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Insulin On Board & Other Basic Pump Features
Getting More from Your Insulin Pump
For background information on insulin and insulin pumps:A Basal-Bolus Approach for Pumps
Your child has an insulin pump and your family has received the initial training at a Pump Start workshop with your child’s diabetes health care team… now what?
You have a choice:
1. you can use the pump as a high-tech “syringe” and continue to perform all the same tasks you did when your child was injecting his insulin (for some families, whose only goal is to vastly reduce injections, this is a reasonable approach);
2. you can read the user’s manual cover-to-cover so you can use each and every pump feature to its utmost; or
3. you can get a few useful features under your belt and then learn more when you need to get more from the pump. The right approach for your family, as always, will be one that fits your family’s needs and resources of time and energy at this time.
If it’s time to learn more, we suggest these seven helpful features to get you moving past the “high-tech syringe” stage.
An insulin pump delivers a single type of rapid-acting insulin in two ways:
– a basal dose that is pumped continuously at an adjustable basal rate to deliver insulin needed between meals and at night.
– a bolus dose that is pumped to cover food eaten or to correct a high blood glucose level.
Basic Pump Feature #1: Individualized Standard Basal Rates
In our article on how a Basal-Bolus Approach applies to the use of insulin pumps, we defined “basal” insulin as the background insulin which keeps blood glucose steady in the absence of food and exercise. We also pointed out that an insulin pump provides basal insulin by infusing rapid-acting insulin (such as Humalog®, Novorapid®, or Apidra®) in small doses every few minutes.
Your child’s insulin pump delivers basal insulin according to the current Basal Rate profile that you have programmed into the pump. The Basal Rate is presented as an hourly rate; that is, it represents the total amount of insulin that will be delivered in a given hour. For example, your child’s 2 pm basal rate could be 0.100 units of insulin/hour (U/hr), which means that in that hour from 2 to 2:59pm, one-tenth of a unit of insulin will be delivered by the insulin pump. Or the 2pm rate could be 4.5 U/hr, which means that in that hour, four and a half units of insulin will be delivered.
We mentioned above that the insulin pump provides basal insulin in small doses every few minutes. So within that hour, if basal insulin is delivered every 3 minutes, then the total basal rate will be split into 20 equal doses within that hour. In the first example of a basal rate of 0.100 U/hr, 0.005 units will be delivered every 3 minutes; in the second example of a basal rate of 4.5 U/hr, 0.225 units will be delivered in each of those frequent, smaller doses.
You can individualize your child’s standard basal rate profile by programming in different basal rates for different times of the day.
- Basal insulin needs vary from person to person, across the day, across different days, and across the lifespan.
- Adults typically need more basal insulin in the early morning hours to deal with the “Dawn Phenomenon”: the liver secretes more glucose as we wake up (creating a need for more insulin).
- Children often need more basal insulin in the late evening hours to deal with the release of growth hormones a few hours after they fall asleep.
- Adolescents typically need more basal insulin in the late evening hours to deal with the release of growth hormone as well as more insulin in the early morning hours to counteract the Dawn Phenomenon.
The insulin pump models currently available in Canada allow for multiple time periods in the day, each of which could have a different basal rate. Basal Rates can range from as little as 0.025 for some pump models (that’s 25-thousandths of a unit in an hour, or just over 1-one-thousandth of a unit every 3 minutes! Amazing!) to as much as 35.0U/hr. Many people find that dividing the day into 4-8 time periods, each with a different basal rate, is the most effective approach. If you have too few basal periods, you may be missing the opportunity to individualize insulin doses as needed across the day which would minimize predictable daily highs and lows; if you have too many basal periods, the excessive complication may make it harder to identify what’s working and what’s not.
The best number of basal periods, and the best basal rate to program into your child’s pump for each basal period, are the ones that best fit your child’s typical needs at different times of the day. To illustrate (but not to be interpreted as appropriate for anyone but him), here is a sketch of my son’s current basal rates:
This shows that a basal rate program is typically divided into several time periods throughout the day, with basal rates changing across those time periods; as a whole, the rates usually do not jump around erratically, but follow a curve (darker blue line, below), sometimes with a few “hiccups” within that curve.
Basal rates can be approximated based on log sheet data, or can be empirically tested as needed. For further details, we suggest you consult your child’s diabetes health care team and check out Waltzing the Dragon’s “Blood Glucose Management – Pump” section on Readiness Level 2, as well as the “Blood Glucose Management” section on Readiness Level 3.
Basic Pump Feature #2: Bolus Calculator
In addition to insulin pump features related to basal, or background, insulin (as outlined above), there are also a number of useful features that relate to bolus insulin…
A “bolus” is a dose of rapid-acting insulin which is delivered either to:
cover the carbohydrate-containing food which we eat. (This is called a “carb bolus” and is specified by an Insulin-to-Carb (I:C) ratio.)
correct high blood glucose. In this case, the bolus is called a “correction bolus” and is specified by some variation of an Insulin Sensitivity Factor (ISF), such as a Correction Formula, Sliding Scale, or ISF setting on a pump.
When a bolus is needed in an injected insulin program, someone — either the parent or the child himself — needs to crunch the numbers. That is, for a carb bolus, the number of carbs needs to be plugged into an insulin-to-carb ratio to calculate the insulin dose; for a correction bolus, the current blood glucose reading needs to be plugged into a correction formula. Or perhaps your child uses a sliding scale and needs to decide what the scale recommends for his current carbs and blood glucose reading. In any case, someone needs to do some form of calculating.
The Bolus Calculator feature on an insulin pump does this calculation for you. When your child plans to eat carb-containing food, you manually input the number of carbs. Then the Bolus Calculator, using the I:C ratios that you previously programmed into the pump, will calculate the insulin dose (bolus) needed to cover those carbs. Similarly, if you also enter a current blood glucose reading (which may be automatically entered for you if you use a blood glucose meter that communicates with your insulin pump), the Bolus Calculator will calculate a correction dose of insulin using the ISF settings that you previously programmed into the pump.
The Bolus Calculator will add or subtract insulin from a carb bolus for an above or below target blood glucose reading. It may also, under certain circumstances, subtract the amount of active insulin which remains from previous boluses (see Basic Pump Feature #3, below).
For further flexibility, if you anticipate needing less insulin because of planned exercise, or more insulin because of a test or other stressor, you can override the default I:C and ISF settings right in the bolus delivery screen on your child’s pump. In this way, you can change the amount of insulin delivered in that one occurrence by bumping up (or down) the I:C and/or ISF a step or two.
Different insulin pump companies use slightly different terminology to refer to the Bolus Calculator:
Omnipod calls it the “suggested Bolus Calculator”;
Animas calls it “ezCarb” for a food bolus, and “ezBG” for a blood glucose correction bolus;
Medtronic calls it “Bolus Wizard”
Accu-Chek calls it “Bolus Advice”
Note that with an insulin pump, you still have the choice to bypass the Bolus Calculator, do the calculations yourself and deliver a chosen number of units of insulin (without having to enter a carb amount nor a current blood glucose reading). That is, you can use the pump as a high-tech insulin pen/syringe when and if you choose to do so. (Animas, Medtronic and Omnipod refer to this function as “Normal Bolus”; Accu-Chek as “Standard Bolus”.)
Basic Pump Feature #3: Active Insulin Remaining
a.k.a. Bolus on Board (BOB), or Insulin on Board (IOB)
Ever had this experience? (If you’re a D-parent, I know you have!) You give your child an insulin dose for high blood glucose, but two hours later the reading is still high. So you give another correction, only to find that an hour later her BG is low. Darn Dragon!
Here is one possible explanation (of many) for what happened. The blood-glucose-lowering effect of the various brands of fast-acting insulin last about 3-5 hours. So when you gave the second dose of insulin 2 hours after the first dose, there was still some “active insulin” remaining, which would have continued to decrease your child’s blood sugar even in the absence of that second correction dose. If this remaining insulin is not accurately taken into account, then the second correction dose amounts to an over-correction of blood glucose, resulting in a low when everything starts rolling downhill. This is known as “insulin stacking”.
The Active Insulin Remaining feature (called “Bolus On Board” (BOB), or “Insulin On Board” (IOB)) takes this unused insulin into account, reducing the potential for insulin stacking which may otherwise result in over-treatment or unnecessary treatment of a high blood glucose reading. How exactly it does so varies between different pump manufacturers:
- For high blood glucose: the amount of active insulin will be subtracted from the correction bolus for above-target blood glucose. For example, if the pump bolus calculator recommends a correction bolus of 1.0U, but BOB is 0.2U, the bolus calculator will recommend delivery of 0.8U to bring that high blood glucose down to target.
- To cover food: the amount of active insulin may also, under some conditions, be subtracted from a carb bolus. Some pumps subtract BOB from a bolus for carbs if blood glucose is below-target (and the current blood glucose reading is taken into account – i.e. you “add BG” into the calculation), while some pumps do not subtract BOB under these conditions. If you are unsure of how your child’s pump deals with active insulin under certain conditions, please contact the pump manufacturer for clarification.
Notes About Active Insulin:
Note 1: Active Insulin Remaining does not involve basal insulin; it only takes bolus insulin into account. For this reason, “Bolus On Board” (rather than “Insulin on Board”) is perhaps a more accurate label for this feature.
Note 2: BOB will only be taken into account if you use the BG Correction Bolus function, or if you “Add BG” to a Carb Bolus. That is, if you have not checked BG lately, or you “Skip BG” when giving a carb bolus, the remaining active insulin will not be taken into account when calculating the recommended insulin dose.
Note 3: BOB recommendations have limited utility in the 90 to 120 minutes post-meal. During this time, the effect of the food is still being worked out, so much of the current remaining insulin may be used to cover the still-digesting carbs (in which case, it is not “excess” insulin at all). Some pumpers choose to disregard BOB during this time, instead covering the intake of any additional carbs with a full carb bolus.
Note 4: Calculations of Active Insulin Remaining are influenced by other programmed rates, such as Duration of Insulin Action (DIA)and the Target BG.
The pump will base its calculations of Active Insulin Remaining on the amount of time you have told it that insulin will last. If you have programmed in 3 hours as the Duration of Insulin Action (DIA), it will calculate how much insulin is left in the portion of those 3 hours which remain; if you have programmed in 5 hours as the DIA, it will calculate a very different recommendation based on this very different time period. As a result, very short DIA settings may underestimate the amount of insulin that is still active, thereby increasing the risk of insulin stacking, and increasing the risk of low blood glucose as a result. Conversely, very long DIA settings may over-estimate the amount of insulin that is still active, thereby increasing the chance that BG will be high later.
In addition, since the pump subtracts BOB for a below-target blood glucose reading, pump recommendations will also be affected by the target blood glucose that you have programmed in. If you have set 8.0 mmol/L as the target, then it may subtract insulin for any current BG reading below that, including, for example, a BG of 7.0 mmol/L. However, if 6.0 mmol/L is the target BG, then the pump would not subtract insulin for a BG reading of 7.0; in fact, it will not subtract insulin until BG is below 6.0. As you can see, these different BG target settings will result in different BOB calculations, which will, in turn, result in different BG readings in the few hours after insulin delivery.
Therefore, your programming of DIA and target BG becomes critical for the BOB function to work effectively. We suggest that you review and make any necessary changes to the DIA and BG Target settings in order to get the most out of the BOB feature of your child’s insulin pump. For more information on how to individualize these settings for your child’s needs, consult your child’s diabetes health care team and check out the following WaltzingTheDragon.ca articles:
More information and tips on individualizing pump settings:Insulin Adjustment Using and Insulin Pump: An Overview
Assessing Pump Settings: Duration of Insulin Action
Basic Pump Feature #4: Pump History
The Pump History feature of your child’s insulin pump keeps track of all the actions taken by the pump, automatically and manually, including the date/time and amount of basal doses, boluses, Total Daily Doses, alarms, primes, and suspensions of pump functioning.
If your child can’t remember if she bolused for lunch… check the pump history. If you get unexpected blood glucose results… check the pump history for clues. If you changed the basal rates and can’t remember when and by how much… check the pump history. Can’t remember if it’s time for a new infusion set?… check the pump history for a “new set” record, or for the date and time that the cannula was last filled. Unlike injected insulin programs, use of an insulin pump provides an automatic record of everything that occurred with regards to the pump… Handy!
Note that if your child’s pump model includes an integrated blood glucose monitor, you can also consult the monitor history for information about past blood glucose readings. Most pump companies even offer data software that integrates results from both the insulin pump history and the blood glucose monitor log, so you can see all the relevant entries in one record on your computer or mobile device.
Basic Pump Feature #5: Reminders
Does your child have a habit of forgetting to bolus for lunch at school? Are you interested in the 2-hour post-prandial (post-meal) blood glucose reading, but keep missing the check at that time? Most insulin pumps have a feature which allows you to set a Reminder which will alert you at a certain time of day (ex. 12:00pm), or when a certain length of time has elapsed since the last bolus (ex. 2 hours after the last bolus), with a reminder to check blood glucose or to bolus (if it was missed).
Basic Pump Feature #6: Lock-Out Feature
If you want to prevent an unauthorized user from pressing pump buttons (and potentially delivering an unintended bolus), most pumps include a Tamper-Resistant (Lock-Out) feature. If you lock the pump each time you finish using it, then pressing pump buttons will have no effect until you “unlock” the pump. This feature is handy for young children or developmentally delayed individuals who wear an insulin pump. It was also an important safe-guard in the eyes of the staff at our young son’s school – they wanted to make sure that other students could not put our son at risk by tampering with the pump.
Basic Pump Feature #7: Insulin Limits
As a safety net, most insulin pumps allow you to set an upper limit on the amount of insulin that can be delivered in a single bolus (as well as multiple boluses over a 2-hour and a 24-hour period, and an hourly limit on basal delivery). For a child who is in the early stages of learning to operate their insulin pump on their own, this gives parents some peace of mind, as the amount of extra insulin their child could accidentally deliver is restricted to the maximum limit set. When the limit is reached, a warning message pops up, which may alert you (the parent) of the need for damage control. And allow you to avoid a potentially dangerous low blood sugar situation.
Limits can be restrictive, however. If you find that your intended boluses too often hit this upper ceiling, it may be time to change the settings to allow for higher insulin limits.
The above information was reviewed for content accuracy by clinical staff of the Alberta Children’s Hospital Diabetes Clinic.
This material has been developed from sources that we believe are accurate, however, as the field of medicine (in particular as it applies to diabetes) is rapidly evolving, the information should not be relied upon, as it is designed for informational purposes only. It should not be used in place of medical advice, instruction and/or treatment. If you have specific questions, please consult your doctor or appropriate health care professional.
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