On an intensive therapy program it is important to keep the concept of Basal and Bolus insulin separate so that each can be adjusted independently to give optimal control.
The Basal insulin is the long acting insulin which is given to support the body’s needs every minute of the day to handle the energy requirement of just living, (breathing, heartbeat, digestion etc.) This needs a fairly constant amount of insulin although there may be peaks in insulin need such as occurs in the early morning, if these peaks are too high then we cannot supply needs with a long acting insulin and will have to consider a pump which will give a variable basal rate.
Basal insulin is provided by an extended action long acting insulin which is given once a day. Since basal insulin is usually about 50% of the body’s need, we determine the basal dose by taking the total daily dose and dividing by 2 to give the basal dose. The best basal insulins are the extended long acting insulin analogues, either Insulin Glargine (Lantus) or Insulin Detemir (Levemir), these can be used once a day and give fairly constant insulin levels over 24 hours. Alternatively in situations in which the extended long acting insulins are not covered by insurance we may have to use the intermediate acting insulin NPH, this insulin peaks in effect in 7-8 hours and does not last for 24 hours so to get a fairly constant insulin level we split the dose and give it twice a day.
Bolus insulin is given in response to carbohydrate intake according to your own carbohydrate to insulin ratio. (1 unit insulin/10-15gm carbohydrate). Adjustments according to glucose levels allow for rapid correction of hyperglycemia.
As a bolus insulin we need a short acting insulin; the action of which closely parallels the action of food. We use a short acting analog which starts to act within a few minutes, peaks in an hour or so and lasts for about 2 hours. Examples of these short acting analogues are Aspart (Novorapid), Lispro (Humalog)and Glulisine (Apidra).
If you have a normal glucose before a meal, take your calculated rapid acting insulin dose.
A 2-3 hour post meal check verifies the accuracy of your carbohydrate to insulin ratio match. If glucose is high, you did not take enough short acting insulin and if glucose is low, you took too much short acting insulin.
If you wish, you can do a further correction for hyperglycemia between meals in order to achieve a normal glucose before the next meal. You need to get the bolus doses right before you go further. It is important when something goes wrong, not only to correct the hyperglycemia but also to figure out the reason so it can be prevented in the future.
Basal Adjustment: Check glucose between meals, if it is normal, check before the next meal, if the glucose is rising you do not have enough basal (long term) insulin. If it is falling then you have too much basal insulin. When you think you have basal insulin pretty well adjusted then try a missed or delayed meal, the glucose value should remain fairly constant.
by Dr. J. R. Conway 20 Jul 2006