Using Bolus Calculators

Bolus calculators are increasingly becoming a standard feature of insulin pumps. This means that some of the difficult mathematical calculations when using a pump become much easier. For example, if you take 1 unit of insulin for 10g of carbohydrate, and you are eating 30g of carbohydrate, it isn't too difficult to work out that you need 3 units of insulin to match. But if you take 1.2 units for every 10g of carbohydrate, and you are having 43g of carbohydrate, suddenly it becomes much more difficult. Rounding figures up and down slightly can work, but it is still very easy to make a mistake.

To use a bolus calculator, you first need to ensure that the pump has the correct information about your doses in its memory. This would include what your ratio of insulin to carbohydrate is (as discussed above), what range of blood glucose you are aiming for (with a highest and lowest value), and what your insulin correction ratio is, ie by how much 1 unit of insulin will lower your blood glucose level.

Once those values are stored, you also need to programme additional information in for the pump to be able to make individual calculations. The pump needs to know what your current blood glucose level is, and what (if anything) you are about to eat. In some cases, the information about your blood glucose level will be transferred automatically, if your pump has a wireless connection to your blood glucose meter or your continuous glucose monitoring system, but for many, this information will still need to be added manually. Depending on the type of pump, there may be other parameters that you can programme in, such as relating to physical activity.

The pump will then take account of all the information you have provided, and will suggest an insulin dose for you. It will not deliver the insulin automatically, as there may be reasons why you would not choose to follow the recommendations, so you need to agree to the dose before it will be delivered.

Bolus wizards have made it much easier for many people to use pumps safely. But there are some important aspects to consider. For example, whether you want your blood glucose level as low as you have programmed into your pump - if you are about to undertake physical activity for example, you may want to aim for a higher level, so will need to calculate how much to reduce the suggested dose by. If you are unwell, your insulin requirements may be much higher than usual, so the dose of insulin the pump has suggested may be much lower than you need. If you are unsure whether you will be eating the amount of carbohydrate you have in front of you, again you may need to have a smaller dose than the pump suggests. And if your meal contains a high proportion of fat or protein, the dose may need to be split or given over a longer period - your pump may or may not provide you with the option of calculating this for you. So when using your bolus wizard, keep in mind the circumstances when you may still need to add some of your own calculations!