All About Basal Rates

You’ve programmed all the necessary data like carb ratios, correction factors, and basal rates into your pump, but now what To help pumpers learn how to get the most out of their pumps, Carb DM hosted a Type 1 Topics event with Dr. Saleh Adi. As Professor of Pediatric Endocrinology and Director of the Madison Clinic for Pediatric Diabetes at UCSF, Dr. Adi helps countless patients with insulin pump therapy. Fondly known as “The Basal Whisperer”, Dr. Adi is a strong advocate for using technology and data to better manage T1D.

One of the main topics of the event was basal rates. Dr. Adi shared his tips and tricks for when and how to adjust basal rates for different situations, times of the day, and stages of life. Here are some highlights:

 

Basal Requirements

A basal rate is the amount of insulin required to manage normal daily blood glucose fluctuations. It is the amount of insulin your body needs even if you didn’t need any additional (bolus) insulin.

Basal insulin’s job is to offset the glucose secreted by the liver. The liver makes sugar (glycagon), mainly to supply the brain and nervous system with energy. Glycagon stores are replenished and restored every day; extra amounts are stored in the liver and muscle. Thus, even without food intake, there is always sugar in the blood, and the body utilizes it constantly.  Insulin is needed to help cells absorb sugar and lower blood sugar levels.

Basal insulin should keep blood sugar steady – and the correct insulin dose should keep it steady. Your basal insulin should match the output of sugar from the liver and from what the body uses. The amount of basal insulin needed varies greatly from person to person. Factors such as body size, activity level, stage of growth, hormone levels can affect basal insulin. In addition, the amount of insulin required differs throughout the day, and from day to day. because the body uses different amounts of energy throughout the day and night, and from day to day.

 

24 Hour Metabolism & Hormone Levels

Every hour of the day requires different amounts of insulin. This means that basal rates should change at certain parts of the day. One factor that can affect insulin needs is hormone levels that also fluctuate throughout the day.

Take, for example, the hormone cortisol, which plays an important role in metabolism, response to stress, and more. At night,  when you go to bed, everything slows down. At midnight, your cortisol level might be zero. It will start to rise at 2:00am.  By 6:00am or 7:00am, the body knows to activate hormones like cortisol. Cortisol will be at its highest level at about 10:00am, then does down through the day.

Why talk about cortisol? Because cortisol contributes to higher blood sugars. Cortisol also makes you resistant to insulin action. Stress makes cortisol levels rise, along with blood sugar and blood pressure. Cortisol is a steroid hormone. More steroids require more insulin, which makes you resistant to insulin. Thus, even the stress of having a test at school might raise blood sugar — and make you resistant to insulin.

Testosterone is another steroid hormone. Since more steroids require more insulin, increases in testosterone levels could also lead to insulin resistance.  Growing children secrete growth hormones at night, which could impact blood sugar.

 

Basal Rates

Typical

Typical basal insulin requirements fluctuate during the day. Fortunately, with an insulin pump, you can program very different basal insulin amounts for different periods of the day, even each hour of the day (or more). Typically, the middle of night from lowest to highest in morning is the hardest time to get right. Lowest might be 1:00-3:00am, and highest at around 6:00-9:00am.

The time you go to bed and your wake time (over the course of several days) dictates timing for basal rates, not the time when you eat breakfast. If sleep patterns change, you may need to make adjustments to timing of basal rates (e.g. teenagers waking up at 11:00am, summer vacations).

Heightened sensitivity to insulin occurs between 1:00-3:00am. This is the most vulnerable time for hypoglycemia. People tend to be super sensitive at this time because no other hormones are available to raise blood sugars.

Pre-teens

For pre-teens, blood sugar goes up at night. Half and hour to one hour after going to bed, they will need a lot of insulin. Later, blood sugar drops and they need less. Bed times and falling asleep greatly affect blood sugars, so bed times need to be consistent and basal rates need to be adjusted accordingly.

Dinner influences what happens for the rest of the evening. It is important to get the timing and dosing of dinner bolus to get night time insulin levels right. Dr. Adi suggests avoiding late meals for your pre-teen. Leave at least two hours between dinner and bedtime. If your pre-teen eats right at bedtime, nighttime blood sugar will not be steady. Pre-teens need to have an empty stomach before bed. If your pre-teen has to eat, make sure it is a healthy snack. Try to make it the same one each night.

Puberty

Dr. Adi likes to see patients every one to two months during puberty because so much is changing. Basal rates are going to be shifting gradually during puberty. Hormones come and go for a few days and back, so it will be difficult to gauge changes. They might have high and low weeks during puberty before seeing more consistent high rates. During puberty (10-18 years old), A1C levels go way up, then back down. Hormones  hormones impact this. Children with T1D need to see their endocrinologists more often during puberty, to make insulin adjustments.

The menstrual cycle also affects basal rate requirements. An increase in hormones can be inflammatory and make you resistant to insulin. Similar to a viral infection, you become more resistant. Having a menstrual cycle is almost like being sick, and needing more insulin. About one to two days before periods start, blood sugars will rise. During ovulation, on the other hand, blood sugars are lower. It is different for each girl — you have to look at your data to identify patterns. You will need to change rates for the cycle (create a separate profile) to increase insulin 2 days prior and 3-4 days into it, but not for the entire duration.

 

Basal rates per hour

How do we calculate how much and when?  Knowing the patient’s weight and total daily insulin dose and age, Dr. Adi can estimate the basal/bolus rate, and then spread the basal based on patterns needed for the day. The patient’s age definitely makes a difference. For adults 40-45% (total insulin) should be basal. For a 2 year-old,  basal insulin should be around 20% and the bolus should be 80%. Two year-olds require less basal but a lot of bolus insulin for carbs. Adults will need less bolus based on body weight.

 

Basals and CGM Readings

Your CGM helps show you when you might need more insulin. For example, if you see your CGM going up at breakfast time, then it is possible you are not getting enough basal insulin at night (and vice versa). If it is rising at 2:00am every night, then increase basal rate – starting at 1:00am. Keep looking at your data to make adjustments.  Remember, daytime activites and pre-bed activities can impact blood sugar levels at night. Keep track of activities to look at patterns (Tidepool is a great resource for this!).

 

Basal Testing

For basal testing, Dr. Adi suggests  having one meal a day for 4-5 days in a row without carbs and look at basals. Or, just keep track of what you are eating and look at patterns.

 

Basals and Stomach Flu

Diarrhea and vomiting will not affect basal rates, but you might need more insulin. A stomach bug might prevent you from eating or keeping food down or digesting properly (absorbing). If you see low blood sugars after eating, then don’t give bolus and instead do a correction to adjust until you are healthy again.

 

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