Now back on Day
Two of this little project I mentioned that the Snap pump lets you choose how
you want it to track insulin on board, called IOB, or sometimes “active
insulin.” And I suggested that you should all send thank you cards to Asante
for doing this, and promised to talk in more detail about this feature later.
So today is later! But before we get into the details, we need to spend a
minute making sure everyone understands what IOB is all about. And it’s all about
specifically, it’s about stacks of pancakes.
American gut-busting tradition of piling good things on top of each other is
the perfect analogy for one of the most wicked risks of modern insulins: Stacking.
Here’s the deal: all of the ’Logs—Humalog, Novolog, Apridralog (OK, I took the liberty of renaming that last
one, but it is an analogue insulin)—are
classified as rapid-acting insulins.
Rapid, my ass. Twenty minute onset, two hour peak, four-to-six hour duration of
action: What’s rapid about that? Nothing at all. They only get the title by
being the fastest of the slow. The insulins that preceded the analogues were
called short-acting. ’Logs are faster
than short, and so the get the honorary title of rapid, but don’t make the mistake of thinking they come anywhere
close to the speed of real insulin in the body of a sugar-normal. Or anywhere
close to the speed we dFolk need.
But back to the pancakes.
Even if you ate a whole stack of pancakes, it’s likely that you’ll be feeding
your face again sometime in the next 4-6 hours. Which also means you’ll take
more insulin (at least you’d better had). The problem is, some of the insulin
from that first stack of pancakes is still in your system, still active, still
able to lower blood sugar. If you test your blood sugar and take insulin for your
sugar and a second round of pancakes without considering that some of the
earlier insulin is still in play, you can stack the insulin doses, and end up
with too much insulin in your body.
stacking causes spectacular hypos.
other classic example of stacking crashes is someone checking their BGL and saying,
“Wow, I’m too dern high”—forgetting that they took 10 units three hours
before—and throwing more fuel on the fire with an hour or more of old insulin
action yet to play out.
using syringes or pens, there’s no good way to keep track of when you dosed,
and how much insulin may still be in play. [Modern
shooters can now use the marvelous RapidCalc Ap on a smart device.] But a
pump has the computing power to track this insulin, and take the insulin on
board into consideration when crunching the numbers and recommending an insulin
“Wonderful,” you say. “So what’s
the problem?” The problem is that no one agrees on the best way to track the
active insulin in our bodies. Now the world has changed, but back in the day there
were two very different ways to look at IOB, and they were called the Medtronic
Way and the Cozmo Way. Medtronic pumps traditionally
only counted correction bolus insulin on the theory that any insulin given
for food would be perfectly cancelled by our superior carb-counting skills. The
Cozmo way realized that was ridiculous,
none of us really knows what the fuck we’re doing, and counted all insulin. I
confess to being a fan of the Cozmo way of looking at IOB.
today’s world, OmniPod’s blue-controller uses the Med-T way, as does the Ping.
Ironically, the new Med-T pumps no longer use the classic Med-T way. The t:slim
uses the Cozmo way, as does, as I understand it, the new black-controller
OmniPod pumps. To be honest, I’m not sure how the “new” Roche pump calculates
IOB. I tend to forget it’s out there. Have any of you ever seen one in the
digress. In truth, there are plusses and minuses to either method. And as long
as you understand what your system is doing, and it makes sense to you, you’ll
be fine. That said, from a clinical perspective, I’ve seen a lot more pumpers
get into trouble with the Med-T-type IOB systems than with the Cozmo-type systems.
In my view, playing with insulin is playing with fire. And if I’m playing with
fire, I really want to see all the fire—not just half of it.
OmniPod first came out, I was disappointed to learn that they had chosen the
Med-T method of IOB tracking. When one of their senior folks came out to set me
up to be one of their pump trainers, I asked why they did that. I don’t know if
it’s true or not, but the answer I was given was that they polled a bunch of
endos and 51% of them preferred the Med-T method. If it was that close, why didn’t you just make it a menu option? I
just shrugged one shoulder.
the good folks at Asante did just that. In the menu, the choices are called Correction or All. In the Snap pump, this menu is buried in the Smart Bolus setup
menu. Go Home>Menu>Bolus Menu>Bolus Setup>Smart Setup>IOB Mode. Getting
there takes a lot more button pushes than it looks like, as you have to skip
over many other options to reach home plate. But I have no qualms about how
deeply it’s buried in the menus because it’s unlikely you’ll ever change it
once you set it the way you believe IOB should be tracked.
to be clear: Correction = Med-T way; All = Cozmo way.
addition to the differences in how the pumps of yesterday tracked IOB, there
were also big differences in how they reported this tracking to the user. On
older Med-T pumps, a lot of this happened under the hood. You couldn’t see it, couldn’t
get to it, and couldn’t interact with it. Even on today’s Revel pump, viewing
the IOB is no easy task. On the old Cozmo pumps, on the other hand, IOB was
center-stage. There was a IOB status screen, and you could even leave the IOB
screen as your default when you turned on the pump!
took a feather from Cozmo’s hat and even upped that ante: the slick Applesque t:slim
really shines amongst other modern pumps when it comes to IOB. You don’t even
have to fully turn on the pump to see your IOB! Just run your finger across the
top of the pump to press the only analog button on the machine, and the unlock
screen appears. At the bottom of the unlock screen (and on the main menu as
well) is your IOB in a little status banner along the bottom of the screen, both
the units in play, and the time remaining.
how does Snap compare? Not very favorably. Viewing your IOB on the Snap is no
snap. It takes three clicks: One to wake the pump, then the right button to get
to Status, then the right button again to view your IOB.
Wait a sec. Something is missing here... I see how much insulin is in play, but
I don’t see how long it’s going to last. Most of us IOB fans are used to
thinking about both volume and duration. Let me give you an example. Let’s say
I check my blood sugar and it’s 197 mg/dL. I look at my IOB and see that there’s
1.4 units on board that will last for another 45 minutes. OK, I’m probably safe
from a hypo. I might even end up a bit high by the time the inulin runs its
course. On the other hand, what if my blood sugar was 109, instead? Oh, crap!
I’m gonna crash!
I grilled the Snappers about why this key piece of critical insulin guidance
data is missing. Their engineers seemed amazed that any of us would care. They
viewed it as a house of cards, and pointed out that most pumps reset the
countdown if even a tiny amount of insulin is added to the pile. One of them
challenged me this way: What if you had, say, 4 units on board with only 30
minutes left? Then you added a quarter of a unit. Now the IOB time re-sets to
four hours. It will show you have 4.25 units running over four hours, which is
misleading. The large volume is gone in half an hour. Only the little splat
left will last longer.
probably right, damn it. But I still don’t like it.
used to making decisions with two facts: volume and time remaining; and I’m
getting old enough that I’m getting stuck in my ways and I don’t want to have
to change, damn it! Intellectually, I get it. I get that if one variable is
misleading, my decisions won’t be the best. But in the trenches, having some
indication of time as well as volume is a big help. It puts my IOB into a
engineers—who clearly don’t have diabetes—also thought it wasn’t that big a
deal to check your bolus history if you wanted to know how much came from when.
Are they kidding? Who has time for that??!
me, a common nocturnal ritual (along with brushing my teeth, kissing the boy
goodnight, and making sure my alarm clock is set) is to think about my IOB and
the time remaining from my dinner bolus while analyzing the risk/benefit ratio of
a bedtime correction bolus. Yes, the pump should be able to tell me if a
correction is safe or not, but I know things the pump doesn’t know. I also have
CGM on my team. So not only do I know my blood sugar, I know my trend. Am I
stable? Am I falling? Am I rising? If I combine that knowledge with how much
insulin is on board and how long it will last, I’m smarter than my pump. If I’m
drifting upwards and the pump thinks a correction is a bad idea, I’ll override
it and give myself more insulin anyway. I know I need it. Other times, Mr. Pump
might think I could use a correction based on blood sugar and IOB, but I know
better because my CGM trace lines are gliding smartly downwards.
bottom line here is that time does
matter. It’s an integral part of the IOB decision-making process in the
trenches, where real diabetes therapy decisions take place. While it’s true
that a pile of little boli would mess up the true accuracy of a typical IOB
timer, I suspect that most of us pumpers don’t really take boli all that often
in the first place. If I’m right about that, the conventional timers work fine
for most people, and are certainly better than nothing, even if they are a technical
house of cards.
I’m willing to concede that the Asante engineers have a point, so my challenge
to them is this: As you guys think the timing is unrealistic; come up with a
solution. Don’t ignore the variable of time. Perfect it instead. Why not
combine time and volume with an impact percentage measure? Using the example
above, it shouldn’t take a rocket scientist to write a piece of code that could
IOB 4.25 units. 94% exhausted in 30
minutes; 6% exhausted in 4 hours.
be happy, you’d be happy, we’d all be happy. Happy, happy, happy.
Monday: Oh, Snap! I have no idea what I’m going to write about next week…
I’d better snap to it and figure out what the Snap I should talk about next.