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I’ve been pumping insulin for the last 14 years, and I travel frequently. In fact, I’m on an airplane every couple of months.

I always struggle with my blood glucose during air travel, and attribute the in-flight fluctuations to the stress of travel, or the crappy fast food breakfast I probably had prior to boarding (must have miscalculated those carbs), or even to sheer diabetes randomness. It was only recently, however, that I learned something critical about insulin pumps and airplanes, something that I hadn’t ever been told – not by device companies, not by my medical team, not by my online friends.

When flying with an insulin pump, you should always disconnect it during takeoff and landing.

This isn’t a US FAA recommendation; this isn’t about turning off your electronic devices. And this certainly isn’t because your diabetes management makes Miss Manners uncomfortable in flight.

It’s physics.

When I was being trained on my current pump – the Asante Snap – by Asante’s Chief Product Architect, Mr. Mark Estes, he was surprised that I had never been told to disconnect when flying with an insulin pump. He asked to me to think about how delicately my ears handle takeoff and landing.

Now consider what that kind of pressure change during ascent and descent do the subtle workings of an insulin delivery device.

The he asked me if I ever experienced “baggage claim lows.”

Absofrigginlutely.

When I’m shaking from a low as my husband picks up our rental car or I’m fumbling with glucose tablets in my cab, I’ve always just assumed I don’t manage myself as well with the changes to my routine that day. I’ve often claimed that “I’m always low the whole first day I’m traveling.”

But there is more going on when I’m jet-setting than I realized.

Enter every pumper’s least welcome buddy – the air bubble. Your insulin pump (regardless of make or model) cannot elegantly handle the pressure changes during ascent and descent and is moving air bubbles and insulin into your body without ever recording evidence of it.

I don’t know why this isn’t bigger news. Even the blurbs I could find on the Internet talk about it being an issue for some children on some pumps and not necessarily for adults. But this happens to all liquids in flight – from our water bottles to our bodily fluids. Estes told me that Dr. Bruce King of John Hunter Children’s Hospital in Australia has tried to bring this to light over the past few years, producing an impressive poster on the study as well as an abstract.

Estes explained two effects of the changes in cabin pressure and how they relate to our pumps – outgassing (due to Henry’s Law) and expansion (due to Boyle’s Law):

“The pressure in a commercial airline starts at the same pressure as the airport (most of them are close to sea level, but some, like Denver’s airport are at a higher elevation).

When the airplane is flying (typically above 20,000 feet), the cabin is pressurized to a pressure of about 8,000 feet. This keeps the people on the plane from passing out (the air is way too thin above 20,000 feet).

The difference in pressure between where they took off to the pressure in the cabin when flying results in some of the air that is trapped in your insulin to leave the liquid and form a bubble. This is because, as the pressure drops, the amount of air that can be dissolved in the insulin decreases. This is called outgassing.”

Another example of outgassing is what happens when you open a can of soda. The pressure change from popping the can open causes carbon dioxide to leave the liquid quickly and form bubbles. Your insulin is doing this as the plane takes off, as are your bodily fluids (which accounts for why people tend to get a bit gassy in flight).

So what happens to these bubbles? Where do they go and how do they affect your insulin delivery?

That’s where the second effect comes into play. The sudden decrease in pressure around the bubbles causes them to expand. And they have to make room for this expansion somehow, so they push insulin out of the way and into your body. There’s no record of the exchange in your pump history, but there you have it – the source of the “baggage claim low.” The reason why I’ve hailed so many cabs while shaking violently and chewing chalky sugar pills is an over-delivery of as much as a unit or more. The effect was observed in both Medtronic and Animas pumps in the original studies. This affects all of us.

So what can we do?

That depends on how sensitive you are to changes in your basal delivery. The average adult, and certainly the average child with diabetes, is likely going to react to receiving an extra unit of insulin they weren’t expecting.

I happen to own user guides for two different Omnipod systems, the Tandem t:slim, the Cozmo 1800, and the Asante Snap. Out of curiosity, I have also downloaded and read the user guides for the Animas Ping and the Accu-Chek Spirit Combo, and reviewed the information about air travel on Medtronic’s website. With the exception of Asante (obviously), none of the pump companies recommends disconnecting during any part of air travel. (Those pump systems with paired meters do recommend disabling pairing or Bluetooth in flight due to electromagnetic interference, but none of the companies go the extra step of asking you to disconnect.)

I needed to see this for myself.

On several flights now, I have taken a small bump of insulin (equal to what I anticipate missing while disconnected between takeoff and cruising altitude) as we are taxiing to the runway. (You could do this as a tubing prime or cannula prime on most pumps, though on tslim, I might suggest doing it as a bolus so as not to reset your site reminder, but keep in mind that delivering it as bolus will include it in your IOB calculations.)

Then I disconnect. I watch that tube and I wait as we climb.

My ears pop and click and adjust and I think about my little insulin pump.

When we reach that 30,000 feet or so and the captain announces we’ve settled at that altitude, I check the tubing and voila.

I prime that puppy out. A unit. Maybe TWO units. Wow.

I then reconnect for the rest of the flight.

About 20-30 minutes before landing, when I feel that descent start, I do it again. Take anticipated missed basal up front. Disconnect. Watch and wait. Estes warned that the air bubbles may take longer to incorporate back into the solution once you’re on the ground.

So…I know what you’re thinking. “Nah, my pump doesn’t do this.

Go ahead. Conduct your own little physics experiment. I have tried it on three flights now. I am dumbstruck.

And what about the Omnipod? This is a great question and one I do not have the answer to. I suggest that you take whatever other precautions you might take if you knew you had a basal surge coming. Since you can’t disconnect, you’d want to discuss with your medical team what the best option is for you in-flight. I experienced these in-flight fluctuations flying with their device many times, too, so my gut tells me that it’s a problem on every pump and not simply a tubed pump issue, though I have a feeling Insulet would say it’s not an issue. If it’s happening to my water bottle though, it’s probably happening to an Omnipod.

What I can tell you is that I am going to listen to my ears. And my ears tell me that something significant is happening to the atmosphere around my body when I fly.

And I am priming that bubble bugger out.