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This is the third and fourth parts of a six part series on "How to Understand and Use Insulin." The goal of this series is to promote a better understanding of insulin for those readers who already take insulin, including the many people with Type II diabetes who have switched from pills to insulin to treat their diabetes. The first and second parts of the series dealt with the technical factors involved in minimizing variations in insulin absorption. These parts focus on adjusting insulin, and parts five and six will focus on insulin research.
Learning to adjust your own insulin is an important aspect of learning to be part of the diabetes health care team. Changing your insulin, daily if necessary, allows many patients to gain the best possible control of their diabetes. In order to adjust insulin, you must know how and when insulin works and how your insulin dose relates to your meal plan and your exercise. Learning to change insulin is a complex task. In this article I hope to start you on the right path, but a full, in depth understanding of how insulin works is beyond the scope of this article.
The adjustments that you make can be either reactive or predictive. The changes that you make in response to a single blood glucose are reactive. You are trying to correct an imbalance that has already lead to a high or low blood glucose. The changes that you make in response to a pattern of abnormal blood glucose measurements, alterations in meal plan or exercise are predictive. You are trying to prevent the high or low blood glucose that might occur in the future. In this article I will try to tell you some of the "hints" that I use to help patients attain the best control.
You should be aware that every patient is different and that the recommendations presented here are averages for all patients. You must check with your own physician before you make any changes to your insulin therapy. Failure to check with your physician could result in serious low blood glucose reactions.
Philosophy of Insulin Therapy
Insulin therapy can be broken down into two broad categories: conventional insulin therapy in which you take two or less doses of insulin per day and intensive insulin therapy, in which you take three or more doses of insulin per day. The major difference between these two types of therapy, however, is not in the number of doses of insulin each day but rather the philosophy of each of these therapies. In conventional insulin therapy the over-riding philosophy is to match food to insulin whereas in intensive insulin therapy the over-riding philosophy is to match insulin to food. Intensive insulin therapy requires you to obtain more diabetes education and be willing to do more glucose monitoring, but it frees you of many of dietary and lifestyle limitations present with conventional insulin therapy. Although most people with diabetes in the US currently use conventional insulin therapy, there is convincing evidence that diabetes control is better with intensive insulin therapy and an increasing proportion of well-educated people with diabetes are using intensive insulin therapy.
The ultimate goal of all diabetes therapy is to bring your blood glucose as close to normal as possible. The best evidence supports the notion that the better your diabetes control, the less likely you are to get diabetes complications. Generally, people taking more injections each day have better blood glucose levels than those taking fewer injections. The number of injections you take each day is often limited by what you and your doctor are willing to learn and do. With modern technology and the sharpest needles, the injection of insulin is usually virtually painless and so it is usually the inconvenience of drawing up insulin or the fear of the injection, rather than the pain of the injection itself that limits the number of times you take insulin each day.
Adjusting insulin with conventional insulin therapy
In order to adjust insulin properly, you must know when it acts. Table I presents the peak action time for insulins (the time at which the insulin has it's greatest action). For most people, Regular is the fast-acting insulin, and NPH or Lente is used as the intermediate-acting insulin. UltraLente, a very long-acting insulin is usually used in intensive insulin therapy.
Single injection of insulin: A single injection of insulin will almost never give good control in Insulin-dependent diabetes and should rarely be used in this group. When used as a single shot of NPH or mixed NPH and Regular insulin in the morning, it produces very high levels of insulin after lunch and frequently leads to mid-afternoon hypoglycemia. The NPH or Lente insulin usually does not last through the next morning and so the person often also has high blood glucose in the morning.
A single injection of insulin will almost never give good control in Insulin-dependent diabetes and should therefore rarely be used in this group.
In some people with Non-insulin-dependent diabetes a single dose of insulin will give acceptable blood glucose levels, usually in combinations with an oral agent. In the most effective regimen, called BIDS (Bedtime Insulin, Daytime Sulfonylurea) , a sulfonylurea (pill) is taken in the morning and insulin is taken at bedtime.
Split-Mixed Insulin: This is the most common regimen for people with Insulin-dependent diabetes and those with Non-insulin-dependent diabetes. In this regimen the person takes a combination of Regular and NPH insulin in the morning and another combination of the same insulins in the evening. The morning dose is usually not the same as the evening dose in either quantity or composition. The idealized curve of blood insulin concentration is shown in Figure 1. Since there are four insulins used, morning Regular, morning NPH, evening Regular and evening NPH, there are 4 peaks of insulin. In the figure, the peak action of each is shown in a different shade.
Adjusting your insulin requires a decision. It should be a rational one and a rational decision always requires information. The more the information, the better the decision. You can only get your information for changes in insulin dose from blood glucose monitoring. Ideally, you should do this four times a day: before breakfast, lunch, supper and at bedtime. The time for monitoring for most people is shown as pentagons in Figure 1. Each monitoring value helps you make a decision about a single insulin. To help you understand this, the monitoring pentagons are shaded the same color as the insulin that you adjust using those values. These relationships are repeated in Table II.
Blood glucose monitoring data is most useful when you can find patterns that will help you adjust your insulin. It is easiest to find a pattern when you write your blood glucose down in an orderly, consistent fashion, using columns for each time of day. Many of the logbooks for keeping your blood glucose values allow you to do this. An example is shown in Table III.
When the values are lined up nicely, as in this Logbook, many of the patterns are obvious. For example, we can easily see that over the three days covered here, the pre-breakfast values are nearly normal, the pre-lunch values are high, the bed-time values are nearly normal except for the period after overeating for a low blood glucose reaction and the pre-supper values are normal to low.
Insulin adjustment can obviously be an increase or a decrease in the appropriate insulin. First, let's consider increases in insulin. You may increase your insulin if you establish a pattern of high blood glucose, if you plan to eat more, during sick days or if you will decrease your exercise. In all cases, you should increase your insulin only with your doctor's knowledge and permission.
If you establish a pattern of high blood glucose values, such the pre-lunch values of Table III, you may want to increase your insulin dose. You need to determine which insulin to change and how much to change it. To determine which insulin to change use Figure 1 and Table II. From either you can see that the pre-lunch SBGM (shaded lightly) corresponds to the Morning Regular. Therefore, you want to increase that insulin. Deciding how much to increase the insulin is harder. Remember, you can adjust insulin often, every three days if necessary, so you can go slowly. You don't want to increase the insulin too much and cause a low blood glucose reaction. As a rough rule of thumb, to lower the blood glucose by 50 mg/dl, people with Insulin-dependent diabetes should increase their insulin by 1 unit and people with Non-insulin-dependent diabetes should increase it by 2 units. Once you have changed your insulin, you must be careful to continue to check you blood glucose to make sure that you have not increased the insulin too much.
It is difficult to adjust insulin for changes in food intake when using conventional insulin therapy. It much easier to do this with intensive insulin therapy. There are some guidelines that you can use. Again you have to know which insulin corresponds to which meal or snack. This is summarized in Table IV.
How much you should increase you insulin is very variable and you will have to determine this by trial and error. As a rough rule of thumb, for one additional bread or fruit exchange, people with IDDM need 2 units of insulin and people with NIDDM need 2-3 units of insulin.
You should decrease your insulin if you have an unexplained low blood glucose (<50 mg/dl). Most low blood glucose can be readily explained as being due to too little food, too much exercise or too much insulin. A few low blood glucose reactions are unexplained and may pose a problem. If you have a significant unexplained low blood glucose reaction, you should reduce your insulin. The exact amount will vary in different people. As a first guess, the reduction should be 2 units or 10% of your insulin, whichever is more. If this reduction is too much, you can increase the insulin in three days when you establish a pattern of blood glucose again. If you know why you had the reaction and plan to overcome this problem, you may not have to reduce your insulin.
In general, when people with diabetes exercise, they require less insulin for good control. This is due both to a more rapid absorption of insulin from exercised sites and an increase in the effectiveness of the insulin. You must, therefore, reduce your insulin when you exercise, but there are few guidelines to help you. Some people only need to reduce their insulin a little, some need only half as much.
Exercise should generally be mild to moderate and aerobic. Resistance exercise, like moderate weights are fine, but you should avoid power exercises like competitive weight lifting. You should try to exercise at the same time each day.
When you exercise determine which insulin you should change. Table V shows which insulin corresponds to which exercise time. For mild exercise like walking or bike riding most people will only need to reduce their insulin by 1-2 units. Some people with diabetes will need to reduce their dose significantly more. For more severe exercise the reduction of insulin dose must be significantly more. If in doubt decrease the dose by a larger amount. If your next blood glucose is too high, you can always decrease the dose less next time. Dr. Bob Arnot has written an excellent pamphlet on exercise in diabetes that will be available for free in July.
If you do prolonged, strenuous exercise, the increased effectiveness of insulin may last longer than the exercise. This can be a serious problem and one that you should discuss with your doctor.
By learning to adjust your own insulin, you gain control over your life. You are able to eat "healthy," exercise properly, perform most activities, and still maintain a normal blood glucose. You can live a near-normal life and still help avoid the complications of diabetes.