Think Like a Pancreas
Page 13
And what if your physician doesn’t agree with your program choice? Ask why. Perhaps they have a good argument that will sway your decision. If not, you might want to look for another doctor. After all, this is your diabetes, and you deserve the right to manage it in the manner that suits you best.
Chapter Highlights___________________________________________
•For an insulin program to be successful, it should include both basal and bolus components.
•Basal insulin may be supplied in the form of NPH, glargine/detemir, or insulin pump therapy. Pump therapy usually provides the best basal insulin coverage.
•Bolus insulin may be supplied in the form of rapid, regular, or NPH insulin. Rapid insulin is by far the most advantageous.
•Various combinations of basal/bolus therapy are possible, each with its own pros and cons. Choose the one that will meet your personal needs the best.
CHAPTER
6
Basal Insulin Dosing
Once you have settled on an insulin program that meets your needs, the next order of business is to determine the right doses. Think of yourself as a giant lump of clay that needs to be molded and sculpted into fine art. (My personal self-sculpture is a cross between Rocky Balboa and Bond, James Bond.) Any artistic creation takes time, so be patient. Make one adjustment at a time, evaluate the results, and then fine-tune before moving on to another area.
Another truism about fine art: Beauty is in the eye of the beholder. What works for some may not work for others. When looking at typical dosing patterns and formulas, use them only as starting points. Individual needs may—no, make that will—vary.
Let’s start with the fine-tuning of basal insulin levels. Basal insulin serves as the foundation for your entire insulin program. With a solid, level foundation, you can build something great, but with a cracked or crooked foundation, you will need to manipulate everything placed on top of it in order to avoid epic disaster. In diabetes terms, when high or low blood sugars appear, knowing what to adjust is difficult unless you have already established the proper basal insulin levels. That’s why it is best to fine-tune your basal doses before attempting to regulate the mealtime/boluses.
In the previous chapter I presented typical basal insulin profiles for people within different age groups. During a person’s growth years (prior to age twenty-one), basal insulin requirements tend to be heightened throughout the night. This is due to the production of hormones (primarily growth hormone and cortisol) that stimulate the liver to release extra glucose into the bloodstream. Following one’s growth years, the production of these hormones is limited primarily to the predawn hours, causing the liver to secrete extra glucose in the early morning. This is commonly called a “dawn effect” or “dawn phenomenon.”
Initial Basal Doses for Those Injecting Insulin
The body’s insulin requirements are affected by a number of factors, including body size, activity level, stage of growth, and the amount of endogenous (internal) insulin production from your own pancreas. To find out how much insulin your pancreas is producing, a blood test called a “C-peptide test” can be performed. C-peptide is attached to the insulin molecule when it is first secreted from the pancreas. They call it C-peptide because it is shaped like the letter C (isn’t that ingenious!). Enzymes in the blood break this piece off, leaving two parts: the active insulin molecule and the C-peptide. By measuring the amount of C-peptide in the blood, we can determine approximately how much insulin the body is making on its own. A result of less than 0.5 ng/ml indicates that the pancreas is producing abnormally low amounts of insulin.
If you are just getting started with a basal/bolus insulin program, start with a conservative dose and increase gradually until your blood sugar levels are within an acceptable range.
For those with type 2 diabetes who are still producing some of their own insulin, the total daily insulin requirement is often less than 0.5 units per kilogram, or about .2 units per pound, of body weight daily. However, this can vary considerably depending on your body’s degree of insulin resistance. For instance, a person with insulin-resistant type 2 diabetes who weighs more than 250 pounds (113 kg) might require hundreds of units of insulin in order to manage blood sugar levels,whereas someone of similar size who still produces some of their own insulin and is only modestly insulin resistant might require only 10 or 20 units of insulin daily.
For individuals who produce virtually no insulin on their own (including those with type 1 diabetes), insulin requirements are somewhat more predictable. Table 6-1 below provides typical ranges for total daily insulin needs.
Table 6-1. Total daily insulin requirements (units per kilogram body weight)
For instance, if you are a moderately active adult, you will likely require .50 to 1.0 units of insulin per kilogram of body weight per day. If you weigh 160 pounds, that equals approximately 73 kilograms (lbs × .454 = kg). Your daily insulin need should be in the range of 37 (73 × .50) to 73 (73 × 1.0) units per day.
Given that basal insulin usually accounts for 40 to 50 percent of a person’s total daily insulin needs (50 to 60 percent covers food), basal insulin doses typically fall within the ranges shown in Table 6-2 below. Keep in mind that those who eat large quantities of carbohydrate will have a smaller percentage of their daily insulin as basal, whereas those who eat very little carbohydrate will have a larger proportion of basal insulin. Basal insulin needs also tend to drop as we pass from middle to older age.
Table 6-2. Daily basal insulin requirements (units per kilogram body weight)
Translating this to units of insulin, let’s look at an example.
Debbie is thirty-eight years old and has type 1 diabetes. She weighs 136 pounds, exercises for an hour every day, and has a very active job.
First, we must convert her weight into kilograms (lbs × .454 = kg).
136 × .454 = 62
Because Debbie is a very active adult, she requires .15 to .40 units of basal insulin for every kilogram she weighs.
62 × .15 = 9 units
62 × .40 = 25 units
Debbie should require somewhere between 9 and 25 units of basal insulin daily. Because the basal/bolus approach is new to her and she has a history of low blood sugars, she and her physician opt to start conservatively with 10 units of basal insulin.
Let’s take another example. Ben is a teenager with type 1 diabetes who gets a moderate amount of exercise and weighs 105 pounds. According to Table 6-2, he will likely require between .30 and .70 units of basal insulin per kilogram of body weight per day.
His weight in kilograms:
105 × .454 = 48
48 × .30 = 14
48 × .70 = 34
Having had mostly high blood sugars recently (as teenagers are prone to do), Ben and his physician elect to start somewhere in the middle, with 25 units of basal insulin.
One more example: Jackie is sixty-eight years old and has type 2 diabetes that is poorly controlled on oral medications. Her doctor has determined that her pancreas makes very little insulin. She weighs 210 pounds and gets hardly any exercise.
Her weight in kilograms:
210 × .454 = 95
According to Table 6–2, she will likely require between .20 and .50 units of basal insulin per kilogram of body weight.
95 × .20 = 19
95 × .50 = 48
Given that Jackie is fairly insulin resistant, she and her physician choose to start with a dose of 40 units of basal insulin.
Fine-Tuning Injected Basal Doses
When injecting basal insulin, our goal is to find a dose that maintains steady blood sugar levels through the night (or while sleeping, for those who work night shifts). Ideally, the doses of glargine, detemir, or nighttime NPH should produce no more than a 30 mg/dl (1.7 mmol/l) change while sleeping—assuming that before you go to sleep you do not eat, take rapid-acting insulin, or perform heavy exercise.
The right dose of basal insulin should keep the blood sugar fairly steady through
the night.
A consistent rise or drop of more than 30 mg/dl (1.7 mmol/l) indicates a need to change the basal insulin dosage. To determine whether your overnight basal insulin dose is set correctly, follow this procedure:
1. Have a fairly healthy dinner (not too much fat; avoid restaurant and take-out food). High-fat food will cause a prolonged blood sugar rise and will alter the test results. Take your usual doses of dinnertime rapid-acting insulin and long-acting/basal insulin.
2. If you normally exercise in the evening, go ahead and do so, but keep the intensity and duration modest. Very heavy exercise may cause the blood sugar to drop several hours later, which would also influence the test results.
3. At least three hours after dinner, perform a bedtime blood sugar check. As long as your blood sugar level is above 80 mg/dl (4.4 mmol/l) and below 250 (13.9 mmol/l), do not take any food or rapid-acting insulin and proceed with the experiment. If you are below 80 (4.4), take a snack and try the test another night. If you are above 250 (13.9), give a correction dose of rapid-acting insulin and try again another night. If you repeatedly have high or low readings at bedtime that keep you from beginning the test, consider making an adjustment to your dinnertime food, insulin, or medication.
4. Check your blood sugar again in the middle of the night (or the middle of your sleep time) and first thing in the morning (upon waking up). You need the middle-of-the-night reading to rule out a potential Somogyi Phenomenon (see page 133).
If your blood sugar rises or falls less than 30 mg/dl (1.7 mmol/l) from bedtime to wake-up time, congratulations! Your basal insulin dose looks good. If it rises more than 30 mg/dl (1.7 mmol/l), increase your basal insulin dose by 10 percent and repeat the test. If it is dropping by more than 30 mg/dl (1.7 mmol/l), decrease your basal insulin by 10 percent and repeat the test. Continue adjusting and repeating the test until your blood sugar holds reasonably steady through the night.
For example, let’s say you’re taking 10 units of detemir in the morning and 10 at night. If your bedtime blood sugar reading was 185 mg/dl (9.2 mmol/l) and your wake-up reading was 122 mg/dl (6.8 mmol/l), your basal insulin dose is too high, as the blood sugar dropped by 63mg/dl (2.4 mmol/l) while you slept. Had your bedtime blood sugar been closer to normal, you probably would have experienced hypoglycemia during the night. Reduce the detemir to 9 units both morning and night, and run the test again the following night.
Had the blood sugar risen from 87 mg/dl (4.8 mmol/l) to 160 mg/dl (8.9 mmol/l)—a rise of 73 (4.1)—an increase in the basal insulin would be in order.
If your bedtime reading was 95 mg/dl (5.3 mmol/l) and you woke up at 77 mg/dl (4.3 mmol/l), shout woo-hoo! You would not need to adjust the basal insulin dose because the blood sugar changed by only 18 mg/dl, or 1 mmol/l, during the night.
Attack of the Killer Somogyi
What about that pain-in-the-neck reading you took in the middle of the night? No one likes having their sleep interrupted (unless, of course, your hot partner is looking for some action). So that extra reading had better be worth it. Believe me, it is.
In many instances, a blood sugar drop during the night—particularly to levels below 70 mg/dl (3.9 mmol/l)—causes the body to secrete hormones that raise the blood sugar by morning, all without your knowledge. This occurrence, known in the medical community as the “Somogyi Phenomenon” (named after its discoverer), can interfere with basal dosing decisions if it goes undetected.
Consider the following example, illustrated in Figure 6-1. Larry and his two brothers, Daryl and Darryl, all have diabetes (now there’s a gene pool to avoid). They each take glargine for their basal insulin. Each starts and finishes the night with the same blood sugar increase. Without knowing the blood sugar in the middle of the night, our first instinct would be to increase the basal insulin for all three. But a closer look at the data in Table 6-3 reveals more effective solutions.
Larry is experiencing a sharp blood sugar rise soon after he goes to sleep. This could be considered an early “dawn phenomenon.” Adding a small dose of NPH at dinnertime or a small dose of rapid insulin at bedtime would probably resolve this problem. An insulin pump might also be a good option for Larry because he could program it to deliver a little more basal insulin during the early part of the night.
Figure 6-1. Three routes to high blood sugar in the morning
Table 6-3.
Daryl experiences a steady rise through the night, so an increase in his glargine dose should do the trick.
Darryl, however, is experiencing a Somogyi Phenomenon. He is dropping to mildly low levels in the middle of the night and rebounding to a higher level by morning. Increasing his basal insulin would make the problem worse, not better. But a reduction in his basal dose, or possibly adding a bedtime snack, would make the most sense.
Initial Basal Doses for Insulin Pump Users
Basal insulin delivered by an insulin pump comes in the form of tiny pulses of rapid-acting insulin infused every few minutes throughout the day and night. Rapid-acting insulin tends to work more efficiently than longer-acting insulin, so there is less waste. As a result, the average pump user requires approximately 20 percent less basal insulin than those who take intermediate- or long-acting insulin by injection.
I prefer to start pump users on one flat rate of basal insulin and then fine-tune using the methodology described later in this chapter. Of course, one flat rate is not likely to meet your needs adequately. But to make assumptions about when and how much of a basal peak you need based on your injection program could be a big mistake. There may be major differences in your basal insulin pattern when transitioning to pump therapy, so it is best to start conservatively in order to avoid unexpected lows.
To determine an initial rate of basal insulin delivery, two approaches are available: the formula methods (which provide a very rough approximation) and the empirical approach (which provides a less rough approximation).
One of the formula methods is based on your current insulin injection program:
1. Add up all the units of insulin you take in an average day, including basal and bolus insulin.
2. Divide the total in half (assuming that 50 percent of your insulin is going to be basal and the other half bolus).
3. Multiply by .8 (to take away 20 percent of the total dose, because basal delivered in the form of rapid-acting insulin tends to work more efficiently than basal delivered as long-acting insulin).
4. Divide by 24 (to figure the hourly rate).
For example, Marley took three injections daily (before going on the pump):
Breakfast: 18 NPH and 5 units Novolog (on average)
Dinner: 8 units Novolog (on average)
Bedtime: 12 units NPH
Marley’s total insulin for the day is 43 units.
Half that amount is 21.5 units.
Taking away 20 percent leaves 17.2 units.
Dividing by twenty-four hours, we get .7 units per hour.
Another formula calculation is based on body weight. Anyone going directly onto the pump without ever having taken insulin injections should use this method.
1. Take your weight in pounds. To convert kilograms to pounds, multiply by 2.2.
2. Divide by 10 (a magic number . . . trust me on this).
3. Divide by 24 (to figure the hourly rate).
If Ben weighs 195 pounds (88.5 kg), we divide 195 by 10 to get 19.5, and divide this by 24 to get .8 units per hour.
A more effective method for determining starting basal insulin doses on the pump 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. Once you determine the injected basal insulin, I recommend you still take away 20 percent when figuring the initial basal requirements on the pump.
Using Marley’s insulin program as an example (see above), I would figure that none of her Novolog doses are used as basal insulin. Because she does not take any insulin at lunchtime, I would assume that approximate
ly 50 percent of her morning NPH serves as basal insulin (the remainder covering lunch and daytime snacks), and 75 percent of her nighttime NPH serves as basal insulin (the remainder covering some of her night snack and some of breakfast). Thus, 50 percent of 18 (9 units) plus 75 percent of 12 (9 units) are being used as basal insulin, for a total of 18. I would then take 20 percent away to come up with 14.4 and then divide by 24 to come up with an initial rate of .6 units per hour.
For someone taking a long-acting basal insulin, I would simply take 20 percent away from the total daily dose of glargine or detemir and divide by 24 to come up with an hourly basal rate.
For example, if Karen is on the following program:
Breakfast: 8 units lispro (on average), 12 units detemir
Lunch: 6 units lispro (on average)
Afternoon snack: 3 units lispro (on average)
Dinner: 8 units lispro (on average)
Bedtime: 2 units lispro (on average), 13 units detemir
I would ignore the lispro doses completely and figure that the detemir is the only basal insulin. Taking 20 percent away from her 25 total units of detemir, we come up with 20 units. Dividing by 24 hours, we get a starting rate of 0.8 units per hour.
Fine-Tuning Pump Basal Rates
When you go on an insulin pump, whatever you do, don’t just assume that the initial basal settings are correct. This is one of the biggest mistakes you can make. The power of the insulin pump is its ability to deliver varied amounts of basal insulin at different times of day.
The purpose of basal insulin is to match the amount of glucose the liver secretes into the bloodstream. The right basal rate is one that keeps your blood sugar at a fairly constant/steady level when you have not eaten or bolused for several hours and are not exercising. You must establish appropriate basal rates in order to obtain quality blood sugar control and enjoy the flexible lifestyle the pump affords.