Tips for calculating a total daily dose of insulin
You can use one of several methods to determine a safe, initial dose
by Phyllis Maguire
Published in the August 2007 issue of Today's Hospitalist.
Evidence keeps mounting that high blood sugars lead to worse outcomes in hospitalized patients—and that sliding scale regimens produce both more hyperglycemia and hypoglycemia.
But as hospitalists switch from sliding scale to basal and bolus dosing, how do they calculate a safe total daily dose to start with? Experts say that physicians can use any of three different strategies, depending on whether patients have been using insulin as either an outpatient or in the ICU.
Any one of these approaches will produce a safe, conservative initial dose, but experts warn that none of the
strategies by itself is a slam dunk. You still have to bring art to each approach, adjusting doses according to such factors as illness severity and eating status.
|“The pharmacology is never going to work if we don’t follow physiology."|
Deepak Asudani, MD
Baystate Medical Center
Related article: Matching insulin regimens to nutritional needs
Here’s a look at how two hospitalists use these strategies in their day-to-day practice.
1. Base total sub-Q dose on insulin infusion rates.
When Deepak Asudani, MD, a hospitalist at Baystate Medical Center in Springfield, Mass., transitions patients from IV insulin in the ICU to sub-Q insulin on the wards, he uses the following formula: Take the average hourly insulin infusion rate over the past six hours and multiply that rate by 20. That gives you a number that should equal 80% of the daily infusion dose.
“It’s a little correction to prevent any hypoglycemia,” says Dr. Asudani. Because patients’ insulin needs are tapering down a bit as they exit the ICU, he adds, you don’t need to supply the same daily dose.
For patients eating substantial amounts of food, you can use that calculated amount as the total daily dose. Between 40% and 50% of that total dose should be administered as basal, with the rest dosed out in nutritional boluses.
For patients who aren’t eating much, that calculation is likewise the total daily dose. You should give 50% of that total dose as basal insulin about four hours before patients’ IV insulin is turned off, Dr. Asudani says. Once patients start eating, add the rest in bolus amounts.
You should also take into account how well the patient’s glucose was controlled in the ICU on the preceding day. For patients with poor control, consider factoring in another 10% to your total daily dose.
Related article: Insulin protocol review: the transition from IV to sub-Q
2. Add up the insulin used in a patient’s home regimen.
Knowing a diabetic patient’s home regimen can be helpful when establishing a total daily dose. Just add up the total amount of insulin a patient is taking, then adjust that dose based on eating status, severity of illness and steroid use, as well as the patient’s level of control at home.
Hospitalist Cheryl O’Malley, MD, who championed a sub-Q insulin protocol at Banner Good Samaritan Medical Center in Phoenix, Ariz., says you should be prepared to ask a lot of questions.
“If you just ask a broad question, like ‘How are your sugars at home?’ ” she says, “they may say, ‘fine.’ But when you ask what the number is, usually they tell you, ‘I don’t really know’ or ‘somewhere in the low 200s.’ ”
You may also be misled if patients tell you that they adjust their home insulin based on their glucose level. Many physicians interpret this as “sliding scale,” but it may mean that patients are using carbohydrate counting with correction factor to match their insulin doses to the food consumed.
For patients who know only that they are taking insulin, Dr. O’Malley explains, you may have to ask what color the bottle is, whether or not the insulin is cloudy, and if patients give themselves shots. “At least I’ve learned from the interview what needs they have at discharge and can use it as an educational opportunity,” she adds.
(Also helpful at discharge: getting an HbA1c on admission. That allows you to separate the patients with stress hyperglycemia from those with previously undiagnosed diabetes.)
Even for some patients who have good control at home, Dr. O’Malley resorts to strategy No. 3, which follows. But for physicians who can base sub-Q dosing on patients’ home regimen, she offers this heads-up: Patients on good home control with 70/30 or 75/25 insulins can be started on the same total daily dose, but not in the same proportion between basal and bolus dosing.
“The biggest mistake people make is just continuing the entire home regimen when that balance of basal to bolus is a bit too much,” she says. For inpatients eating less than usual, a 70/30 or 75/25 regimen is too heavily weighted to basal insulin.
“Patients are then predisposed to hypoglycemia if they start eating even less or if they become NPO for a procedure,” Dr. O’Malley says. Instead, divide the total daily dose equally between basal and bolus doses.
3. Use the patient’s weight, body habitus or diabetic status.
For patients who aren’t transitioning from IV insulin or who aren’t on an insulin regimen at home, many experts offer these rules of thumb for estimating total daily dose:
- 0.3 units/kg/day for patients who are lean, on hemodialysis, frail and elderly, insulin-sensitive, or at risk for hypoglycemia;
- 0.4 units/kg/day for a patient at normal weight;
- 0.5 units/kg/day for overweight patients; and
- 0.6 units/kg/day or more for patients who are obese, on high-dose steroids or insulin-resistant.
According to Dr. O'Malley, this formula tends to underestimate what patients' needs really are.
"For very obese patients," she says, "some hospitals start out giving up to 1 unit per kilogram per day as their initial total daily dose. But when people are used to using sliding scale only, even the 0.6 units per kilo that we use to calculate their total daily dose can make physicians leery." As hospitals and physicians become more comfortable controlling hyperglycemia, initial dosing can become more aggressive.
The dosing protocol that Dr. Asudani uses takes patients' diabetic status into account. He offers these dosing guidelines for basal insulin:
- 0.4 units/kg/day of long-acting insulin for patients with poorly controlled or newly diagnosed type 2 diabetes; and
- 0.2 units/kg/day for type 1 diabetics.
He uses the following parameters for bolus dosing:
- 0.1, 0.15 and 0.15 units of short-acting insulin/kg for breakfast, lunch and dinner, respectively, for type 2 diabetics; and
- 0.05-0.1 units of rapid-acting insulin/kg, administered before meals, for type 1 diabetics.
Dr. Asudani and his colleagues also take patients' steroid use into account when factoring the total daily dose. They adjust the total daily dose 20% higher for patients on low-dose prednisone of 10-20 mg/day; 30% higher for those on medium-dose prednisone of 21-40 mg/day; and a full 50% higher for those on high-dose predisone of 41 or more mg/day.
Once patients are started on sub-Q insulin, they should be closely monitored.
“That’s when the fine-tuning comes in, and we change about 10% or so every day,” Dr. Asudani points out. “The pharmacology is never going to work if we don’t follow physiology.”
Patients who are NPO or on continuous tube feeds should have their blood sugars checked every four hours if you are using a rapid-acting insulin, while patients given regular insulin can be checked every six hours. Those who are eating should be checked before meals and at bedtime.
When making insulin adjustments, “a little aggression is good, and increments should not be in just one or two units,” Dr. Asudani says. At the same time, he adds, “we err on being under-corrected rather than over-corrected, and I’m thankful that at least under-correction is being done.”
Until now, he adds, worries about hypoglycemia often led physicians to not even take hyperglycemia seriously enough to correct it. “With the availability of diverse types of insulins,” Dr. Asudani points out, “patients don’t need to live with inpatient hyperglycemia anymore.”
Phyllis Maguire is Executive Editor of Today’s Hospitalist.
Sign up for e-newsletter on inpatient diabetes management
The first issue of the Inpatient Diabetes Management newsletter is now available, with information on insulin dosing, the evidence for controlling hyperglycemia and getting “glucometrics” off the ground. Sign up now at the Today’s Hospitalist Web site.
Online dosing resources
The Glycemic Control Implementation Guide, published this year by the Society of Hospital Medicine is available online through links in SHM’s Resource Center.
The workbook offers methods to estimate insulin as well as several examples of insulin-dosing protocols from around the country.