Successful blood sugar control using an insulin pump requires
good record keeping. Candidates should be willing to check blood glucose levels a
minimum of 4 times daily, optimally 6–8 times daily, in order to detect
hyperglycemia and avoid diabetic ketoacidosis. Candidates should also be
able to troubleshoot problems related to pump operation and
have a willingness to maintain frequent contact with
members of the health care team.
Basal insulin is the supply of insulin that is
needed to maintain good blood sugar control without taking into account
eating any food. The basal insulin accounts for about 40 to 50% of the
daily insulin requirement. The hourly basal insulin infusion rate may
need to be adjusted to account for diurnal variations in insulin
resistance. Blood glucose levels are obtained throughout a 24 hour period :
If adjustments to the basal rate are required, the
overnight basal rate is adjusted first if necessary. The basal rate is
usually adjusted by 10 to 20 % increments two to three hours
before the expected rise or fall in blood sugar. The lowest infusion rate
of the day is typically between 11 PM to 4 AM . The basal rate will
sometimes need
to be increased between 5 am to 10 am to cover the insulin
resistant period (dawn effect) in early morning [4]. The basal rate may
also need adjustment due to stress or exercise during a given time
period.
Meal Related Bolus
The dose of a meal related bolus of insulin may be
calculated or sometimes derived empirically. In either case the dose
should be sufficient to return a patient's blood glucose value to a
near pre-meal level 3-4 hours post-meal.
The American Association of Clinical Endocrinologists Protocol [1]
The AACE Protocol estimates the total daily insulin requirement for 24 hours
based on the patient's pregnancy status or gestational age and weight in
kilograms
| Gestation
|
Total Daily
Insulin |
| Prepregnant
|
0.6 units X
weight (kg) |
| First trimester |
0.7 units X
weight (kg) |
| Second trimester |
0.8 units X
weight (kg) |
| Third trimester |
0.9 units X
weight (kg) |
| Term pregnancy |
1
units X weight (kg) |
Calculation of Insulin Basal Rates
1/2 the total daily dose is given as the total daily basal dose. The hourly
insulin basal rate is calculated by dividing the total basal dose by
24.
The AACE Protocol recommends the calculated hourly
basal rate be adjusted to account for the
diurnal variations in insulin resistance as discussed above.
| Time of day |
Infusion rate |
| 12-4 AM |
˝ calculated basal rate |
| 4-10 AM |
1˝ calculated basal rate |
| 10-6 PM |
calculated basal
rate |
| 6-12 PM |
calculated basal
rate |
After second trimester, in case of dislodgment at infusion site AACE suggests
giving a dose of NPH 0.1 × weight (in kg) before bed; then lower early morning insulin
infusion.
Calculation of Meal
Related Insulin Bolus
1/2 the total daily dose is divided into thirds for a dose before each meal
Medtronic® Protocol [2]
The Medtronic® Protocol estimates the total daily insulin requirement for
24 hours using several methods.
Method 1
Total Daily Dose (TDD) for insulin infusion = 0.75 X total daily insulin
dose prior to starting the insulin pump.
Method 2
Total Daily Dose (TDD) for insulin infusion =0.23 X weight (lbs) or 0.5
X weight (kg)
Method 3
Total Daily Dose (TDD) for insulin infusion = (Method 1 +Method)/2
Calculation of Insulin Basal Rate
Total Basal Insulin Requirement = 1/2 Total Daily Dose (TDD) for insulin
infusion
Adjustment of Basal Rate
The overnight basal rate is adjusted by checking the blood sugar
at 12 AM, 3 AM and 7AM.
- If the glucose level rises more than 30 mg/dL between readings, the
basal rate should be increased by 10 to 20 percent two to three
hours before the rise is observed.
- If the glucose level decreases by more than 30 mg/dL (or falls
below target) between readings, treat the low blood sugar and
decrease the basal rate by 10 to 20 percent two to three hours
before the decrease is observed. [3, 5]
To adjust other daytime basal rates the patient is instructed to NOT
to eat between meals and NOT to correct post-meal high blood sugars. The
two hour post-meal blood sugar is then compared to the next
pre-meal blood glucose.
- "If the blood glucose decreases more than 60 mg /dL or falls below blood
glucose target: decrease basal rate by 10 -20 percent.
- If the blood glucose decreases less than 30 mg/dL , or stays the same ,
or rises : increase the basal rate by 10 - 20 percent" [3].
Calculation of Meal
Related Insulin Bolus
Meal related insulin boluses are calculated by the pump according to
the carbohydrate content of the meal using the carbohydrate-to-insulin
ratio (CIR)
The carbohydrate-to-insulin ratio (CIR) is the number of grams of
carbohydrate that are covered by 1 unit of insulin. The CIR is calculated
by dividing the constant 450 by the Total Daily Dose (TDD).
The CIR may be different for different meals of the day.
CIR-= 450 / TDD
Example:
TDD= 50 units insulin
CIR= 450 /50 = 9 grams/unit
The meal has 90 grams of carbohydrate
Meal insulin bolus = carbohydrates/carbohydrate to insulin ratio CIR =90/9= 10 units
- If the post meal blood sugar is above the targeted blood
sugar range for 2 to 3 days then consider decreasing the CIR by 10 to 20
percent
- If the post meal blood sugar is less than the targeted
blood sugar range for 2 to 3 days then consider increasing the CIR by 10 to 20
percent
Calculation of Correction Dose
If the premeal blood sugar is out of the targeted range , the
meal related insulin dose may need to be adjusted accordingly. To return
the blood sugar to the desired premeal blood sugar from the current blood
sugar it is necessary to determine the amount blood glucose is lowered by
the injection of 1 unit of insulin. The amount blood glucose is lowered by the injection of 1 unit of insulin
is called the insulin sensitivity factor (also known as the correction
factor), and is calculated by dividing
the constant 1700 by the Total Daily Dose of insulin (TDD).
Insulin Sensitivity Factor (Correction Factor) =
1700 / TDD
Example
TDD= 50 units insulin
ISF= 1700 /50 = 34 mg/dL
The current premeal blood sugar is 160 mg/dL
The target premeal blood sugar is 90 mg/dL
Correction dose =
(Current blood sugar -Target blood sugar) / ISF = (160-90)/ 34
= 2.1 units
SEE Insulin Correction Dose
Calculator
More information on insulin pumps is available
at:
American Diabetes Association
Animas
Diabetes.net
Insulin pumpers
Medtronic
REFERENCES
1. Grunberger G,Statement by the American Association of Clinical
Endocrinologists Consensus Panel on insulin pump management.
Endocr Pract. 2010 Sep-Oct;16(5):746-62.
PMID:
PMID: 21356638
2. Davidson PC, et al. Analysis of guidelines for basal-bolus insulin dosing:
basal insulin, correction factor, and carbohydrate-to-insulin ratio. Endocr
Pract. 2008 Dec;14(9):1095-101.PMID: 19158048
3. Medtronic Pumping Protocol A Guide to Insulin Pump
Therapy Initiation . Bode W , Bruce Atlanta Diabetes Association Atlanta
Georgia Medtronic
4. Moore TR and Catalano PC. Diabetes in Pregnancy. In Creasy and Resnick's
Maternal Fetal- Medicine Principles and Practice sixth ed.Ed Creasy R et al. ,
2009, Saunders. pp 976-980
5. Insulin Pump Therapy: Guidelines for Successful Outcomes
American Association of Diabetes Educators 2008 Consensus Summit
September 18, 2008 • Chicago, Illinois
The American Association of Diabetes Educators
http://www.diabeteseducator.org/export/sites/aade/_resources/pdf/Insulin_Pump_White_Paper.pdf
6. Getting Started with an Insulin
Pump. Copyright 1995-2012, American Diabetes Association
http://www.diabetes.org/living-with-diabetes/treatment-and-care/medication/insulin/getting-started.html
