The
American Diabetes Association advises that postprandial blood glucose shouldn’t
exceed 180 mg/dl (plasma value) at two hours after the start of a meal.
Personally I find this number exceedingly high and was surprised it was not
lowered in their recent January 2009 Standards of Care. Many other diabetes educators I know find it high as well and several other associations and
experts believe the two-hour postmeal goal should be less than 140 mg/dl. Whew!
Better.
I've
placed two posts here in the last two weeks that are excerpts from Hope
Warshaw's (R.D., B.C.-A.D.M., C.D.E.) wonderful article, "Rapid-Acting Insulin
Timing It
Just Right." Diabetes educator and dietitican
Warshaw explains how to better time your insulin with your meals to get
your post prandial blood sugars where you want them. Among the suggestions are occasionally
checking your blood glucose after a meal at hours one, two, and three to help
you determine when your blood glucose level peaks and starts to come down
again. The overall key to controlling postprandial highs is better timing of
rapid-acting insulin. Here are several other useful tips from her article:
Low
glycemic index foods - If your blood glucose is less than 100 mg/dl before a
meal and you plan to have a meal with a low glycemic index, wait until you
start to eat to take your rapid-acting insulin.
Uncertain
carbohydrate intake - If you don’t know how much carbohydrate you will eat
at a meal, consider splitting your rapid-acting insulin dose. Take enough
insulin before the meal to cover the amount of carbohydrate you are sure you
will eat. Then as the meal goes on and you know how much more carbohydrate you
will eat, take more insulin to cover that amount. This method is easiest if you
are on an insulin pump. (But I can attest that it’s doable even on Multiple
Daily Injections)
Drawn-out
meals - Pump users who are planning to have a meal that is eaten over
time, such as a cocktail party or Thanksgiving dinner or a meal that is higher
in fat or lower in glycemic index and high in fiber, (it will slow your glucose
rise) may use one of the optional bolus delivery tools on their insulin pump.
Most insulin pumps allow you to deliver a bolus over time rather than all at
once or to deliver some of the bolus immediately and the rest over the next few
hours. People who inject insulin could take half their bolus at the start of a
meal and the other half an hour or two later. (I do this and sometimes even
inject 3 x as I graze. No it’s not fun but it does help more closely match the
correct dose of insulin to what and when you’re actually eating.)
Snacks
- Alison Evert, R.D., C.D.E., a diabetes educator at Joslin Diabetes
Center at Swedish Hospital in Seattle, advises people to "take
rapid-acting insulin with any amount of carbohydrate over 10 grams."
Although it is common to think that a few grams won’t make a big difference,
the reality is that 10 grams of carbohydrate can raise many peoples’ blood
glucose 30 or more points.
Unused
bolus insulin - While the
duration of action of rapid-acting insulin is usually given as 3–4 hours, some
diabetes experts believe it may continue to lower blood glucose level for as
long as 5 hours. You can assume that about 20% of a dose of rapid-acting
insulin is used each hour after it is given. In John Walsh’s book Using
Insulin and on his Web site http://diabetesnet.com/diabetes_control_tips/bolus_on_board.php,
he provides a table that shows insulin activity at 1, 2, 3, 4, and 5 hours
after bolus doses of insulin from 1 to 10 units.
When
two doses of rapid-acting insulin overlap, their effects overlap, too, and the
result can be hypoglycemia. Therefore, when you’re considering the size of a
bolus dose of insulin, it is critical that you factor in what Walsh calls
"the unused insulin" or "bolus [insulin] on board." This is
the amount of "active" rapid-acting insulin left from a previous
injection or bolus dose from a pump that continues to lower your blood glucose.
For
instance, before lunch, you take a bolus of rapid-acting insulin. Three hours
later you decide to have a snack with 30 grams of carbohydrate. You check your
blood glucose and find that it’s high at 195 mg/dl. Assuming 1 unit of insulin
for you covers 45 mg/dl, you calculate you’ll need two units of insulin
to bring your blood glucose level down to your premeal target of 100 mg/dl and
another two units to cover the snack you’re about to eat. You take the insulin,
and several hours later, your blood glucose has dropped to 55 mg/dl. Why?
Because you didn’t factor in the hour or so of action left from the bolus or
injection you took at lunch.
To
prevent hypoglycemia from unused insulin, get in the habit of thinking about
when you took your last bolus dose and how much (if any) action is still left
before taking another bolus to "correct" high blood
glucose. Most pumps have a built-in feature that keeps track of how much
of a previous bolus dose is still active. For us MDI people we have to log it
on paper or in our heads.
Even though
I've had diabetes for 37 years and injected insulin for 32 (Yes, I'm a type 1
who was misdiagnosed with type 2 and on oral meds the first 5 years) you can
always learn something new or refresh what you know.
Thank you Hope.
