Think Like a Pancreas

by Gary Scheiner

  Testing, adjusting, and retesting basal rates can be a bothersome process, 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/snack and then observe what happens. This will give the carbs time to finish digesting and the bolus time 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/snack before beginning the test.

  •The meal/snack preceding the basal test should be low in fat. (No restaurant food or take-out; these tend to raise blood sugar for many hours).

  •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 in the meal/snack preceding 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 to begin the test (six hours if using regular insulin).

  •The bolus given for the last meal/snack should be delivered normally (not extended in any way).

  •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 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 put the pump into suspend 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.

  Maintain your normal level of physical activity.

  •Do not exercise during the blood sugar evaluation phase of your basal test.

  •You may perform light/moderate exercise soon after your pretest meal/snack if you normally do so at that time.

  •Perform your usual daily activities during the basal test.

  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. This 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 chosen time period. Remember, you should wait at least four hours since the last bolus of rapid-acting insulin.

  2. If the blood sugar 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 a basal test, check your blood sugar with a fingerstick reading every couple hours. Less frequent testing may cause you to miss a temporary rise or fall. Alternatively, collect your data using a continuous glucose monitor.

  Basal testing should be set up around the framework of your usual mealtimes and sleep patterns. The schedule shown below in Table 6-4 can be used as a general guide for performing a complete set of basal tests. Running the basal tests for longer periods of time is fine if you can tolerate fasting for more than eight to ten hours at a time, as is breaking the daytime tests into smaller intervals (e.g., for young children).

  Table 6-4. Example basal testing schedule

  If pricking your finger mercilessly doesn’t appeal to you, another excellent way to collect basal testing data is by wearing a continuous glucose monitor. Say what you will about CGMs: They are not always as accurate as we would like them to be, but when they show an upward trend, you can bet your family jewels that your blood sugar is rising. And when they show a downward trend, you are almost certainly dropping. So because basal testing is all about checking the stability of blood sugar levels in a fasting state, a CGM can serve as an ideal source of information, not to mention that it saves you from waking up during the night to prick your finger!

  Grounds for Adjustment

  Whether you use fingerstick or CGM data, if your blood sugar drops 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.

  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 huge amount, the cause may be something other than the basal insulin being a bit off. 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, infinitesimal 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 a bit of collateral damage. Hopefully you get the idea. Table 6-5 should serve as a useful starting point.

  Table 6-5. Suggested magnitude of basal insulin adjustments

  Timing of Adjustment

  Having diabetes teaches us that we need to plan ahead. Increasing (or decreasing) a basal rate at 6 p.m. is not going to affect the blood glucose at 6 p.m. Basal rates need to be changed one to two hours prior to observed blood sugar changes because the rapid-acting insulin the pump infuses does the majority of its work one to two hours after delivery. I prefer to make changes two hours ahead for most adults and one hour ahead for most children and very lean/active adults.

  For example, if an adult’s blood sugar rises between 3 a.m. and 7 a.m., I would recommend increasing the basal rate between 1 a.m. and 5 a.m. If a child’s blood sugar drops between 8 p.m. and 1 a.m., I would recommend a basal reduction between 7 p.m. and 12 a.m.

  Incidentally, even though most pumps allow basal rates to be adjusted on the half-hour, I prefer to make setting changes on the hour (i.e., 1:00 rather than 1:30). Remember, basal insulin is made up of tiny boluses of rapid-acting insulin, and rapid insulin works over a three- to four-hour period. Basal insulin levels in the body don’t change dramatically all at once; there is more of a gradual shift. Thus I simply find it more practical and manageable to make changes on the hour.

  Quality of Adjustment

  When setting up a twenty-four-hour basal program, our objective is to mimic normal physiology as closely as possible. A healthy pancreas secretes basal insulin in a circadian pattern, based mainly on how other hormone levels vary during the course of a full day. It produces more basal insulin at certain hours, less at others. Normally, there is one peak period and one valley period—not multiple peaks and valleys. A basal program that includes multiple peaks and valle
ys is almost always incorrect—or at least compensating for some other aspect of the insulin program that is not set up properly. For example, consider the basal pattern in Figure 6-2.

  Figure 6-2. Basal pattern with one peak and one valley

  12 a.m.–5 a.m.: .70

  5 a.m.–8 a.m.: .90

  8 a.m.–1 p.m.: .60

  1 p.m.–10 p.m.: .50

  10 p.m.–12 a.m.: .60

  This pattern has one peak (between 5 and 8 a.m.) and one valley (1 to 10 p.m.). It has integrity, as far as basal programs go.

  Now consider the pattern in Figure 6-3.

  Figure 6-3. Basal pattern with multiple peaks and valleys

  12 a.m.–5 a.m.: .50

  5 a.m.–8 a.m.: .80

  8 a.m.–11 a.m.: 1.10

  11 a.m.–1 p.m.: .20

  1 p.m.–4 p.m.: .50

  4 p.m.–6 p.m.: .85

  6 p.m.–8 p.m.: .60

  8 p.m.–12 a.m.: .40

  This program has two peaks: a big peak from 7 to 10 a.m. and a smaller peak from 4 to 6 p.m. Given that the basal rate is .5 continuously from 2 p.m. until 7 a.m. except for those few hours in the late afternoon, the 4 to 6 p.m. rates may be set inappropriately. Perhaps the basal peak in the late afternoon is compensating for an afternoon snack that is not covered sufficiently with a bolus.

  Examples

  The following are examples of basal tests and the recommended adjustments for each.

  April is a compulsive forty-one-year-old accountant who recently started using a pump and has a flat basal rate of 1.2 units per hour throughout the day and night. To verify her overnight basal rate, she had a low-fat dinner at 6 p.m. and nothing else to eat the rest of the night. Her blood sugars through the night were as follows:

  10 p.m.: 117 mg/dl (6.5 mmol/l)

  12 a.m.: 187 (10.4)

  2 a.m.: 238 (13.2)

  4 a.m.: 240 (13.3)

  6 a.m.: 218 (12.1)

  April’s blood sugar rose sharply between 10 p.m. and 2 a.m. and then held steady from 2 a.m. until 6 a.m. (the slight drop-off from 4 to 6 a.m. is likely due to the loss of some sugar through the urine). Based on this, I would recommend that she increase her basal rate by .3 units per hour (to 1.5) from 8 p.m. until 12 a.m. and repeat the early phase of the test (taking readings just until 2 a.m.). Her basal rate from 12 a.m. until 4 a.m. appears to be set correctly, as the blood sugar level remained fairly constant from 2 a.m. to 6 a.m.

  Mindy is a manipulative ten-year-old whose basal rates are .20 units per hour from 3 a.m. until 9 a.m., and 0.15 units per hour the rest of the day. To confirm her morning basal rate, her parents had her skip breakfast and check her blood sugars through the morning (they promised her a Happy Meal for lunch if she complied). The results were as follows:

  7 a.m.: 184 mg/dl (10.2 mmol/l)

  8 a.m.: 192 (10.7)

  9 a.m.: 177 (9.8)

  10 a.m.: 190 (10.6)

  11 a.m.: 224 (12.4)

  12 p.m.: 259 (14.4)

  Mindy’s blood sugar held steady from 7 a.m. to 10 a.m., so the .2 basal from 6 a.m. to 9 a.m. looks good. The blood sugar rise from 10 a.m. to 12 p.m. requires a basal increase to 0.20 from 9 a.m. to 11 a.m. Mindy’s parents could combine her next (afternoon) test with a recheck of late morning by having her eat breakfast at 6 a.m. and then perform blood sugar checks from 10 a.m. until 2 or 3 p.m.

  Lily is an artsy-fartsy college student using an insulin pump. Her current basal rates are as follows:

  12 a.m.–7 a.m.: 0.5 units/hr

  7 a.m.–1 p.m.: 0.4 units/hr

  1 p.m.–8 p.m.: 0.3 units/hr

  8 p.m.–12 a.m.: 0.4 units/hr

  Lily noticed that her blood sugars in the morning were higher than they were at bedtime, so she decided to wear a continuous glucose monitor for a week. She was careful not to snack after 8 p.m. so that we could find out what was going on. The results are shown below in Figure 6-4:

  Figure 6-4

  As you can see in the box, her glucose levels were rising steadily through the night from approximately 1 a.m. to 6 a.m. She was not dropping low and then rebounding to a higher reading (Somogyi Phenomenon), and because she was not eating after 8 p.m., food was probably not causing the rise. So Lily concluded that she needed to increase her basal insulin by .1 from midnight through 5 a.m.

  Paul has been using a pump for a short while and also uses a continuous glucose monitor. His current basal rate is flat at .8 units per hour. He found that he was experiencing frequent lows since starting on the pump, but he wasn’t sure if the problem was too much basal or too much bolus insulin. Here is a look at a day’s CGM data for Paul.

  Figure 6-5

  Notice in the ovals that his blood sugar is dropping starting after 3 a.m. and after 3 p.m., both approximately four hours after his last bolus was given. This indicates that his basal insulin dose is likely too high. Paul reduced his basal rate from .8 to .7 units per hour and began a series of scheduled basal tests to fine-tune his overall program.

  Idiosyncrasies about Basal Testing

  Life is never simple when you have diabetes. Basal insulin levels and basal testing don’t always follow the rules according to Hoyle. There are a few “quirks” that you should be aware of.

  For starters, never test your basal rates the first day or night when you start on your pump or injected basal insulin program. You need at least twenty-four hours (and sometimes as long as forty-eight hours) for previously injected long-acting insulin to clear from your body.

  Anytime the blood glucose level is above 180 mg/dl (10 mmol/l), the kidneys will channel some sugar into the urine. This may produce a slight decrease in the blood sugar concentration. Thus, when performing a basal test with elevated blood sugars, a slight drop-off in the blood sugar is to be expected and does not necessarily mean that the basal setting is too high.

  In some people even near-lows will cause a hormonal response that induces a mild blood sugar rise. Again, this does not necessarily mean that the basal setting is too low.

  After finishing a fasting test, don’t be surprised to see a significant spike in the blood sugar soon after eating. This is a natural response to fasting; the digestive system puts food on the fast track to reaching the bloodstream.

  In terms of the basal patterns observed, people who are still producing some of their own insulin tend to have flatter basal profiles than those who are truly insulin-dependent. For those with type 2 diabetes or LADA as well as type 1s still in a honeymoon phase, the pancreas will adjust its own insulin secretion to offset some of the peaks and valleys in the liver’s glucose secretion.

  Beyond Basal Basics

  In addition to allowing the user to set a multitude of different basal delivery rates throughout the day and night, all pumps can store settings for more than one complete twenty-four-hour program. Alternate basal programs can be useful during periods of heightened insulin need (such as sick days, travel days, or prior to menstruation) or decreased insulin need (such as days filled with physical activity or postmenstruation). Use of alternate basal programs will be discussed in more detail in Chapter 8, along with the use of short-term basal rate adjustments called “temporary basal rates.”

  Obviously, fine-tuning basal insulin levels can become complex. This is a great opportunity to work with members of your health care team who specialize in this sort of thing—most likely your CDE or pump trainer. And if you don’t have local access to someone who really knows their stuff, give my office a call! We consult people worldwide via phone and the Internet, so you’re never without options. We even offer a class at Type-1 University (www.type1university.com) that focuses specifically on the ins and outs of fine-tuning basal insulin.

  Remember, you are the ultimate decision maker regarding your diabetes plan, but it never hurts to seek out expert advice!

  Chapter Highlights___________________________________________

  •Basal insulin is the foundation of your entire insulin program.

  •Basal insulin’s job is
to match the liver’s output of glucose. It should hold your blood sugar steady in the absence of food, exercise, and bolus insulin.

  •Basal insulin usually makes up 40 to 50 percent of the total insulin for the day.

  •For those taking basal insulin by injection, the right dose should keep your blood sugar from changing more than 30 mg/dl (1.7 mmol/l) through the night.

  •Pump users should test and fine-tune their basal settings at each phase of the day and night.

  •Basal programs typically feature one peak and one valley.

  CHAPTER

  7

  Bolus Calculations

  Ahhh, pizza, hot from the oven. The aroma of freshly popped popcorn. Cold Italian ice on a warm summer day. That mysteriously tasty cream center in Oreo cookies.

  Basal insulin would meet our needs just fine . . . if we never ate. But we do eat (praise the lord!), and the carbohydrates in the things we eat make blood sugars rise. So for everything from Philly pretzels to Philly cheesesteaks as well as countless other culinary delights, we have something called bolus insulin.

  Boluses are bunches of rapid-acting insulin used to cover carbs or lower high blood sugar levels.

  Boluses are bunches of rapid-acting insulin given to cover the blood sugar rise that the carbohydrates in our meals and snacks produce. Boluses are also used to lower blood sugars that are higher than we want. Boluses can be adjusted based on several factors, including the amount of rapid insulin that is currently working and our level of physical activity before and after eating. There are many other secondary factors that influence bolus requirements; these will be discussed in the next chapter. For our purposes here, we will focus on the four primary factors that are used to determine bolus doses: