Insulin pumps without tubing, the patch type

A pump without external tubing, of the patch type, is a small device that you wear stuck directly onto the skin and that delivers your insulin subcutaneously [1]. A pump without external tubing holds the insulin reservoir, the pump mechanism and a short cannula (it goes under the skin) all in one place, in a single compact housing [2]. Because there is no external tubing, the insulin travels a very short path, from the pump straight into the subcutaneous tissue.

All the components sit on the skin, so you do not carry a separate device in a pocket or clipped to your clothes. You operate the pump only from a distance, with a small handheld controller or with a phone app [3]. It is the main alternative to the pump with tubing and it is often called a "pod", as the figure below shows [4].

The patch pump has a sticky adhesive layer on its underside, like a strong medical plaster. You will need to clean and dry the skin well, then peel off the protective film. Press the patch pump onto the skin, so that it grips as tightly as possible [5]. Most patch pumps then insert the cannula automatically, as part of the activation process [2]. At the press of a button, a fine needle places the cannula (a small soft tube) under the skin and then withdraws, leaving only the cannula in place.

The adhesive is designed to hold for the whole wear period, being resistant to sweat and water. If your skin is very oily or you sweat a lot, skin preparation wipes or an extra fixing tape can help you fix the pump better [5]. Every time a patch pump comes to an end it will be replaced with a new one, which must always be applied onto a clean area of skin [6].

You control a pump without tubing wirelessly, from a separate device, such as a small handheld controller or an app on your phone [2]. From there you set the basal insulin, give the meal and correction doses and check what the patch pump is doing [3]. The pump and the controller communicate through a wireless link (of the Bluetooth LE type), over a short distance. The communication is secured, so that another person or device cannot interfere in an unauthorized way [7].

In practice, the controls are on a screen you already know how to use, not on the pump itself. You need to keep the controller or the phone at a short distance from the pump (in your hand, for example), so that they stay connected. If the controller runs out of battery or is too far away, the patch pump carries on delivering the basal insulin exactly as it was programmed [2]. This situation is very unlikely, because the range is a few meters, and a controller held in your hand is far closer to the pump than that [7]. It becomes relevant only for a parent who controls a child's pump from a distance.

A patch pump can be placed where the subcutaneous tissue has a layer of fat suitable for the pump cannula. The site also has to let the pump sit comfortably and safely. The usual areas are:

• the abdomen;
• the back or outer part of the arm;
• the thighs;
• the lower back;
• the upper part of the buttocks [8].

As practical rules, when you choose the site:

• stay clear of the waistband, the belt and harder seams, which rub the area;
• avoid scars and the navel;
• avoid the places you lean on or lie on from time to time [5].

Every time you change the pump you also have to change where you place it. In this way the skin under the adhesive and the cannula site have time to recover [9].

A patch pump can usually store up to about 200 units of insulin [2] [3]. This amount is generally smaller than what the reservoir of a pump with tubing holds, because all the components have to fit into a single small housing, worn on the skin [1].

The smaller reservoir of the pump without external tubing is nevertheless enough for most patients over the wear period of the pump. If, however, you use a lot of insulin every day, you may be limited in how long you can use a patch pump [1].

You usually wear a pump without tubing for three days. You then have an extra window of up to eight hours in which to replace it with a new one [2]. This interval matches the one at which the cannula site would have had to be changed anyway on a pump with tubing [4] [10].

The patch pump warns you when it is approaching the end of its wear period. It then stops when it reaches the wear limit (including the grace period) or when it runs out of insulin [2]. As long as you plan the pump change at a suitable moment, not very close to bedtime or to a long journey, things stay simple and safe [5].

Yes, the part you wear on the skin is single-use. When the wear period ends, you have to take the pump off and throw it away, then apply a new one [2]. The controller or the phone with which you program the pump are reused and stay with you.

Some patch pump models divide things differently, with a reusable pump part and a single-use base which contains the adhesive and a plastic frame that holds the reusable pump [3]. The piece that touches the skin is always replaced regularly, generally every three days [11].

Yes, although a patch pump has no external tubing, it does have a very short cannula (a soft tube). The cannula goes straight from the pump into the skin, hidden under the adhesive [2]. From the outside you see only the patch pump, sitting on your body.

This is the main difference compared with a pump with tubing, where visible tubing connects the device in your pocket to the place where the cannula is inserted [1]. On a patch pump, the pump and the insertion site are at the same point. There is no tubing to hang down, to catch on things or to hide.

If the patch pump comes off the skin, the cannula comes out with it. At that moment the transfer of insulin from the pump into the subcutaneous space stops [12]. A patch pump that has come off usually cannot be stuck back safely, so you will have to replace it with a new one, placed somewhere else [6]. If the pump has come off, part of the insulin delivered in the last few hours may have leaked onto the skin from a partly dislodged cannula instead of reaching the subcutaneous space.

Check your blood glucose carefully in the period after the pump comes off, because the values can sometimes rise very quickly and ketone bodies may appear [13]. Measure ketones in the blood whenever your glucose rises after such an episode. 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. To prevent the patch pump coming off accidentally, press the edges down well after applying it. Add a fixing tape if you notice a corner of the adhesive starting to lift [5].

The main advantage is the absence of tubing. Nothing hangs down, nothing catches on door handles or on clothes, and the device is more discreet under clothing [1]. Everything is in a single small housing, worn on the skin, water-resistant, which suits an active life with a lot of sport very well. In addition, it is easier to sleep with a pump without external tubing [14].

Applying it onto the skin is simple. First you stick the pump onto the skin, and the cannula often goes in at the press of a button on a controller [2]. In the end you find that you can control everything from a screen you use very easily. A patch pump is easier to wear and easier to hide. It has no separate device to clip onto your clothes and no tubing to arrange out of sight [15].

Whatever the type of pump, the best results appear when the pump works together with the glucose sensor, in an automated system [16].

The main disadvantages come from the all-in-one construction. Unlike a pump with external tubing, which you can disconnect at the cannula, a patch pump cannot be taken off temporarily and stays on the skin until it is replaced. The reservoir is smaller, so it may not be suitable for very large daily insulin needs [1] [3]. In addition, you replace the whole pump each time, not just a small part, which can mean more waste and a higher cost in the long term [11]. The pump forms a small bump on the skin, noticeably thicker than the cannula of a pump with external tubing. This bump can be knocked against or caught on a door if you are not careful.

The adhesive stays in the same place for the whole wear period, so it can irritate the skin or come off in the swimming pool [6] [17]. If the adhesive or the pod itself fails, you lose the whole unit, not just one component of the infusion set as in the version with external tubing [1]. In addition, you always have to keep the controller or the phone at hand so that you can give the mealtime or correction insulin doses [15].