Changes in the Position of Conventional Insulin Pumps Shown to Significantly Impact Accuracy of Insulin Delivery

This press release is an announcement submitted by Sansum Diabetes Research Institute , and was not written by Diabetes Health.

Study Published in Journal of Diabetes Science and Technology

Jan 27, 2010

Researchers at Sansum Diabetes Research Institute and University of California, Santa Barbara have concluded that changing the height of a conventional insulin pump in relation to its tubing and infusion set can significantly impact expected insulin delivery rates. Such changes can occur during routine daily activities like dressing, sleeping or showering. The study, "Siphon Effects of Continuous Subcutaneous Insulin Infusion Pump Delivery Performance," evaluated the siphon or hydrostatic pressure action effects on continuous subcutaneous insulin infusion and was published in the January issue of Journal of Diabetes Science and Technology.

"In this study we found a pronounced siphon effect in conventional insulin pumps, which caused significant fluctuations in the accuracy of insulin delivery rates when the pump position was moved higher or lower relative to its tubing and infusion site," said lead investigator Howard Zisser, MD, Director of Clinical Research and Diabetes Technology at the Sansum Diabetes Research Institute in Santa Barbara, CA. "Insulin pump therapy allows for precise control of insulin delivery for patients with type 1 diabetes. The unintended fluctuation in insulin delivery, which may arise from pump movement during normal daily use, can increase blood glucose variability, a risk factor for the progression of complications of diabetes. The effect of hydrostatic pressure was most significant at low basal rates and therefore these findings may be particularly important for pediatric diabetes patients, who often use insulin pumps at low basal rates."

The investigators reached this finding by quantifying the effect of hydrostatic pressure (the pressure exerted on a portion of a column of fluid as a result of the weight of the fluid above it) on insulin delivery during bolus dosages, basal rates and static changes in insulin pumps. They tested conventional insulin pumps from Medtronic Diabetes (MiniMed 512 & 515, which uses 110 cm tubing) and Smiths Medical (Deltec Cozmo 1700, which uses 80 cm tubing), and also compared them to the tubing-free pump from Insulet Corporation (the OmniPod System).

The researchers found that raising or lowering a conventional insulin pump, to the full extent of its tubing, can significantly affect the accuracy of insulin delivery, especially at low basal infusion rates. The most pronounced differences were seen during basal delivery in the Cozmo and MiniMed pumps. For the 1U/hr rate, differences ranged from 74.5% of the expected delivery when the pumps were below the pipettes and pumping upward to 123.3% when the pumps were above the pipettes and pumping downward. For the 1.5U/hr rate, differences ranged from 86.7% to 117.0% when the pumps were below or above the pipettes, respectively.

In contrast, the OmniPod, which has no external tubing, was the least affected by pumping orientation and direction. With the OmniPod System, the 1U/hr rate differences only ranged from 98.3% when its delivery cannula was in a level pumping position to 101.3% when the cannula was in an upward pumping position. For the 1.5U/hr rate, its differences only ranged from 96.0% in a level pumping position to 102.5% in an upward pumping position.

The researchers measured the change in the fluid level in an in-line graduated glass pipette when the Cozmo and MiniMed pumps were moved either up or down to its maximum length in relation to the end of the tubing/pipette. For the OmniPod, the unit was held in a clamp vertically with the delivery cannula up for "upward" pumping position and the delivery cannula down for the "downward" pumping position. The OmniPod was horizontal for the level pumping position.

The study was supported by a grant from Insulet Corporation of Bedford, MA.

Sansum Diabetes Research Institute is a non-profit research center devoted to the prevention, treatment and cure of diabetes through research and education. In particular, it is known for its work on methods to detect and chart the progress of diabetes, its success in developing protocols to increase the incidence of healthy babies born to women with diabetes, and its expertise in new diabetes technology.

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Posted by Anonymous on 28 January 2010

I'm wondering if the length of the tubing on the infusion set makes a difference.

Posted by Anonymous on 29 January 2010

I have a question for pumpers. I have many allergies, including sensitivity to tape or anything sticking to my skin. Therefore, I have been advised by my diabetic educator that I should not try a pump because it is stuck on the skin. Has anyone had this problem and what was the outcome? I did wear a "bandaid" for an hour recently when I got my H1N1 vaccine with no reaction. So is there something out there that might work for me?

Posted by angivan on 29 January 2010

Well, this is a big thumbs-up for Omnipod. I'm due for a new pump later this year so I'll have to look into it more.

Posted by Anonymous on 29 January 2010

Silly study.

If this is realistic or a significant finding, then the last 20+ years of pump therapy should not have worked.

It appears they looked at the longest possible tubing for each mfgr and stretched it to the full length vertically, failed to use the full ISO recommended 49 hour trumpet curve accuracy test and failed to put what would be a one time under or over delivery into the proper context. Not very realistic and a poor use of resources.

IEC standards 6061-2-24 have specific methods for measuring accuracy. Why weren't these well accepted test methods used here?

This report uses non standard test methods and questionable "real world" inputs to develop dubious results. I smell a test ginned up to show some advantage for the omnipod.

So, first question: Who wears their pump in their hat with the site at their knee? Anyone? If the infusion site is 110 cm above or below the pump ( as per this test), that would be 1.1 meters or 43+ inches or 3 feet nine inches).

The element in play here, hydrostatic pressure, is linear with height. Thus, the effect is cut in half with a 60 cm tube, at most. (by mot I mean that you would have to wear the tube absolutely vertical (almost 2 feet).

Most folk, put their site anywhere from their butt to their shoulder, and wear their pump on the belt, in a pants pocket, or in a bar/bro. For these people, the pressure difference is no more than 30 cm ( 1 foot). This is about 1/4 of what this study looked at).

The study cautions about people on low basal rates. Think about who this is most likely to be. Kids? Small adults? Are these people likely to be sporting a 110 cm infusion set? Some of them are not even 110 cm tall!

The other thing to note is that the effect of raising or lowering the pump to the full extent of the infusion set, is a one time event. In other words, if you raise your pump to 1 meter above the infusion site, a small negative pressure will develop due to the hydrostatic pressure. This pressure will act on the reservoir to pull some tiny amount of insulin from your reservoir based on the overall "stiffness" of the reservoir and tubing.(as shown in the study). If you do not move your pump after that, then there is no more over delivery (i.e. your pump would deliver as programmed). If you later return your pump to it's original position, the pressure will go back to the original level and the pump will under-deliver for a time and make up for the previous over delivery. (like a spring returning to it's original position)

Thus for this effect to be real, you would have to develop a habit of holding your pump in your hand when reaching for items on the top shelf and then tucking it into your sock over and over and over again.

Were the proper iso testing methods used in conjunction with real world positions of site and pump and the routine motions of a pump during use, the results would suggest a far smaller error and when this was examined relative to other errors involved in pump therapy, (meter accuracy, meal/ carb estimation, unknown activity levels, unknowable hormone changes)... one would think little of the results.

Posted by bbjaspan on 29 January 2010

Re tubing length -- perhaps with longer tubing, that drops down from pump then up to infusion site, there is bad effect. This may explain recent problems I am having.

Posted by pumpmavin on 29 January 2010

Tubing length: It is not a function of length as it is about the vertical distance your pump is located (or moves) vs. your infusion site. In this study, they stretched the tubing to it's full length. In the case of minimed, this was moving the pump 1.1 meters (44 inches) above or below the site. That is not a typical distance for a pump wearer.

If this were really a big concern then pump therapy would not have worked for the past 20 + years.

Posted by pumpmavin on 29 January 2010

Silly study:

Position of site to pump does not reflect what real patients do: It is a rare person who raises their pump 1.1 meters above their site. That is almost 4 feet!

The under or over delivery would be much smaller if one used a real world vertical distance like 1 foot. (1/4th the distance = 1/4th the pressure = 1/4th the under or over delivery)

Study did not use IEC test methods that have been adopted world wide and are even used by the FDA to look at accuracy.

Study did not point out that the under or over delivery is a one time event and that it reverses as soon as you move the pump back to the original position. For example, if you start wit your pump level with your site, and raise the pump a full 1.1. meters above your site you will get a one time over delivery of what looks to be
0.225 units. (based on 117% of 1.5 u/h basal). This is all. if you keep your pump there (in your hat) it would continue from that point as programmed. If later you moved it from your heat back to even with your site, it would under delivery by the same amount and you would be back to exactly the insulin you programmed (with a small excursion).

If we scale the error they reported from a 1.1. meter movement to a 1 foot ( 30 cm) raise of the pump relative to the site, we would likely see a 0.08415 unit over delivery. That is NOTHING. It is the same error you would get by overestimating your carbs by 2.5 grams (with an insulin sensitivity of 30 g/unit).

And remember, it is a one time event that is reversible by putting your pump back into it's original position.

Pumps are great. Pods are great. There are plenty of good reasons to pick one or the other. Please do not let bad science be a reason to buy an omnipod. This is bad science.

Posted by Anonymous on 31 January 2010

R U kidding? Sponsered by Insulet? No detail about the study? This type of study is how pharma, medical device and non-questioning HCP have dubious credibility.

Posted by Anonymous on 8 February 2010

It would be helpful to point out the Insulet, the people who paid for the study are the makers of the Omnipod, the pump that came through with such flying colors. Also, the photo of the Minimed pump shows the infusion site about 2-3 inches above the pump. The study says nothing about the hydrostatic effects of such an arrangement, which is probably much more typical than the arrangement that was studied.
Have any studies been done on the detection of air bubbles in the tubing? That's a problem that merits study.

Posted by Jody on 25 February 2010

This sounds like an absolutely absurd study. The basal rates vary from diabetic to diabetic, from hour to hour and even sometimes from minutes to minutes. The amount of insulin that goes thru the tubing is dependant upon the basal rates that are set as well as the variable rates that are set by other types of rates.

In response to ANONYMOUS and your inquiry about the way that the infusion set sticks to your skin... You purchase a small box of wipes (like for alcohol wipes). uyou wipe your skin where the infusion set is inserted. Once this area dries & the infusion set is inserted, the substance on the wipe is supposed to help it to stay in position for 2-3 days. Your infusion set should be changed every 2-3 days or your BS levels will start to rise. If you are allergic to the substance on the pad, there are other types of skin preps that may be used. I did develop an allergic reaction to the original skin prep that I was on. Now I am using a milder form of the skin prep. It is thru minimed and they call it an IV prep pad. I have not had any problems with my infusion sets staying in place. I do however change the site every 2 days. I have been told that if I develop an allergic reaction to this skin prep, there is an alternative available. I hope that this helps.

The CGM actually tests your BS every 5 seconds and registers an average BS every 5 minutes thru your pump. I cannot wait until they develop the closed loop system that can determine if your BS is rising or falling and then suspend the insulin and or give a warning that your BS is rising. This would be so beneficial to those of us who are brittle diabetics and striving for a lower A1c and or a tighter control.

I am unfamiliar with the variety of CGMs available and the accuracy of their results. Is there one that tends to be more accurate than others? I am hopeful that soon I will be able to purchase a CGM to work with my minimed insulin pump.

I previously read on one of the blogs that there is a CGM and an insulin pump that is reasonably priced, as well as the supplies that are needed to keep things running smoothly over the month. Which pump was it, that was being referenced?

Which insurance companies were paying for insuli9n pump therapy and CGM therapy as a standard for diabetics. I have been unable to find this information thru my own research. Can anyone point me in the right direction? Thanks.

Make it a great day.

Posted by Anonymous on 3 April 2010

Jody, regarding insulin pump and CGM payment by insurance company- you can contact your insurer to determin if it ic covered. There needs to be a statement of need filled out by your endocrinologist or PCP. The pump companies can also do the leg work for you if you fill out their forms. For CGM, a patient has to meet certain criteria - document lows in order to qualify. Support is also needed from your endo. or PCP

Anonymous with the skin allergy- if you check with you Medtronic rep. or call the company, there are a few different types of adhesive pads available if you experience an allergy. Good Luck!!

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