The patch pump for basal insulin

The patch pump for basal insulin is a small device with no external tubing, stuck directly onto the skin [1]. Inside there is a reservoir of rapid-acting insulin, and underneath it there is a cannula, that is a thin, short tube that goes under the skin [1]. The insulin is delivered at a constant rate, for the whole time you wear it [2]. The role of this type of pump is to replace the daily basal insulin injection [3].

Once you have filled the pump with insulin, you apply it to the skin and wear it with practically nothing else to do. At the end of the wear period you remove it and apply a new one. This type of pump has no screen, no menus and needs no phone or remote control while it is working [3]. In essence it is a patch insulin pump with a fixed rate.

The main difference lies in the route the insulin takes towards its final destination, the blood vessel. When you give an injection of long-acting insulin, a large subcutaneous depot forms. From this depot the insulin passes slowly, gradually, into the blood, over 24 hours or even longer [4]. The patch pump for basal insulin does not form such a depot. Purely mechanical models release the insulin at a fixed, continuous rate [2]. Electronic models instead deliver small amounts of rapid-acting insulin at short intervals, so that the preset dose for 24 hours is reached [1].

The aim is to have a background level of insulin, present between meals and during the night. In practice you feel the difference in the number of punctures, because a single insertion, that is a single application of the device, covers up to three days [1]. You also feel the difference in how steady the effect is. A constant rate is more predictable than a large depot, which is sometimes absorbed differently from one day to the next [5].

Long-acting insulin was created to be given as an injection. Its long duration of action comes from the way it is released from the initial depot formed under the skin [4]. A device that delivers insulin continuously under the skin does not need this artificial prolongation of the time of action [5]. The constant availability of insulin for the body comes from the mechanism of the pump, not from a special chemical formula of the insulin [6].

Rapid-acting insulin enters and is used up quickly by the body. The small amounts delivered continuously by the pump ensure a steady rate of insulin from the subcutaneous space into the body [5]. For this reason, long-acting insulin is never put into an insulin pump [7].

The rate is chosen by the medical team, starting from your daily basal insulin dose [1]. The devices are not programmed; they come ready prepared, in a few fixed dose steps [3]. The steps run from about 20 to about 50 units a day, depending on the model, which means a rate of about 1-2 units per hour [1] [2]. The rate then stays constant, from the first to the last minute you wear it. You have no basal rates programmed by the hour and you cannot change the rate once it has started [3]. The risk of hypoglycemia, that is a fall in blood glucose below 70 mg/dL (3.9 mmol/L), rises when you move more than usual or when you skip a meal, precisely because the pump does not change its rate.

On such days you measure your blood glucose more often and keep 15 g of fast-acting carbohydrate within reach. For days with more physical effort, with illness or when you are fasting, you have to discuss it with the medical team in advance, so that you have alternatives ready [7]. When your basal insulin need changes significantly, you will have to use a pump set at the factory for a different dose over 24 hours [3]. There is no way to modify the pump you have so that it delivers more or less insulin.

The duration depends on the model. Some models are changed daily, at 24 hours [2]. Others are worn for up to 72 hours, that is three days [1]. The purely mechanical mechanism is generally used in the one-day models, and the electronic one in the three-day models [3].

The one-day models are removed completely at the end of the wear period [2]. In the three-day models the reservoir is thrown away and the electronic part is reused for up to a year [1]. The reservoir covers the basal dose for 24 hours, plus up to 36 units given on demand [2].

The basal insulin pump has to be taken off before an investigation such as magnetic resonance imaging, because the device contains metal parts [8]. You also take it off before a CT scan, if the scan covers the area where you wear it. With an ordinary X-ray the risk is considered very small, but some instructions for use require removal for any X-ray investigation [8]. It is best to seek advice in advance from your medical team and from the imaging department.

It depends on the model. Some devices give only basal insulin, and the mealtime doses remain, if you need them, in the form of injections [3]. Other devices add on-demand doses to the basal rate. These devices release two units with each press of the two buttons, up to a maximum of 36 units a day [2] [9]. Each extra press means two more units of insulin, and so a higher risk of hypoglycemia.

You make the choice between the two options together with the medical team, according to your needs. If you use only basal insulin, the simple model, without boluses, is enough. If you also need insulin at meals, the model with buttons can cover both needs with a single device [2]. There is also a third type of patch device, which gives only mealtime doses, with no basal rate at all [10]. That one is generally used together with a daily injection of basal insulin [10].

The suitable places for such a pump are the classic ones for the patch format [11]:

• the abdomen;
• the front or the side of the thigh;
• the back of the arm;
• the lower back or the buttock.

Skin closer than five centimeters to the navel should be avoided [11]. Avoid moles, scars, tattoos and skin that is irritated for any reason as well [12].

Choose an area that is as flat as possible and that does not stretch much when you move [13]. Change the place each time you fit a new device, so that the skin has time to recover [12]. Most devices are water-resistant, tested to specific waterproofing standards, so showering, bathing and ordinary swimming are not a problem, within the depth and time limits given in the instructions for your model [8]. The strong heat of a jacuzzi or a sauna is, however, to be avoided, because it speeds up insulin absorption [8]. After prolonged contact with water, check the edges of the adhesive and dry the surrounding skin well [13].

In this case the basal insulin stops on the spot and you no longer have any reserve under the skin for insulin to come from [14]. Rapid-acting insulin is used up quickly by the body, so blood glucose values can rise very fast [15]. When it is used in type 2 diabetes, the risk of producing ketone bodies is much smaller than in type 1 diabetes. The explanation is that in this type of diabetes some insulin secretion of your own is usually preserved, but the amount varies a great deal from one person to another [16]. The risk of ketone bodies does not disappear completely, though, so you measure your blood glucose more often until you apply a new device. If vomiting, difficulty breathing or drowsiness appear, go to the emergency room straight away.

You still need a backup plan for such situations, agreed in advance with your medical team [7]. Keep an injection pen within reach, so that you can cover at any time the interval until a new pump is applied. Check the pump with your hand a few times a day: whether the edges of the adhesive have lifted, whether the skin around it is damp or smells of insulin, and whether the device is still firmly stuck. Follow the course of your blood glucose very carefully whenever something looks out of order [14].

Yes, just as often as before. The basal pump does not measure anything, does not connect to a sensor and does not change its insulin rate by itself [3]. It works in the same way whatever your blood glucose values are [3]. 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.

Assessing your blood glucose remains the only way you can establish whether the dose step delivered by the pump really suits you [7]. The overnight and morning blood glucose values are the most valuable for judging whether the basal insulin is sufficient during the night [17]. The daytime values round out the picture, but they are influenced by meals and by physical activity, so they are harder to interpret on their own. The glucose profile should be discussed with your medical team at check-ups, and that is when the decision may be taken to change the dose step [1].

The pump for delivering basal insulin, with or without boluses, is generally intended for adults with type 2 diabetes [18]. It is meant for those who already use basal insulin or who need to start insulin treatment [19]. It suits you especially if you want fewer punctures or if you find it hard to inject yourself in front of other people [20]. Another sound reason is that you sometimes forget to give your daily basal insulin injection [21].

To use this type of pump you need a few things:

• to see well, with glasses if needed;
• to be able to fill the reservoir with the syringe supplied in the pump kit;
• to measure your blood glucose repeatedly every day or to use a glucose sensor [7].

Choosing a pump for delivering basal insulin is a trade-off: you gain simplicity, but you lose fine adjustment of the doses [22]. The device does not adapt to your blood glucose values, does not calculate the doses and does not record the data [3]. For this reason it is not a treatment method suited to type 1 diabetes, where fine adjustment of the doses is essential [7]. For better control in type 1 diabetes there are automated insulin delivery systems [23]. Choosing the type of pump is a decision you and your medical team take together, according to your situation and your preferences [18].