How a Sensor-Augmented Insulin Pump (SAP) Works

Sensor-augmented insulin pump

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A sensor-augmented insulin pump (SAP) combines the technology of an insulin pump with a continuous glucose monitoring sensor that transmits glucose readings to the person wearing the device. The SAP has made great strides in improving glucose control for people with diabetes. Unlike a closed-loop insulin delivery system, the device still requires some manual adjustment and input from the wearer.

Uses

Insulin pumps may be useful for in cases of both type 1 and type 2 diabetes. People with type 1 diabetes generally don't produce insulin and must take insulin via injection at regular intervals throughout the day. Using an insulin pump cuts down on the need for repeated injections and can make blood glucose management easier and less variable, with less risk of hypoglycemic or hyperglycemic reactions.

People with type 2 diabetes may also require an outside insulin source, especially if they've become insulin resistant or their bodies have stopped producing adequate insulin. If other methods such as medication, diet, and exercise haven't worked, insulin pump therapy may be necessary to help control glucose levels.

How It Works

Standard insulin pumps provide the user with a continuous flow of short-acting insulin that has been shown to improve glucose management in many people and overrides the need for long-acting insulin. The addition of the continuous glucose monitoring sensor in the SAP that works in tandem with the insulin pump has many benefits. This allows the user to have continuous, real-time glucose readings that enhance the ability to monitor blood glucose levels, especially when making decisions that involve food, exercise, and sick-day management, ultimately reducing the risk of hypoglycemic episodes.

The pump itself usually looks like a small smartphone and is about the size of a deck of cards. The pump is worn on your body and connects to a catheter that delivers insulin through a cannula that is inserted into a layer of fat under your skin, usually around your stomach, abdomen, hips or upper arm. The pump may clip onto your belt, bra, or be tucked into a pocket or an armband.

As each pump is slightly different, your healthcare team will teach you how to maintain and use your pump properly and effectively, including how to prime the pump, fill the pump reservoir, change tubing, choose your infusion site, calculate your basal/bolus dosages, etc.

Features

SAPs offer several features to help with improved glycemic control, such as safety reminders and alarms.

Bolus Calculator

In addition to the delivery of small amounts of short-acting insulin (your basal rate) throughout the course of the day, the SAP is also capable of delivering a larger amount of insulin before meals (called a bolus). Your personal basal rate should be customized and set within the pump by your doctor, but you would be responsible for determining your bolus rate before meals. Most pumps feature a built-in bolus calculator for this purpose.

You'll input the number of carbohydrates you intend to consume, and the pump calculates the corresponding units of insulin that should be used to cover those carbs.

Automated Insulin Suspension

This feature allows insulin delivery to be suspended automatically for up to two hours when the continuous glucose monitor detects that the glucose level has fallen and there is a risk of hypoglycemia.

A 2013 study in Australia of 95 patients with type 1 diabetes concluded that this reduced the rate of severe and moderate hypoglycemia episodes compared with standard insulin pump therapy.

Custom Reminders

Many SAPs offer settings so you can set personal reminders to check your glucose or set a bolus amount, in addition to safety alerts such as a missed bolus dose or an alarm if there's a blockage in the tubing or cannula.

Questions for Your Doctor

If you're interested in trying an SAP, make an appointment with your doctor and talk to her about whether this type of insulin therapy is right for you. Here are a few other questions to consider asking:

  • Will this device help me better manage my glucose levels?
  • What are the possible side effects of using this device?
  • What should I do if my diabetes medications cause my blood sugar to drop too low?
  • What should I do if I'm sick or if I exercise?
  • Should I take a bolus of insulin before or after meals and snacks?
  • If I travel, how can I continue to effectively manage my condition?

Side Effects

The major side effect that comes with using an insulin pump or any form of insulin is a risk of hypoglycemia. Accidentally using too much insulin will remove glucose too quickly from the bloodstream, reducing circulating glucose and may cause extreme fatigue, thirst, dehydration, urination, dizziness, headache, etc. Keep on the lookout for the symptoms of hypoglycemia and talk to your doctor about an action plan to treat it.

Contraindications

Ask your doctor if before using an SAP if you are pregnant or breastfeeding, have heart, liver, or kidney problems, or other medical condition.

Cost

On average, an insulin pump costs around $6,000 and annual supplies may range from an additional $3,000 to $6,000. Most insurance companies will cover insulin pump therapy though may vary on out-of-pocket expenses (such as for supplies). Talk to your physician and insurance company about which products are covered.

SAPs Versus Closed-Loop System

Sensor-augmented pumps are an advancement from standard insulin pumps but are not yet a perfect match for a healthy human pancreas, in that they are not autonomous. New research in this field is ongoing, and recent developments have brought about the closed-loop system—a smart device that automatically delivers insulin based on your glucose readings.

SAPs are a stepping stone toward a closed-loop insulin delivery system, which means that the pump acts as an artificial pancreas—it reads the glucose levels in the blood and dispenses the exact dose of insulin needed to maintain a stable glucose level. This requires a precise algorithm that coordinates the communication between the sensor and the pump. The closed-loop system still requires some manual oversight, but for the most part, it delivers adjusted insulin every five minutes based on readings from the built-in continuous glucose monitor and doesn't require self-input for bolus insulin.

Some may benefit from this less hands-on approach, whereas others may want more manual control. Ask your doctor whether the SAP or the closed-loop system is right for you and your lifestyle.

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