I got my first CGM three and a half weeks before I ran the Vienna marathon. I used it on my final long training run (23 miles), and on my short runs leading up to the marathon. I was trying to learn how to use the information to improve my blood glucose while running. Knowing there is a delay in results, and that a CGM isn’t as accurate as a finger prick, I anticipated a learning curve.
I continued to check my blood sugar with a glucometer during pre-marathon runs, and I then compared the results with those of the CGM. I learned that when the CGM indicates a drop in BG it means that my BG is already low, and that I need an energy gel. I also learned that while the 15-20 minute delay in results might not be that important in normal life, it can be critical in a long run. In one instance, the CGM told me my BG had gone from the mid 150s to 85, but my BG was actually under 70.
I flew to Vienna a couple of days before the race, accompanied by my two older sons, Tom and Guy. We did some sightseeing before marathon day. I was nervous, but my sons were a wonderful distraction.
Marathon day was almost perfect. No sun, chilly but not too cold, and no rain (after two wet days). Although I had the new CGM data to work with, I didn’t change my usual marathon plan: take a gel every 10K starting at the 5k point. I planned to fine tune along the way according to the information from my CGM.
I was very nervous at the starting line, and as a result my blood sugar kept creeping up, as it always does pre-marathon. I was around 220, and so stressed about messing up that I forgot to reduce my basal insulin rate to 60%.
The race began with classical music, and within a few minutes I was away from the starting line and running over the Danube River. “I’m doing it!” I thought to myself. I tried to relax and enjoy the scenery. Then I realized I’d forgotten to set my basal rate. I quickly made the adjustment, and all seemed good.
I checked my watch every few minutes to make sure I wasn’t going too fast, and I looked at my CGM expecting to see my blood sugar drop as it usually does a few miles in to my runs. But the CGM kept showing my BG at around 220.
As I approached the 5K point, I wondered if I should take a gel as planned although my blood sugar was still quite high. I decided to stick to the plan and took the gel. To be safe, I bolused a half a unit of insulin with it and kept an eye on my CGM. I waited for my blood sugar to go down, but it didn’t. It stayed high and even started creeping into the 230’s. I had no understanding of why my BG was not coming down after 5-6 miles of running. At the 10.5K mark, a quarter of the distance in, I decided I had to check my blood sugar with a glucometer. I stopped on the side of the road, took out my meter, and checked – 133. My CGM was totally off. Relieved, I continued to run (calibrating my CGM).
I ran through the pretty streets of Vienna trying to enjoy the race. Things were under control and I was keeping my pace up. The CGM corrected itself (following the calibration) but then indicated that my BG was on its way up again, However, since I felt good, I believed that maybe the race was going to turn out better than I had originally planned.
At the 15K point water station I looked at my CGM again before taking another gel. It was back up to the 180s so I waited with the gel. At the next station (2 miles later) I looked at the CGM again, and my BG wasn’t coming down. I stopped again and checked BG with the glucometer. It was 130, the same as my last stop. I figured the half unit of insulin had been a good decision, so I did it again. One gel and half a unit of insulin.
Around the 25K mark I started to feel bad. It wasn’t my legs, although I did feel I was slowing down. I just felt bad. Around this same time my CGM alerted me that it was shutting my basal off (Minimed 640G, low glucose suspend), detecting the drop in BG, although my CGM reading was still in the 130’s or 140’s. I stopped again and checked my blood sugar, and it was 101. Relieved, but annoyed at myself for wasting time, I had a third gel, and resumed my basal insulin.
At around the 30K mark I stopped again, feeling much worse. My CGM numbers were down around the 90’s. I checked my BG again. I was 80, but I felt more like 50. I had the shakey, terrifying feeling of rapidly dropping blood sugar. I took out my 4th gel, squeezed it into my mouth and gaged. I tried to swallow it, but couldn’t. I spat it out.
My blood sugar continued to drop, but I didn’t stop, not even when the CGM now showed numbers in the 80’s. Instead, I tried to consume my last gel. This time I got around half of it down. The sweet taste made me feel sick, but I knew I had to keep it down. I was out of gels, and had nothing else on me that would raise my blood sugar. If I threw up, the marathon would be over and I’d probably need medical help. I didn’t stop running and repeated the mantra ‘don’t throw up’. At around the 36th kilometer, there was a station giving out halved bananas. A miracle! I took one and ate it slowly. I kept running, telling myself that if I ran fast enough I’d finish the race before my blood sugar dropped too low.
As I approached the end of the race, knowing my children may see me, I tried to run as well as I could. My legs felt hard and heavy, and I felt a rush of emotions, like I was about to cry. I continued, passing by the Vienna Opera House, where my kids were supposed to be waiting. I searched the crowd, but couldn’t see them. I hoped they were making their way towards the finish line.
I felt like shit, but I remembered to raise my hands as I crossed the finish line. I must have looked terrible because a medic came up to me. I told her I was fine and after I caught my breath she let me go.
I received my medal, goodies bag, and a bottle of water. I drank half of the bottle, threw up (finally!), collected my things, and made my way slowly towards Tom and Guy.
When I saw them I, tears filled my eyes. I grabbed them, hugged them and gave Guy a kiss on his head.
They asked me how it was. I told them it wasn’t so good, I felt sick, and that I had just thrown up.
“So you kissed me on the head with throw up mouth?” Guy said.
“Yes.” I smiled, “But it’s okay.”