Continuous Subcutaneous Insulin Infusion: Pump Settings and Safety

Using an insulin pump isn’t like plugging in a phone charger and forgetting about it. If you’re on continuous subcutaneous insulin infusion (CSII), you’re managing a small, programmable device that’s delivering insulin into your body 24 hours a day. One wrong setting, one clogged tube, one missed bolus - and things can go south fast. This isn’t science fiction. It’s real life for over 30% of people with type 1 diabetes in the U.S., and growing numbers of those with unstable type 2 diabetes too.

How Insulin Pumps Actually Work

Insulin pumps don’t use long-acting insulin. They only use rapid-acting analogs like Humalog or Novolog. That’s key. These insulins start working in 10-15 minutes, peak around 1 hour, and wear off in 3-4 hours. The pump mimics how a healthy pancreas works by giving you a steady trickle of insulin all day (basal rate) and extra bursts when you eat (bolus).

Think of it like a drip feed system. Your body needs different amounts of insulin at different times. You might need more insulin overnight because of the dawn phenomenon - that natural rise in blood sugar before you wake up. Or less during exercise. The pump lets you program these changes hour by hour. Most modern pumps let you store multiple basal profiles: one for weekdays, one for weekends, one for illness, one for workouts.

Setting the Basal Rate: The Foundation

Your basal rate is the most important setting. Get this wrong, and your blood sugar will drift up or down all day - even when you haven’t eaten. Most people start with 40-50% of their total daily insulin dose spread across 24 hours. But that’s just a guess. The real test? A 24-hour fast.

Here’s how to check it: skip a meal. Don’t bolus. Don’t exercise. Test your blood sugar every 2-3 hours. If your numbers stay steady, your basal is right. If it climbs, you need more insulin. If it drops, you need less. Dr. John Walsh, author of Pumping Insulin, says improper basal testing is the #1 reason pump users end up in the hospital. Most people skip this step or do it too quickly. Do it right. Do it slowly. Do it when you’re healthy.

Bolus Settings: Mealtime Math

When you eat, you need to cover the carbs. That’s where your insulin-to-carbohydrate ratio (ICR) comes in. If your ICR is 1:10, that means 1 unit of insulin covers 10 grams of carbs. But that’s not the whole story. You also need your insulin sensitivity factor (ISF) - how much 1 unit of insulin lowers your blood sugar. If your ISF is 1:3, then 1 unit drops your glucose by 3 mmol/L.

Here’s where it gets tricky. Not all meals are the same. A pizza or a curry with coconut milk digests slowly. A regular sandwich? Fast. That’s why pumps have extended and dual-wave boluses. An extended bolus spreads the insulin over 2-4 hours. A dual-wave gives half right away, half later. If you’re eating high-fat meals and only using a normal bolus, you’ll spike after eating and crash hours later. That’s not a pump failure. That’s a missed setting.

Infusion Sets and Site Care

Your cannula sits under your skin - usually in the abdomen, thigh, or upper arm. Change it every 2-3 days. No exceptions. If you leave it in longer, you risk infection, poor absorption, or lipohypertrophy - those lumpy scar tissue areas that absorb insulin poorly. A 2022 study found 27% of new pump users developed lipohypertrophy because they rotated sites poorly.

Rotate your sites like clockwork. Don’t reuse the same spot. Don’t stick it in the same spot every time you eat. Keep a simple log: Monday - left abdomen, Tuesday - right hip, Wednesday - left upper arm. That’s it. It sounds basic, but it’s the difference between stable glucose and wild swings.

Safety: What No One Tells You

Here’s the scary part: if your tubing gets kinked, your infusion set falls out, or your pump runs out of insulin, it keeps going - but now you’re not getting any insulin. Diabetic ketoacidosis (DKA) can happen in 2-4 hours. That’s faster than most people realize.

That’s why you need to check your pump every time you test your blood sugar. Look at the tubing. Make sure the reservoir is full. Check for alarms. If your blood sugar is high and you haven’t bolused recently, suspect a blockage. Remove the set. Inject insulin by pen. Call your clinic. Don’t wait. Don’t assume it’s just a bad day.

And if you’re sick? Your insulin needs go up. Your basal might need a 20-50% increase. Your ISF might change too. Don’t guess. Test every 2 hours. Adjust. Keep a backup pen handy. Always.

Special Situations: Surgery, Pregnancy, and Sleep

If you’re having surgery, your pump might stay on - but only if you’re eating within a few hours. For longer procedures, you’ll need IV insulin. Hospitals have protocols for this. Make sure your care team knows your settings.

After giving birth, your insulin needs drop fast - often by 30-50%. Breastfeeding drops them even more. Many women get dangerously low in the first few days. Talk to your diabetes team before delivery. Have a plan. Adjust your basal rates immediately after birth.

At night? Some pumps now have predictive low-glucose suspend. If your glucose is dropping fast, the pump stops insulin for 30-120 minutes. That’s helpful. But it’s not perfect. You still need to check your glucose before bed. Set a low alarm. Keep glucose tabs by your bed. Don’t rely on tech alone.

Technology Is Helping - But Not Replacing You

The Tandem Mobi is tiny - smaller than a credit card. The Medtronic 670G and Omnipod 5 can auto-adjust basal rates. They’re called hybrid closed-loop systems. They’re amazing. But they still need you. You still have to bolus for meals. You still have to enter carbs. You still have to change the set. You still have to test.

Dr. Anne Peters says it best: “CSII is not an artificial pancreas.” It’s a tool. A powerful one. But if you don’t use it right, it won’t save you. It might hurt you.

What You Need to Succeed

Successful pump users don’t just follow instructions. They learn the why behind the numbers. They track patterns. They adjust. They ask questions.

You need to be able to:

• Count carbs accurately - within 5 grams
• Understand insulin action times
• Recognize signs of high and low blood sugar
• Test at least 4 times a day - more when you’re sick or changing settings
• Carry backup: insulin pen, extra sets, batteries, glucose tabs

Most people take 2-4 weeks to get comfortable. Six months to master it. Don’t rush. Don’t skip training. The Association of Diabetes Care & Education Specialists recommends at least 15 hours of education before starting.

Common Problems and How to Fix Them

Here’s what users actually run into:

• High blood sugar after meals - Probably under-bolused. Check your ICR. Did you forget fat/protein? Try an extended bolus next time.
• Low blood sugar overnight - Basal too high. Do a fasting test.
• Site infections - Changed set too late. Switch sites. Use alcohol wipes before inserting.
• Pump alarm going off constantly - Air in tubing. Prime again. Check for kinks.
• Unexplained high glucose - Check your infusion set. 45% of pump users have had a device failure within the first year.

Keep a log. Not just glucose. Write down meals, activity, stress, illness. Look for patterns. Your pump downloads can show you trends - but only if you’re paying attention.

Cost and Access

Insulin pumps cost $6,500-$8,200 a year in the U.S. - including supplies and insulin. That’s $2,000 more than multiple daily injections. In Australia, Medicare and private insurance cover most of it, but you still pay out-of-pocket for sets and reservoirs. If you’re struggling, talk to your diabetes educator. There are programs. There are options. Don’t give up because of cost.

Final Thought: You’re the Boss

The pump doesn’t think for you. It doesn’t know if you’re stressed, sick, or eating pizza. It just follows the code you gave it. You’re the one who has to interpret the numbers. You’re the one who has to adjust. You’re the one who has to stay alert.

There’s no magic button. No auto-fix. Just discipline, attention, and the willingness to learn every single day. That’s what makes CSII work - not the technology. You.