed by an ABL 625 blood gas analyzer (Paco2[ABL625]). For statistical analysis the Bland-Altman method was used. A p < 0.05 was considered statistically significant. One hundred seventy data sets (Paco2[IRMA], Paco2[ABL625], Petco2, Ptcco2) were obtained in 34 patients (61 years +/- 16 years old; 19 male patients, 15 female patients). The mean Paco2(ABL625) was 43.2 mm Hg +/- 8.8 mm Hg ranging from 24.9 mm Hg to 72.4 mm Hg. Bland-Altman analysis revealed a bias and precision of -0.6 mm Hg +/- 2.5 mm Hg for the arterial blood gas analysis with the mobile IRMA device and -0.6 mm Hg +/- 7.5 mm Hg for the transcutaneous measurement (p > 0.05). Bias and precision (-5.3 mm Hg +/- 6.1 mm Hg) of endexpiratory CO2-measurement differed significantly (p < 0.003) when compared with the reference. During interhospital transport Paco2(IRMA) and Ptcco2 provide the best accuracy when compared with the reference measurement. Patients who either require a tight control of Pco2 or endured lengthy transportation could benefit greatly from the combination of expiratory capnography with mobile arterial blood gas analysis or the transcutaneous measurement of Pco2.

Transcutaneous Pco2 Monitoring During Initiation of Noninvasive Ventilation

To assess the efficacy of transcutaneous Pco2 (Ptcco2) measurements for monitoring alveolar ventilation in patients requiring noninvasive positive-pressure ventilation (NPPV). In a prospective study on method agreement pairs of Paco2 and Ptcco2 (SenTec Digital Monitor; SenTec AG; Therwil, Switzerland), measurements were performed every 10 min during the establishment of NPPV over a 4-h period in 10 patients (8 patients with COPD) presenting with acute-on-chronic hypercapnic respiratory failure, thus providing 250 pairs of measurement. Mean (+/- SD) Paco2 decreased from 67.2 +/- 11.9 mm Hg (Ptcco2, 65.5 +/- 13.9 mm Hg) to 54.6 +/- 8.8 mm Hg (Ptcco2, 47.8 +/- 8.8 mm Hg), and mean pH increased from 7.36 +/- 0.03 to 7.44 +/- 0.04. Following Ptcco2 assessment, Ptcco2 in the ensuing 2-min period was the strongest predictor for Paco2 compared to Ptcco2 in the ensuing 5-min period and to real-time measurements. Ptcco2 was highly correlated with Paco2 (r = 0.916; p < 0.001), as determined by linear regression analysis. The mean difference between Paco2 and Ptcco2 was 4.6 mm Hg, and the limits of agreement (bias +/- 1.96 SDs) ranged from -3.9 to 13.2 mm Hg, following the Bland and Altman analysis. Retrospective drift correction produced an even higher correlation (r = 0.956; p < 0.001) with lower limits of agreement (-1.7 to 7.5 mm Hg). Ptcco2 measurements provide a sensitive, continuous, and noninvasive method for monitoring alveolar ventilation in patients who are receiving short-term NPPV therapy. Drift correction of Ptcco2 measurements improves the accuracy of Ptcco2 monitoring compared to the "gold standard" Paco2 assessment. A lag time of approximately 2 min is present for reliable Ptcco2 values compared to Paco2 values. However, individual variance between Paco2 and Ptcco2 cannot be excluded. www.uniklinik-freiburg.de/zks/live/uklregister/Oeffentlich.html Identifier:UKF001271.

A reply

We are grateful to Drs McCormack and Kelly for their interest in our publication on the accuracy of non-invasive carbon dioxide monitoring. They correctly point out that transcutaneous Pco2 (Ptcco2) measurement may be influenced by low cardiac output, and that we did not obtain cardiac index values at the time of the measurements. Because most of our study patients had normal cardiac function, insertion of a pulmonary arterial catheter was rarely indicated or justified. Therefore, cardiac index values were available only in a small minority of our patients. However, pre-existing normal cardiac function and haemodynamic stability make low cardiac output a very unlikely confounder of our study. Drs McCormack and Kelly have also missed data on the effects of vasopressor therapy on Ptcco2 values in our study. We have not reported these data in detail but stated in the Results section that vasopressors did not influence the accuracy of Ptcco2 monitoring in our study patients. As mentioned in the discussion, these findings are in agreement with those of two recent studies [1, 2] that also failed to find an influence of administered of vasopressors on Ptcco2 measurements. Drs McCormack and Kelly postulate that interpretation of data from patients with pulmonary pathologies may be difficult because of the disturbed pulmonary carbon dioxide transfer. We agree that pulmonary pathologies may influence the arterial Pco2 level. However, why should transcutaneous carbon dioxide transfer be influenced by pulmonary disease, unless the latter is combined with major haemodynamic consequences? The same holds true for low PEEP (2–8 mmHg), as used in our patients. PEEP has been found to influence Ptcco2 measurements only at higher PEEP levels [3]. Drs McCormack and Kelly correctly state that findings of industry-sponsored trials may not necessarily be invalid. However, conflicts of interest may arise at various levels when industry representatives perform or co-author studies involving their own products, thus questioning the reliability of their study results [4]. We are grateful to the manufacturers for providing the monitors and all disposables based on a contract that confirmed our unrestricted right to interpret and publish the data. We fully support Drs McCormack and Kelly's call for further scientific evaluation of transcutaneous Pco2 monitoring. We only tested its usefulness in the specific setting of patients during and shortly after major surgery. Our conclusion may not apply to patients in different clinical settings.

Transcutaneous Blood Gas CO2 Monitoring of Induced Ventilatory Depression in Mice

We assessed a simple, noninvasive method of monitoring transcutaneous partial pressure of CO2 (Ptcco2) in mice to determine whether it would provide an accurate and reproducible method to assess ventilatory depression in mice. To this end, Ptcco2 and Paco2 (partial pressure of arterial CO2) measurements were performed on isoflurane-anesthetized male C57Bl/6 mice breathing differing percentages of CO2 or fentanyl, a known ventilatory depressive drug. All doses of fentanyl produced a sharp increase in Ptcco2 values within 20 min with difference in Ptcco2 values between saline and all fentanyl groups being statistically significant (P < 0.0001). A good correlation between Paco2 and Ptcco2 values was established (r2 = 0.91). A Bland-Altman analysis likewise found that Ptcco2 measurements in the mice reliably and accurately reflected their Paco2 values. Therefore, under controlled conditions, Ptcco2 measurements were found to reliably reflect Paco2 values in mice. Consequently, the Ptcco2 method can be used as a means to rapidly and quantitatively assess the ventilatory depressive properties of a wide spectrum of drugs, under varying conditions in numerous mouse models.

Evaluation of a New Combined Transcutaneous Measurement of Pco2/Pulse Oximetry Oxygen Saturation Ear Sensor in Newborn Patients

Arterial oxygen saturation (Sao(2)) and arterial carbon dioxide partial pressure (Paco(2)) are 2 of the most important respiratory parameters in the treatment of critically ill neonates. Noninvasive monitoring of these parameters is desirable for continuous estimating of the respiratory status and reducing blood loss because of repeated blood gas analyses. Transcutaneous measurement of Pco(2) (Ptcco(2)) represents a simple and noninvasive technique for continuous monitoring of ventilation. However, sensor preparation, positioning, taping, and repeated changes of the sensor location make the handling difficult and complicate its use in the neonatal care unit. Recently, a new sensor for combined assessment of pulse oximetry oxygen saturation (Spo(2)) and Ptcco(2) has been introduced (TOSCA Monitor; Linde Medical Sensors, Basel, Switzerland). The monitor combines pulse oximetry and Ptcco(2) measurement in a single ear sensor, which works at 42 degrees C to enhance blood flow in capillaries below the sensor. In a prospective, open, nonrandomized study of 60 ill neonates, the new ear sensor for combined assessment of Spo(2) and Ptcco(2) at 42 degrees C was tested. The sensor was adapted to the ear of a neonate with a Varihesive layer (Conva Tec; Princeton, NJ). Data obtained from the ear sensor were compared with Spo(2 Finger/Heel), Sao(2), and Paco(2) obtained from arterial blood gas in 30 patients and with a capillary blood gas in an additional 30 patients using Bland Altman bias analysis. Data are presented as median (range). The postconceptional age of the patients was 38.3 weeks (range: 28 5/7-40 5/7) in the arterial group and 37.9 weeks (range: 29 6/7-41 0/7) in the capillary group. Age of the newborns studied was 3.5 days (range: 1-28) in the arterial blood sample group (n = 30) and 6 days (range: 2-28) in the capillary blood sample group (n = 30). Patient weight was 3.02 kg (range: 1.5-4.5) in the arterial group and 2.76 kg (range: 1.0-3.71) in the other group. Three patients had weights of <1500 g. Twenty-one of 60 patients were conventionally ventilated, 4 patients received high-frequency oscillation, and 35 were not ventilated. Mean difference (bias) and precision (2 SD of the mean difference) between Ptcco(2 TOSCA) and Paco(2) were -0.44 kPa (-3.21 mm Hg) and 0.82 kPa (6.02 mm Hg) and between Ptcco(2 TOSCA) and Pcapco(2) were -0.09 kPa (-0.67 mm Hg) and 1.11 kPa (8.07 mm Hg), respectively. Spo(2) assessment by the TOSCA revealed slightly higher values compared with Sao(2) (bias: -0.48%), whereas Spo(2) (Finger/Heel) values were slightly lower than Sao(2) (bias: 0.52%). The TOSCA monitor with the ear sensor adapted to ears of neonates allows reliable estimation of Sao(2) and Paco(2). A potential benefit is the reduction in motion artifacts because of less head movement in newborns and that only a single cable leads form the patient to the monitor. In addition, the sensor is not removed for chest radiograph or for nursing the infant on his or her parent's lap. Long-term studies in a large population with continuous measurements are required to confirm these preliminary findings and to elucidate the benefits in detection of respiratory deterioration and the potential side effects of this sensor.

Comparison of arterial, end-tidal and transcutaneous PCO2 during moderate exercise and external C02 loading in humans

Static relationships between arterial, transcutaneous and end-tidal PCO2 (PaCO2, PtcCO2, PetCO2) as well as the dynamic relationship between PetCO2 and PtcCO2 were studied during moderate bicycle ergometer exercise with and without external CO2 loading. The exercise pattern consisted of 5-min intervals of constant power at 40 W and 100 W and 900 s of randomised changes between these two power levels. The external CO2 loading was achieved by means of controlled variations of inspiratory gas compositions aimed at a constant PetCO2 of 6.5 kPa (49 mm Hg). The PetO2 was regulated at 17.3 kPa (130 mm Hg). Under steady-state conditions all PCO2 parameters showed close linear relationships. PaCO2/PtcCO2 was near to identity while the PetCO2 systematically overestimated changes in PaCO2l No relationship showed a significant influence of the exercise intensity. Transients of PtcCO2 are considerably slower than PetCO2 transients. The dynamic relationship between both parameters was found to be independent of whether internal or external CO2 loadings were applied. It is concluded that the combination of PetCO2 and PtcCO2 measurements allows an improved non-invasive assessment of PaCO2. While PetCO2 better reflects the transients, PtcCO2 can be employed to determine slow changes of the absolute PaCO2.

Physiological and clinical significance of PtcO2 and PtcCO2 measurements.

Physiological and clinical significance of PtcO2 and PtcCO2 measurements.