®	Pump Review Criteria

In order to make an informed decision when choosing a pump, it is important to know what factors to use for comparison. Although each pump manufacturer can provide a wealth of quality information on their particular pump models, simple comparison charts can be unintentionally biased and there is often so much information it is easy to get overwhelmed.

In the individual reviews, descriptions of technical specifications and features will be presented for each pump. Pump technical specifications, while important in describing a pump's physical configuration and inner workings, generally have little observable impact on day-to-day usage of a pump by the wearer. Pump features, on the other hand, have more to do with how the wearer interacts with the pump on a daily basis. Since you will be living with and using the pump on a constant basis, pump features will likely weigh more heavily in your decision.

Since all insulin pumps available on the market today have gone through the rigorous FDA approval process, all pumps deliver on their promise to safely and reliably provide insulin at programmed rates (basal and bolus) regardless of features. So a potential pumper could pick any of these FDA approved devices and be assured of its safety and basic operation. However, beyond this it is also important to consider how a particular pump's functional features will work with a patient's lifestyle. The ultimate success of insulin pump therapy can be impacted by how well the pump's features complement a patient's lifestyle.

Here is a summary listing of both technical specifications and features with general descriptions which are not specific to any one particular pump. This is a collection of specifications and features found over the entire range of pumps... specific features may or may not be found on any one particular pump. See the individual reviews to determine which features a pump has.

1. Technical Specifications

• Size
  In general, insulin pumps run about the size of a pack of cards or a beeper. The average size is just over 3 inches in length, around 2 inches wide, and about 0.75 inches thick. Obviously some pumps are smaller than this and some are larger, but not by too much.

• Weight
  Insulin pumps range in weight anywhere from 1.8 ounces to 4.2 ounces. The average weight is right around 3.5 ounces.

• Physical Delivery Mechanism
  Pumps deliver insulin using one of two general methods, determined primarily by the type of motor utilized in the design. These two categories are continuous DC motor and solenoid/stepping motor, described below. While debates may occur over the advantages of one design over the other, it is our opinion that there is no significant difference in either effectiveness or occlusion rate between designs. This is born out by user reports over many years.

  The output rotation of the motor is most often transferred finally to a geared shaft called a "lead screw" (pronounced leed screw). This transfers the movement of the motor to the linear movement of the insulin cartridge plunger. Depending on then individual pump design, the lead screw can either be permanently captive within the pump, or it can alternatively be a replaceable part which is assembled with the insulin cartridge.

• DC Motor
  The operation of DC motors in insulin pumps is similar to the operation of motors commonly found in items such as a VCR or cordless drills, although in a much more precise manner. When the motor is energized, the rotation of the output shaft is converted into linear displacement of the insulin cartridge plunger through a geared mechanism. One or more sensors detect the number of motor rotations for dosage calculation and error checking. The number of units of insulin delivered is a function of how many times the output shaft rotates, so delivering the correct insulin dosage is simply a matter of engaging the motor until the correct number of output rotations has been achieved.

  Pumps using DC motors generally deliver the basal insulin on a fixed time interval/variable dosage schedule (every 3 minutes, for instance). For example, if the basal rate is set for 1.2 units per hour, a pump could deliver 0.06 units of insulin every 3 minutes. As another example, if the basal rate is set for 2.4 units/hour, a pump could deliver 0.12 units of insulin every 3 minutes.

  The DC motor generally delivers bolus insulin faster than a stepper type motor. Occasionally this may cause a very minor discomfort at the infusion site for some individuals when a very large bolus is delivered.

• Solenoid / Stepping Motor
  The solenoid/stepping motor provides a small discrete (singular/fixed) output each time it is energized. One simple example of a stepper motor is an electric door lock on a car. When voltage is applied to a stepper motor, it creates a discrete output cycle (either a fixed rotation or fixed extension/retraction of the output shaft). In an insulin pump, this fixed output can be mechanically transferred into a fixed linear displacement of the insulin cartridge plunger. Pumps using a stepper motor deliver insulin in discrete increments, so the dosage delivered must be a multiple of the increment amount. Output cycles can sometimes be heard as audible "click" sounds.

  Pumps with stepping motors generally deliver basal insulin on a fixed dosage/variable time interval scheme. Assuming that 0.1 units is the delivery increment (the amount delivered for each "click") our examples might look as follows. If the basal rate is set for 1.2 units per hour, the pump would deliver one "click" every 5 minutes. Our second example of a 2.4 unit per hour basal rate would find the pump delivering one "click" every 2.5 minutes.

• Priming
  Priming is used in three specific instances. The first is to fill the insulin tubing with insulin prior to use. The second is to fill the canula or needle of a newly inserted infusion set with insulin (since it only contains air once it is initially inserted and it can take time for the basal rate alone to finally fill it up with insulin before delivery can occur). The third use is to engage and tighten the actuator mechanism between the motor and insulin cartridge plunger.

  Priming of the insulin tubing can be either manual or motorized, generally depending on the pump motor type. For stepping motors, priming is usually performed by manually pressing the cartridge plunger to force insulin through the tubing, since this is faster using the pump motor. The cartridge is than inserted into the pump after the manual priming is complete.

  Pumps with DC motors generally provide some type of motorized priming in which the pump itself pushes the insulin through the tubing, although it is often possible to manually prime the tubing for these types of pumps as well, as it is often faster and easier to do so.

  Some pumps provide a prime feature to fill a newly inserted infusion set canula or needle with a dose recommended by the infusion set manufacturer (usually a small amount in the range of 0.5 to 1.0 units of U-100). Generally this primed insulin is not counted towards the daily total insulin stored in the pump's memory. For pumps without this priming feature, a small bolus is used in place of the prime, although that bolus would be counted in the daily total.

  When a new insulin cartridge is installed into an insulin pump, the actuating mechanism needs to be seated to the insulin cartridge plunger to ensure accurate insulin delivery. Generally if a pump has a motorized tubing prime feature and that feature is used, that process will automatically seat the mechanism to the cartridge correctly. If the tubing is manually primed, usually the pump will require priming after cartridge installation to ensure that the mechanism and cartridge are properly seated.

• Battery Type
  Many pumps use standard 357 alkaline watch/camera batteries for power. However, some manufacturers use other standard disposable batteries or proprietary battery packs.

• Cartridge Type and Capacity
  Cartridges are often proprietary to the company who manufactures the corresponding insulin pump. The can be made of either glass or plastic. Cartridge capacities generally range between 1.5mL (150 units of U100) to 3.0 mL (300 units of U100). Many of the pumps offering 3.0 mL capacities allow a "short fill" option to restrict capacity to 1.5 mL in case a user doesn't use insulin very quickly or doesn't want the Luer lock mechanism to protrude from the pump.

• Water Resistance
  Many pumps offer some form of water resistance. Certain models advertise that they can be submerged with or without adapters to allow swimming or bathing. If a pump is not rated for submersion, oftentimes the pump can be disconnected via the infusion set or placed in a special waterproof case during that water activity.

  Common ratings for water resistance are IPX7 and IPX8. IPX7 specifies that the pump is resistant to splashed water and accidental submersion in shallow water (for instance, accidentally dropping the pump into a sink filled with water). IPX7 basically says the pump in resistant to transient/accidental water exposure and does not certify a pump for submersion for activities such as swimming, showering, or bathing.

  IPX8 specifies that the pump is waterproof for submersion, per manufacturer guidelines. This certification must be provided along with guidelines from the manufacturer for depth and time of submersion, such as "8 feet for 24 hours".

• Warranty
  A four year warranty appears to be standard with most insulin pumps models.

• Basal Programming Options
  Most recent pump designs allow multiple basal programs, each consisting of a basal profile for a 24 hour period. Basal insulin is used to match the body's fasting metabolic needs. Many pumpers use only a single basal profile and manage changes using temporary basal rates or adjustments. Pump models with multiple basal profiles allow the user to enter several different profiles which they can then select depending on the situation. For instance, some people have different schedules and activities on the weekends than the weekdays requiring different basal profiles. Additionally, many women have differing basal requirement just prior to the onset of their monthly cycle.

• Temporary Basal Rate
  Most pumps provide a temporary basal rate feature which allows the user to increase or decrease the basal rate for a specified period of time. As examples for when this feature might be useful, illness is among the common reasons for a temporarily increase a basal rate, and exercise is a common reason for temporarily decreasing basal rate.

  Pumps generally use one of two methods for setting a temporary basal rate. The first method is to allow the user to program in an arbitrary fixed rate, which could be greater or less than the active basal profile. This method overrides the normal basal program for a specified amount of time, and the active basal profile resumes once the specified time expires. Note that if the time period lies across two different segments in a basal profile, the temporary basal rate does not "follow" the original shape of the active basal rate curve but stays at the fixed value.

  As an example of this first method, say a hypothetical pump has an active basal profile which is set to 1.2 units/hour from 00:00 to 12:00, and 1.0 from 12:00 to 24:00. Because of exercise, at 11:00 the user sets the temporary basal rate feature to be 0.8 for 3 hours. So then the actual delivered basal rates for that day (in units/hour) would be 1.2 from 00:00 to 11:00, 0.8 from 11:00 to 14:00, and then 1.0 from 14:00 to 24:00.

  The second method is to allow the user to program in a percentage increase/decrease which is applied to the active basal profile for a specified amount of time. The temporary basal rate which is delivered "follows" the same shape as the original basal profile, and again the active basal profile resumes once this time period expires.

  Using this second method and working from our previous example, lets say at 11:00 the user sets a temporary basal rate of -30% (a decrease) for a duration of 3 hours. The actual rates of basal insulin delivered (in units/hour) would be 1.2 from 00:00 to 11:00, 0.84 from 11:00 to 12:00, 0.7 from 12:00 to 14:00, resuming at 1.0 from 14:00 to 24:00.

• Bolus Programming Options
  All of the pumps allow for bolus programming. Bolus insulin covers the carbohydrate consumed for a meal or to adjust for a high blood glucose reading. Many pumps also offer advanced bolus options including audio and extended.

  Audio bolus is supported by most insulin pumps. An audio bolus feature allows you to program a bolus by sound instead of by sight, which can be handy if you have impaired vision or wear your pump in a location which can be difficult to access. The basic premise is that you press a button on the pump multiple times to increment the amount of the bolus, then the pump plays a series of beeps to confirm the amount you programmed in. For instance, if the pump is set to give 1.0 units of insulin for every button press, and the audio bolus button is pressed 10 times, then the pump would deliver 10 units of insulin. Generally the Audio bolus feature has to be enabled from a setup menu or screen.

  Extended bolus is called by different names, but the general premise is that instead of having the pump deliver the bolus immediately, it is programmed to deliver the bolus over a longer interval in the range of 30 minutes to a few hours (30 minute increments are common). Extended bolus can help compensate for slowly digested food (such as pizza) or gastroparesis, so this is an option that requires some experimentation. Some pumps also allow you to program and deliver another normal bolus during and in addition to an extended bolus, which can be handy if you later decide to eat something extra that wasn't covered under the extended bolus amount. As with the Audio bolus, the Extended bolus features often have to be enabled from a setup menu or screen.

• Remote Control
  Some pumps offer a remote control unit which can be useful if you are the parent of a child who has an insulin pump, or if you wear the pump in a location that is inconvenient to access.

• User Interface and Display
  Most insulin pumps use some type of LCD display to display information, and buttons you can press to review information and program the pump. Certain models have larger and more readable displays than others, and each pump sets up the menu or screen structure differently. The best way to find out which one suits you is to try them out.

• Backlight
  Some pump models offer a backlight for viewing in low light conditions.

• Vibrating Mode
  Some pump models offer vibration feedback in addition to audio feedback for things such as alarms and audio bolus confirmation.

• Child Lock Mode
  Recent pump models offer a child lock mode which can be used to keep children or impaired patients from inadvertently delivering extra insulin or changing important settings.

• Warnings and Alarms
  The following warnings and alarms appear on most insulin pumps. Some models may have additional alarms related to specific features or options not listed here.
  • Low Battery
  • Dead Battery
  • Low Insulin Cartridge
  • Empty Insulin Cartridge
  • Insulin Limit Exceeded
  • Warning: Pump Suspended
  • Pump Malfunction (represents many different error types)
  • Occlusion

• History
  Most pumps store a certain number of previous boluses, daily insulin totals, and alarms which can either be viewed using the front display or downloaded to a computer.

• Automatic OFF
  This feature, if enabled, will automatically turn the pump off if there has been no interaction with the pump for a specified time interval (usually set to several hours).