Got questions about life with diabetes? You came to the right place! Our weekly Q&A column Ask D'Mine , hosted by veteran type 1 and diabetes author Wil Dubois.

Today, Wil is looking at the issue of dosing insulin while en route via air travel. There is some question about whether special precautions need to be taken while in the air. Read on for more...

{Got your own questions? Email us at AskDMine@diabetesmine.com }

 

Riva, type 1 from New York, writes:Wil, can I ask you a travel question? I was once told injecting via syringe on a plane that you don’t first draw air into the syringe to put in the vial, you just draw out your dose. Does this mean you wouldn’t first prime an insulin pen?

 

Wil@Ask D’Mine answers: Actually, I’d never heard the advice of skipping the air injection into the vial, and when I tried to research it for you, I ran up against a deluge of material on how to get insulin onto airplanes with all the modern security restrictions. Your needle was lost in an unrelated haystack, but I can only assume that you were given that advice on the assumption that the vial was pre-pressurized for you. 

Let me explain.

The purpose of injecting air into the vial is to avoid creating a vacuum that makes it hard to draw the insulin out. Well, more than that. By adding air to the vial, you’re essentially increasing the pressure inside the vial. Just as nature abhors a vacuum, so too, does it abhor differential pressure. If you pressurize the vial, given the opportunity, it will want to equalize itself with the surrounding environment. When you tip the vial upside down on top of the syringe, the high-pressure air at the top of the vial seeks to escape, and pushes the insulin down into the waiting syringe below, making it easy to fill. 

Now, back to airplanes. Most airliners maintain a cabin pressure close to 8,000 feet above sea level. So if you take off from Kennedy Airport and your plane climbs up to 35,000 feet, the air around you thinks it’s only at 8,000 feet. Your insulin vial, however, is still at higher-pressure sea level. So it’s already got an air shot in it. No need to add more.

Maybe. 

Share on Pinterest

I say maybe because what if, instead of taking off from Kennedy, you’re taking off from Denver International at a mile above sea level? Or El Alto in Bolivia, at 13,323 feet above sea level? I think you can see that this isn’t one-size-fits-all advice, which is maybe why it’s not common wisdom.

So what to do? As a real-world hack, here’s my suggestion: If you take off from sea level, or anything close to it—say under 3,000 feet—you probably don’t need to worry about injecting air into your vial. If you take off higher, I’d inject half your dose (unless you’re in Bolivia). Needless to say, if you’re having trouble drawing up the dose, just start over and add more air.

Of course, you didn’t ask about vials, you asked about pens. Now insulin pens are built differently. In normal use, the only air work involved with a pen is our “air shot” to make sure there’s no air in the pen needle. You never have to inject air into a pen cartridge before dialing up a dose because unlike a vial, the back end of the pen cartridge (in both disposable and refillable pens) is open, “plugged” by a sliding rubber cork that’s pushed by the pen’s plunger mechanism.

As the cork slides, a pen cartridge can’t create a vacuum. Pumpers who’ve needed an emergency reservoir fill from a pen know this; they can suck all the insulin out of the pen’s cartridge with no air injection. So, given all of that, you’d think that a pen would be immune from air pressure changes in flight—but there’s more going on with airborne insulin than meets the eye. And to better understand how changes in air pressure affect open-ended insulin containers, we need to look to a 2011 study on the effects of air travel on insulin pumps. 

After reading reports about insulin pump users who were routinely experiencing low blood sugar during air travel, the researchers began to wonder if the dynamics of flight were somehow affecting insulin pumps. They took ten insulin pumps and loaded them into a hypobaric chamber to mimic the air pressure changes on a commercial flight, and guess what? They discovered that the changes in the cabin pressure caused the insulin pumps to deliver un-commanded bolus dose. Next, they loaded the pumps onto a Boeing 767 on a commercial flight—no doubt in economy class—to compare the results.

They were the same. 

So was air pressure forcing insulin out of the pump? Actually, no. The ghost boli doses were created by a different sort of physics altogether: Pressure changes caused existing bubbles in pump reservoirs to expand by 36%, and also for new bubbles to form as air suspended in the insulin was forced out of solution in the cartridge. Picture the cap being popped off of an old-fashioned Coke bottle -- where’d all those bubbles come from?! Both sets of bubbles in the reservoir displace liquid insulin, forcing it out of the cartridge, down the infusion line, and—in the real world—into the PWD (person with diabetes).

How much insulin was being delivered in this “un-commanded” way? Consistently, 0.623% of the cartridge volume. For perspective, in a 300-unit pump, this amounts to a 1.8-unit surprise bolus. Obviously, a smaller reservoir pump would deliver less. 

For some people, especially kiddos, that’s enough insulin to be a real problem. For others, maybe not so much. Pumpers can minimize the risk by being extra careful to fill their cartridge bubble-free before airline travel, but the physics of air coming out of a solution is something we are powerless to do anything about.

Now, this happens after takeoff, as the airplane is climbing to cruise flight. Interestingly, on the other end, as the plane descends, the opposite effect happens—bubbles shrink and air is forced back into the solution, and the pump’s reservoir sucks insulin back in. So now, a pumper isn’t getting the insulin they’re supposed to be getting. 

Yeah. Air travel is full of ups and downs. Highs and lows.

This has led to the not-as-well-publicized-as-it-should-be advice to unhook your pump until the Captain turns off the seat belt sign. Then connect again in cruise flight, and unhook again as the descent to your destination begins.

As a side note, I have to mention the other finding of the study, which mimicked “catastrophic” airplane depressurization, to see how that would affect insulin pumps. No mere bubbles now... instead, rapid depressurization actually caused the plungers of the pumps to move foward, on average delivering more than 8 full units in less than a minute. 

Mayday, Mayday!

Yeah. If you have the bad luck to be an extra in a real-life episode of Air Disasters, you might survive the group disaster but have your own personal diabetes disaster once you’re “safe” on the ground. I guess the lesson here is: Put on your Oxygen Mask, then break out the glucose.

OK, so what’s our takeaway for pens from all of this? Pens, like pumps, are not immune to the effects of bubbles, but unlike pens, have no infusion hose connected to them for the displaced insulin to escape down. If, like me, you ignore the manufacturer’s advice and just leave a needle on all the time, the front of the pen will be the path of least resistance for the insulin displaced by the bubbles, and it will escape forward, leaking out of the needle, pre-priming it for you. This creates an automatic air shot. In fact, you might even find a little puddle of insulin inside the cap. On the other hand, if you’re a girl scout and use a fresh needle each time, then your cartridge will be pressurized. Perhaps overly so. When you screw a new needle on in flight, you’ll be rewarded with a vigorous stream of insulin from the tip. 

My tip: Don’t point your pen toward the passenger in the next seat. 

So needle kept on or not, for the first half of the flight, you don’t need to prime the pen.

Of course, as with insulin pumps, the process reverses itself as the plane descends to land. The bubbles shrink, some go back into solution, and the outside air will push any insulin in the needle back up the pen needle and into the cartridge.

In this case, if you fly with your needle attached, you can land with a puddle of insulin in the cap and an empty needle. If you use a fresh needle each time, and take a shot at altitude, you might need several air shots on the ground to prime the needle.

Yep, you get the point: Diabetes-wise, all things being equal, it’s just easier to take the damn train.

 

This is not a medical advice column. We are PWDs freely and openly sharing the wisdom of our collected experiences — our been-there-done-that knowledge from the trenches. Bottom Line: You still need the guidance and care of a licensed medical professional.