Monday, January 25, 2016

Dexcom G4 (505): likely trauma drop and recovery

A quick post, just because I found this example particularly clear and interesting.


Tennis Saturday, late wake up, sensor calibration a bit before 10:00 AM. That sensor has behaved extremely well, with a running MARD around, or even below, 10%. There's a breakfast spike, a correction that is a tad high, but that we let go. The late low carb lunch comes at 13:30 (trying to time our small Novorapid injection optimally for the tennis). We do a small warmup on a bike at 14:50 to avoid an early BG climb. We start carb loading at 15:30, with 10 grams every 15 minutes from that point (typically: 15:30, 15:45, 16:00, 16:15, 16:30...)


Tennis starts at 16:00 – we see a huge drop (50 mg/dl in one reading) at 16:25. We stop and double BG test at 16:30: 95 mg/dl. The sensor goes to LOW and starts beeping. A new BG still tests around 90 mg/dl while the sensor is now in LOW. At 18:30, tennis is over and, since the sensor is stable, we recalibrate. We are still around 100 mg/dl. The algorithm picks up the new calibration factor almost at once. That would have been very different with the G4 non AP: a new significantly different value would have had a variable impact depending on the previous values the calibration table held (or even the number of calibrations in the table if the sensor had been recent)

Since we’ve not seen an evening meal rise (frequently absent after intense exercise), I suspect a delayed hypo is in the book, which is why I double check and re-enter a calibration just in case. The guesstimate was spot on: we go down the slide. The sensor then accurately tracks the real delayed hypoglycemic even, which we correct (duh!).

Follow up

Sensor has now resumed its accurate behavior, initially with a clearly decreased conversion factor that seems to be creeping up a bit.


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