by Gary Scheiner MS, CDE
Hypoglycemia has been called the greatest limiting factor in intensive diabetes management. Were it not for the risk of hypoglycemia, we could simply load up on insulin and keep blood sugars from ever rising too high. Unfortunately, hypoglycemia does exist, and it creates a number of problems for those of us who take insulin: risk of accidents, seizures and loss of consciousness; rebound highs; impaired intellectual and physical performance; unwanted weight gain; and worsening of hypoglycemia unawareness.
It is not realistic to achieve tight blood glucose control without any episodes of hypoglycemia. However, we should make every effort to minimize the frequency and severity of lows. To do this, we need to do everything possible to match the insulin we need with the insulin we take. After all, it is the simple act of taking too much insulin that is the root cause of hypoglycemia.
One of the main advantages offered by insulin pump therapy is the ability to closely mimic the actions of a healthy pancreas. There are a number of reasons why pump users tend to experience fewer and less severe bouts of hypoglycemia compared to those on injections. First is the ability to carefully match basal insulin to the body’s needs. Long-acting insulin (NPH, Lantus, Levemir) cannot be adjusted and fine-tuned the way basal insulin delivered with a pump can. Most people need extra basal insulin at certain times of day and less at others. Injected long-acting insulin does not usually provide a drop-off in the insulin level when less basal insulin is needed, and thus sets a person up for low blood sugar. But the pump’s basal insulin delivery can be reduced at times of day when less insulin is needed.
Pumps also allow for temporary reductions in basal insulin during periods of heightened physical activity, post-menses, alcohol consumption, gastritis (stomach upset), or any other time when there is potential for hypoglycemia. By lowering the rate of basal insulin delivery for several hours when the blood sugar is likely to be dropping you can reduce the risk of hypoglycemia.
Another insulin pump feature that helps to reduce the risk of hypoglycemia is the “insulin-on-board” or “active insulin” calculation. Most modern pumps calculate mealtime insulin based on carb intake and the pre-meal blood sugar. They will also reduce the bolus based on the amount of insulin still working from recent boluses. In most cases, rapid-acting insulin takes 3-4 hours to finish working, so the pump determines the percentage of each previous bolus that is still working. By taking this “unused” insulin into account, the pump’s bolus calculation saves us from accidentally taking too much insulin at mealtimes or when correcting high blood sugar levels.
Hypoglycemia sometimes can occur when a mealtime bolus peaks before food has a chance to digest and raise the blood sugar. For example, foods with low glycemic index values (such as pasta, beans and dairy products) usually take several hours to digest. Very large portions of food, especially with a high fat content, might take several hours to make their way through the stomach. Likewise, food consumed over a long period of time – such as a holiday meal or a bucket of popcorn at the movies – takes a while to digest. In addition, anyone who suffers from gastroparesis – a nerve condition that causes the stomach to empty more slowly than usual – is susceptible to hypoglycemia soon after eating. To prevent lows in these situations, boluses delivered by pumps may be delivered over a prolonged period of time (a “square”, “dual”, “extended” or “combination” bolus). Prolonged boluses, delivered over a period of two or three hours, peak later and less abruptly than injected rapid-acting insulin, thus reducing the risk for post-meal hypoglycemia.
Accurate carb counting is yet another important component of effective blood sugar control. Over-counting carbs can lead to overdosing on insulin. To improve carb-counting precision, many pumps now include food databases with nutrient contents (including carbohydrates) for hundreds of foods.
To Capitalize On What Pumps Have to Offer…
Simply wearing and using a pump does not guarantee success. For example, basal rates will only help to prevent lows (and highs) if they are set properly. Testing/fine-tuning basal rates requires fasting to see if the blood sugar is holding steady at all different phases of the day and night. Correction boluses (insulin given to lower high blood sugar) need to be based on appropriate target glucose levels as well as accurate correction/sensitivity factors. If targets or correction/sensitivity factors are set too low, hypoglycemia is more likely. Similarly, mealtime insulin (insulin:carb ratios) should be customized for each separate mealtime. It is common to need different I:C ratios at different meals. And don’t forget, the right I:C ratio is one that produces normal blood sugars 3-4 hours after bolusing… not 2 hours! Work with your health care team to fine-tune all of your pump’s insulin delivery parameters. (If they can’t help, give my office a call and we can work on it by phone.)
When Lows Happen…
Even with our best efforts and intentions, hypoglycemia may not be entirely avoidable. When it happens, treat it right. Suspending the pump when a low occurs is not the answer. Suspending or disconnecting will take almost an hour to make any difference in your blood sugar level, and it can lead to a sharp rise a few hours later. Instead, treat your low with rapid-acting carbohydrates such as glucose tablets, crackers, pretzels, dry cereal, or anything that has “dextrose” as a main ingredient. Use an amount of carbohydrate that is appropriate for your body size and the severity of your blood sugar level (the bigger and “lower” you are, the more carbs you will need).
If hypoglycemia happens multiple times in the course of a week, don’t
just sit there and take it. Repeated lows at the same time of day or under similar
conditions mean that a change to your insulin dosing is in order. Remember,
it’s not going to fix itself! Talk to your health care team and come up
with a practical solution.
Gary Scheiner MS, CDE is a diabetes educator with a private practice (Integrated Diabetes Services) near Philadelphia, and author of Think Like A Pancreas: A Practical Guide to Managing Diabetes With Insulin. He has had Type 1 diabetes for 20 years, and offers diabetes education and management consultations via phone, fax, and Internet to patients throughout the world. Submit inquiries to firstname.lastname@example.org, or call (877) SELF-MGT.