Overview
Continuous subcutaneous insulin infusion (CSII) uses an external battery-driven pump, containing an insulin reservoir. The pump continuously delivers rapid-acting insulin1 at a basal rate via a subcutaneous cannula, and the user initiates delivery of bolus doses immediately before meals. On average, a CSII pump results in a reduction in HbA1c of 0.3 to 0.4% more than a multiple daily injection (basal–bolus) insulin regimen, and is associated with a lower incidence of nocturnal hypoglycaemia.
The usual indication for a CSII pump is patient preference; other indications include glycaemic targets not being achieved despite good adherence, and frequent severe hypoglycaemia. Patients who use a CSII pump need to be motivated and appropriately educated about use of the CSII pump, and must attend a multidisciplinary diabetes service. Patients need to check their blood glucose concentration frequently, assess and monitor carbohydrate intake, and carefully select bolus insulin doses accordingly. Additional care is required because disposable cannulae are used, and the infusion site needs to be changed at least every 3 days.
All patients on a CSII pump must have a written emergency action plan and access to a supply of long-acting (basal) and rapid-acting (bolus) prefilled insulin injector pens to use in the case of disruption of insulin delivery from their CSII pump (see Disruption of pump–delivered subcutaneous insulin).
CSII pumps are expensive but may qualify for a rebate from the patient’s private health insurance company, depending on their level of insurance cover. At the time of writing, the Australian Government subsidises pumps for use in patients under the age of 18 years. Additional costs to the patient include the purchase of batteries, reservoirs and infusion sets for insulin delivery. Most of these items are subsidised through the National Diabetes Services Scheme (NDSS).
A sensor-augmented CSII pump links the insulin pump with a subcutaneous continuous glucose monitor, enabling more intensive blood glucose concentration monitoring. These pumps stop the infusion automatically if the blood glucose concentration is low (or if low blood glucose concentration is predicted to occur), which reduces the risk of hypoglycaemia. Hybrid closed-loop systems allow sensor-augmented CSII pumps to provide algorithm-driven automated basal insulin delivery, combined with manual mealtime boluses.