Understanding insulin pump technology

The pump holds a reservoir of rapid-acting insulin [1]. A thin flexible tube carries the insulin from the pump to a very fine cannula placed under your skin, in the subcutaneous fat, usually on your abdomen. The insulin doesn't go straight into your bloodstream; instead it's released into this layer beneath the skin, from where it's gradually absorbed into your circulation.

The cannula stays in place and is changed every few days to avoid irritation and infection [2]. This way you get your insulin without giving yourself several injections a day. The permanent connection to your body provides a continuous flow, close to the way a healthy pancreas would release insulin.

The basal rate is the small amount of insulin the pump delivers continuously, in the background, throughout the day and night [3]. It covers your body's baseline need, that is, the insulin required between meals and during sleep, when you're not eating. Its job is to keep your blood glucose steady during these periods.

The basal rate is expressed in units per hour. The pump doesn't release this amount all at once; instead it splits it into very small pulses, repeated every few minutes [4]. In this way it mimics the slow, steady release of insulin that your body produces naturally.

Yes. Your insulin need isn't the same all day long, because your body follows different rhythms. For example, in the early morning your body often becomes more resistant to insulin, and your glucose tends to rise (the dawn phenomenon). The pump lets you set several basal rates, each active during a particular time period [5].

Together with your medical team you can build a personalized basal profile, with higher or lower values depending on the time of day. This flexibility is a significant advantage of the pump compared with basal insulin given by injection [5]. It gives you finer control that's closer to what your body actually needs, as the figure below shows.

A bolus is a larger amount of insulin that the pump delivers over a short time, on your request [6]. Unlike the basal rate, which flows continuously in the background, a bolus covers occasional needs. You use it mainly when you eat or when you want to correct a raised glucose value.

In practice, a bolus is the equivalent of the dose you would have given with an injection pen before a meal. The difference is that the pump calculates it and delivers it at a simple command, using the same rapid-acting insulin from the reservoir. This lets you quickly adapt the dose to what's happening at that moment.

Before a meal you enter into the pump the amount of carbohydrates you're about to eat and, often, your current glucose value. The pump uses your personal insulin-to-carbohydrate ratio, set together with your doctor, to calculate the right dose [7]. It then suggests a bolus, which you confirm with a few button presses.

For meals high in fat and protein, some pumps allow an extended bolus, in which the insulin is released gradually over a longer period [6]. This way the dose better matches the way the food raises your glucose. This feature helps you avoid both values that are too high and sudden drops after the meal.

A correction bolus is an extra dose of insulin that you use when your glucose is higher than your target. Its purpose is to bring the value back into the desired range. You can give it on its own or together with a meal bolus [8].

The pump calculates this dose based on your correction factor, which shows how much your glucose drops for one unit of insulin [8]. It also takes into account the active insulin still left in your body from previous boluses, so as not to give too much [7]. This reduces the risk of your glucose then dropping below the normal limit.

Yes, you can pause the pump for a short time, for example when you shower, when you get changed, or when your glucose drops too low. The pump keeps your settings and resumes delivery when you restart it. This pause gives you flexibility in everyday life. Restarting it, though, is up to you, because the pump doesn't start again by itself. After a shower or a change of clothes, it's easy to forget that it's still paused. If your pump has a reminder alarm, it's worth using it.

Even so, you need to be careful. The pump uses only rapid-acting insulin, and your body has no reserve of long-acting insulin. If delivery stays off for too long, your glucose can rise quickly and ketones can appear [9]. That's why the pause should not exceed one hour. If it does, measure your blood glucose, check for ketones, and give yourself the missing insulin according to the protocol agreed with your medical team. If vomiting, difficulty breathing or drowsiness appear, go to the emergency room straight away.

Inside the pump there's a small, very precise electric motor, of the stepper type [4]. It pushes the piston of the insulin reservoir forward in very small increments, not all at once. Each tiny movement of the motor releases an extremely small amount of insulin through the tube and cannula.

Thanks to this mechanism, the pump can release very small fractions of a unit, much smaller than what you can dose with an injection pen [4]. This precision is especially important for children and for people who are very sensitive to insulin. It gives you fine control, close to what your body actually needs.

Yes. One of the pump's main advantages is that it delivers your basal insulin automatically, without interruption, including while you sleep [10]. You don't have to wake up to give yourself an injection. Your body receives its baseline insulin steadily, all night long.

You can program a basal rate specially adapted for the night hours and for the morning, when glucose tends to rise. Automated systems, which combine the pump with a glucose sensor, can adjust delivery on their own during sleep [11]. This makes it more likely that you wake up in the morning with values close to target, after a more restful night's sleep.

Yes, and this is very useful. During physical activity your muscles use more glucose, and your insulin sensitivity increases. Without an adjustment, your glucose can drop too much, which leads to hypoglycemia. The pump lets you set a temporary, lower basal rate for the period of exercise [12]. Hypoglycemia means a blood glucose below 70 mg/dL (3.9 mmol/L): you take 15 g of fast-acting carbohydrate and recheck after 15 minutes.

The complete steps are on the pages about what hypoglycemia is and about how to treat it. For a good effect, the reduction usually needs to be made some time before you start the activity, because the insulin already delivered goes on acting for a while. Automated systems often have a special activity mode, which raises the glucose target and delivers insulin more cautiously [12]. This way you can protect your blood glucose during exercise, such as a game of tennis or a run.