Insulin pump use in adults with type 1 diabetes--practical issues

Minimizing the Risk of Exercise-Induced Glucose Fluctuations in People Living With Type 1 Diabetes Using Continuous Subcutaneous Insulin Infusion: An Overview of Strategies

Physical activity (PA) is important for individuals living with type 1 diabetes (T1D) due to its various health benefits. Nonetheless, maintaining adequate glycemic control around PA remains a challenge for many individuals living with T1D because of the difficulty in properly managing circulating insulin levels around PA. Although the most common problem is increased incidence of hypoglycemia during and after most types of PA, hyperglycemia can also occur. Accordingly, a large proportion of people living with T1D are sedentary partly due to the fear of PA-associated hypoglycemia. Continuous subcutaneous insulin infusion (CSII) offers a higher precision and flexibility to adjust insulin basal rates and boluses according to the individual's specific needs around PA practice. Indeed, for physically active patients with T1D, CSII can be a preferred option to facilitate glucose regulation. To our knowledge, there are no guidelines to manage exercise-induced hypoglycemia during PA, specifically for individuals living with T1D and using CSII. In this review, we highlight the current state of knowledge on exercise-related glucose variations, especially hypoglycemic risk and its underlying physiology. We also detail the current recommendations for insulin modulations according to the different PA modalities (type, intensity, duration, frequency) in individuals living with T1D using CSII.

Detailed Analysis of Insulin Absorption Variability and the Tissue Response to Continuous Subcutaneous Insulin Infusion Catheter Implantation in Swine

BACKGROUND

Worldwide, ∼1 million people manage their type 1 diabetes with an insulin pump and a continuous subcutaneous insulin infusion (CSII) catheter. Patients routinely insert a new catheter every 2-3 days due to increasing variability of insulin absorption over time. Catheter insertion and maintenance damage capillaries, lymphatics, cells, and connective tissue leading to an acute inflammatory response.

METHODS

We compared an investigational CSII catheter (IC) and a commercial CSII catheter (CC) regarding insulin absorption pharmacokinetics (PK) and tissue inflammation. The two different catheter designs were implanted into the subcutaneous tissue of six swine for 5 days. Insulin boluses were given on days 1, 3, and 5 of wear-time to assess PK. Tissue around catheters was excised and stained to visualize inflammation and morphological changes of adjacent tissue.

RESULTS

Insulin absorption was better when infused through a CC with highest Cmax and fastest tmax values on day 5 of catheter wear-time. Both catheter types produced high intra- and intersubject day-to-day insulin absorption variability. The IC caused significantly more tissue disruption and lead to irregular changes in tissue morphology. Both catheter types were surrounded by a layer of inflammatory tissue that varied in composition, thickness, and density over time. A catheter that was manually inserted by pushing a sharp tip through the skin caused more trauma and variability than a 90° Teflon cannula with automated insertion.

CONCLUSIONS

Insulin absorption variability could be attributed to the layer of inflammatory tissue, which may function as a mechanical barrier to insulin flow into adjacent vascular tissue. The impact of the acute inflammatory tissue response on insulin absorption has to be considered in future catheter designs. A catheter that was manually inserted by pushing a sharp tip through the skin caused more trauma and variability than a 90° Teflon cannula with automated insertion.

Insulin Infusion Sets: A Critical Reappraisal

An insulin infusion set (IIS) is a key component of insulin pumps. In daily practice issues with the IIS appear to be as relevant for a successful insulin therapy as the pumps themselves. The insulin is applied to the subcutaneous tissue via a Teflon(®) (Dupont, Wilmington, DE) or steel cannula. There are intensive discussions about the impact the choice of material for insulin application has on insulin pharmacokinetics. In this review, this factor and others that are known to have an impact on the successful usage of IIS are discussed.

Evaluation of Intradermal and Subcutaneous Infusion Set Performance Under 24-Hour Basal and Bolus Conditions

BACKGROUND

This study sought to assess the function and delivery reliability of intradermal (ID) infusion sets used with commercial insulin pumps.

METHOD

Healthy subjects (n = 43) were randomized to either ID or subcutaneous (SC) arms, and received basal/bolus placebo delivery for 24 hours. Subjects received 4 of 8 infusion set combinations (ID: microneedle design A or B, with 2 pump brands [Animas or MiniMed]; SC: Teflon Quickset or steel Rapid-D, Animas pump only, with or without overtaping) and were evaluated for pump occlusion alarms, fluid leakage, pain, and tissue tolerability. A novel algorithm was developed to determine flow consistency based on fluid pressure, and the duration and occurrence rate for periods of unalarmed but interrupted flow ("silent occlusions'") were compared.

RESULTS

ID delivery was successfully maintained over the 24-hour infusion period. The number of silent occlusions was lower for ID microneedle cannula design B than A (P < .01) and lower for Rapid-D SC device compared to Quick-set (P = .03). There was no significant difference in the number of occlusion alarms between the ID and SC devices with the Animas pump. However, the pumps tested with ID devices had significantly different alarm rates (MiniMed 29.5%, Animas 0%, P < .001). Leakage and tissue tolerability were comparable across devices.

CONCLUSION

The ID infusion set reliably delivered diluent for an extended 24-hour period in healthy subjects and was well tolerated. Silent occlusion flow interruptions could be detected in both ID and SC infusion sets using a proprietary algorithm. This algorithm is a promising method for quantitatively evaluating infusion set flow performance.

Closed-loop system in the management of diabetes: past, present, and future

Intensive insulin therapy (IIT) has been shown to reduce micro- and macrovascular complications in patients with type 1 diabetes mellitus (T1DM). However, IIT is associated with a significant increase in severe hypoglycemic events, resulting in increased morbidity and mortality. Optimization of glycemic control without hypoglycemia (especially nocturnal) should be the next major goal for subjects on insulin treatment. The use of insulin pumps along with continuous glucose monitors (CGMs) has made it easier but requires significant resources and patient education. Research is ongoing to close the loop by integrating the pump and the CGM using different algorithms. The currently available closed-loop system is the threshold suspend. Steps needed to achieve a near-perfect closed-loop are (1) a control-to-range system that will reduce the incidence and/or severity of hyper- and/or hypoglycemia by adjusting the insulin dose and (2) a control-to-target system, a fully automated or hybrid system that sets target glucose levels to individual needs and maintains glucose levels throughout the day using insulin (unihormonal) alone or with other hormones such as glucagon or possibly pramlintide (bihormonal). Future research is also focusing on better insulin delivery devices (pumps), more accurate CGMs, better predictive algorithms, and ultra-rapid-acting insulin analogs to make the closed-loop system as physiological as possible.

Nonmetabolic complications of continuous subcutaneous insulin infusion: a patient survey

BACKGROUND

Little is known about the frequencies and types of nonmetabolic complications occurring in type 1 diabetes patients being treated by modern insulin pump therapy (continuous subcutaneous insulin infusion [CSII]), when recorded by standardized questionnaire rather than clinical experience.

SUBJECTS AND METHODS

A self-report questionnaire was completed by successive subjects with type 1 diabetes attending an insulin pump clinic, and those with a duration of CSII of ≥6 months were selected for analysis (n=92). Questions included pump manufacturer, insulin, infusion set type and duration of use, frequency of infusion set and site problems, pump malfunctions, and patient-related problems such as weight change since starting CSII.

RESULTS

Median (range) duration of CSII was 3.3 (0.5-32.0) years, and mean ± SD duration of infusion set use was 3.2 ± 0.7 (range 2-6) days. The commonest infusion set problems were kinking (64.1% of subjects) and blockage (54.3%). Blockage was associated with >3 days of use of infusion sets plus lispro insulin in the pump (relative risk [95% confidence interval], 1.71 [1.03-2.85]; P=0.07). The commonest infusion site problem was lipohypertrophy (26.1%), which occurred more often in those with long duration of CSII (4.8 [2.38-9.45] vs. 3.0 [1.50-4.25] years; P=0.01). Pump malfunction had occurred in 48% of subjects (43% in the first year of CSII), with "no delivery," keypad, and battery problems commonly occurring. Although some patients reported weight gain (34%) and some weight loss (15%) on CSII, most patients (51%) reported no change in weight.

CONCLUSIONS

Pump, infusion set, and infusion site problems remain common with CSII, even with contemporary technology.

Model-based sensor-augmented pump therapy

BACKGROUND

In insulin pump therapy, optimization of bolus and basal insulin dose settings is a challenge. We introduce a new algorithm that provides individualized basal rates and new carbohydrate ratio and correction factor recommendations. The algorithm utilizes a mathematical model of blood glucose (BG) as a function of carbohydrate intake and delivered insulin, which includes individualized parameters derived from sensor BG and insulin delivery data downloaded from a patient's pump.

METHODS

A mathematical model of BG as a function of carbohydrate intake and delivered insulin was developed. The model includes fixed parameters and several individualized parameters derived from the subject's BG measurements and pump data. Performance of the new algorithm was assessed using n = 4 diabetic canine experiments over a 32 h duration. In addition, 10 in silico adults from the University of Virginia/Padova type 1 diabetes mellitus metabolic simulator were tested.

RESULTS

The percentage of time in glucose range 80-180 mg/dl was 86%, 85%, 61%, and 30% using model-based therapy and [78%, 100%] (brackets denote multiple experiments conducted under the same therapy and animal model), [75%, 67%], 47%, and 86% for the control experiments for dogs 1 to 4, respectively. The BG measurements obtained in the simulation using our individualized algorithm were in 61-231 mg/dl min-max envelope, whereas use of the simulator's default treatment resulted in BG measurements 90-210 mg/dl min-max envelope.

CONCLUSIONS

The study results demonstrate the potential of this method, which could serve as a platform for improving, facilitating, and standardizing insulin pump therapy based on a single download of data.

Improving the computational effort of set-inversion-based prandial insulin delivery for its integration in insulin pumps

OBJECTIVE

Set-inversion-based prandial insulin delivery is a new model-based bolus advisor for postprandial glucose control in type 1 diabetes mellitus (T1DM). It automatically coordinates the values of basal-bolus insulin to be infused during the postprandial period so as to achieve some predefined control objectives. However, the method requires an excessive computation time to compute the solution set of feasible insulin profiles, which impedes its integration into an insulin pump. In this work, a new algorithm is presented, which reduces computation time significantly and enables the integration of this new bolus advisor into current processing features of smart insulin pumps.

METHODS

A new strategy was implemented that focused on finding the combined basal-bolus solution of interest rather than an extensive search of the feasible set of solutions. Analysis of interval simulations, inclusion of physiological assumptions, and search domain contractions were used. Data from six real patients with T1DM were used to compare the performance between the optimized and the conventional computations.

RESULTS

In all cases, the optimized version yielded the basal-bolus combination recommended by the conventional method and in only 0.032% of the computation time. Simulations show that the mean number of iterations for the optimized computation requires approximately 3.59 s at 20 MHz processing power, in line with current features of smart pumps.

CONCLUSIONS

A computationally efficient method for basal-bolus coordination in postprandial glucose control has been presented and tested. The results indicate that an embedded algorithm within smart insulin pumps is now feasible. Nonetheless, we acknowledge that a clinical trial will be needed in order to justify this claim.

Emerging diabetes therapies and technologies

The prevalence of diabetes is increasing globally and is expected to increase to 439 million people by the year 2030. Several studies have shown that improved glycemic control measured by glycosylated hemoglobin (A1c) in patients with type 1 and type 2 diabetes results in a reduction of both the micro- and macrovascular complications associated with the disease. The recent introduction of new oral medications, insulin analogs (long and rapid acting), insulin pens and pumps, better SMBG meters and continuous glucose monitoring (CGM) have all resulted in improvement of glycemic control. Closed-loop devices currently in development aim to integrate the CGM and pump system in order to more closely mimic the human pancreas. The other upcoming new basal insulin (Degludec), prandial insulin, other new technologies and improved oral therapies will significantly improve patient acceptance of intensive therapy, glycemic control and quality of life in patients with diabetes.

Deus ex machina: the use of technology in type 1 diabetes

Deus ex machina: in ancient Greek theatre, towards the end of a performance, a crane-like device was often used to lower an actor playing a god onto the stage in order to solve an apparently intractable problem in a plot-line. Nowadays, perceived wisdom believes that difficult clinical scenarios in diabetes can be alleviated by the introduction of technologies such as insulin pump therapy and glucose sensing. This "God from the Machine" approach to problem solving has been enthusiastically embraced by a small number of enthusiasts within the diabetes care community but access to these technologies is still very limited in the UK. The question is can the use of technology reduce or even eliminate the biological and psychological variables that prevent people living with diabetes achieving the standard of blood glucose control desired and if so should availability be more widespread?

Crossing the technology divide: practical strategies for transitioning patients from multiple daily insulin injections to sensor-augmented pump therapy

PURPOSE

To describe the benefits of continuous glucose monitoring (CGM) and continuous subcutaneous insulin infusion (CSII) systems compared with self-monitoring of blood glucose (SMBG) and multiple daily injection (MDI) therapy; to assess the benefits of sensor-augmented pump therapy (SAPT) in patients with type 1 diabetes; and to present an evidence-based practical protocol for introducing SAPT in patients with no prior pump or CGM experience.

CONCLUSION

Continuous glucose monitoring and CSII have advantages over SMBG and MDI, respectively, in terms of A1C and hypoglycemia reduction. The Sensor-Augmented Pump Therapy for A1C Reduction (STAR) 3 trial demonstrated that initiating both CGM and CSII in selected adult and pediatric patients with type 1 diabetes unable to meet glycemic goals with intensive insulin injection therapy significantly improved glucose control. In all subjects using SAPT, A1C levels fell rapidly from baseline to 3 months and remained significantly lower than among subjects in the SMBG+MDI group for 1 year. A distinguishing feature of the STAR 3 study was its stepwise protocol for systematizing education and self-management support using Web-based training modules and therapy management software. The demonstrated strengths of this education protocol recommend it as a model for implementing SAPT in the broader population of patients with type 1 diabetes who have not achieved their glycemic goals with optimized MDI therapy.