The implantable insulin pump

The implantable insulin pump is a complete pump, placed entirely inside the body. It has the shape of a (titanium) disc, about 8 cm in diameter and about 2 cm thick [1]. Inside it are the insulin reservoir, the pumping mechanism, the electronic components and the battery.

Unlike an ordinary pump, it has no part on the outside. You have no infusion set, tubing or cannula on the skin, so you no longer have to worry about changing them regularly, either. You give the commands from a remote control, which communicates wirelessly with the pump. From the same remote you set the basal rates (the insulin delivered continuously, in the background) and the boluses (the larger doses given at meals or to correct a high blood glucose) [2].

The pump is placed in the abdominal wall, in a pocket created by a surgeon. The usual site is the lower part of the abdomen, more often on the left [1]. The pump sits between the fat tissue and the fascia of the muscles, and the surgeon fixes it there with a few sutures, so that it does not move.

Fixing it also has a practical role. The membrane through which the pump is refilled is on the side facing the skin and has to remain accessible to a needle at all times (introduced from the outside when needed) [1]. A thin catheter comes out of the pump, passes through the abdominal wall towards the inside, and its end stays free, in the abdominal cavity [3].

Yes, fitting it requires an operation. The procedure is usually done under general anaesthesia, in a specialized center with experience in this technique [1]. You will have to stay in hospital for a few days, and then comes a period of wound healing, during which you are not allowed to lift heavy weights [1].

The operation to fit the pump is not the only one you have to go through. Removing the pump, replacing it at the end of its lifespan and solving some catheter problems also require surgery [4]. This is an important aspect in the decision to choose an implantable pump.

The insulin reaches the body through the catheter that opens into the peritoneal cavity, the space in the abdomen where the internal organs lie [1]. From there, the insulin is absorbed mainly into the portal vein and passes first through the liver [5]. This is the same route taken by the insulin produced by a healthy pancreas.

This route significantly changes the way insulin acts. A significantly larger share of the insulin given will be available to the liver, and relatively less insulin will reach the general circulation [5]. In addition, the effect starts sooner and wears off sooner than with insulin given subcutaneously [6].

The pump is refilled with insulin through the skin, with a needle, by the doctor at the center where the pump was fitted [1]. The doctor or the nurse disinfects the skin, finds the membrane in the middle of the pump by palpation and passes the needle through the skin, into the reservoir. You do not need anaesthesia, and the sensation is similar to that of a blood draw.

Before filling, the insulin left in the reservoir is withdrawn and measured. The amount of insulin withdrawn can be used to check whether the pump has delivered exactly as much insulin as had been programmed [7]. Fresh insulin is then introduced, and the whole procedure takes around 30 minutes. Refilling is not done at home and you cannot do it yourself [1].

Refilling is usually done once every 6-12 weeks, that is, about every 2-3 months [8]. In general, around four visits a year are arranged. The exact interval depends on your daily insulin dose and on the volume of the reservoir [1].

There is also a second reason for a more fixed schedule. The insulin in the reservoir sits at body temperature, and its stability over time is limited [1]. The reservoir is emptied and refilled at a set date, whether or not insulin has been left in it. At these visits the maintenance procedures are also carried out, such as rinsing the pump and the catheter [7].

The implantable pump has no part directly visible on the outside. You have no tubing, patch or infusion set on the skin, because the pump is entirely inside the body [2].

The presence of the pump is nevertheless very noticeable through the skin, as a round, fairly large bulge on the abdomen [1]. The pump is easy to feel on touch and the swelling of the skin shows more if you are thin. In addition, the operation itself leaves a scar. Clothes generally cover the area where the pump is placed. In the shower, when swimming or in contact with water you do not have to do anything special, because intact skin keeps water out.

The implantable pump uses a special human insulin, with a concentration of 400 units per milliliter [8]. It is four times more concentrated than the ordinary insulin in external pumps. The high concentration allows a small reservoir to cover several months of treatment [1].

None of the ordinary insulins you are already familiar with is used. The formula of this insulin is special, designed for difficult conditions of use. The insulin in the implantable pump stays for whole weeks at the core temperature of the body, of about 37 degrees Celsius. It has to withstand this without aggregating [1].

Insulin aggregates can block the catheter or can reduce the amount delivered, because they narrow the outlet path [3] [7]. For this reason, the ordinary insulins designed for classic pumps cannot be used in this device [1]. A blocked catheter first shows up as a high blood glucose with no explanation, which you report the same day to the center that fitted your pump. If vomiting, difficulty breathing or drowsiness appear, go to the emergency room straight away.

No, implantable pumps are not widely available. At present, fewer than 500 patients worldwide use them, followed up in specialized centers in a few European countries [5]. Production of the only model that made it to the market stopped at the end of 2020, because of the shortage of components.

Since then, no implantable pumps have been fitted in new patients. The remaining devices are kept for the replacements needed in patients who already have a pump implanted, and the special insulin continues to be produced for them. New implantable systems are being developed, still at the stage of clinical research, but none of them is available on the market at this time, for the general public [9].

The implantable pump is aimed at a narrow group of adults with type 1 diabetes [10]. These are patients who do not reach acceptable control with insulin given subcutaneously, even though they correctly use an automated system and have good quality therapeutic education [11].

The typical situations are:

• large and hard to explain swings in blood glucose [10];
• repeated severe hypoglycemia, with loss of the warning signs [12];
• poor or irregular absorption of insulin from the subcutaneous tissue [10];
• severe skin diseases that interfere with the absorption of insulin from the subcutaneous space [10].

If you are thinking about this treatment option, you have to be willing to accept the operation to fit it, the one to remove the pump and any repeat operations if needed [4]. You will also have to attend the scheduled visits, only at the center where the pump was fitted (you cannot go elsewhere). The decision is made together with a specialized medical team, whose opinion carries more weight than usual [10]. The implantable pump is not a suitable option at this time for children.

The lifespan of the pump is given by the battery. The battery is sealed inside the device, it is not recharged and it is not changed separately. When it runs down, the whole pump is replaced, through a new operation [1].

In practice, half of the patients have the pump replaced within the first 4-5 years, whatever the reason [4]. The battery alone is designed to last 7-10 years, and the newer models have had fewer failures than the old ones [1] [2].

When the pump is changed, the catheter in the peritoneal cavity can often stay in place and is reconnected to the new pump. Early replacement can happen if a technical fault appears, with an infection of the subcutaneous pocket or with blockage of the catheter [4]. An infection of the pocket shows on the outside as redness, swelling or pain over the pump, sometimes with a fever, while a pump fault shows up first as a high blood glucose with no explanation. Tell the center that fitted your pump the same day, because the insulin may no longer be reaching your body. If vomiting, difficulty breathing or drowsiness appear, go to the emergency room straight away.