In insulin pump therapy, the need for basal insulin is normally reduced because rapid-acting insulin delivered every few minutes in small doses is more effective than a large dose of slowly absorbed basal insulin.
In practice, the initial insulin rate is planned on the basis of the previously required amount of insulin. Depending on the glycated haemoglobin HbA1c, the total daily insulin is reduced by 10–25%. The basal insulin pump dose starts at less than half of the reduced total amount. This is divided by the 24 hours in a day, either evenly or initially into approximately three steps.
Example:
A person administers a total of 46 units of insulin in a day. Their glycated haemoglobin HbA1c is 56 mmol/mol. The amount of insulin is reduced by 25%, making the new daily amount of insulin 0.75 x 46 = 34 units. The planned initial basal insulin rate is roughly half of this, or 17 units. In even doses, this would mean 0.7 units per hour. However, the need for insulin is reduced early in the night and it increases again after midnight. Instead of even doses, the doses could be, for example, from 21.00 to 03.00: 0.5 units per hour, from 03.00 to 09.00: 0.9 units per hour, and 09:00 to 21.00: 0.7 units per hour.
Starting day
No long-acting basal insulin is taken on the day the pump therapy is started. The basal insulin dose taken the night before is halved. It may be necessary to slightly reduce the insulin delivered by the pump on the first day due to the “tail effect” of the long-acting insulin. The pump’s temporary reduced dose function is used for as long as previous long-acting basal insulin is estimated to remain in the system. In the future, the basal insulin rate is reviewed and potentially adjusted on the basis of glucose sensor and blood sugar self-measurements.
The remaining 50–60% of the total insulin is reserved for bolus insulin. The insulin-to-carbohydrate ratio (ICR) of bolus insulin is estimated separately for each meal. If necessary, high blood sugar is corrected with additional bolus insulin in accordance with the personal insulin sensitivity factor (ISF).
During the first week, the blood sugar target range may be slightly higher than normal. The diabetes nurse is in more frequent contact during the first week(s) to ensure that the pump therapy starts smoothly.