Bubble and infusion set update – September, 2013 Miscellaneous comments. These apply only to Minimed Paradigm pumps and Dexcom System 7 Plus CGMs – we don’t know anything about other systems. 1. Minimed infusion sets. The last time I wrote, we had switched from 6 mm Quick-Sets to 13 mm Silhouette infusion sets, because of problems with both bubbles and infusion sets “going bad” after 2 to 2½ days (“going bad” means there were rapid, unexplained increases in blood glucose, not associated with food or anything else, and with the blood glucose rapidly brought down by a new infusion set). The Silhouettes resulted in fewer infusion sets going bad, and fewer bubbles, but at the cost of more bleeding and bruising at the insertion site. Eventually, we decided to try the 9 mm Quick-Sets. A quick geometry calculation shows that a 13 mm Silhouette at a 45° angle goes in about 9 mm, the same as the 9 mm Quick-Sets. These Quick-Sets appear to be the best solution we’ve found. a. Bubbles are minimized. We find about 1 significant bubble in the tubing (more than 1” long in the tubing) about once a week, although we still check for bubbles three times a day. We still have no idea why the bubbles form; I’ve written about that in detail previously. I’ve since read about some sort of vents in the infusion sets. Maybe the bubbles have something to do with pressure fluctuations at the infusion site causing small back-and-forth motion at the O-rings in the reservoir, which could cause air to leak into the reservoir, but that’s only speculation. b. Infusion sets almost never go bad. In the 6 months or so we’ve used the 9 mm Quick-Sets, only one time have we had to change an infusion set before three days were up. c. Bleeding and bruising are much, much less of a problem than with the Silhouettes. Different people have different thicknesses of fat in their tummies, different activity levels, etc., so what works for us may well not work for everyone – your mileage may vary. 2. Dexcom Seven Plus CGM. There’s been much talk of the “artificial pancreas,” where the pump responds to CGM readings to determine how much insulin to deliver. Unfortunately, CGMs – although they are lifesavers!! – just aren’t accurate enough to be given the task of giving orders to the pump. As our most extreme example of a non-so-good sensor, of 22 calibrations of CGM readings against a BG meter, the CGM was off by more than 40 mg/dL 7 times. One example: CGM: 151, BG meter: 74. In this case, if we had followed the CGM reading, a bolus would have been given, which could have led to a BIG problem with hypoglycemia. We changed out that CGM sensor, and the next one worked much better. But occasionally we find the CGM reading to be in error by as much a 100 mg/dL. When this happens, sometimes we even do two calibrations with two different BG meters and test strips from two different batches. The readings from the BG meters are very seldom erroneous (note: “very seldom” doesn’t mean “never”; perhaps once every six months we get readings from two different BG meters that differ significantly.)