Transcutaneous Blood Gas Monitoring Research Articles

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

Current methods for transcutaneous blood gas monitoring (TBM) - a common health monitoring method in neonatal care - comes with a suite of challenges like limited attachment opportunities, and risks of infections from burning and tearing of the skin, which limits its use. This study presents a novel system and method for rate-based transcutaneous CO2 measurements with a soft, unheated skin-interface that can address many of these problems. Additionally, a theoretical model for the gas transport from the blood to the system's sensor is derived. By simulating CO2 advection and diffusion through the cutaneous microvasculature and epidermis to the system's skin interface, the effect of a wide range of physiological properties on the measurement has been modeled. Following these simulations, a theoretical model for the relationship between the measured CO2 concentration and that in the blood was derived and compared to empirical data. Applying the model on measured blood gas levels, even when the theory was based solely on the simulations, produced blood CO2 concentrations within ∼35% of empirical measurements from a state-of-the-art device. Further calibration of the framework, also using the empirical data, yielded an output with a Pearson correlation of 0.84 between the two methods. Compared to the state-of-the-art device the proposed system measured the partial CO2 pressure in the blood with an average deviation of 0.04 kPa and 1.97σ of ±1.1 kPa. However, the model indicated that this performance could be hampered by different skin properties. Given its soft and gentle skin interface and lack of heating, the proposed system could significantly decrease health risks like, burns, tears, and pain, currently associated with TBM on premature neonates.

PDMS-polyimide transcutaneous blood gas collector with self-folding out-of-plane heater elements

This paper introduces and evaluates a novel, highly scalable fabrication technique for folding flexible printed circuit board (PCB) features into polydimethylsiloxane (PDMS). The technique is then used to create fast and effective skin-heaters in a prototype gas collector for transcutaneous blood gas monitoring (TBM), a well-established technique to non-invasively measure the amount of CO2 and O2 in a patient’s blood. Previous studies have shown that TBM can be made safer by heating the patient’s skin with short pulses rather than continuously. Hence, the effects of incorporating a resistive heater with folded heating elements into a PDMS gas collector was investigated and compared to a heater with surface mounted heating elements. The results show that the fabrication technique provides consistent, controllable folding angles using only the surface and viscous forces of the flexible PCB and PDMS. With the investigated design- and material parameters a maximum folding angle of 30° was achieved, resulting in a 2000% increase in initial surface heating compared to an un-folded reference. For the intended application, this corresponds to reducing the time needed to heat the skin of a patient to less than half. The presented fabrication technique is, however, not limited to the application investigated in this paper, but rather offers the possibility to quickly and automatically fold complex structures and circuits into the bulk of the PDMS without introducing any time overhead as the number of features and folds grow.

Improving the Clinical Interpretation of Transcutaneous Carbon Dioxide and Oxygen Measurements in the Neonatal Intensive Care Unit

Introduction: Transcutaneous blood gas monitoring allows for continuous non-invasive evaluation of carbon dioxide and oxygen levels. Its use is limited as its accuracy is dependent on several factors. We aimed to identify the most influential factors to increase usability and aid in the interpretation of transcutaneous blood gas monitoring. Methods: In this retrospective cohort study, transcutaneous blood gas measurements were paired to arterial blood gas withdrawals in neonates admitted to the neonatal intensive care unit. The effects of patient-related, microcirculatory, macrocirculatory, respiratory, and sensor-related factors on the difference between transcutaneously and arterially measured carbon dioxide and oxygen values (ΔPCO₂ and ΔPO₂) were evaluated using marginal models. Results: A total of 1,578 measurement pairs from 204 infants with a median [interquartile range] gestational age of 27³/₇ [26¹/₇–31³/₇] weeks were included. ΔPCO₂ was significantly associated with the postnatal age, arterial systolic blood pressure, body temperature, arterial partial pressure of oxygen (PaO₂), and sensor temperature. ΔPO₂ was, with the exception of PaO₂, additionally associated with gestational age, birth weight Z-score, heating power, arterial partial pressure of carbon dioxide, and interactions between sepsis and body temperature and sepsis and the fraction of inspired oxygen. Conclusion: The reliability of transcutaneous blood gas measurements is affected by several clinical factors. Caution is recommended when interpreting transcutaneous blood gas values with an increasing postnatal age due to skin maturation, lower arterial systolic blood pressures, and for transcutaneously measured oxygen values in the case of critical illness.

Transcutaneous blood gas monitoring and tissue perfusion during common femoral thromboendarterectomy

Background Improving tissue perfusion can improve clinical outcomes in surgical patients, where monitoring may aid clinicians in detecting adverse conditions and guide interventions. Transcutaneous monitoring (TCM) of oxygen (tcpO2) and carbon dioxide (tcpCO2) is a well-proven technology and could potentially serve as a measure of local circulation, perfusion and metabolism, but the clinical use is not thoroughly explored. The purpose of this proof-of-concept study was to investigate whether TCM of blood gasses could detect changes in perfusion during major vascular surgery. Methods Ten patients with peripheral arterial disease scheduled for lower limb major arterial revascularization under general anaesthesia were consecutively included. TcpO2 and tcpCO2 were continuously recorded from anaesthesia induction until skin closure with a TCM monitor placed on both legs and the thorax. Peripheral oxygen saturation was kept ≥94% and mean arterial blood pressure ≥65 mmHg. The primary outcomes were changes in tcpO2 and tcpCO2 related to arterial clamping and declamping during the procedure and analyzed by paired statistics. Results Femoral artery clamping resulted in a significant decrease in tcpO2 (−2.1 kPa, IQR-4.2; −0.8), p=.017)), followed by a significant increase in response to arterial declamping (5.5 kPa, IQR 0–7.3), p=.017)). Arterial clamping resulted in a statistically significant increase in tcpCO2 (0.9 kPa, IQR 0.3–5.4), p=.008)) and a significant decrease following declamping (−0.7 kPa, IQR −2.6; −0.2), p=.011)). Conclusion Transcutaneous monitoring of oxygen and carbon dioxide is a feasible method for detection of extreme changes in tissue perfusion during arterial clamping and declamping, and its use for improving patient outcomes should be explored. Clinical Trials identifier: NCT04040478. Registered on July 31, 2019.

P12‐10: Additional use of propofol during flexible bronchoscopy in difficult‐to‐sedate cases with transcutaneous blood gas monitoring, anesthetized with midazolam and fentanyl: A retrospective study

P12‐10: Additional use of propofol during flexible bronchoscopy in difficult‐to‐sedate cases with transcutaneous blood gas monitoring, anesthetized with midazolam and fentanyl: A retrospective study

Partial least squares modelling of spectroscopic data from microplasma emissions for determination of CO2 concentration

The spectral emissions from a microplasma have been used to predict the CO2 concentration in gas samples covering a concentration range of 0%–100%. Different models based on partial least squares have been evaluated, comparing two different spectral pre-processing filters –multiplicative scatter correction (MSC) and standard normal variate correction (SNV) – and three different wavelength ranges. The models were compared with respect to accuracy, precision, stability and linearity. CO2 samples were mixed with either air or nitrogen. The choice of mixing gas influenced the predicted concentration and basing the models on data from only one mixing gas resulted in higher prediction power. Using air as mixing gas and SNV filtering resulted in a root mean square error of prediction (RMSEP) of 0.03 for an independent test dataset. This RMSEP was of the same range as the experimental error. On the other hand, the models with the best long term stability, reaching the lowest Allan variance, were based on observations with both mixing gases. Models based on MSC filtering generally had slightly higher RMSEP than those based on SNV filtering. Generally, the CO2 concentration could be accurately predicted in the concentration range of 5%–90%. For higher and lower concentrations, the models underestimated the CO2 concentration and were less accurate and precise. Basing the models on fewer wavelengths resulted in reduced linearity. The models were also evaluated by applying them for transcutaneous blood gas monitoring, where they helped to reveal new physiological information.

Transcutaneous blood gas monitoring among neonatal intensive care units in Japan.

This study aimed to investigate the utility of transcutaneous (tc) measurements of partial pressure of oxygen (tcPO2 ) and carbon dioxide (tcPCO2 ) monitoring in neonatal intensive care units (NICUs) in Japan. At the end of 2016,we sent a survey questionnaire on tc monitoring to all 106 NICUs registered with the Japanese Neonatologist Association. The questions included usage, subjects, methods, management, and the practical usefulness of tc monitoring. The questionnaire was returned by 69 NICUs (65.1% of response rate). Seventeen institutions (24.6%) measured both tcPCO2 and tcPO2 , and 42 (60.9%) measured tcPCO2 alone. Transcutaneous PCO2 or tcPO2 monitoring was applied for "pre-viable" infants born at 22-23weeks' gestational age (18.6% vs 23.5%), and infants of <500g birthweight (30.5% vs 17.6%). The tcPCO2 and tcPO2 monitoring was started at birth in 49.2% and 70.6% of the newborn infants, respectively. The temperature of the sensor was set at <38°C for tcPCO2 in 54.3% and >42°C for tcPO2 in 58.9% of NICUs. The accuracy for tcPO2 was rated as good in 35.3% or moderate in 64.7%, of institutions but or for tcPCO2 as 1.7% or 93.2%of institutions , respectively. Transcutaneous monitoring was widely, but limitedly, used for preterm infants. The lower temperature of the tcPCO2 sensor compared to that reported in other developed countries might compromise the accuracy but increase the feasibility of tc monitoring in Japan.

Compliance of a microstructured, soft sampling device for transcutaneous blood gas monitoring.

Premature neonates are too small for repeated blood sampling, but still require precise monitoring of blood gas levels. The standard method therefore involves transcutaneous blood gas monitoring (TBM), i.e. analyzing gas that permeates the skin. The method involves skin heating and requires frequent relocation of a rigid sensor that is adhesively mounted to the skin, which makes the monitoring intermittent and can cause tissue damage. To mitigate this, this paper introduces a TBM concept that replaces the sensor with a small, non-adhesive, flexible, polydimethylsiloxane patch, routing the gases through skin-facing microchannels laid out in various configurations, to an external optical emission spectroscopy system (OES). As the OES depends on a constant flow of gas, we have investigated the effects external loads, both vertical and with a transverse component, have on the aerodynamic resistance of the patches. The experiments show that patches with 200 μm wide channels can withstand uniformly distributed forces up to 25 N with a change in aerodynamic resistance of about 0.01 mbar per sccm per newton. In subsequent measurements, the proof of concept (POC) TBM system showed a strong and fast blood gas signal that was unaffected by all likely loads in the intended application. Moreover, the rise time of the signal is shown to be inversely proportional to the aerodynamic resistance, and the signal strength to be proportional to the skin area exposed to the microchannels. With these results, the POC TBM system is a viable first step towards truly continuous blood gas monitoring of prematurely born children.

Different characteristics of ventilator application between tracheostomy- and noninvasive positive pressure ventilation patients with amyotrophic lateral sclerosis.

The aim of the study was to investigate the appropriate home ventilator settings for patients with amyotrophic lateral sclerosis (ALS).In total, 71 patients with ALS, who had received either a noninvasive positive pressure ventilation (NIPPV) or tracheostomy positive pressure ventilation (TPPV), were included. Accordingly, patients were divided into 2 groups (the TPPV and NIPPV groups). We retrospectively evaluated the values used in home ventilators for patients with ALS, who had maintained a stable level of CO2 on both the arterial blood gas analysis (ABGA) and transcutaneous blood gas monitoring. To measure the main outcome, we also investigated the actual body weight (ABW) and predicted body weight (PBW) of patients, and the following setting values of ventilators were also recorded: the inspired tidal volume (VTi), minute ventilation (MV), peak inspiratory pressure (PIP), positive end expiratory pressure (PEEP), and inspiratory time (Tins).VTi and MV showed a significantly positive correlation with both PBW and ABW of patients in the TPPV group. However, both VTi and MV had greater significant correlation with PBW than ABW in the TPPV group. In addition, VTi and MV did not show a significantly positive correlation with either PBW or ABW in the NIPPV group.In patients with ALS, PBW was more useful for predicting VTi and MV than ABW. Moreover, it will be helpful to know the differences of setting values between TPPV and NIPPV, especially because ALS patients are usually treated with TPPV due to the initial difficulties associated with NIPPV.

Lung Ultrasonography Score to Evaluate Oxygenation and Surfactant Need in Neonates Treated With Continuous Positive Airway Pressure.

Lung ultrasonography (LUS) is a bedside technique useful to diagnose neonatal respiratory problems, but, to our knowledge, no data are available about its use for monitoring lung function or eventually guiding surfactant therapy. To determine the diagnostic accuracy of a neonatal-adapted LUS score to evaluate oxygenation and predict need for surfactant administration. Prospective diagnostic accuracy study following STARD (Standards for the Reporting of Diagnostic Accuracy Studies) guidelines at a tertiary level academic neonatal intensive care unit in 2014. All neonates admitted to the neonatal intensive care unit with signs of respiratory distress were eligible, and 130 neonates were enrolled. The LUS score was calculated in the first hours of life under continuous positive airway pressure. The transcutaneous partial pressure of oxygen (Ptco2) to fraction of inspired oxygen (Fio2) ratio, alveolar-arterial gradient, oxygenation index, and arterial to alveolar ratio were calculated within 30 minutes from LUS, using transcutaneous blood gas monitoring. Surfactant was administered according to 2013 European guidelines. Correlation between LUS score and indices of oxygenation and prediction of surfactant administration. Among the 130 neonates in this study, the LUS score was significantly correlated with all indices of oxygenation, independent from gestational age (GA) (Ptco2 to Fio2 ratio: GA ≥ 34 weeks: ρ = -0.57; GA <34 weeks: ρ = -0.62; P < .001; alveolar-arterial gradient: GA ≥ 34 weeks: ρ = 0.62; GA <34 weeks: ρ = 0.59; P < .001; oxygenation index: GA ≥ 34 weeks: ρ = 0.63; GA <34 weeks: ρ = 0.69; P < .001; and arterial to alveolar ratio: GA ≥ 34 weeks: ρ = -0.60; GA <34 weeks: ρ = -0.56; P < .001). The LUS score predicted the need for surfactant better in preterm babies with a GA less than 34 weeks (area under the curve = 0.93; 95% CI, 0.86-0.99; P < .001) than in term and late-preterm neonates with a GA of 34 weeks or greater (area under the curve = 0.71; 95% CI, 0.54-0.90; P = .02); the areas under the curve for these 2 GA subgroups are significantly different (P = .02). In babies with a GA less than 34 weeks, a LUS score cutoff of 4 predicted surfactant administration with 100% sensitivity and 61% specificity, yielding a posttest probability of 72%. The LUS score is well correlated with oxygenation status in both term and preterm neonates, and it shows good reliability to predict surfactant administration in preterm babies with a GA less than 34 weeks under continuous positive airway pressure.

A fiberoptic sensor for tissue carbon dioxide monitoring.

We present a new fiberoptic carbon dioxide sensor for transcutaneous and mucosa (indwelling) blood gas monitoring. The sensor is based on optical fluorescence of molecules sensitive to pH changes associated with dissolved CO2. A three layer chemical coating was dip-coated onto the distal tip of an optical fiber (600μm core radius). It contained the 50mg/ml `polym H7', a coating polymer bonded to a fluorescence indicator dye, along with 125mg/ml of the transfer agent tetraoctylammonium hydroxide (TONOH). Light from a blue (460 nm) LED was launched into the fiber to excite the sensing film. The sensing film fluoresced green (530 nm), the intensity of which decreased in the presence of CO2. The sensor was tested in vitro, finding a correlation between change in fluorescence (in AU) and aqueous CO2 concentration with a minimum detection threshold of 40%. The sensor is being developed for medical applications where its small size and ability to continuously monitor the partial pressure of CO2 (PCO2) will make it an extremely useful diagnostic tool.

Evaluation of a transcutaneous blood gas monitoring system in critically ill dogs

To describe the use of a transcutaneous blood gas monitoring system in critically ill dogs, determine if transcutaneous and arterial blood gas values have good agreement, and verify if clinical or laboratory variables are correlated with differences between transcutaneous and arterial blood gas measurements. Prospective observational study. University teaching hospital ICU. Twenty-three client-owned dogs. In critically ill dogs undergoing arterial blood gas monitoring, a transcutaneous blood gas monitor was used to measure transcutaneous partial pressure of carbon dioxide (PtcCO2 ) and transcutaneous partial pressure of oxygen (PtcO2 ) values 30 minutes after sensor placement, which were compared to PaCO2 and PaO2 values measured simultaneously. Clinical and laboratory variables were concurrently recorded to determine if they were correlated with the difference between transcutaneous and arterial blood gas measurements. Bland-Altman analysis revealed a mean bias of 4.6 ± 26.3 mm Hg (limits of agreement [LOA]: -46.9/+56.1 mm Hg) between PtcO2 and PaO2 and a mean bias of 9.3 ± 8.5 mm Hg (LOA: -7.5/+26.0 mm Hg) between PtcCO2 and PaCO2 . The difference between PtcCO2 -PaCO2 was strongly negatively correlated with HCO3 (-) (r(2) = 0.52, P < 0.001) and PaCO2 (r(2) = 0.58, P < 0.001) and weakly positively correlated with diastolic blood pressure (r(2) = 0.21, P = 0.044), whereas the difference between PtcCO2 -PaCO2 was moderately negatively correlated with diastolic blood pressure (r(2) = 0.33, P = 0.008). Agreement between transcutaneous and arterial PO2 and PCO2 measurements in these critically ill dogs was inferior to that reported in similar adult and pediatric human studies. The transcutaneous monitor consistently over-estimated PaO2 and PaCO2 and should not be used to replace arterial blood gas measurements in critically ill dogs requiring blood gas interpretation.

Hypocapnia in Patients with Chronic Neck Pain

The aim of this study was to investigate whether patients with chronic neck pain have changes in their transcutaneous partial pressure of arterial carbon dioxide (PtcCO2) and whether other physical and psychologic parameters are associated. In this cross-sectional study, 45 patients with chronic idiopathic neck pain and 45 healthy sex-, age-, height-, and weight-matched controls were voluntarily recruited. The participants' neck muscle strength, endurance of the deep neck flexors, neck range of movement, forward head posture, psychologic states (anxiety, depression, kinesiophobia, and catastrophizing), disability, and pain were assessed. PtcCO2 was assessed using transcutaneous blood gas monitoring. The patients with chronic neck pain presented significantly reduced PtcCO2 (P < 0.01). In the patients, PtcCO2 was significantly correlated with strength of the neck muscles, endurance of the deep neck flexors, kinesiophobia, catastrophizing, and pain intensity (P < 0.05). Pain intensity, endurance of the deep neck flexors, and kinesiophobia remained as significant predictors into the regression model of PtcCO2. Patients with chronic neck pain present with reduced PtcCO2, which can reach the limits of hypocapnia. This disturbance seems to be associated with physical and psychologic manifestations of neck pain. These findings can have a great impact on various clinical aspects, notably, patient assessment, rehabilitation, and drug prescription.

Transcutaneous blood gas monitoring during neonatal intensive care

To evaluate the accuracy in transcutaneous (Tc) blood gas monitoring in newborn infants, including extremely low birth weight infants, during neonatal intensive care. Tc PO(2) /PCO(2) was monitored in the neonatal intensive care unit (NICU) during stable infant conditions. In comparison, simultaneous arterial PO(2) and PCO(2) was measured. Sixty measurements were taken in 46 infants with median (range) birth weight of 0.93 (0.53-4.7) kg and at median (range) age of 8.5 (1-44) days. Comparison of measurements was performed using Bland-Altman plots, and the mean (95% CI) of the difference was calculated. Comparison was also performed in relation to body weight, postnatal age and oxygen requirement. The mean (95% CI) difference in PO(2) (TcPO(2)-aPO(2)) was 0.3 (-0.2-0.9) kPa, and the corresponding difference in PCO(2) (TcPCO(2)-aPCO(2)) was 0.4 (0.03-0.8, p < 0.05) kPa. Some differences were related to body weight, age and oxygen requirement, but these differences were small. There was good agreement between TcPO(2)/TcPCO(2) and corresponding arterial measurements. The mean difference between the methods was small and clinically acceptable in a current NICU. Tc blood gas monitoring could be recommended as a valuable complement for blood gas monitoring also in extremely low birth weight infants.

Evaluation of transcutaneous CO2 responses following acute changes in PaCO2 in healthy subjects

Transcutaneous blood gas-monitoring systems with miniaturized SpO(2) (peripheral blood oxygen saturation)/PCO(2) combined sensors (TOSCATM) have been widely used. There are no reports of the inter- and intra-individual variability in transcutaneous measurements of PaCO(2) (PtcCO(2)) in response to acute progressive changes in PaCO(2). This study examined inter- and intra-individual variability of PtcCO(2) measurements under semi-steady-state conditions, and characterized the behaviour of PtcCO(2) in response to acute progressive changes in PaCO(2). Subjects breathed mixed gases through a mouthpiece connected to an automatic arterial blood gas controller. Using end-tidal PCO(2) and PO(2) as guides, PaCO(2) was controlled to increase and/or decrease between baseline and > or = 60 mm Hg, in a stepwise (n = 9) or progressive fashion (n = 6). Arterial blood was sampled when needed. Intra-individual correlation coefficients between PtcCO(2) and PaCO(2) were excellent in all subjects (0.971-0.989); however, the slope of the regression line varied among subjects (1.040-1.335). Bias and limits of agreement (+/- 2 SD from bias) between PtcCO(2) and PaCO(2) were -1.8 mm Hg and -7.7 to 4.1 mm Hg. Changes in PtcCO(2) in response to acute progressive changes in PaCO(2) also varied among subjects. The PtcCO(2) measurement system allows reliable estimation of PaCO(2) in a given subject. However, caution is needed when comparing absolute values between subjects or when acute changes in PaCO(2) occur.

A flexible transcutaneous oxygen sensor using polymer membranes

A wearable and flexible oxygen sensor for transcutaneous blood gas monitoring was fabricated and tested. The sensor has a laminar film-like structure, which was fabricated by pouching KCl electrolyte solution by both non-permeable (metal weldable) sheet and gas-permeable membrane with Pt- and Ag/AgCl-electrodes patterned using microfabrication process. The electrolyte solution was fixed only by heat-sealing the edges of the weldable membranes without any chemical adhesives. The wearable oxygen sensor (thickness: 84 mum) was applied to the electrochemical measurement with a constant potential of -600 mV vs. Ag/AgCl, thus obtaining the calibration range to dissolved oxygen (DO) from 0.0 to 7.0 mg/l with a correlation coefficient of 0.998 and the quick response time (53.4 s to 90% of a steady-state current), which operate similarly to a commercially available oxygen electrode. The sensor was also utilized to transcutaneous oxygen monitoring for healthy human subject. The sensing region of the wearable oxygen sensor was attached onto the forearm-skin surface of the subject inhaling various concentrations of oxygen. As a result of physiological application, the output current was varied from -6.2 microA to -7.8 microA within 2 min when the concentration of inhaling oxygen was changed from atmospheric air to 60% oxygen. Thus, the transcutaneous oxygen was successfully monitored without any inconveniences such as skin inflammation, etc.

Studies on the Temperature Distribution of a Thick Film Transcutaneous Oxygen Sensor and Its Thermal Influences on Oxygen Measurement

The partial pressures of gases, namely oxygen and carbon dioxide, in the arterial blood are important parameters for doctors to determine the respiratory conditions of patients. Currently in practice, there are a number of ways to measure these parameters, one of which is transcutaneous blood gas monitoring. This technique is a popular noninvasive measurement method for obtaining fast and relatively accurate responses. In this investigation, thick film technology has been employed to develop an amperometric oxygen sensor which consists of a heating module to elevate the temperature at the skin surface to transcutaneous levels. The heating module includes a heating element and its temperature is regulated by a temperature control circuit. Using an infrared camera, the transient and steady-state temperature distributions as well as the stability of the heating element have been analysed. The influence of temperature on the oxygen sensing module is also studied. In addition, a three-dimensional theoretical model is established to evaluate the thermal response of the sensor and subsequently compared with the results from the practical prototype. With this model, the design stages can be simplified and future heating modules for transcutaneous sensors could be generated and improved more easily and effectively.

Biomedical sensor using thick film technology for transcutaneous oxygen measurement

Transcutaneous blood gas monitoring is a non-invasive measurement technique for obtaining fast and relatively accurate responses to determine the respiratory conditions of patients. In this investigation, a screen-printed, disposable, transcutaneous oxygen sensor based on the working principle of amperometry, incorporates an integral heating element to enhance transcutaneous diffusion of blood gases typically at 44 °C. A Clark cell configuration is employed with gold working and counter electrodes and a silver/silver chloride reference electrode. Two different types of electrolytes namely potassium nitrate gel and polyelectrolyte (Nafion ®) have been studied under laboratory test conditions. A fully computer-controlled gas testing rig has been constructed to automate the varying of oxygen levels. Linear relationships have been established with an averaged sensitivity level of 0.029 μA/mmHg. In addition, a brief pilot clinical trial involving a fully grown human subject has been carried out alongside a commercial transcutaneous blood gas analyser. The investigations have shown that although the measured signals are weaker than those obtained from the laboratory test, the thick film sensor displays a repeatable and linear relationship when correlating with the commercial system. This study has greatly contributed towards the understanding for the suitability of the materials in achieving a viable, low-cost biomedical sensor.

A survey of transcutaneous blood gas monitoring among European neonatal intensive care units

BackgroundPCO2 and PO2 are important monitoring parameters in neonatal intensive care units (NICU). Compared to conventional blood gas measurements that cause significant blood loss in preterms, transcutaneous (tc) measurements allow continuous, non-invasive monitoring of blood gas levels. The aim of the study was to survey the usage and opinions among German speaking NICUs concerning tc blood gas monitoring.MethodsA questionnaire was developed and sent to 56 head nurses of different NICUs in Germany, Switzerland and Austria.ResultsA completely answered questionnaire was obtained from 41 NICUs. In two of these units tc measurements are not performed. In most NICUs (77%), both PtcO2 and PtcCO2 are measured simultaneously. Most units change the sensors every 3 hours; however, the recommended temperature of 44°C is used in only 15% of units. In only 8% of units are arterial blood gases obtained to validate tc values. Large variations were found concerning the targeted level of oxygen saturation [median upper limit: 95% (range 80–100%); median lower limit: 86% (range 75–93%)] and PO2 [median upper limit: 70 mmHg (range 45–90 mmHg); median lower limit: 44 mmHg (range 30–60 mmHg)].ConclusionOur survey shows that the use of tc monitors remains widespread among German speaking NICUs, despite earlier data suggesting that their use had been abandoned in many NICUs worldwide. In addition, we suggest that the current method of monitoring oxygenation may not prevent hyperoxemia in preterm infants.

Historical Perspectives

Among the factors considered “standard operating procedure” in neonatal intensive care units today, the presence of monitors is key. Bedside monitoring almost defines neonatal intensive care. It is difficult to recall that it is less than 40 years ago that cardiopulmonary monitors were introduced into routine intensive care. Prior to their introduction, the bedside nurse was responsible for taking vital signs at intervals dictated by the severity of illness of the baby. This month’s contribution comes from Dr Joe Daily, who describes the early attempts to incorporate electronic monitoring into the care of premature (preterm) infants who had apnea. The technique involved the use of transthoracic impedance, which can detect both respiration and heart rate activity. At the time it was introduced, the application of electrodes to the chest seemed rather “invasive,” and subsequent attempts were made to use other types of monitoring devices that did not require attachment to the baby’s chest. As indicated by Dr Daily, our major concern at the time was the detection of apnea, and air mattresses were used in some nurseries for a while because they could detect breathing movements. However, other types of motion artifact (particularly seizure activity) could trigger the sensors for breathing and produce “false-negatives.” Not long after the apnea monitor was introduced, it became evident that monitoring of heart rate could provide additional useful information. Consequently, cardiopulmonary monitoring became the norm, to be followed by blood pressure monitoring (see NeoReviews , May 2003), transcutaneous blood gas monitoring (see NeoReviews , September 2003), and oxygen saturation monitoring. In providing this recollection, Dr Daily was quick to point out to me that many people, over a long period of time, were involved in the evolution of the technology that led to the first apnea monitors used at Stanford.