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See detailContinuous glucose monitoring: Using cgm to guide insulin therapy virtual trials results
Mombaerts, L.; Thomas, Felicity Louise ULg; Signal, M. et al

in IFAC Proceedings Volumes (IFAC-PapersOnline) (2015), 48(20), 112-117

Continuous glucose monitoring (CGM) devices can measure blood glucose levels through interstitial measurements almost continuously (1-5min sampling period). However, they are not as accurate as glucose ... [more ▼]

Continuous glucose monitoring (CGM) devices can measure blood glucose levels through interstitial measurements almost continuously (1-5min sampling period). However, they are not as accurate as glucose readings from blood measurements. The relation between tissue and blood glucose is dynamic and the sensor signal can degrade over time. In addition, CGM readings contains high frequency noise and can drift between measurements. However, maintaining continuous glucose monitoring has the potential to improve the level of glycemic control achieved and reduce nurse workload. For this purpose, a simple model was designed and tested to see the effect of inherent CGM error on the insulin therapy protocol, STAR (Stochastic TARgeted). An error model was generated from 9 patients that had one Guardian Real-Time CGM device (Medtronic Minimed, Northridge, CA, USA) inserted into their abdomen as part of an observation trial assesing the accuracy of CGM measurements compared to a blood gas analyser and glucometer readings. A resulting error model was then used to simulate the outcomes if the STAR protocol was guided by CGM values on 183 virtual patients. CGM alarms for hyper- and hypo-glycaemic region were included to improve patient safety acting as 'guardrails'. The STAR CGM protocol gave good performance and reduced workload by ∼50%, reducing the number of measurements per day per patient from 13 to 7. The number of hypoglycaemic events increased compared to the current STAR from 0.03% <2.2mmol/L to 0.32%. However, in comparison to other published protocols it is still a very low level of hypoglycaemia and less than clinically acceptable value of 5% <4.0mmol/L. More importantly this study shows great promise for the future of CGM and their use in clinic. With the a newer generation of sensors, specifically designed for the ICU, promising less noise and drift suggesting that a reduced nurse workload without compromising safety or performance is with in reach.? © 2015, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. [less ▲]

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See detailAccuracy and performance of continuous glucose monitors in athletes
Thomas, Felicity Louise ULg; Pretty, C. G.; Signal, M. et al

in IFAC Proceedings Volumes (IFAC-PapersOnline) (2015)

Continuous glucose monitoring (CGM) devices, with their 1-5 minute measurement interval, allow blood glucose dynamics to be captured more frequently and less invasively than traditional measures of blood ... [more ▼]

Continuous glucose monitoring (CGM) devices, with their 1-5 minute measurement interval, allow blood glucose dynamics to be captured more frequently and less invasively than traditional measures of blood glucose concentration (BG). These devices are primarily designed for the use in type 1 and type 2 diabetic patients to aid BG regulation. However, because of their increased measurement frequency and reduced invasiveness CGM devices have been recently applied to other subject cohorts, such as intensive care patients and neonates. One unexamined cohort is athletes. Continuous monitoring of an athlete's BG has the potential to increase race performance, speed recovery, and aid training, as BG can reflect metabolic and inflammatory conditions. However, before these benefits can be realized the accuracy and performance of CGM devices in active athletes must be evaluated. Two Ipro2 CGM devices (Medtronic Minimed, Northridge, CA, USA) were inserted into an athlete (resting HR 50 beats per minute (bpm), training 10-17hrs per week). Two fasting exercise tests were carried out 3 days apart, involving 2 hours of continuous exercise and a glucose bolus at the end of the 2 hours. Reference BG measurements were taken regularly. These tests were then repeated while the athlete was sedentary, HR < 80bmp. CGM devices agree well with each other and reference measurements during rigorous exercise with a median [IQR] MARD of 7.3 [5.4-10.9] %. During sedentary periods the accuracy of the CGM trace compared to reference measurements was reduced, 25.1 [16.9 35.4] %. However the good agreement between the sensors is maintained. This decrease in accuracy is likely related to the fact interstitial fluid is not actively pumped like blood. It relies on muscle movement to circulate and mix. Thus, it can be expected that during exercise more accurate results are seen as the rigorous movement allows rapid mixing and equilibrium between the blood and interstitial fluid. © 2015, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. [less ▲]

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See detailMAGiC DRAGONS: A protocol for accurate glycaemic control in general wards
Thomas, Felicity Louise ULg; Tomlinson, H.; Waston, A. et al

in IFAC Proceedings Volumes (IFAC-PapersOnline) (2014), 19

Accurate glycaemic control (AGC) has been shown to be beneficial to the outcomes of critically ill patients. These benefits may also extend to patients in less acute wards, particularly those with ... [more ▼]

Accurate glycaemic control (AGC) has been shown to be beneficial to the outcomes of critically ill patients. These benefits may also extend to patients in less acute wards, particularly those with existing diabetes. However, the clinical demands of an intensive care glycaemic control protocol are not appropriate for the general wards where the nurse-to-patient ratio is much lower and patients do not typically have an intravenous line available for insulin delivery. Thus, there is a need for a safe, effective glycemic control protocol tailored to the needs of general wards to enable appropriate care for diabetic patients and further testing of the benefits of glycaemic control for this cohort. This paper presents the development and testing of such a protocol for glycaemic control in the general wards. The DRAGONS protocol (Dynamic Regulation for Accurate Glycaemic-control Optimising iNsulin Subcutaneously) was designed to use subcutaneous insulin and only require blood glucose (BG) measurements every four hours, while maintaining BG concentrations within the range 4.4-8.0 mmol/L. Virtual trial simulation indicated an expected time in the target band of 73.0%, with < 2% risk of BG < 4.0 mmol/L. In the first patient recruited to the pilot trial, the DRAGONS protocol achieved 46% time in band and no severe hypoglycaemic episodes. This trial has also highlighted the need for careful selection of the insulin injection site to prevent excessively rapid transport to plasma. © IFAC. [less ▲]

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See detailProcessing aortic and pulmonary artery waveforms to derive the ventricle time-varying elastance
Stevenson, D. J.; Hann, C. E.; Chase, G. J. et al

in IFAC Proceedings Volumes (IFAC-PapersOnline) (2011), 18(PART 1), 587-592

Time-varying elastance of the ventricles is an important metric both clinically and as an input for a previously developed cardiovascular model. However, currently time-varying elastance is not normally ... [more ▼]

Time-varying elastance of the ventricles is an important metric both clinically and as an input for a previously developed cardiovascular model. However, currently time-varying elastance is not normally available in an Intensive Care Unit (ICU) setting, as it is an invasive and ethically challenging metric to measure. A previous paper developed a method to map less invasive metrics to the driver function, enabling an estimate to be achieved without invasive measurements. This method requires reliable and accurate processing of the aortic and pulmonary artery pressure waveforms to locate the specific points that are required to estimate the driver function. This paper details the method by which these waveforms are processed, using a data set of five pigs induced with pulmonary embolism, and five pigs induced with septic shock (with haemofiltration), adding up to 88 waveforms (for each of aortic and pulmonary artery pressure), and 616 points in total to locate. 98.2% of all points were located to within 1% of their true value, 0.81% were between 1% and 5%, 0.65% were between 5% and 10%, the remaining 0.32% were below 20%.© 2011 IFAC. [less ▲]

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See detailUnique parameter identification for model-based cardiac diagnosis in critical care
Hann, C. E.; Chase, J. G.; Desaive, Thomas ULg et al

in IFAC Proceedings Volumes (IFAC-PapersOnline) (2009), 7(PART 1), 169-174

Lumped parameter approaches for modeling the cardiovascular system typically have many parameters of which many are not identifiable. The conventional approach is to only identify a small subset of ... [more ▼]

Lumped parameter approaches for modeling the cardiovascular system typically have many parameters of which many are not identifiable. The conventional approach is to only identify a small subset of parameters to match measured data, and to set the remaining parameters at population values. These values are often based on animal data or the "average human" response. The problem, is that setting many parameters at nominal fixed values, may introduce dynamics that are not present in a specific patient. As parameter numbers and model complexity increase, more clinical data is required for validation and the model limitations are harder to quantify. This paper considers the modeling and the parameter identification simultaneously, and creates models that are one to one with the measurements. That is, every input parameter into the model is uniquely optimized to capture the clinical data and no parameters are set at population values. The result is a geometrical characterization of a previously developed six chamber heart model, and a completely patient specific approach to cardiac diagnosis in critical care. In addition, simplified sub-structures of the six chamber model are created to provide very fast and accurate parameter identification from arbitrary starting points and with no prior knowledge on the parameters. Furthermore, by utilizing continuous information from the arterial/pulmonary pressure waveforms and the end-diastolic time, it is shown that only the stroke volumes of the ventricles are required for adequate cardiac diagnosis. This reduced data set is more practical for an intensive care unit as the maximum and minimum volumes are no longer needed, which was a requirement in prior work. The simplified models can also act as a bridge to identifying more sophisticated cardiac models, by providing a generating set of waveforms that the complex models can match to. Most importantly, this approach does not have any predefined assumptions on patient dynamics other than the basic model structure, and is thus suitable for improving cardiovascular management in critical care by optimizing therapy for individual patients. © 2009 IFAC. [less ▲]

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