Insulin pump
The insulin
pump is a medical device used for the administration of insulin in the
treatment of diabetes
mellitus, also known as continuous subcutaneous insulin infusion therapy. The device includes:
- the
pump itself (including controls, processing module, and batteries)
- a
disposable reservoir for insulin (inside the pump)
- a
disposable infusion
set, including a cannula for subcutaneous insertion (under the skin) and a tubing system to
interface the insulin reservoir to the cannula.
An
insulin pump is an alternative to multiple daily injections of insulin by insulin
syringe or an insulin
pen and allows for intensive insulin therapy when used in conjunction with blood glucose monitoring and carb counting.
To
use an insulin pump, the reservoir must first be filled with insulin. Some
pumps use with prefilled cartridges that are replaced when empty. Most,
however, are filled with the insulin variety prescribed for the user (usually Apidra or NovoLog).
Setting
up includes:
- Opening
a new (sterile) empty pump reservoir;
- Withdrawing
the plunger;
- Inserting
the needle into a vial of insulin;
- Injecting
the air from the reservoir into the vial to prevent a vacuum forming in
the vial as insulin is withdrawn;
- Drawing
insulin into the reservoir with the plunger, and then removing the needle;
- Squirting
out any air bubbles from the reservoir, and then removing the plunger;
- Attaching
the reservoir to the infusion set tubing;
- Installing
the assembly into the pump and priming the tubing (pushing insulin and any
air bubbles through the tubing). It is essential that this is done with
the pump disconnected from the body to prevent accidental insulin
delivery;
- Attaching
to the infusion "site" (and priming the cannula if a new set has
been inserted).
Dosing
An
insulin pump allows the replacement of slow-acting insulin for basal needs with
a continuous infusion of rapid-acting insulin.
The
insulin pump delivers a single type of fast-acting insulin in two ways:
- a bolus dose that is pumped to cover food eaten or to
correct a high blood
glucose level.
- a basal dose that is pumped continuously at an adjustable basal rate to
deliver insulin needed between meals and at night.
Bolus
Shaping
An
insulin pump user has the ability to influence the profile of the rapid-acting
insulin by shaping the bolus. While each user must experiment with bolus shapes
to determine what is best for any given food, they can improve control of blood sugar by
adapting the bolus shape to their needs.
A standard
bolus is an infusion of insulin pumped completely at the onset of the
bolus. It is most similar to an injection. By pumping with a "spike"
shape, the expected action is the fastest possible bolus for that type of
insulin. The standard bolus is most appropriate when eating high carb low
protein low fat meals because it will return blood sugar to normal levels
quickly.
An extended
bolus is a slow infusion of insulin spread out over time. By pumping with a
"square wave" shape, the bolus avoids a high initial dose of insulin
that may enter the blood and cause low blood sugar before digestion can
facilitate sugar entering the blood. The extended bolus also extends the action
of insulin well beyond that of the insulin alone. The extended bolus is
appropriate when covering high fat high protein meals such as steak, which will
be raising blood sugar for many hours past the onset of the bolus. The extended
bolus is also useful for those with slow digestion (such as with gastroparesis
or Coeliac
disease).
A combination
bolus is the combination of a standard bolus spike with an extended bolus
square wave. This shape provides a large dose of insulin up front, and then
also extends the tail of the insulin action. The combination bolus is
appropriate for high carb high fat meals such as pizza, pasta with heavy cream
sauce, and chocolate cake.
A super
bolus is a method of increasing the spike of the standard bolus. Since the
action of the bolus insulin in the blood stream will extend for several hours,
the basal insulin could be stopped or reduced during this time. This
facilitates the "borrowing" of the basal insulin and including it
into the bolus spike to deliver the same total insulin with faster action than
can be achieved with spike and basal rate together. The super bolus is useful
for certain foods (like sugary breakfast cereals) which cause a large
post-prandial peak of blood sugar. It attacks the blood sugar peak with the
fastest delivery of insulin that can be practically achieved by pumping.
Bolus Timing
Since
the pump user is responsible to manually start a bolus, this provides an
opportunity for the user to pre-bolus to improve upon the insulin pump's
capability to prevent post-prandial hyperglycemia. A pre-bolus is simply a
bolus of insulin given before it is actually needed to cover carbohydrates
eaten.
There
are two situations where a pre-bolus is helpful:
- A
pre-bolus of insulin will mitigate a spike in blood sugar that results
from eating high glycemic foods. Infused insulin analogs such as NovoLog and Apidra typically
begin to impact blood sugar levels 15 or 20 minutes after infusion. As a
result, easily digested sugars often hit the bloodstream much faster than
infused insulin intended to cover them, and the blood sugar level spikes
upward as a result. If the bolus were to be infused 20 minutes before eating,
then the pre-bolused insulin will be hitting the bloodstream
simultaneously with the digested sugars to control the magnitude of the
spike.
- A
pre-bolus of insulin can also combine a meal bolus and a correction bolus
when the blood sugar is above the target range before a meal. The timing
of the bolus is a controllable variable to bring down the blood sugar
level before eating again causes it to increase.
Similarly,
a low blood sugar level or a low glycemic food might be best treated with a
bolus after a meal is begun. The blood sugar level, the type of food
eaten, and a person's individual response to food and insulin have an impact on
the ideal time to bolus with the pump.
Basal
Rate Patterns
The
pattern for delivering basal insulin throughout the day can also be customized
with a pattern to suit the pump user.
- A
reduction of basal at night to prevent low blood sugar in infants and
toddlers.
- An
increase of basal at night to counteract high blood sugar levels due to
growth hormone in teenagers.
- A
pre-dawn increase to prevent high blood sugar due to the dawn effect in
adults and teens.
- In
a proactive plan before regularly scheduled exercise times such as morning
gym for elementary school children or after school basketball practice for
high school children.
Basal
Rate Determination
Basal
insulin requirements will vary between individuals and periods of the day. The
basal rate for a particular time period is determined by fasting while
periodically evaluating the blood sugar level. Neither food nor bolus insulin
must be taken for 4 hours prior to or during the evaluation period. If the
blood sugar level changes dramatically during evaluation, then the basal rate
can be adjusted to increase or decrease insulin delivery to keep the blood
sugar level approximately steady.
For
instance, to determine an individual's morning basal requirement, they must
skip breakfast. On waking, they would test their blood glucose level
periodically until lunch. Changes in blood glucose level are compensated with
adjustments in the morning basal rate. The process is repeated over several
days, varying the fasting period, until a 24-hour basal profile has been built
up which keeps fasting blood sugar levels relatively steady. Once the basal
rate is matched to the fasting basal insulin need, the pump user will then gain
the flexibility to skip or postpone meals such as sleeping late on the weekends
or working overtime on a weekday.
Many
factors can change insulin requirements and require an adjustment to the basal
rate:
- continued
beta cell death following diagnosis of type 1 diabetes (honeymoon period)
- growth
spurts particularly during puberty
- weight
gain or loss
- any
drug treatment that affects insulin sensitivity (e.g. corticosteroids)
- eating,
sleeping, or exercise routine changes
- whenever
the control over hyperglycemia is degrading
- and
according to the seasons.
A
pump user should be educated by their diabetes care professional about basal
rate determination before beginning pump therapy.
Temporary
Basal Rates
Since
the basal insulin is provided as a rapid-acting insulin, the basal insulin can
be immediately increased or decreased as needed with a temporary basal rate.
Examples when this is helpful include:
- During
a long car drive, when more insulin is needed due to inactivity.
- During
and after spontaneous exercise or sports activities, when the body needs
less insulin.
- During
illness or stress, when basal demand increases due to insulin resistance.
- When
blood ketones are present, when additional insulin is needed.
- During menses, when
additional basal insulin is needed.
Advantages
of pumping insulin
- The
use of rapid-acting insulin for basal needs offers relative freedom from a
structured meal and exercise regimen previously needed to control blood
sugar with slow-acting insulin. The alternative basal insulins, such as
the long lasting insulins injected once a day, often release their insulin at a very unpredictable
rate.
- Many
pumpers feel that bolusing insulin from a pump is more convenient and
discreet than injection.
- Insulin
pumps also make it possible to deliver more precise amounts of insulin
than can be injected using a syringe. This supports tighter control over
blood sugar and Hemoglobin A1c levels, reducing the chance of long-term complications associated with diabetes. This is
predicted to result in a long term cost savings relative to multiple daily
injections.[1]
- Many
modern 'smart' pumps have a 'bolus wizard' which calculates how much
'bolus' insulin you need taking into account your expected carbohydrate
intake and current blood sugars.
Disadvantages
of pumping insulin
- Insulin
pumps, cartridges, and infusion sets are far more expensive than syringes
used for insulin injection.
- Since
the insulin pump needs to be worn most of the time, pump users need strategies to participate in activities that may damage
the pump, such as rough sports and activities in the water. Some users may
find that wearing the pump all the time (together with the infusion set
tubing) is uncomfortable or unwieldy.
- An
episode of diabetic ketoacidosis may occur if the pump user does not
receive sufficient fast acting insulin for many hours. This can happen if
the pump battery is discharged, if the insulin reservoir runs empty, the
tubing becomes loose and insulin leaks rather than being injected, or if
the cannula becomes bent or kinked in the body, preventing delivery.
Therefore pump users typically monitor their blood sugars more frequently
to evaluate the effectiveness of insulin delivery.
- Possibility
of insulin pump breaking and having to resort back to multiple daily
injections until new pump arrives.
Acceptability
Use
of insulin pumps is increasing throughout the world because of:
- easy
delivery of multiple insulin injections for those using intensive insulin therapy.
- accurate
delivery of very small boluses, helpful for infants.
- growing
support among doctors and insurance companies due to the benefits
contributing to reducing the incidence of long-term complications.
- improvements
in blood glucose monitoring. New meters require smaller
drops of blood, and the corresponding lancet poke in the fingers is
smaller and less painful. These meters also support alternate site testing for the most routine tests for
practically painless testing. This compensates for the need for pump users
to test blood sugar more frequently.
- support
groups demonstrating techniques for adapting insulin pump use to sports,
exercise, and water sports. Expert help is becoming common in user groups
and books. The pump can be effectively combined with partial basal insulin
from the pump and partial basal insulin from a long-acting insulin such as Lantus and Levemir. This is
becoming known as the Untethered Regimen.
Recent
developments
New
insulin pumps are becoming "smart" as new features are added to their
design. These simplify the tasks involved in delivering an insulin bolus.
- insulin
on board:
Based on the time and quantity of the last bolus, the pump software keeps
track of the insulin remaining in the bloodstream and displays it on the
screen. This supports the process of performing a new bolus before the
effects of the last bolus are complete, and thereby helps prevent the user
from overcompensating for high blood sugar with unnecessary correction
boluses.
- bolus
calculators:
Pump software helps by calculating the dose for the next insulin bolus.
The user enters the grams of carbohydrates to be consumed, and the bolus
"wizard" calculates the number of units of insulin needed. It
adjusts for the most recent blood glucose level and the insulin on board,
and then suggests the best insulin dose to the user to approve and bolus.
- custom
alarms:
The pump can monitor for activities during specific times of day and then
alarm the user if an expected activity did not occur. Examples include a
missed lunch bolus, a missed blood glucose test at 10am, a new blood
glucose test 15 minutes after a low blood glucose test, etc. The alarms
can be customized to support each user.
- touch
bolus:
For persons with visual impairments, this button on the pump can be used
to bolus for insulin without using the display. This works with a system
of beeps to confirm the bolus parameters to the pump user. This feature is
described as 'touch', 'audio', or 'easy' bolus depending on brand. The
feature was first introduced in the mid to late 90's.
- interface
to personal computers:
Since the late 90's, most pump have had the ability to interface with
personal computers for managing and documenting pump programming and/or to
upload use data from the pump. This simplifies record keeping and can be
interfaced with diabetes management software.
- integration
with blood glucose meters:
Blood glucose data can be manually entered into the pump for supporting
the bolus wizard for calculation of the next insulin bolus. Some pumps are
supporting an interface from the insulin pump to a blood glucose meter.
- The Medtronic Diabetes Minimed Paradigm series of insulin
pumps allow for radio frequency (RF) communication. This enables the pump
to receive data from a BD or Ascentia blood glucose meter. The RF link
also supports a continuous blood glucose sensor known as
the "Paradigm Real Time Continuous Glucose Monitor" which
wirelessly provides the blood glucose value every 5 minutes on the pump
screen. The Medtronic "Real Time System" is the first to link a
continuous monitor with an insulin pump system.
- The
DANA Diabecare IISG insulin pump has blood glucose meter integrated
within its body. After blood glucose check with blood glucose meter in
it, the user can use bolus wizard and deliver a required bolus.
- The
Insulet Omnipod has a separate remote that features a built-in
meter that uses Freestyle test strips.
- full
featured remote:
The Insulet Omnipod has a separate electronic display and controls.
This remote features a built-in meter that uses Freestyle test strips.
- simple
remote:
The Medtronic pumps offer an optional RF remote control: allowing the user
to deliver a discrete bolus or stop insulin delivery when the pump is
concealed or inaccessible. This feature was first introduced in 1999.
- tubeless
pod: The
Omnipod pump can be attached directly to the skin by its infusion set,
eliminating the tube from the pump.
Current
insulin pump manufacturers
the
model given is the latest available model from each distributor
Future developments
- When
insulin pump technology is combined with a continuous blood glucose monitoring system, the
technology seems promising for real-time control of the blood sugar level.
Currently there are no mature algorithms to automatically control the
insulin delivery based on feedback of the blood glucose level. When the
loop is closed, the system may function as an artificial pancreas.
- Insulin
pumps are being used for infusing pramlintide (brand name Symlin, or
synthetic amylin) with
insulin for improved postprandial glycemic control compared to insulin alone.
- An
insulin pump that can be surgically implanted inside the body will be
available soon by Medtronic. It is the approximate size of a hockey puck,
and communicates via RF to an external control. It is refilled by
injection through the skin, and holds approximately 2 weeks of insulin.
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