The Diabetes Control and Complications Trial (DCCT) clearly established that intensive therapy could facilitate a considerable improvement in glycaemic control and this was associated with a significant reduction in risk of development and/or progression of microvascular and neurological complications (1). Continuous subcutaneous insulin infusion (CSII) was successfully used in the DCCT to this effect (2).
Precise and Reproducible Insulin Delivery
Rates of absorption of subcutaneously injected insulin have been shown to vary significantly, especially with intermediate and long acting insulins (3,4) and this may contribute to problems in achieving glycaemic control in many people. Increased mobilisation of subcutaneous insulin depots is facilitated by increased blood flow which may occur during exercise and warm baths (5) and this can cause sudden or unexpected hypoglycaemia. CSII employs only rapid acting insulin which is delivered continuously in very small amounts. Consequently, variability in insulin absorption is minimised in CSII (6) and this ensures a reliable insulin supply with reproducible post-prandial peaks.
Physiological Insulin Delivery
CSII, with the option of different programmable basal rates, enables the individual’s physiological insulin requirements to be met. In particular, early morning increases in blood glucose concentrations and insulin requirements (known as the ‘dawn effect’) provide particular problems for people with diabetes. Increasing injected insulin in order to counteract high blood glucose levels on waking increases the risk of nocturnal hypoglycaemia. Using CSII, an appropriately timed step-up in insulin delivery during the early hours of the morning can successfully prevent the dawn effect (7,8).
Reduction in Severe Hypoglycaemia and Hypoglycaemia Unawareness
The DCCT documented a three-fold increased risk of severe hypoglycaemia in those patients receiving intensive insulin therapy either by way of multiple injections or CSII (9). However, this increased risk actually ranged from 1 to 11 fold across the 29 centres (2) which suggests that factors other than simply the intensive therapy may have played a part.
A number of studies have demonstrated a reduction in the occurrence of severe hypoglycaemia in patients using CSII (10-13). Of note, in the latter study, the use of insulin lispro in CSII was reported not to affect the counterregulatory hormone response to hypoglycaemia (13). Kanc and associates reported a significant improvement in hypoglycaemia warning symptoms on substituting nighttime CSII (using the regular human insulin, Velosulin) for bedtime NPH insulin (14). Another recent report suggested that the use of insulin lispro improved the sensitivity of the liver to glucagon; it was proposed that increased hepatic glucose output in response to mild hypoglycaemia could potentially reduce the risk of severe hypoglycaemia (15). These studies suggest that CSII may be a favourable treatment option for patients encountering problems with severe hypoglycaemia or hypoglycaemia unawareness on conventional injection regimens.
Optimisation of glycaemic control, both prior to conception and during pregnancy, is essential for a successful outcome (16,17). CSII can provide a means of normalising blood glucose levels during this critical period (18-20). Insulin pump therapy also affords flexibility, which may be of particular importance during the first trimester, when morning sickness and a tendency towards hypoglycaemia with loss of warning symptoms may compromise glycaemic control. The ability to adjust insulin doses quickly with a pump also makes control of blood sugars during labour, during delivery and post delivery much more predictable.
Patient lifestyle benefits
Flexibility of Lifestyle
The successful outcome of any intensive insulin treatment is dependent upon a number of factors, one of the most critical being compliance. Many patients find their lifestyle restricted by insulin injection therapy, particularly with respect to the timing of meals and the need to plan activities; this can hinder compliance and the ability to achieve desirable levels of blood glucose control.
The ability to tailor bolus insulin delivery to the individual’s food intake, independently of the basal rate, allows flexibility in terms of meal timing. This allows the user to successfully accommodate changes in daily routine that are often enforced e.g. through travel or variable working hours.
Problems encountered with the “dawn effect” may be compounded at weekends and during holidays when patients wake later. Insulin pump therapy eliminates the need for early morning injections and facilitates better blood glucose control on such occasions (21). Patients using CSII are therefore able to delay (or even omit) breakfast without compromising glycaemic control.
Improved Quality of Life
CSII thus obviates the need for adherence to a strict daily schedule and this flexibility may increase the quality of life in selected patients, in addition to improving glycaemic control. A number of studies have reported an improved quality of life associated with CSII therapy (22-24).
A survey among pump users in the USA, Germany, the Netherlands and Austria was conducted. When directly asked about their quality of life 98% of people responded by saying that they experience a better, or even much better, quality of life using an insulin pump.
The advantages of CSII over conventional insulin injection therapy are centred upon the ability to provide a physiological insulin supply that can be specifically tailored to the individual’s requirements. This enables optimisation of glycaemic control whilst allowing greater flexibility of lifestyle.