The decision of how to manage one’s blood sugar when living with diabetes is very much a personal one. There are pros and cons to both primary methods of insulin delivery – insulin pump vs. MDI (manual multiple daily injections). Whether you are newly diagnosed, or considering a change in your insulin delivery options, this blog outlines the differences between the 2 methods and the considerations for both when deciding which route will work best for you.
Multiple daily injections is arguably the most reliable method of insulin delivery, as there is rarely an issue of poor absorption or kinked needles interrupting the flow of insulin. If you opt for MDI, you will require a long acting insulin shot that can either be delivered once daily, or half every 12 hours to control your baseline glucose levels. You will also require a fast acting insulin for bolusing meals and correcting glucose levels. This can be delivered using an insulin pen, typically in half unit increments, or with a manual syringe. This is a great option if you do not want to have anything attached to you at all times. It also means you will have less to carry with you in your diabetes management bag, as you’ll need a vial of insulin, pen & sharps, or syringes and alcohol swabs, but will not require back-up pump equipment.
This method is not ideal if you prefer infrequent injections and would rather not have to deliver shots several times a day. Moreover, people with diabetes often find that they require varying levels of baseline or long acting insulin needs depending on the time of day, or food consumed. Incremental tweaks and adjustments especially to long acting insulin needs with MDI is not as flexible or easily obtained compared to using an insulin pump. If the baseline insulin is insufficient, you will tend to have elevated glucose levels and require several corrections, if long acting insulin is too much, you will be chasing lows. Additionally, long acting insulin can have residual impact for more than 24 hours. If you need to make adjustments to your insulin needs, it can take several days to get the dosages correct.
For those individuals who prefer the reliability of MDI, but do not want shots several times a day, an alternative option to consider is the I-Port. This is an injection port that lets you take your injection without having to puncture your skin for each shot. It is effectively an infusion site without the pump attached, it is easy to apply and easy to use. The port can be worn for up to three days and during all normal activities, including exercising, sleeping, and bathing.
Another method to help keep track of insulin timing and delivery is the InPen. This is a “smart” insulin pen that enables the user to easily keep track of insulin delivery, IOB and trends through a smart phone ap.
Insulin pumps have dramatically changed the ways in which diabetes is managed. It offers the ease and flexibility to micro-dose insulin and adjust basal insulin settings fluidly throughout the day depending on glucose levels and insulin needs. An insulin pump uses only fast acting insulin for both controlling baseline glucose levels and bolusing for meals and correcting glucose levels to bring them back into target range. It has been argued by insulin pump users that to use a pump merely to bolus for meals/corrections in replacement for MDI is akin to using a sophisticated piece of scientific equipment to simply swat a fly. Thus, an insulin pump has various settings that can be adjusted and tweaked throughout the day to react to the body’s need (the details of which can be discussed at length). The purpose of this is to introduce the basic functions of an insulin pump as a viable and reliable option for managing glucose levels.
Insulin pump infusion sites are typically worn 48-72 hours before needing to be changed. When an infusion site is changed, the insulin pump cartridge is refilled with fresh insulin. The need to change the site every few days is due to the fact that insulin at higher temperature (average body temp or higher depending on the weather) makes insulin unstable and as a result, unviable. Insulin pumps are either tubed and need to be clipped to an item of clothing or worn in a pouch, or tubeless, but are attached to the body with adhesive tape.
The biggest cons for insulin pumps typically include:
- the need to change the site frequently,
- the risk of poor insulin absorption (and as a result, unwanted elevated glucose levels) due to insulin pooling under the skin, kinked cannulas or faulty infusion sites, and/or
- the need to remove the pump’s insulin delivery if tubed for certain activities (swimming, bathing, certain contact sports) (NB. currently the only tubeless pump available is Omnipod, and can be worn 24/7 including during water activities).
As a rule of thumb, it is good practice to always carry a backup insulin pen, or vial and syringe to correct elevated glucose levels that are not responding to a correction using the pump. This mitigates against the risk of ketones/DKA and helps ensure glucose levels are returned to target range relatively quickly, thus minimizing extended periods of high glucose levels.
Insulin Pump Settings
In replacement of long acting insulin, basal insulin is delivered via the pump. This is a small incremental amount of fast acting insulin delivered at an hourly rate, broken down into mini-doses, units (or partial units) per hour, as determined by your doctor. It usually takes 2 hours on average to see the effects of basal, ie. whatever your glucose level is now (notwithstanding food etc), is a result of your basal rate approximately 1.5-2hours prior. The translation from long acting insulin to basal requires some fine tuning. It is not simply a matter of taking your long acting insulin needs and dividing the amount by 24 hours to determine your hourly basal rate.
Your basal rates are pre-programmed and delivered automatically. They can be adjusted throughout the day depending on your needs (as determined with your provider). For example, if your glucose levels tend to spike prior to waking (the “dawn phenomenon”), it is possible to set your basal rate to be much higher 1-2 hours prior to waking up, to prevent the spike, or need to correct your BG upon waking up. Moreover, if you tend to drop low overnight, you can adjust your basal rate to be much less in the late night hours to prevent an unwanted middle of the night low.
Insulin pumps also allow you to temporarily increase or decrease your basal rate as needed.* For example if you anticipate a high carb and high fat meal, you may wish to temporarily increase your basal rate for the next several hours to curtail an unwanted delayed spike hours after eating this meal. Conversely, if you intend to do intense exercise that has the tendency to lower your glucose levels, you can temporarily decrease your basal insulin 1-2 hours prior to the exercise to prevent an unwanted low glucose level mid-workout.
*any changes to your insulin pump settings/basal rates should be confirmed by a doctor prior to implementing
Insulin pumps have a built-in bolus calculator to assist with calculating insulin amounts for food and correcting glucose levels. The settings of the insulin pump allows the user to pre-program the following (as determined by the user’s doctor):
- Target Blood Glucose Level / Range
- Insulin-to-Carbohydrate Ratio (I:C)
- Insulin Sensitivity Factor (ISF) or Correction Factor
- Duration of Insulin Action (DIA)
- Insulin on Board
Target blood glucose is the desired blood glucose level or range. It can be entered into a pump’s settings as a single target for the entire day (e.g., 100 mg/dl) or as a range (e.g., 80-120 mg/dl). Pumps usually allow you to set different targets for different times of day e.g., 80 mg/dl in the morning, 120 mg/dl at night. The bolus calculator uses the target level to determine how much correction dose insulin is needed in cases of elevated glucose levels. For example, if the target is set at 80 mg/dl, and current blood sugar is 180 mg/dl, the bolus calculator will recommend an amount of insulin to reduce blood glucose by 100 mg/dl.
Insulin sensitivity factor (ISF) or “correction factor” represents how much 1.0 unit of insulin is expected to lower blood sugar (as determined through experience and upon referral from your doctor). For example, if 1.0u drops your blood sugar by 25 mg/dl, then your insulin sensitivity factor is 1:25. Using this example, the pump would recommend 4 units of insulin to bring blood glucose from 180 mg/dl down to 80 mg/dl. Different ISFs can be pre-programmed for different times of the day. Many people find that they are more insulin resistant in the morning, which requires a stronger correction factor.
Insulin to carbohydrate ratio is the number of grams of carbohydrates “covered” by 1.0u. For example, a 1:10 insulin to carbohydrate ratio means one unit of insulin will cover every 10 grams of carbohydrates consumed. Using this ratio, with 30 grams of carbohydrates, a bolus calculator will recommend 3.0u of insulin for this meal. The I:C ratio can also be programmed differently depending on the time of day. For example in the morning you may require a ratio of 1:10 carbs, verses 1:15 for lunch or dinner time.
Duration of insulin action (DIA) (or active insulin time) is how long insulin takes to finish lowering blood glucose. The DIA time starts when a bolus is given and ends when the bolus is no longer lowering blood glucose levels. An accurate DIA will minimize insulin stacking and low blood sugar (hypoglycemia), which can happen when boluses are given too close together. The DIA varies for each individual, typically it is 2.5-4 hours, after which, the insulin is no longer active or working.
Insulin on board (IOB) is how much insulin is still active inside the body from the previous bolus dose. It is calculated based on your DIA, though the exact calculation varies depending on the pump. Typically, for a DIA of three hours, a three-unit bolus dose taken at 12pm would have about one unit of IOB remaining two hours later, at 2pm. IOB is important to take into account, as it can help avoid insulin stacking. This is also helpful at bedtime when determining whether or not you need more insulin to correct an above range glucose level.
Closed loop systems
Basal rates operate differently in an automated insulin delivery (hybrid closed loop) system. A closed loop system functions where the user has an insulin pump and continuous glucose monitor (CGM) that share data with one another, thus enabling the insulin pump to semi automate basal rates several times an hour, depending on the current glucose level reading. CGMs provide a live reading every 5 minutes, and depending on the direction, stability and trend of the current glucose levels, basal rates are adjusted accordingly. Effectively, acting to temp basal up and down through the day automatically, to keep glucose levels in range as much as possible. Currently, the Medtronic’s MiniMed 670G, Tandem Control-IQ, or DIY Loop or OpenAPS offer closed loop systems. The closed loop systems still do not automate bolus delivery for meals or BG corrections, though, the pump does suggest bolus amounts based on current basal rates, IOB and BG trends.
As with any medical decision, before deciding which option works best for you, always consult with your doctor first. When used properly, MDI and insulin pumps both result in very well managed glucose levels. Each method has pros and cons, and takes some practice to learn how the body reacts. Whichever method you choose, remember to be patient with the process, as the fine tuning optimal time in range takes practice and time.