📘 Understanding insulin pump technology

An insulin pump is a small medical device that delivers rapid insulin through continuous subcutaneous infusion [1]. The device contains an insulin reservoir, a programmable microprocessor and a pumping mechanism, which ensures precise insulin administration through an infusion set inserted into the subcutaneous tissue.

The pump operates by administering insulin as a basal rate, which provides a small and constant amount of insulin throughout the day, and boluses, which are additional doses administered at meals or for correction [1]. According to guidelines, this method represents the gold standard of treatment for patients with type 1 diabetes.

The pump delivers insulin through repeated microboluses at intervals of several minutes (most frequently five minutes), created by either a stepper motor or a piezoelectric system [2]. Each microbolus represents a very small amount of insulin, even in the order of hundredths of a unit. The summation of these microboluses achieves the programmed basal rate per hour.

The infusion mechanism uses a piston, which pushes insulin from the reservoir through the connection tube to the cannula inserted subcutaneously [2]. This continuous delivery eliminates the need for multiple daily injections and allows fine adjustments of doses.

A healthy pancreas secretes insulin in two ways. There is a basal, continuous secretion (with small pulsations), which maintains blood glucose between meals and at night, and large pulsatile secretions in response to food intake [3]. The insulin pump reproduces this physiological pattern through programmable basal rates (with small pulsations every five minutes) and boluses at meals.

Unlike long-acting insulin injected subcutaneously, the pump allows hour-by-hour adjustment of basal rates [4]. This flexibility is essential for managing the dawn phenomenon. Glycemic variability associated with physical activity or stress is ameliorated through the ability to comfortably deliver small and repeated boluses. Studies show that this approach significantly reduces glycemic variability [5].

A complete pump system includes the device itself with processor, motor, piston, battery, insulin reservoir and the infusion set consisting of connection tube and cannula [1]. Added to these are the cannula insertion device and software solutions for programming.

Modern integrated systems also include the continuous glucose monitoring sensor, which communicates wirelessly with the pump [6]. Consumable components, such as reservoirs and infusion sets, require replacement, generally every three days (more recently also every seven days) [7]. Control devices can be built into the pump or external, in the form of a phone or dedicated remote control.

The pump uses a bolus calculator based on individualized parameters entered by the medical team [8]. These include the insulin-to-carbohydrate ratio, insulin sensitivity factor and glycemic target. When entering the current blood glucose and carbohydrates from the meal, the algorithm calculates the optimal dose.

The calculation also considers active residual insulin from previous boluses (insulin on board), thus preventing dose overlap and hypoglycemia [8]. The duration of insulin action is programmable in the pump (usually 2-8 hours), but pharmacokinetic studies indicate a real duration of 4-6 hours for rapid insulins [9]. Setting values too short (2-3 hours) can cause dose stacking and hypoglycemia. This automation reduces calculation errors and improves dosing precision compared to manual calculation.

The basal rate represents the amount of insulin administered continuously to maintain stable blood glucose in periods without food intake [10]. It is expressed in units per hour and can vary throughout the day according to physiological needs. Studies on pump users show that this covers approximately 30-50% of daily insulin requirements, with actual values often towards the lower limit (~30%) [10].

A bolus is a discrete dose of insulin administered to cover carbohydrates from meals or for hyperglycemia correction [11]. It is calculated individually, based on carbohydrate content and current blood glucose. Pumps allow different types of bolus, including with an extended release component, for adaptation to meal composition.

Conventional pumps require manual entry of all parameters for bolus calculation and cannot independently modify basal rates. Therapeutic decisions remain the responsibility of the user or parent. These function as administration instruments, not decision-making ones.

Hybrid closed-loop systems represent the exception [12]. These automatically adjust basal rates based on glycemic values received from the sensor, but still require manual entry of boluses for meals. These pumps can make small correction boluses [12]. No current commercial system offers complete automation of insulin administration, hence the term "hybrid" instead of "complete".

Communication between the pump and the continuous glucose monitoring sensor is achieved through wireless protocols, most frequently Bluetooth Low Energy [13]. The sensor transmits glycemic values at intervals of 1-5 minutes to the pump or to an intermediary device such as the phone (in DIY closed-loop systems).

Integrated systems display glycemic values and trends directly on the pump screen [6]. In the case of closed-loop systems, the algorithm uses this data for automatic adjustment of basal rates and sometimes for automatic delivery of small correction boluses. Integration requires specific compatibility between system components and is not universal between different device brands [6].

Most pumps use a stepper motor, which actuates a gear to move the insulin reservoir piston [2]. Each motor step corresponds to a precise amount of insulin, allowing increments of 0.025 to 0.05 units. The mechanism ensures dosing precision.

Patch pumps use alternatives such as shape memory systems or piezoelectric pumps. Infusion sets are made of soft Teflon [7]. Cannulas are Teflon or stainless steel, with lengths between 6 and 17 mm [14]. Insertion is performed at an angle of 90 or 30-45 degrees, depending on the set type.

The insulin pump alone does not constitute an artificial pancreas. The term artificial pancreas refers to closed-loop systems that integrate the pump, the CGM sensor and a control algorithm that automatically adjusts insulin administration [15]. The pump represents only the delivery component of this system.

Current systems are called hybrid because they partially automate insulin administration [12]. Boluses for meals still require human intervention. A true artificial pancreas, fully automated and bihormonal, which also administers glucagon, remains still in the research stage [16].