Pre-soak, hotswap, and 65 minute “warm up” for G6

Since we use Loop (ok…and because we just like having as much continous BG coverage as we can possibly get with the supplies we have)…we had gotten into the habit of “pre-soak and hotswap” with the G5 system.  If you haven’t heard of those terms before, let me explain them quickly.

Pre-soak:  Inserting a sensor hours in advance of before you intend on putting it into service.  Why pre-soak?  When you insert a sensor, there are micro-traumas under the skin that take some immune response.  Chemical changes and tiny micro-responses to the “insertion trauma”.   Plus there’s a coating on sensor wires that needs to come into equilibrium with the surrounding tissues where you have inserted.  That time to equilibriate with the new tissue surrounding is why there is a 2 hour warm-up.  It’s a balancing time for the system to settle down from the trauma of insertion.  You’ve probably already seen this yourselves if you’ve noticed that even the first 6-10 hours after warm-up can still be jumpy.  So, pre-soaking a sensor is a way to let the new sensor settle into its surroundings before putting it into use.  This helps the sensor start off right away with less jumpiness and more closely holding calibrations quickly.

In order to pre-soak, you need to NOT wait for your existing sensor to fail.  In other words, when you start to suspect that your sensor is going to fail soon, or you notice that it isn’t holding calibrations well, then you would want to go ahead and insert a new sensor ahead of time.  YES, this means that the person is wearing two sensors at once…(1) the existing one that is soon to fail and still has transmitter in it and (2) a new one, just inserted, that doesn’t have a transmitter in it yet.  For safety, you want to go ahead and put a band-aid, wrap, or dead transmitter to hold down the little flap in the middle of the new sensor that attaches to the wire in the skin.  You don’t want that flap accidentally being pulled up while the sensor is presoaking.

Hotswap:  Hotswap is when you take the transmitter directly from one sensor over to another without stopping the sensor session.  The idea being that you are trying to avoid the two-hour warmup.  While some people get lucky and have minimal downtime during a hotswap…I have ALWAYS had 65 minutes without CGM data right after a hotswap.  It’s not surprising to have some ??? from the hotswap as the transmitter is noticing that the environmental conditions from one reading (in old sensor) and next reading (in new sensor) are very different.  The ??? is giving the sensor time to “find its legs” again and get used to the new surroundings.  From what I’ve experienced, that’s a 65 minute wait for the ??? to clear and BG data to start coming in.  So, while the hotswap doesn’t totally avoid the whole 2-hour warm up, it can shorten it to about 65 minutes of time without BG data.

Here’s the important part though…you really should only do hotswaps with a presoaked sensor.  That 2-hour warm up gives a chance for the sensor to settle in…so hotswaps should only be done onto a sensor that has had at least 2 hours soaking, if not more.

For the G5, the hotswap wouldn’t stop your existing session…it would just keep going.

But, for the G6 as outlined below, it does involve stopping and starting a new sensor session.  So…technically not the same kind of “hotswap” that you did (or will do) with a G5…but same idea.  Avoiding the full 2-hour warmup by using a pre-soak with it.

Can the G6 do a pre-soak and hotswap?

Tonight I experimented with trying a pre-soak/hotswap with the G6 for the first time.  Our sensor was starting to show signs of wear.  Normally we test once each morning to make sure the sensor is still accurate.  This morning the sensor was off by about 15 mg/dl.  Sure, not a huge amount…but for the G6 this is usual for us.  And then we noticed a few steep BG changes that clearly were just out of place and unusual for the G6 trends we normally see.  If you look at the screenshot below, the red dots are what her finger check was on the meter.  You can tell that the first check of the morning was quite a bit higher than the sensor value, and then the second check of the morning (done to test the sensor since it was off in the first check) showed that it was off quite a bit but this time low.

Noticing that the sensor was on its end of days (this was day 11.5 for us…about average), we did the following steps to have just 65 minutes of lost BG data vs the usual 2-hours.  Extra bonus?  When a pre-soaked sensor comes online, it doesn’t have the jumpiness that a new sensor usually has.

Pre-soak, Hotswap Procedure

1. 1. Got out a new sensor.  Took note of the new sensor’s code.

1. Got out the receiver and WHILE between BG readings (they happen every 5 minutes), did a “stop sensor”, “new sensor”, entered sensor code from above, and then “start sensor”.  Immediately after starting the new sensor, I put the receiver in a faraday bag (you can put it in microwave, etc) to let the two hour warm up go by without connecting to transmitter again.
2. Inserted the new sensor from step 1 onto Anna’s other arm.  Wrapped the new sensor in vet wrap to keep the sensor protected while no transmitter was in it.
3. Waited 4 hours.  Ideally, I like to pre-soak for about 6 hours with the G5 system, but 4 hours is the way our life worked out tonight.  It was my first try doing this with the G6, so I wasn’t sure what to expect.  (Spoiler alert: four hours seems to have worked nicely)
4. After 4 hours, we took the old sensor off and removed the vet wrap from the new sensor.  Immediately moved the transmitter over to the new sensor and then took the receiver out of the faraday bag.  Pretty soon after (less than 5 minutes), the transmitter connected and we got the following on the screens (both I expected).  The transmitter noticed the dramatic difference between the old sensor’s surroundings and the new sensor’s surroundings…and thus begins the ??? time period. 
5. The next thing that happened was we got one errantly high BG before the session when to ??? sensor error for 65 minutes.
6. After 65 minutes, the G6 came back online with a value of 149, and finger check was 163.
7. We calibrated and VOILA…our new pre-soaked sensor was online, super accurate and not jumpy at all with only 65 minutes of lost BG data.  Here’s to the next 10 days of awesome G6 use.

So why doesn’t everyone do this?  Because a lot of us like to squeeze every last day out of our sensors and we end up having them completely fail before we start a pre-soak.  BUT, I have found that I usually can see a G6 sensor failure coming up about 6 hours ahead.  We tend to see either a few missed BG readings start to happen, jumpiness in the data, or calibration drifting.  Given that heads up, this process will be pretty easy to implement for the G6 going forward.  Small amount of pre-planning and we can get immediately smooth CGM data on a new sensor session with just 65 minutes of downtime.  Pre-soak, receiver warming up in faraday bag, hotswap, wait 65 minutes and new session underway.