Bolus Calculator: A Review of Four "Smart" Insulin Pumps

The use of continuous subcutaneous insulin infusion (CSII) pumps has been gaining popularity since 1979, when the first research report on insulin pumps was published. Insulin pumps-small medical devices that are programmed to infuse insulin through a catheter placed under the skin-are a replacement for multiple daily injections of insulin. They are currently being used by 375,000 people with type 1 diabetes, many of whom prefer CSII to multiple daily injections because of the increased flexibility of diet and exercise, increased convenience and precision when dosing, and better predictability of blood glucose levels that insulin pumps can provide when used correctly. Recent pump manufacturers have engineered a new feature called a bolus calculator, which calculates bolus insulin doses based on input from the pump wearer, which functions to help patients obtain optimum control over blood glucose levels. The bolus calculator takes into account the patient's current blood glucose, target blood glucose, amount of carbohydrate consumed, and other factors such as insulin sensitivity and insulin-to-carbohydrate ratio as well as duration of insulin action ("insulin on board"). Each pump company calculates insulin doses in a slightly different way. This article will review differences in bolus calculator recommendations between four insulin pumps, as well as errors that may occur when using bolus calculators. It will also include an in silico simulation of a meal followed by a snack using multiple insulin decay curves.