Insulin pumps for diabetes: how they work

The insulin pump is an electrically powered medical device, about the size of a doctor's stamp (some slightly larger), that delivers insulin almost continuously through a thin catheter and a cannula placed subcutaneously [1]. It works on the principle of partially replacing the human endocrine pancreas (only the insulin part, and in the future perhaps also glucagon), by delivering a programmable basal rate (basal insulin) at rates of 0.025-2 units/hour (for metabolic needs between meals), plus occasional boluses for meal coverage and hyperglycemia correction. The pump's motor pushes a piston, which in turn pushes the insulin from the reservoir through the infusion tube.

Unlike multiple injections, where you use two types of insulin (rapid-acting and long-acting), the pump uses only rapid-acting analog insulin, which through semi-continuous delivery (every five minutes) also replaces basal insulin [1]. The pump's software can automatically calculate doses based on certain previously programmed parameters (insulin-to-carbohydrate ratios, sensitivity factors, active insulin). The system records all deliveries and allows the data to be downloaded for a detailed analysis of glycemic patterns.

The main advantage is treatment flexibility [2]. You can have different basal rates for each hour of the day (useful for the dawn phenomenon or night shifts), you can temporarily stop insulin delivery, or you can increase the basal rate (in the case of an acute illness). Dosing precision is superior to external insulin injections, with an increment of 0.025-0.1 units compared with 0.5-1 unit for pens. This is essential for young children or people who are very sensitive to insulin. The integrated bolus calculator automatically accounts for active insulin, preventing dose stacking.

Quality of life improves significantly through the elimination of 4-8 daily injections (only one insertion every 3 days), the freedom to eat spontaneously, without preparation, and the discretion of administering a bolus. Studies conducted with modern pumps show a reduction in HbA1c, in severe hypoglycemia, and in glycemic variability [2]. The disadvantages include the higher cost, the dependence on technology, the constant visibility of the device, and the need for specific technical education.

Of course you can. The pump offers major advantages for sport through the ability to reduce the basal rate by 20-80% starting 40-90 minutes before exercise, thereby preventing hypoglycemia, even without consuming additional carbohydrates [3]. For contact sports (soccer, martial arts) or water sports, you can temporarily disconnect the pump for an hour [4]. Sometimes the idea of first giving a compensation bolus of 50% of the basal that will be missing and then watching the effect works well. Many pumps have specific exercise modes that automatically adjust glycemic targets and insulin sensitivity.

For physical protection, there are special elastic belts, neoprene pockets, or waterproof cases that securely fix the pump to the arm, thigh, or waist. Endurance athletes prefer patch-type pumps, without external tubing, for maximum freedom of movement. It is important to check your blood glucose before exercise, to have fast-acting carbohydrates on hand, and to monitor yourself carefully for at least 12 hours after physical effort, because insulin sensitivity is increased during this period [5].

Most users place the pump loose in bed next to them, under the pillow, or in the pajama pocket. The 30-110 cm tube provides enough freedom of movement for the usual nocturnal turning [1]. You can use a soft fixation belt around the waist or arm, a special pocket sewn into the pajamas, or even fix it with a sheet clip to prevent the tube from tangling. Modern pumps have a keypad lock function to avoid accidental presses during sleep.

For couples, the partner quickly gets used to the pump's presence, and temporarily disconnecting it for intimacy is simple and quick. Young children can wear the pump in a special vest or small backpack to prevent them from playing with the buttons. It is important to check in the morning that the tube has not twisted or bent, which could sometimes (very rarely) lead to catheter occlusion.

All companies offer replacement within 24-48 hours for malfunctions under warranty, and in the meantime you must immediately return to the multiple injection regimen, using backup pens, which you must always have available. You calculate the long-acting insulin dose as the sum of the basal rates over 24 hours, and you give the boluses with the rapid-acting insulin also used in the pump, using the same ratios and sensitivity factors. Without insulin delivered in the form of basal rates released by the pump, the risk of ketoacidosis rises rapidly, sometimes in just 2-4 hours [6].

Most malfunctions are in fact simple, solvable problems. Check that you do not have a dead battery, air bubbles in the reservoir, a bent cannula, or an occluded infusion set [7]. These are not real pump defects. Always keep an emergency kit with rapid-acting and long-acting insulin pens, urine test strips for ketone bodies, and contact numbers for 24/7 technical support. Learn to recognize the pump's alarms and to resolve them quickly. Most problems reported as “malfunctions” are resolved by changing the infusion set or restarting the pump.

The infusion set (reservoir, tube, and cannula) is generally changed every three days, following the manufacturer's recommendations and individual tolerance [7]. Changing it more frequently than three days prevents local infections, lipodystrophy, and decreased insulin absorption caused by local tissue inflammation, but adds significant additional costs [8]. The main signs that the infusion set needs to be changed include unexplained high blood glucose, redness or pain at the insertion site, or insulin leakage.

The optimal time to change it is in the morning, so that you have time to monitor that the new set is working properly. Changing the set before bedtime or before a large meal is not recommended. Systematic site rotation (a minimum of 2.5 cm distance from the previous site) is essential [9]. Use a mental or even drawn diagram to track the areas you have used. The monthly cost of sets represents a significant percentage of the total cost of insulin pump therapy, being partially or fully reimbursed for certain categories of patients.

Standard pumps only deliver the doses that you program yourself. The preset basal rate and the calculated boluses that you manually approve before administration cannot be decided automatically by a standard pump [1]. Hybrid closed-loop systems can automatically adjust the basal rate every five minutes, based on data from the glucose sensor, but they still require manual input for meal boluses [10]. The predictive algorithm anticipates the evolution of blood glucose 30 minutes ahead, or sometimes even more, and increases, decreases, or stops the basal rate preventively. Sometimes it also gives correction boluses automatically.

Even the most advanced current systems are not completely autonomous. They still require the manual setting of meal boluses (a hybrid system) [10]. Safety limitations prevent the delivery of dangerous doses. There are maximum basal rate and bolus limits that you set yourself. The near future promises fully automated systems (full closed loop), which will no longer require the manual entry of a meal bolus. For now, the pump remains an instrument that requires active and informed use.

You can temporarily disconnect the pump (one hour) for various everyday activities, such as showering, swimming, intimacy, or other medical investigations incompatible with wearing it [4]. For disconnections under one hour, no compensation insulin is needed. If you want to stay longer without the pump, you can try a bolus before disconnection equivalent to half of the basal that will be missing afterwards. Pump disconnections longer than two hours are not recommended because of the risk of significant hyperglycemia [6].

For longer "pump vacations" (days to weeks), you can temporarily return to pens, with careful dose recalculation and careful subsequent adjustments [2]. Many people do this in summer at the seaside or on adventurous holidays, where technology is sometimes (rarely) an impediment. Returning to the pump requires fine readjustment of the initial settings, because insulin sensitivity may change in the meantime. It is important to always have a backup plan and to prevent forced breaks due to a lack of supplies or financial problems.

The closed-loop system (artificial pancreas) combines the insulin pump with the glucose sensor and a control algorithm that automatically adjusts insulin delivery based on the current estimate of blood glucose and the predictions for the next 30-60 minutes [10]. Current commercial systems are "hybrid," in the sense that they automatically adjust the basal rate. Some systems can also give automatic micro-correction boluses. The user, however, must manually announce meals and give the prandial boluses [11]. The algorithm learns from your patterns and becomes more efficient after a few days of continuous use.

Studies show that closed-loop systems increase time in target (70-180 mg/dl) from 60% to 70-76%, reduce time in hypoglycemia by 35-50%, and massively improve glycemic control overnight [11]. Current limitations include the insulin's effect being too slow because of subcutaneous administration (it cannot perfectly prevent post-prandial peaks), the need for technical maintenance, and the high cost. The future brings bi-hormonal systems (insulin + glucagon), ultra-rapid insulins, and AI algorithms that will bring performance even closer to that of the natural pancreas [10].