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Continuous subcutaneous insulin infusion

Continuous subcutaneous insulin infusion (CSII), otherwise known as insulin pump therapy, is a method of delivering insulin to individuals with type 1 diabetes mellitus (T1DM).

CSII comprises of a pump which is pre-set to deliver a continuous infusion of rapid acting insulin which attempts to mimic an individual's physiological requirements. This continuous infusion is then supplemented with bolus doses of insulin as calculated by the patient.

The technology

Insulin pumps are small, computerised battery-operated delivery systems roughly the size of a small mobile phone. This device is attached to the wearer by an infusion set, which is connected to a subcutaneous cannula, or via 'patch pump' technology, as inserted by the patient. Infusion sites include the abdomen, upper outer buttocks, loin areas and the legs.1 A pump can be worn in various places such as a pocket, clipped to a waistband, or tucked into a bra.

A single-use cartridge containing up to 300 units (3ml) is filled with insulin by the patient and placed inside the pump. Within the pump a plunger that delivers the insulin in a precise, variable, pre-set programme which is known as the basal rate.

The basal rate is supplemented by bolus doses of insulin as calculated by the patient to correct either a raised blood glucose value or counter the raised glucose that would occur after the consumption of carbohydrate based on CHO counting.1 This bolus dose of insulin is delivered by the patient, sequencing buttons on the pump. To help the patient with decision-making, modern insulin pumps now contain software which can assist with bolus dose calculations. Some pumps can also be linked up to continuous blood glucose monitoring.

Individuals using insulin pump therapy do not use long or intermediate-acting insulin. The insulin type of choice in pump therapy is rapid-acting analogue insulin, such as lispro, glulisine or aspart, as it causes less glycaemic variation and better long-term glycaemic control than soluble insulin.2 

The advantage of insulin administration via a pump is that it is more exact and physiological than a modern injection regimen.3 However, despite the many advantages of using a pump for insulin delivery, the insulin is still delivered into subcutaneous tissue as opposed to the portal system as in normal physiology.4 

Who benefits from CSII?

For NHS funding of insulin pump therapy, a potential candidate must have T1DM and meet NICE5 criteria. Even taking NICE5 guidance into consideration, decisions regarding an individual's suitability for CSII can be a potentially controversial area of clinical practice, which can take considerable time to undertake. It is essential that professionals recognise insulin pump therapy is not a 'cure-all' for diabetes and if it is not used appropriately there is great potential for life-threatening harm.6

Suitable candidates for CSII are those who despite an optimised insulin regimen and a high level of self-care in relation to their diabetes management experience glycaemic instability. Such situations could include individuals with a dawn phenomenon, hyperglycaemia based on a HbA1c >69mmol/mol, and frequent hypoglycaemia.6

Circumstances where a pump would not be a suitable option include those individuals who do not work in partnership with family, friends and healthcare professionals. Other poor predictors for CSII are in those patients who have significant psychological or mental health issues which impact on their ability to manage diabetes, or in individuals who lack motivation to make appropriate decisions regarding diabetes management.6-8

Positive aspects of CSII

The benefits of CSII stem from the fact that it is a precise insulin delivery system. The pump user is able to make decisions and adjustments concerning their insulin requirements on a moment-by-moment basis.9 

Insulin pump therapy provides enhanced glycaemic control and a reduction in hypoglycaemia. Factors that contribute to increased glycaemic stability include the more predictable insulin absorption, reduction in insulin requirements and the individualisation of insulin delivery.3,10-12 

Background insulin requirements are personalised to match the actual diurnal variation of an individual at a particular times of the day.13,14 In addition the basal rate can be increased or decreased on a temporary basis to accommodate short-term changes in insulin requirements. These situations include changes in physical activity, infection, stress and menstruation.1

Once the patients actual background insulin demands corresponds to the actual needs of the individual, food can then be skipped or delayed whilst maintaining glycaemic stability.1,6 On a pump, a patient has total dietary freedom and flexibility. Bolus doses for carbohydrate intake are manipulated so that they are delivered to match normal physiology and fit in with the anticipated pattern of glucose release from various types of food.1

As glycaemic fluctuations are less in pump therapy, patients feel better than when they use insulin injections even if the HbA1c does not improve.15 An increased sense of wellbeing leads to an improved quality of life.16 

Negative aspects of CSII

As the insulin pump only uses rapid acting insulin should the flow of insulin be interrupted for even a short time, then the individual's blood glucose will rise quickly. If the situation is not effectively dealt with, ketoacidosis will rapidly develop, which could be life-threatening.6,17 

Cannulas are a potential source of infection and if not changed at appropriate time, intervals and infection can occur, which may lead to abscess formation.1,6

A pump can be viewed as an obstacle to the participation in contact or water sports. Waterproof pumps are available and strategies can be taught which allow the pump user to exercise without a pump while maintaining glycaemic control.1

Wearing an insulin pump can have a negative impact on body image for some individuals.1,6 Many people also feel worried about sleeping with a pump or being reliant on the technology to manage their diabetes.1,6 

Role of the practice nurse

As insulin pump patients need to access primary care for their health needs it, is essential that the practice nurse has insight into this treatment option. Evidence of a working knowledge of CSII is reassuring for patients who are using pumps. 

The practice nurse is also in an ideal place to be able to discuss the pros and cons of insulin pump therapy with any prospective pump user. This can allow patients to make an informed choice regarding their diabetes management as highlighted by the DOH National Service Framework (NSF).18 

 

Conclusion

There are many advantages of CSII, such as improved glycaemic control, reduced risk of hypoglycaemia, and improved quality of life and wellbeing. However insulin pump therapy is not an appropriate treatment option for all and it should be considered as one of a range of treatment options for people with T1DM. 

For insulin pump therapy to be successful, key skills and knowledge must be learnt and implemented by the patient. This will only be achieved with appropriate patient selection, education and ongoing professional support from primary care and experienced secondary care teams.

 

References

1. Walsh J, Roberts R. Pumping Insulin, Fourth edition. California: Torrey Pines Press; 2006.

2. Colquitt J, Royal P, Waught N. Are analogue insulins better than soluble in continuous subcutaneous insulin infusion? Results of a meta-analysis. Diabet Med 2003;20:863-6.

3. Marcus AO, Fernandez MP. Insulin pump therapy - Acceptable alternative to injection therapy. Symposium Postgraduate medicine; 1996;99. 

4. Baggaley A. Human body. London: Dorling Kindersley Limited; 2001.

5. National Institute for Health and Care Excellence. NICE technology appraisal guidance 151. Continuous subcutaneous insulin infusion for the treatment of diabetes mellitus (review of technology appraisal guidance 57). London: NICE; 2008. Available at: www.nice.org.uk/TA151.

6. Bolderman KM. Putting your patients on the pump. American Diabetes Association; 2002.

7. Marcus AO. Patient selection for insulin pump therapy. Practical Diabetology 1992;12-8.

8. Pickup J. What are the clinical indications for continuous subcutaneous insulin infusion? Infusystem International 2005;4(1):1-4.

9. NHS Technology Adoption Centre (NTAC). How to why to guide on insulin pump therapy. 2012. Available at: www.ntac.nhs.uk/HowToWhyToGuides/ContinuousSubcutaneousInsulinInfusion/I...

10. Bode BW, Steed RD, Davidson PC. Reduction in severe hypoglycaemia with long-term continoussubcutaineous insulin infusion in type 1 diabetes. Diabetes Care 1996;19(4):324-7.

11. Lauritzen T, Pramming S. Pharmacokinetics and clinical aspects of continuous subcutaneous insulin infusion. Diabetologia 1983;24:326-29.

12. Shaw K. Insulin lispro: insulin with a rapid onset of action. The Prescriber 19 February 1997.

13. Lager I, et al. Reversal of insulin resistance in Type 1 diabetes after treatment with continuous subcutaneous insulin infusion. BMJ 1983;661-1663.

14. Hoss C et al. Insulin pump therapy compared to ICT/MDI. Diabetologica 1996;39(Supp1);A214:812.

15. Hirsch IB, Bold BW, et al. Continuous subcutaneous insulin infusion (CSII) of insulin aspart versus multiple daily injections of insulin aspart/insulin glargine in type 1 diabetic patients previously treated with CSII. Diabetes Care 2005;28(3):533-8.

16. Chantelau E, Schhiffers T, Schute J, Hansen B. Effect of patient-selected intensive insulin therapy on quality of life. Patient Education and Counseling1997;30:167-73.

17. Torlone E, Pampanelli S, et al. Effects of the short acting analogue [Lys (B28), Pro(B29)] on postprandial blood glucose  control in IDDM. Diabetes Care 1996;19/9:945-52.

18. Department of Health. National Service Framework for Diabetes: Standards. London: Department of Health; 2001.