3. Divide by 24 (to figure the hourly rate).
For example, if John weighs 195 pounds (88.5 kg), we divide 195 by 10 to get 19.5, and divide this by 24 to get 0.8 units per hour.
A more effective method for determining the starting basal insulin dose for pump use involves taking your current insulin program, breaking it down into basal and bolus components, and then taking the basal total to figure your hourly rate on the pump. I still recommend taking away 20 percent when figuring the initial basal requirements on the pump (because of the increased efficiency of pumped basal insulin).
Using Marley’s insulin program as an example (glargine morning and evening, aspart with each meal and snack), I would figure that none of her aspart doses are used as basal insulin, only the glargine.
If she used NPH insulin in the morning, I would assume that 50 percent of the morning NPH served as basal insulin and the rest as bolus insulin; if she took NPH at nighttime, I would assume that 75 percent of this dose would serve as basal insulin.
Without using NPH, the calculation is much easier: She takes a total of 20 units of basal insulin (glargine).
Take 20 percent away to come up with 16, and then divide by 24 to come up with an initial rate of approximately 0.65 units per hour.
Fine-Tuning Pump Basal Rates
When you start using an insulin pump, don’t just assume that the initial basal settings are correct . This is one of the biggest mistakes you can make, second only to telling your partner that you don’t like their outfit. To be honest, I can’t remember the last time I guessed exactly right on a pump user’s basal settings on the first try. The initial settings are merely a starting point; adjustments will be necessary.
If you’re using or planning to use a hybrid closed-loop system, you may be thinking to yourself, “Cool!
I don’t need to worry about this!
My pump adjusts the basal rates for me, automatically !” Sorry, dude, but you’ve been misinformed.
Hybrid closed-loop systems do adjust basal insulin levels in an attempt to fix high (or rising) and low (or falling) glucose levels.
But if you want the system to perform as well as possible, your basal settings need to be fine-tuned first.
Some hybrid closed-loop systems use your usual basal program as a starting point and adjust from there.
If your usual program isn’t set up correctly, the system is going to be doing a lot of chasing.
Also, consider all of the situations when you’ll be in manual mode: during sensor change-outs or warm-ups, whenever calibrations are delayed, any time the system isn’t performing properly, or by choice in order to use advanced pump features, just to name a few.
In these situations, you’ll need your standard basal settings working correctly for you.
Remember, the purpose of basal insulin is to match the amount of glucose secreted into the bloodstream by your liver. The right basal rate is one that keeps your blood sugar at a fairly constant and steady level when you have not eaten or bolused for several hours and are not exercising.
Testing, adjusting, and retesting basal rates can be a bit of a nuisance, but it is well worth the effort.
To determine whether your basal insulin rates are set properly, you will need to wait approximately four hours after your last bolus and meal or snack and then observe what happens.
Four hours is usually enough time to allow the carbs in the previous meal to finish digesting and the bolus to finish working.
The conditions that must be met in order to run a successful basal test are listed below.
No food should be digesting.
• Wait at least four hours after your last meal or snack before beginning the test.
• The meal or snack preceding the basal test should be low in fat. (No restaurant food or take-out food; these tend to take many hours to digest, and the extra fat content can influence your blood sugar many hours later.)
• Do not consume any calories during the basal test unless your blood sugar drops below 80 (4.4). Even fat and protein can affect blood sugar levels. You may have water or diet beverages during the test.
• Avoid caffeinated beverages during the basal test, caffeine can cause blood sugar to rise.
• Do not consume alcohol immediately prior to or during the basal test, alcohol can reduce the liver’s normal glucose secretion.
No bolus insulin should be working during the basal test.
• Wait at least four hours after your last bolus of rapid insulin before beginning the test (six hours if using regular insulin). If you delivered an extended bolus at your previous meal, wait four hours after completion of the bolus delivery. For example, if you programmed an extended (or dual, square, or combo) bolus lasting two hours, you will need to wait six hours after programming the bolus to start your basal test.
• Do not bolus during the test unless your blood sugar rises above 250 (13.9).
Your body should be producing its normal amount of glucose.
• Do not perform the test if you have had a low blood sugar reading within the previous four hours. Hypoglycemic episodes tend to produce a hormonal response that can raise the blood sugar for several hours.
• Do not run the test if you are ill or experiencing unusual stress.
• Do not run the test if you are taking a steroid medication unless it is a medication that you plan to continue taking indefinitely at a steady dose.
• Avoid testing just prior to or at the start of your menstrual cycle.
Allow basal insulin to be delivered at its normal rate.
• Do not place the pump into suspend mode just before or during the test.
• Do not disconnect from the pump just before or during the test.
• Do not run a temporary basal rate just before or during the test.
• Do not change your infusion set just before or during the test.
If your pump has hybrid closed-loop capabilities, turn them off four hours before starting a basal test until the test is complete.
Maintain your normal level of physical activity.
• Do not exercise during the blood sugar evaluation phase of your basal test (starting four hours after the last meal or bolus).
• You may perform light or moderate exercise soon after your pretest meal or snack if you normally do so at that time.
• Perform your usual daily activities during the basal test.
In terms of order, I usually start by testing and fine-tuning the nighttime basal rates. Once you have matched the overnight rate to your liver’s output of glucose, your blood sugar should hold steady through the night. Waking up near normal will make testing the morning segment easier, followed by the afternoon segment and, finally, the evening segment.
To start the test, follow these steps
1. Check your blood sugar at the start of the test (via fingerstick or CGM). Remember, you should wait at least four hours since the last bolus of rapid-acting insulin before starting a basal test.
2. If the glucose is above 250 (13.9), bolus for the high blood sugar, and cancel the test. If below 80 (4.4), eat to bring your blood sugar up, and cancel the test. If the blood sugar is not too high or too low, proceed with the test.
3. During the basal test, if you’re not using a CGM, check your blood sugar with a fingerstick reading every two hours. Less frequent testing may cause you to miss a rise or fall. If using a CGM to collect your glucose data, be sure to calibrate it (if required) prior to the start of the test, and try not to calibrate again until the test is completed.
Basal testing should be set up around the framework of your usual mealtimes and sleep patterns.
The schedule shown below in Table 6-4 is an example for someone who uses rapid-acting insulin for their boluses.
If your meals tend to be on the late side, it is fine to shift the testing schedule.
For example, if you normally have dinner at 8 p.m., you can start the overnight basal test at midnight rather than 10 p.m.
You may also run basal tests for longer periods of time if you can tolerate the extended fast.
Some people are able to complete the basal tests in only two or three segments.
It is also reasonable to break the tests into smaller time intervals and complete the testing in five or six intervals (for example, for very young children).
When evaluating your basal settings, it is always preferable to use a CGM rather than pricking your finger relentlessly. Because CGM data is continuous and great at showing subtle rises and falls in glucose levels, it truly is the ideal source of information. If you don’t currently use a CGM, consider obtaining one for personal use, or ask your health care team if they can provide a temporary loaner.
Grounds for Adjustment
Whether you use fingerstick or CGM data, if your glucose level falls more than 30 mg/dl (1.7 mmol/l) during the test period, the basal rate is probably too high. If it rises more than 30 mg/dl (1.7 mmol/l), the rate is most likely too low. You should adjust and retest the basal rate (the next day, if possible) to determine whether the adjustment is working. Continue to adjust and retest until you obtain a reasonably steady result.
For example, Figure 6.5 provides an example of an evening basal test that indicates a basal setting that may need to be reduced. Nancy had lunch (and bolused) at 12:30, and then fasted until her glucose started to drop low at around 7 p.m. She was stable until 5 p.m., then started to drop, indicating that she has too much basal insulin working between 5 p.m. and 7 p.m.
Figure 6.5: Nancy’s basal test showed that she is receiving too much basal insulin in the late afternoon.
In the example shown in Figure 6.6 , Alicia had an early lunch and bolused at 11 a.m., and then fasted until 8 p.m. Her glucose stayed between 150 and 180 (8.3 and 10) from 3 p.m. until 8 p.m., so her basal insulin is matched to her body’s needs at this time.
Figure 6.6: Alicia was stable from 3 to 8 p.m., confirming her basal settings.
If the result of a basal test appears to be very erratic (rises, falls, rises, falls), try repeating it the next day to see if a similar pattern appears. Inconsistent readings usually mean that an unforeseen variable is affecting the results. Likewise, if the glucose level rises or falls by a very large amount, the cause may be something other than a discrepancy in the basal insulin. Again, repeat the test to see if the results are similar.
Quantity of Adjustment
The amount of the change made to basal rates depends on a number of factors, including your sensitivity to insulin, the magnitude of the blood sugar change during the basal test, and the precision of your pump.
For someone on relatively large doses of insulin, making tiny basal adjustments is like trying to take down a charging rhino with a water pistol.
Likewise, making relatively large changes if you are on very small doses is like shooting a mosquito with a bazooka, there might be some collateral damage.
See Table 6-5 for suggested adjustments to basal settings.
For example, let’s take Nancy’s basal test results from Figure 6.5 . Her current basal rates in the afternoon are 0.5 and 0.6 unit per hour. Given that her glucose declined by a large amount, she should reduce her basal setting by 0.2 unit per hour.
Timing of Adjustment
Having diabetes teaches us that we need to plan ahead for just about everything.
Increasing (or decreasing) a basal rate at 6 p.m. is not going to affect the blood glucose at 6 p.m .
The rapid-acting insulin infused by the pump does its greatest work one to two hours after delivery, so basal rates need to be adjusted one to two hours prior to observed blood sugar changes.
I prefer to make changes two hours in advance for most adults and one hour ahead for most children and very lean or active adults.