Insulin pumps with external tubing

A pump with external tubing is a small electronic device, about the size of a compact phone, which you wear outside your body. Inside there is a reservoir of rapid-acting insulin, which is pushed continuously, in very small amounts, through a thin and flexible tube [1]. The tube ends in a soft cannula, placed subcutaneously, through which the insulin reaches under the skin [2].

The name "with external tubing" describes exactly what this system looks like. The body of the pump sits in a pocket or clipped to your clothes. From there the thin tube (made of Teflon) runs towards the body, ending in the device attached to the skin, called a cannula [1]. It is the oldest and best known type of pump. Some pumps also stick directly onto the skin, without having any external tubing, but those represent a different type of pump [3].

The tubing is essentially the path the insulin travels from the reservoir inside the body of the pump to the cannula placed subcutaneously [2]. When the motor of the pump pushes the insulin out of the reservoir, it advances through the tubing and finally reaches the subcutaneous tissue, through the cannula [4]. Without the tubing, the body of the pump could not stay in a pocket or clipped to your clothes, at a distance from the place where the cannula is inserted [1].

The tubing gives you the freedom to put the pump wherever it is comfortable for you, while the cannula stays, for example, on the abdomen or on the thigh [2]. At its end, the tubing has a connector that attaches to the cannula fixed on the skin. The pump, the tubing (the catheter) and the cannula thus work as a single assembly [5].

Yes, you can choose the length that suits you when you choose your infusion set [5]. The catheter (the tubing) is available in several lengths, usually between about 30 and 110 cm, and some manufacturers offer versions that are even shorter or longer [6].

A short tube sits more tidily and hangs less if you wear the pump close to the site of the cannula, for example at the waistband of your trousers. A long tube helps you if you keep the pump in a pocket while the cannula is placed further away. In practice, you match the length to the place where you like to wear the pump. Taller patients tend to prefer longer catheters [5].

The body of the pump has to sit close enough for the tubing to reach the cannula. Usually you wear the pump clipped to a belt or to the waistband of your trousers, or in a trouser or shirt pocket. Other patients tuck it into a bra or hold it with an arm or thigh band [1] [2].

Most pumps have a clip, and in addition there are cases, pouches and elastic bands designed for sport, sleep or clothing without pockets [1]. You have to secure the pump as well as you can, so that it does not fall easily and does not pull on the tubing [6]. It is good to choose a place that is comfortable for you, easy to reach when you need to use the buttons of the pump [2].

The reservoir of a tubed pump usually has a capacity ranging between 180 and 300 units of insulin [2]. Tubed pumps generally have larger reservoirs than patch pumps, which stick to the skin and as a rule stop at 200 units [7].

A larger reservoir means that the insulin in the pump lasts for longer. In practice the reservoir is not topped up part way through, but replaced with a new one, usually together with the infusion set. That is why it matters that the reservoir holds enough insulin for the three days of typical use of the infusion set [1]. How long a reservoir lasts therefore depends on your daily insulin need, because someone who uses more insulin per day empties the reservoir faster [2].

Yes. The tubing sits between the pump and the body, so from time to time it can catch on something. It snags on door handles, on drawer handles, on the seat belt or even on clothes when you move suddenly. A strong tug is unpleasant and can pull on the cannula, and accidental traction on the catheter is one of the problems commonly met in everyday life [6]. Complete detachment of the cannula is less common than simple traction on the catheter, but it cannot be ruled out.

There are a few ideas with which you can reduce the risk of the catheter catching on various objects. You can tuck the excess tubing under the waistband of your trousers or into a pocket. You can also route the tubing to run under your clothes as much as possible [2]. If a snag pulls on the set, look at the cannula before you go on using the set: the adhesive patch should be stuck down over its whole surface, with no lifted corners, and no insulin or blood should appear on the skin. If you have any doubt, put in a new set in a different place [8].

Yes, small air bubbles can appear in the tubing and they are common [9]. They usually form when the insulin warms up from the storage temperature in the fridge to body temperature. Cold insulin can contain dissolved air, which then comes out as small bubbles as the temperature rises [5]. Sometimes they also appear if the tubing was not completely filled with insulin from the start [9]. Every section of tubing filled with air is a section without insulin, so a large bubble can mean that you are not getting all the insulin you need [5].

In an online survey from Canada, answered by 115 adults with type 1 diabetes on pump therapy, 46% said they had had air bubbles in the tubing [10]. The practical habit is to fill the reservoir only with insulin that has already reached room temperature. Then fill the tubing until insulin comes out at the other end. Look carefully at the tubing for air bubbles, both at the start and afterwards, from time to time [9]. If you see a large bubble, first disconnect the infusion set from your body and only then remove the bubble by priming the tubing further [5].

Tubed pumps are very widespread. They represent the oldest type of pump, having been available for decades, and most of the insulin pumps used today are of the external tubing type [2]. Pump treatment, whatever the type of pump, is used more and more in people with type 1 diabetes. In pediatric diabetes registries from Europe, the United States and Australia, the proportion of children and adolescents treated with a pump rose from 42.9% in 2013 to 60.2% in 2022 [11]. More recently, the pump is also used by some patients with type 2 diabetes who need insulin treatment [12].

Tubeless pumps, stuck onto the skin, have become more and more popular, but the tubed model remains the most used and the best known by medical teams [3]. Current guidelines recommend pump treatment, especially in the form of automated systems, for all people with type 1 diabetes who can use it safely [13]. Having the longest history, it gives you a wide range of tubed pumps and infusion sets to choose from [2] [6].

The advantages brought by a pump with external tubing include:

• a larger insulin reservoir — it allows you a longer autonomy [2];
• a wide range of infusion sets, with different lengths [6];
• buttons or a screen on the device itself — so that you no longer need another device to control the pump [2].

In addition, you can detach the pump from the cannula, more precisely from the tubing, when you want to take it off for a limited time, as the figure below shows [1].

The tubed pump works with more automated systems, which have led to better metabolic control in everyday practice [14]. It is generally better known by medical teams, so medical support is easier to obtain. The reservoir, the catheter and the cannula are separate parts. If one of them has a problem, you can replace only what you know for certain no longer works properly, not the whole device [2]. Long-term costs are generally lower with a tubed pump than with a model of similar functionality but without external tubing. Cost and the way it is reimbursed remain the factors that most often decide which pump you get in practice [15].

The main disadvantage is the tubing itself, which is visible, can catch on things and needs a route of its own under your clothes [2] [6]. Added to this is the pump, which is generally larger. In addition, you carry a separate device, which has to be clipped on or kept in a pocket. Some people find it bulky or uncomfortable with certain outfits, when they play sport or during sleep [1] [3]. The tubing can become blocked, thereby interrupting insulin delivery, and the occlusion alarm does not always go off in time or even at all [2] [6] [16].

That is why, if your blood glucose stays high after the correction given by the pump, repeat the correction with an insulin pen, at the dose set in your treatment plan. Then change the infusion set together with the reservoir and check for ketone bodies in your blood (acidic substances produced when insulin is lacking). Between 1.5 and 2.9 mmol/L, contact your medical team immediately. At 3.0 mmol/L or above, or if vomiting, difficulty breathing or drowsiness appear, go to the emergency room straight away. Preparing the reservoir and filling the tubing require a few extra steps compared with an all-in-one patch pump [2]. For most patients these are small compromises in exchange for the large reservoir, the flexibility and the glycemic control brought by the automated systems built around tubed pumps. In reality, however, a great many choices are in fact guided by costs and access [15].