The Diabetes Control and Complications Trial (DCCT) has shown convincingly that in type I diabetes, lower HbA1c levels achieved through intensive insulin treatment are associated with reduced long-term risk for the development of microvascular complications (DCCT Research Group, 1993).
Unfortunately, normoglycaemia is rarely achieved in these patients. In many, the price of lowering HbA1c levels is a substantially increased (nearly three-fold) risk of severe hypoglycaemia.
The insulin regimen for type I patients is usually based on a basal/bolus approach, i.e. short-acting insulin before each meal and long-acting insulin at night. This approach is not universally popular with patients, particularly teenagers and young adults (Shaw, 1997). This is not altogether surprising, given that it entails four injections every day (furthermore, most patients are also advised to leave a gap between injecting soluble insulin and eating).
Early use of CSII
Continuous subcutaneous insulin infusion (CSII) was introduced into clinical practice in the 1970s. Unfortunately, the pump looked and felt like a house brick. As well as providing a continuous background infusion of insulin, the early devices produced pre-meal boluses that were simply multiples of the baseline rate and took up to 17 minutes to deliver (Pickup et al, 1978).
Despite sporadic enthusiasm, the pumps fell out of favour over the next decade, owing to reports that CSII was associated with increased rates of:
- Diabetic ketoacidosis
- Severe hypoglycaemia
- CSII-associated deaths.
Other negative factors included high cost and high drop-out rates (Mecklenburg et al, 1985).
Recent studies with CSII
Publication of the DCCT sparked renewed interest in intensive insulin regimens. This interest was augmented by the introduction of very rapid acting insulin analogues (Koivisto, 1998).
The technology associated with pumps has improved and, just as importantly, so has patient education about intensive insulin treatment. Within the DCCT, 42% of the intensively treated arm were using CSII to control their diabetes by the end of the study.
More recent studies suggest that CSII can improve diabetes control and reduce the risk of severe hypoglycaemia (Farkas-Hirsch and Hirsch, 1994; Bode et al, 1996). The reasons for this are not fully understood but may relate to:
- More predictable insulin absorption (Lauritzen et al, 1983)
- Reduction in total insulin requirements (Bode et al, 1996)
- The ability to pre-programme infusion rates to reduce hypoglycaemia risk, e.g. at night (Hoss et al, 1996).
For other patients, even if HbA1c does not change significantly, pump use is associated with an improved quality of life compared with multiple daily injections Chantelau et al, 1997).
Pump therapy defined
Briefly, pump therapy is the continuous delivery of short-acting insulin from a pump. The pump can be programmed to suit individual requirements.
The insulin is delivered at a pre-determined continuous basal rate supplemented by boluses. The patient decides the amount of insulin contained in each bolus. Considerations include carbohydrate consumed, current blood glucose value and anticipated exercise. The subcutaneous infusion set is replaced by the patient every 2–3 days.
CSII in use
The advantages and disadvantages of the pump, from the patient’s viewpoint, are listed in Tables 1 and 2 respectively
The three case histories outlined below demonstrate some advantages of pump therapy. In the authors’ experience, patients using pump therapy generally feel that the advantages far outweigh the disadvantages.
Healthcare professionals may have many concerns regarding the use of pumps. Some of these are addressed below.
One of the major concerns about the pump is that it may continue to deliver insulin during hypoglycaemia or that the pump will malfunction and deliver too much insulin.
The most up-to-date insulin pumps are very reliable. Hypoglycaemia can also be more easily controlled.
In the authors’ experience, pump therapy reduces the frequency of hypoglycaemic episodes. Also, warning symptoms of impending hypoglycaemia return in all patients in whom they were reduced (Everett et al, 1999). This increases patients’ confidence in managing and treating hypoglycaemia. All the authors’ patients use an insulin analogue in their pumps. As soon as they develop symptoms of impending hypoglycaemia, they switch off the pump for 30 minutes and take 10g of quick-acting carbohydrate such as glucose tablets or Lucozade.
Patients are taught to routinely reduce the basal rate of insulin during and after exercise, to reduce the possibility of hypos. Similarly, the basal rate can be decreased after alcohol consumption.
Because short-acting insulin is used, any interruption to supply will lead to hyperglycaemia and diabetic ketoacidosis within a short time. Under controlled conditions, ketones appear after 4.2 hours of interrupted supply of an insulin analogue and after 6.4 hours of regular insulin (Pein et al, 1996).
Hyperglycaemia can develop for the following reasons:
- The infusion set becomes dislodged, clogged-up or develops a leak, interrupting the insulin supply
- Insulin is not being absorbed properly
- Insulin requirement is increased due to illness or infection.
All of these situations can be detected and prevented by the patient using trouble- shooting strategies. This underlines the importance of patient education. It is essential that blood glucose readings are taken at least four times a day to detect any problems. Patients are given specific instructions and guidelines about the treatment of hyperglycaemia. They must test for ketones if blood glucose is above 15mmol/l. If ketones are present, insulin should be given via a pen or syringe.
Infusion sets should be changed every 2–3 days to avoid infection of the infusion site. In most cases, simple washing of the skin is all that is necessary before inserting infusion sets. The importance of hand washing and the ‘no touch’ rule (i.e. not touching the ends of the infusion sets unnecessarily) should always be explained to the patient. In the US, the skin is routinely cleaned with an antiseptic. This is not the case in some European countries.
The site needs to be inspected daily for inflammation, warmth, pain or leakage. If any of these are present, a different site must be used.
Implications for practice
At present, about 320 people use CSII in the UK, compared with 60 000 in the USA and 40 000 in Europe.
Demand for information about pump therapy is exploding as a result of patients’ access to the internet. Diabetes healthcare professionals in the UK must, at the very least, be knowledgeable about current literature on CSII because it is a tool that some patients have found useful in managing their diabetes more effectively. As with all tools, there are certain skills and knowledge to be learnt both by the patient and the professional.
Pump therapy is innovative and exciting. The benefits are clear: improved glycaemic control; reduced risk of hypoglycaemia; and improved quality of life. However, the full potential will only be realised with adequate education and careful patient selection.
Case study 1
A 33-year-old male with recurring fasting hyperglycaemia despite frequent adjustment 1c was formerly 9–10% (normal range 4–6.5%). With CSII, his overnight insulin requirements could be more accurately matched by increasing the basal rate between 3am and 8am (at least twofold), compared with the rest of the day. Currently, he has fasting glucose levels of 6–7mmol/l and an HbA1c of 7.5%. He also has much more energy, his skin has cleared of acne and he feels ‘more alive’.
Case study 2
A 58-year-old male, of BMI 26, with good glycaemic control (HbA1c 7%). Despite this good control he complained of his blood glucose swinging between ‘lows and highs’. This complaint was largely ignored because of his good HbA1c. He said that his life was controlled by diabetes. He ate regularly to minimise hypos and stopped going out on his own. Despite these measures, he was having 10 hypos a week. There were very few warning symptoms of hypoglycaemia.
The patient started pump therapy 18 months ago and says it has made a tremendous difference to his life. His HbA1c has not changed, but his blood glucose is more level and mostly within normal limits. He now has warning symptoms and recognises when his blood glucose falls below 4mmol/l or rises above 11mmol/l. He has reached his therapeutic target weight, reduced the amount of insulin he takes and eats when and what he likes. He has become active in local events, states that ‘pump therapy is the best thing that has happened to him’, and now feels that he controls his diabetes.
Case study 3
A 40-year-old male who, subsequent to a pancreatectomy, found his diabetes very difficult to manage on a basal/bolus regimen. His HbA1c was 11% despite four injections a day and a total daily insulin dose of 76 units. Since commencing CSII, his HbA1c has dropped to 7.1% and he has been able to gain some much-needed weight.