By: Barry Ginsberg
This is the final installment of Dr. Ginsberg’s three-part series called “Intensive Insulin Therapy,” which was written in response to the DCCT results. Part one defined intensive therapy and gave an overview of the theories and techniques involved. The second part explained how to start an intensive therapy regimen and calculate your daily insulin doses. The last part deals with adjusting insulin doses when using intensive therapy. The goal of this series is to educate people with diabetes about intensive therapy and enable them to choose the therapy that is right for them.
Dr. Barry H. Ginsberg, MD, PhD, and Endocrinologist, is currently the Medical Director for Becton-Dickinson, the largest manufacturer of syringes in the United States. The opinions in this article are those of Dr. Ginsberg and do not necessarily represent those of Becton Dickinson and Company.
Adjusting Insulin Doses
There are three types of adjustments to the insulin dosage. Two are made at each and every insulin shot, to adjust for any abnormal blood sugars that you find on your SMBG (Self-Monitored Blood Glucose) and to adjust for any alterations that you plan to make in your diet or exercise. These changes apply only to the next dose. The third is made less frequently and is designed to change the basic dose to take account of three day patterns of glucoses and will apply to all subsequent doses.
Changing the Dose Based Upon a 3-Day Pattern
Changes to the bolus doses during intensive insulin therapy are very easy to understand since each dose of regular insulin is designed to work with a specific meal. Thus, the insulin that you take at breakfast is designed to work with breakfast and if the dose is correct, the insulin will exactly match the food at breakfast and your blood sugar when you next measure it, at lunch, will be exactly the same as the breakfast measurement. A higher blood glucose would mean you took too little insulin, a lower value that you took too much insulin (or conversely ate too much or too little, respectively). The same would be true with the lunch bolus (SMBG measured at supper) and the supper bolus (SMBG measured at bedtime). Thus, you can tell if any insulin dose is proper by the relationship of the blood glucose just before the bolus and that of the next measurement.
Obviously, any single blood glucose measurement is too little data on which to base a permanent change in insulin dose, so we use the average of the last three days. Since changes are made frequently (every three days), you can make small changes and have a significant but safe cumulative effect over a very short period of time. Using the example from above, suppose that after three days the average blood glucose was 115 at breakfast and 175 at lunch. This would suggest that the breakfast dose of 20 units of Regular insulin was insufficient and should be raised to 21 units. After an additional three days the breakfast glucose was 110 and the lunch 145 and the breakfast dose was again raised by 1 unit to 22. This brought the lunchtime blood glucose to 120, so that the dose was correct. Similar changes could be made to the lunchtime and suppertime doses of Regular insulin. Insulin is generally increased by only one unit every three days.
Patterns of low blood glucose are more dangerous and should be treated more rapidly. If you establish a two day pattern of lowered blood glucose, you should reduce your dose by 2 units. If this causes higher than normal blood glucoses, you can raise the dose by one unit later. So, patterns of high blood glucose are treated by raising insulin by one unit at a time, but patterns of low blood glucose are treated by lowering insulin by two units at a time.
Although changes in the bolus doses are easy to make and can almost always be made by you, changes in the basal dose are much more complicated and should generally be made by the health care team. In order to make these changes, however, you will need to check your blood sugar at 3 AM periodically (we asked our patients to do this weekly).
Changes in Insulin for High or Low Blood Glucose Values
In an ideal world, once the best dose is established, it would always control blood glucose. In the real world this is not always true. Unexpected changes in diet, exercise, insulin absorption, or a variety of other factors may cause unexpected changes in blood glucose. As we mentioned above, if you are taking exactly the correct bolus dose of insulin, your blood glucose will not change between meals. Thus, theoretically, if you ever developed a high blood glucose these bolus doses would maintain the high values, just as they maintained a normal glucose.
To correct for this, many patients on intensive therapy alter each insulin dose to correct for any abnormalities in blood glucose. The amount that you have to change your dose is specific for you but can vary by the time of day. Only you and your doctor can determine this correction dose for you. When patients start intensive therapy, however, we use an average dose. On average, one unit of insulin will lower blood sugar about 50 mg/dl (in the absence of food). Thus, you might start by adding 1 unit of insulin for every 50 m/dl that your blood glucose is high. If you use a small syringe, such as the BD 3/10, you can accurately judge half units and then can take one half unit for each 25 mg/dl that your glucose is high. Using our previous example, if your target blood glucose is 125 and your blood sugar is 175 before breakfast, you would take 21 units of Regular insulin, the normal dose of 20 units and 1 extra unit for the 50 mg/dl high value.
With time, you may find that 1 unit for every 50 mg/dl is too little for you and does not bring your glucose back to normal by the next meal, or that it is too much and you have a low blood glucose reaction. You then need to adjust the correction dose appropriately. With time many careful patients find that this dose is higher at breakfast that at other meals and lower if they are going to be active.
You should adjust your dose more aggressively for low blood sugars. As a first guess, you may want to lower your dose by 25% for every 10 mg/dl that your sugar is below your target. For example is your target was 75 mg/dl, you would take 75% of your dose at a blood glucose of 65, 50% at 55, 25% at 45 and no insulin at a blood glucose of 35 mg/dl. Again, this is only an approximation and experience is necessary to determine your dose.
Changing the Dose for Changes in Diet
If you can quantitate the amount of glucose in your meal, you can change your insulin dose for changes in diet. To do this, we teach our patients the TAG, or total available glucose system, for quantifying their nutrition. It can be used as a simple variation of the exchange system as shown in Table II.
Once you can quantitate your food, you can change your insulin if you change your food. To do this you use the simple equation:
New insulin = old insulin x new food (gms TAG) old food (gms TAG)
As an example, suppose you normally take 13 units of insulin at lunch and your meal plan is 2 bread, 2 meat, 2 fat, 1 fruit and one milk. This would be a TAG of 69 grams. If you were going to eat a second sandwich (2 more bread and 2 more meat), you would have a TAG of 107 grams. For this new meal, you would take (13) x (107) / (69) = 20 units of regular insulin.
This same system can be used to lower the insulin for less food. You should beware, however, that patients may tend to gain weight when they start intensive insulin therapy and you should avoid overeating.
The same system can be used to eat an unexpected meal or snack. You simply use the insulin and corresponding TAG of the nearest meal.
Changing the Dose for Changes in Exercise
Since each insulin dose lasts only a short period, it is fairly easy to make alterations in the dose for exercise. This change, however, is very specific for each patient, and the guidelines that we use generally need significant alteration based upon the experience of the patient.
As a first guess, I generally lower the insulin by 2-4 units for mild to moderate exercise and by 4-8 units for moderate to heavy exercise. You need to check you blood glucose before and after exercise and, working with your physician or nurse, make frequent changes to this scheme.
The results of the DCCT have ushered in a new era of diabetes control that will require the health care team and the patient to do more to bring blood glucose levels as close to normal as possible. This will require intensive insulin therapy in most patients with type I and many patient with type 2 diabetes. In the next article we’ll discuss a system for helping primary care physicians provide this level of care.
DIABETES HEALTH Disclaimer: You should consult your diabetes professional before changing insulin doses.