When Hypoglycemia Sneaks Up

It’s happened again. You test and the number that pops up on your meter is low. Way too low! But you feel fine. Shouldn’t you be experiencing that fuzzy-headed, heart-pounding, shaky-bodied, world-swirling feeling that goes with hypoglycemia?

What you have is hypoglycemia unawareness. Basically, this means that you’re unaware of low blood glucose and thus cannot take action to correct it. Your body has lost its ability to sense a falling glucose level. Episodes may occur when you’re awake or asleep.

In people without diabetes, a back-up safety system, the hormone counter-regulation system, causes the hypothalamus in the brain to trigger a decrease in insulin production when the blood-glucose level is about 83 mg/dl. If you have diabetes and have previously injected insulin, it is of course impossible to decrease the amount of insulin you’ve already injected, and you must instead ingest glucose to steady your levels or they will continue to fall.

Two Mechanisms

Two major mechanisms in the body respond to falling glucose levels: the autonomic nervous system and the central nervous system.

The Autonomic Nervous System

This system stimulates the release of adrenaline (epinephrine) when blood glucose falls to a low level and is responsible for most of the symptoms of hypoglycemia. A critical range for the response to occur is approximately 50 to 70 mg/dl, before more dangerously low levels are reached. Glucagon, an assisting hormone, helps the liver release stored glucose.

Adrenaline assists the liver’s production of glucose and limits the use of glucose in other parts of the body. The main goal of these actions is to supply the brain with fuel. Think of it as an overall body response to your brain being frightened of starvation.

Signs that this process is at work are trembling or shaking; sweating; rapid, pounding heartbeat; changes in body temperature; and/or tingling in hands and feet—the normal, early symptoms that tell you to test your blood glucose and take action.

The Central Nervous System

The second mechanism involves the central nervous system. When blood-glucose levels drop too low, motor and thinking functions are disrupted. Early symptoms include slowed performance of motor skills and difficulty in concentrating or reading. These symptoms can affect decision-making for self-treatment and are frequently the cause of accidents or injuries.

Often, the first symptoms in hypoglycemia unawareness are emotions that are displayed in negative or embarrassing ways. Chronic low blood-glucose levels stress the neurons in the nervous system.

Losing Response: How Did This Happen?

Over time, adrenaline and glucagon activity can become “blunted.” This is especially common in individuals who have low A1Cs, a history of frequent low blood-glucose episodes, widely swinging glucose levels, or frequent lows at night. It is also found among children under 10, pregnant women, the elderly, people with failing kidney function, and those with a chronic illness who might be taking beta-blocking medications. Alcoholic beverages can increase the risk of unawareness by masking the symptoms and blunting the action of counter-regulatory hormones.

While hypoglycemia unawareness is most common in people with type 1 diabetes, individuals who have had type 2 for a long duration may be at risk if any of the above situations exist. Anyone with poor nutrition can also be susceptible, especially if they skip or delay meals. When physical exertion is added, the risk of episodes increases if precautions are not taken.

Getting Back to Awareness: How a Pump Can Help

If you have a diagnosis of hypoglycemia unawareness, you have some urgent goals: Avoid it! Prevent it!

Insulin pump therapy most closely mimics the response of a normally functioning pancreas. And, because an insulin pump uses only rapid-acting insulin, the peaking effect of a longer-acting insulin is removed. Basal insulin delivery can be lowered temporarily, when necessary, for exercise or anticipated events that might cause low blood glucose. Meal boluses can be delayed or spread out over a specified time to match food absorption. The use of fast-acting insulin analogs is recommended.

If you have hypoglycemia unawareness, you should set your target ranges higher for both blood-glucose levels and A1C results. A target range of 100 to 200 mg/dl is not unusual. You might raise your correction target for high blood glucose to 150 mg/dl. Your bedtime blood-glucose target should be in the range 100 to 150 mg/dl. Your target for an A1C should be between 6% and 7%—not 4% to 6%.

Physically fit, leaner athletes are more sensitive to insulin and should set exercise target blood-glucose levels higher.

You should plan to do more frequent testing, including periodic tests between 2 a.m. and 4 a.m. Always test before driving, and aim for a blood-glucose level of over 100 mg/dl.

Clinical studies show that awareness symptoms can return within a few weeks.

Ask your team if blood-glucose awareness training programs are available in your area. The University of Virginia, for example, has a Blood Glucose Awareness Training (BGAT) program (www.avery.med.virginia.edu/~bgat/bgat.html).

Overall, insulin pump therapy can have a positive impact on glucose control. Training for self-management, smoothing out blood-glucose levels, and a return of warning symptoms can give you back control and improve your quality of life.

Editor’s note: Always check with your diabetes management team before making treatment adjustments. Keeping a diary of symptoms for each event can be a useful tool in identifying treatment options.

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