“Watch out on planes, you’ll go low," my dad’s friend (at the time, a Medtronic engineer) said. It was 2005; I had started on my insulin pump a couple of days before, and been diagnosed with T1D just 3 weeks prior to that. My dad had worked at Medtronic (or back then, Minimed) for the past seven years.
I hadn’t gotten on a plane with an insulin pump yet, but he explained to me how the changes in barometric pressure would expand any microscopic (or macroscopic) air bubbles in the reservoir and tube, advancing insulin through the cannula, and causing a low.
“I would suspend your pump on planes”, he said.
That was 14 years ago. But I have thought about this conversation probably every single one of the hundreds and hundreds of times I have gotten on a plane with my insulin pump since (like the 5 times in the past 72 hours!).
In fact, today I suspended my pump to avoid a low blood sugar on a plane.
So I looked it up and someone actually studied this!
In 2011, King et al. found that during ascent, Animas (RIP) and Medtronic pumps each delivered about 1 unit more than expected, purely due to the formation and expansion of air bubbles.
The change in pressure wasn’t enough to move the plunger, but when they mimicked “catastrophic depressurization” (when the oxygen masks drop), all pumps delivered more than 8 units of insulin due to actual plunger movement.
At the end of the paper, the team actually gave recommendations for flying with pumps:
- The cartridge should contain no more than 150 units (more insulin, more bubbles)
- Disconnect before take off
- Disconnect and prime the bubbles at cruising altitude
- Disconnect and prime after you land (to refill after bubbles contract)
- If the cabin loses air pressure, disconnect the pump
Have I ever actually done any of these things? Nope! Do I always go low on planes? Also nope.
These changes in pressure don’t occur in a vacuum (physics puns anyone?) and there are a billion other factors at play that impact blood sugars!
This is not to say you will always go low when flying! Even the authors of this paper say what happens to blood sugar on a plane depends on many factors, like insulin on board, food, activity, stress, and insulin sensitivity in addition to this.
This is simply one part of the ongoing blood sugar equilibrium equation, and specific only to people on pumps!
On a side note, plenty of people with diabetes report always going high when traveling (long hours, international flights), which could be because of stress, adrenaline, sitting for hours, and airplane food!
But as always, the more we know, the better able we are to handle whatever comes our way. Happy travels!