Glucose monitoring by means of an intravenous microdialysis catheter technique

Comparison of Intravenous Microdialysis and Standard Plasma Sampling for Monitoring of Vancomycin and Meropenem Plasma Concentrations-An Experimental Porcine Study

Microdialysis is a catheter-based method suitable for dynamic sampling of unbound antibiotic concentrations. Intravenous antibiotic concentration sampling by microdialysis has several advantages and may be a superior alternative to standard plasma sampling. We aimed to compare concentrations obtained by continuous intravenous microdialysis sampling and by standard plasma sampling of both vancomycin and meropenem in a porcine model. Eight female pigs received 1 g of both vancomycin and meropenem, simultaneously over 100 and 10 min, respectively. Prior to drug infusion, an intravenous microdialysis catheter was placed in the subclavian vein. Microdialysates were collected for 8 h. From a central venous catheter, plasma samples were collected in the middle of every dialysate sampling interval. A higher area under the concentration/time curve and peak drug concentration were found in standard plasma samples compared to intravenous microdialysis samples, for both vancomycin and meropenem. Both vancomycin and meropenem concentrations obtained with intravenous microdialysis were generally lower than from standard plasma sampling. The differences in key pharmacokinetic parameters between the two sampling techniques underline the importance of further investigations to find the most suitable and reliable method for continuous intravenous antibiotic concentration sampling.

Dynamic Methods for Childhood Hypoglycemia Phenotyping: A Narrative Review

Hypoglycemia results from an imbalance between glucose entering the blood compartment and glucose demand, caused by a defect in the mechanisms regulating postprandial glucose homeostasis. Hypoglycemia represents one of the most common metabolic emergencies in childhood, potentially leading to serious neurologic sequelae, including death. Therefore, appropriate investigation of its specific etiology is paramount to provide adequate diagnosis, specific therapy and prevent its recurrence. In the absence of critical samples for biochemical studies, etiological assessment of children with hypoglycemia may include dynamic methods, such as in vivo functional tests, and continuous glucose monitoring. By providing detailed information on actual glucose fluxes in vivo, proof-of-concept studies have illustrated the potential (clinical) application of dynamic stable isotope techniques to define biochemical and clinical phenotypes of inherited metabolic diseases associated with hypoglycemia. According to the textbooks, individuals with glycogen storage disease type I (GSD I) display the most severe hypoglycemia/fasting intolerance. In this review, three dynamic methods are discussed which may be considered during both diagnostic work-up and monitoring of children with hypoglycemia: 1) functional in vivo tests; 2) in vivo metabolic profiling by continuous glucose monitoring (CGM); 3) stable isotope techniques. Future applications and benefits of dynamic methods in children with hypoglycemia are also discussed.

Semi-Implantable Bioelectronics

Developing techniques to effectively and real-time monitor and regulate the interior environment of biological objects is significantly important for many biomedical engineering and scientific applications, including drug delivery, electrophysiological recording and regulation of intracellular activities. Semi-implantable bioelectronics is currently a hot spot in biomedical engineering research area, because it not only meets the increasing technical demands for precise detection or regulation of biological activities, but also provides a desirable platform for externally incorporating complex functionalities and electronic integration. Although there is less definition and summary to distinguish it from the well-reviewed non-invasive bioelectronics and fully implantable bioelectronics, semi-implantable bioelectronics have emerged as highly unique technology to boost the development of biochips and smart wearable device. Here, we reviewed the recent progress in this field and raised the concept of "Semi-implantable bioelectronics", summarizing the principle and strategies of semi-implantable device for cell applications and in vivo applications, discussing the typical methodologies to access to intracellular environment or in vivo environment, biosafety aspects and typical applications. This review is meaningful for understanding in-depth the design principles, materials fabrication techniques, device integration processes, cell/tissue penetration methodologies, biosafety aspects, and applications strategies that are essential to the development of future minimally invasive bioelectronics.

Wireless and battery-free platforms for collection of biosignals

Recent progress in biosensors have quantitively expanded current capabilities in exploratory research tools, diagnostics and therapeutics. This rapid pace in sensor development has been accentuated by vast improvements in data analysis methods in the form of machine learning and artificial intelligence that, together, promise fantastic opportunities in chronic sensing of biosignals to enable preventative screening, automated diagnosis, and tools for personalized treatment strategies. At the same time, the importance of widely accessible personal monitoring has become evident by recent events such as the COVID-19 pandemic. Progress in fully integrated and chronic sensing solutions is therefore increasingly important. Chronic operation, however, is not truly possible with tethered approaches or bulky, battery-powered systems that require frequent user interaction. A solution for this integration challenge is offered by wireless and battery-free platforms that enable continuous collection of biosignals. This review summarizes current approaches to realize such device architectures and discusses their building blocks. Specifically, power supplies, wireless communication methods and compatible sensing modalities in the context of most prevalent implementations in target organ systems. Additionally, we highlight examples of current embodiments that quantitively expand sensing capabilities because of their use of wireless and battery-free architectures.

Enzyme-Based Glucose Sensor: From Invasive to Wearable Device

Blood glucose concentration is a key indicator of patients' health, particularly for symptoms associated with diabetes mellitus. Because of the large number of diabetic patients, many approaches for glucose measurement have been studied to enable continuous and accurate glucose level monitoring. Among them, electrochemical analysis is prominent because it is simple and quantitative. This technology has been incorporated into commercialized and research-level devices from simple test strips to wearable devices and implantable systems. Although directly monitoring blood glucose assures accurate information, the invasive needle-pinching step to collect blood often results in patients (particularly young patients) being reluctant to adopt the process. An implantable glucose sensor may avoid the burden of repeated blood collections, but it is quite invasive and requires periodic replacement of the sensor owing to biofouling and its short lifetime. Therefore, noninvasive methods to estimate blood glucose levels from tears, saliva, interstitial fluid (ISF), and sweat are currently being studied. This review discusses the evolution of enzyme-based electrochemical glucose sensors, including materials, device structures, fabrication processes, and system engineering. Furthermore, invasive and noninvasive blood glucose monitoring methods using various biofluids or blood are described, highlighting the recent progress in the development of enzyme-based glucose sensors and their integrated systems.

Microdialysis Monitoring of CSF Parameters in Severe Traumatic Brain Injury Patients: A Novel Approach

Background: Neuro-intensive care following traumatic brain injury (TBI) is focused on preventing secondary insults that may lead to irreversible brain damage. Microdialysis (MD) is used to detect deranged cerebral metabolism. The clinical usefulness of the MD is dependent on the regional localization of the MD catheter. The aim of this study was to analyze a new method of continuous cerebrospinal fluid (CSF) monitoring using the MD technique. The method was validated using conventional laboratory analysis of CSF samples. MD-CSF and regional MD-Brain samples were correlated to patient outcome.

Materials and Methods: A total of 14 patients suffering from severe TBI were analyzed. They were monitored using (1) a MD catheter (CMA64-iView, n = 7448 MD samples) located in a CSF-pump connected to the ventricular drain and (2) an intraparenchymal MD catheter (CMA70, n = 8358 MD samples). CSF-lactate and CSF-glucose levels were monitored and were compared to MD-CSF samples. MD-CSF and MD-Brain parameters were correlated to favorable (Glasgow Outcome Score extended, GOSe 6–8) and unfavorable (GOSe 1–5) outcome.

Results: Levels of glucose and lactate acquired with the CSF-MD technique could be correlated to conventional levels. The median MD recovery using the CMA64 catheter in CSF was 0.98 and 0.97 for glucose and lactate, respectively. Median MD-CSF (CMA 64) lactate (p = 0.0057) and pyruvate (p = 0.0011) levels were significantly lower in the favorable outcome group compared to the unfavorable group. No significant difference in outcome was found using the lactate:pyruvate ratio (LPR), or any of the regional MD-Brain monitoring in our analyzed cohort.

Conclusion: This new technique of global MD-CSF monitoring correlates with conventional CSF levels of glucose and lactate, and the MD recovery is higher than previously described. Increase in lactate and pyruvate, without any effect on the LPR, correlates to unfavorable outcome, perhaps related to the presence of erythrocytes in the CSF.

Continuous on-line glucose measurement by microdialysis in a central vein. A pilot study

Introduction

Tight glucose control in the ICU has been proven difficult with an increased risk for hypoglycaemic episodes. Also the variability of glucose may have an impact on morbidity. An accurate and feasible on-line/continuous measurement is therefore desired. In this study a central vein catheter with a microdialysis membrane in combination with an on-line analyzer for continuous monitoring of circulating glucose and lactate by the central route was tested.

Methods

A total of 10 patients scheduled for major upper abdominal surgery were included in this observational prospective study at a university hospital. The patients received an extra central venous catheter with a microdialysis membrane placed in the right jugular vein. Continuous microdialysis measurement proceeded for 20 hours and on-line values were recorded every minute. Reference arterial plasma glucose and blood lactate samples were collected every hour.

Results

Mean microdialysis-glucose during measurements was 9.8 ± 2.4mmol/l.No statistical difference in the readings was seen using a single calibration compared to eighth hour calibration (P =0.09; t-test). There was a close agreement between the continuous reading and the reference plasma glucose values with an absolute difference of 0.6+0.8mmol, or 6.8+9.3% and measurements showed high correlation to plasma readings (r = 0.92). Thelimit of agreement was 23.0%(1.94 mmol/l) compared to arterial plasma values with a line of equality close to zero.However, in a Clarke-Error Grid 93.3% of the values are in the A-area,and the remaining part in the B-area.Mean microdialysis-lactate was 1.3 ± 1.1mmol/l. The measurements showed high correlation to the blood readings (r = 0.93).

Conclusion

Continuous on-line microdialysis glucose measurement in a central vein is a potential useful technique for continuous glucose monitoring in critically ill patients, but more improvements and testingare needed.

Continuous glucose monitoring by intravenous microdialysis: influence of membrane length and dialysis flow rate

BACKGROUND

The benefit of tight glucose control in the intensive care unit is controversial. Part of the debate is around the frequency of glucose measurements, and therefore, a continuous glucose monitoring system is needed. Previously, we have shown that intravenous microdialysis has the potential for this purpose but that the accuracy must be improved. The aim of this study was to investigate the effects of the microdialysis membrane length and the perfusion rate on improving the accuracy.

METHODS

Two volunteer studies were performed, one comparing intravenous microdialysis catheters with different lengths (10 and 20 mm) and one comparing different perfusion rates (0.5, 1 and 2 μl/min) with plasma glucose reference levels. Median values of seven samples taken over 70-min periods were compared using Bland-Altman plots.

RESULTS

When microdialysis membranes of 10 and 20 mm perfused at a rate of 1 μl/min were used, the differences with measured plasma glucose levels were 30% ± 21% and 14% ± 13%. In comparison, plasma glucose measured in two different veins gave a difference of 3% ± 3%. In the second study, the differences between measured plasma glucose and that estimated with a microdialysis membrane of 30 mm perfused at 0.5, 1 and 2 μl/min were 8% ± 7%, 25% ± 19% and 39% ± 28%. Bland-Altman analyses gave the best line of equality (-0.11 mM) and the lowest limits of agreement (1.13 and -1.35 mM) when using the 30-mm membrane perfused with 0.5 μl/min.

CONCLUSION

The agreement of the intravenous microdialysis with plasma glucose levels improved significantly when increasing the microdialysis membrane length, and thereby the membrane area, and decreasing the perfusion rate.

Microdialysis--a versatile technology to perform metabolic monitoring in diabetes and critically ill patients

Continuous subcutaneous glucose monitoring has been tested in type 1 diabetes (T1D). Since in critically ill patients vascular access is granted vascular microdialysis may be preferential. To test this hypothesis comparative accuracy data for microdialysis applied for peripheral venous and subcutaneous glucose monitoring was obtained in experiments in T1D patients. Twelve T1D patients were investigated for up to 30 h. Extracorporeal vascular (MDv) and subcutaneous microdialysis (MDs) was performed. Microdialysis samples were collected in 15-60 min intervals, analyzed for glucose and calibrated to reference. MDv and MDs glucose levels were compared against reference. Median absolute relative difference was 14.0 (5.0; 28.0)% (MDv) and 9.2 (4.4; 18.4)% (MDs). Clarke Error Grid analysis showed that 100% (MDv) and 98.8% (MDv) were within zones A and B. Extracorporeal vascular and standard subcutaneous microdialysis indicated similar performance in T1D. We suggest microdialysis as a versatile technology for metabolite monitoring in subcutaneous tissue and whole blood.