Re-Written Android App

App Inventor was a lot of fun, but is being discontinued 12/2011.

I’ve since re-written the Drip Timer app so it’ll still be available. The good news is that the app went from 3.89 MB (App Inventor) to 320KB (native). If you’ve already installed it from here, please Menu -> Settings -> Applications -> Manage Apps and de-install it. Reinstall from the Market, or:

https://market.android.com/details?id=com.DTsEMT.DripTimer&feature=search_result#?t=W251bGwsMSwyLDEsImNvbS5EVHNFTVQuRHJpcFRpbWVyIl0.

Free*3 (no purchase, no ads, no fee)

Thanks!

DTs

Calls and Classes and Android Oh My.

I’ve written a couple of Android applications, which various folk have expressed interest in using, so here they are.  Absolutely free, tell your friends, etc. blah yadda.  Each comes with absolutely no warranty, use at your own risk, warning: choking hazard, and all that good stuff.  If you find an error, comment here to let me know and I’ll address it ASAP (which may not be all that S, be patient.)  These were written for and tested on my HTC Evo 4G.  Your screen may look slightly different if the aspect ratios are very much different.

The first Android app I wrote was Oxygen.  This allows you to enter PSI on the tank and the flow rate in LPM.  Press “Done” on your keyboard to move it out of the way, then tap the tank size you’re using.  The time remaining for the tank is calculated.  PSI is automatically reduced by 200 prior to calculation because most consider 200 PSI the “safe residual pressure” – at which point you should be looking for that new tank.  If you tap “Countdown” a counter will appear and you can put your phone away.  It’ll start buzzing when the tank nears empty.

The other “Hey-that’s-kind-of-neat-let-me-have-it” program is DripTimer.  Instead of watching the IV drip chamber and your watch, and losing count and all of that fun stuff, just run DripTimer.  Tap the upper portion of the screen each time a drop falls into the chamber.  I made the tap area quite large so you can hit it without having to look at it.  Tap  “10″ if you’re using a 10-drop set, or “60″ for a microdrip set.  Sorry, 15-drip-guys, I didn’t have room.  The ML/Min and ML/Hr is displayed.  Two or three drip-taps work, obviously the more actual drops you count the more accurate the calculation will be.  If you’d like to use it to count Breaths or Heartbeats (useful for tapping out neonate heart rates), tap “Breath” instead of “10″ or “60″.  The display changes from “Gtts/min” to “Breaths/min” and you should ignore the ml/hour numbers, of course.  Maybe next version I’ll just blank those…

Unfortunately, WordPress does not allow the hosting of files and mine own host, alas, no longer provides this service.  The files are small enough that I feel no guilt or shame.  I was however forced to rename the files as DOC files so WordPress would allow the upload.

Windows users:  Right click either Driptimer or Oxygen and select “Save link as”.  For the file name, change the extension from “.DOC” to “.APK” (capitalization is unimportant.)

Next, you may either email the file to your Android device as an attachment, or connect the phone via USB and copy it to your SD card.

Finally, you’ll need a free file explorer program (like Astro, available in the Market) to open the file.  Android knows what to do with APK files and will install the program for you.   Since my program isn’t coming from the Market, though, you’ll need to first press [Menu button] Settings -> Applications -> Unknown Sources and make sure there’s a check mark in the box.

Have fun, leave comments if you find bugs, etc.  Again, I have other things on my plate at the moment and can’t promise features/bugfixes right away but I would appreciate any feedback.

Science!

Blinded Enlightened by Science!

In the post, Reading a Map, we found our hero DTs attempting to yet again simplify EMS math, as he has done so successfully in the past.  And lo! it seemed he had again succeeded!

Indeed.  Behold the hideous formula for mean arterial pressure,

((Diastolic BP * 2) + Systolic BP) / 3

Too horrible for words!  Too grotesque for thought!  And too much damned work for 2 am.  With parry and jab, the plucky DTs vanquished the offending formula with a simple,

(Systolic / 10) + Diastolic


Yes, as flash bulbs popped, our hero stood proudly upon the podium and explained his conquest, with concrete examples – and even a table!  Yet even as he spoke, the silhouette of the beastly equation (quite undead) rose stealthily in the background to the horrified gasps of the press…

In other words, it seems that simplistic equation don’t work so well.

The two methods agree completely when (Systolic / Diastolic) = 1.43.  For instance, 120/84 results in MAP=96 using either formula.  80/56 results in MAP=64, again using either formula.

The examples in the original post, plucked randomly from mine own head, all just happened to work out to within a few mmHg, making it an attractive theory.  Without peer review, my team published (I count my hands as two separate co-workers, while typing, to help spread the blame).

Further field research blew the thing apart.  A simple 120/61 provides traditional MAP=81, DTsMAP=73 – too much error to ignore.  As did 137/76, MAP=96 and DTsMAP=90.

A random number generator was quickly pressed into service – with rules (eg Systolic must always be greater than diastolic, etc.)  The results did not bear out the usefulness of the formula.

And THIS, folks, is why we have to relearn CPR every couple of years, always with new rules; and why ET tubes in the field are losing support, and a host of other data-driven changes we see all the time in the field.

Cuz it’s Science!

Reading a MAP

I’ve figured a 2-am cheat for the MAP, which doesn’t work half-bad.  Not the linesy-roadsy MAP, the other kind.

Blood pressure is one of the more important measurements we can take, we all know that and I won’t belabor the point.  If we’ve been in the business long enough, we get a feel for a blood pressure that’s “not right”, in the overall picture of patient age, habitus, etc.

The real golden nugget of the BP is, of course, the mean arterial pressure or MAP.  This is the number which some studies suggest must be maintained over 60 (other sources state 65), and failure to do so results in poor organ perfusion or even organ ischemia.  We’re talking kidney failure, liver problems, the works.

So, what is the mean arterial pressure or MAP?

Wikipedia defines it as “… a term used in medicine to describe an average blood pressure in an individual.  It is defined as the average arterial pressure during a single cardiac cycle.”  Great.  Okay.

The article proceeds to inform us that to find the MAP, all we need to do is multiply the cardiac output by the systemic vascular resistance, and add the central venous pressure.  Wiki tells us that the CVP “is usually small enough to be neglected in this formula”.

So the MAP is (CO x SVR).

And cardiac output is…?  Along with systemic vascular resistance, it is hard to measure in the field, that’s what it is mes amis.

Wiki goes on to state that there are several ways to estimate the map, using the systolic blood pressure (SBP) and diastolic blood pressure (DBP).  This is more my speed – I got those numbers.  There are a few ways to use them to figure out MAP, to whit:

MAP = DBP + (0.33 x (SBP – DBP))

(English translation:  Subtract diastolic from systolic, multiply that number by 0.33, then add diastolic back in.)

-OR-

MAP = 2/3 DBP + 1/3 SBP

(English: multiply diastolic by 0.66, multiply systolic by 0.33, add those products)

-OR-

MAP = ((2 * DBP) + SBP ) / 3

(multiply diastolic by 2, add in systolic, divide this number by three)

Yeah, right.  This is just uno poquito mas math than I like doing.

Now, I’ve noticed a lot of ambulance folk are equipped with PDAs and the like, which is wonderful if you don’t mind whipping it out to calculate all this – with blood or vomit or worse on your gloves.  Better and easier to do it in your head, if you need it.

Here’s how:

For comparison purposes we’re going to use the third MAP equivalency formula, 2 times the Diastolic, plus Systolic, then divide the whole shebang by three.  That’s the formula I’ve most seen touted in books and such for us field grunts.  Using that formula, we see that for a patient with a BP of 80/40, this equals ((2 x 40) + 80 / 3), or (80 + 80)/3, or a MAP of 53.33.

Again, this is too much work.

The DTs 2-am MAP formula is:  Systolic / 10 + Diastolic.  Easy-peasy.  This yields, from a BP of 80/40:  80/10 = 8, plus 40 is 48.

Like any good 2am rule, this is fast, easy, and wrong.  Notice we’re a full five mmHg off the “official” estimated MAP.

Notice also that you wouldn’t probably bother figuring this out in this example, anyway – 80/40 is Not a Good BP, and you already know that.   But if you’re wondering about the mean arterial pressure for a patient with a better-sounding BP, the formula works very nicely:

BP MAP DTs MAP
100/65 77 75
108/75 86 86
144/100 115 114
136/90 105 104
192/160 171 179

… and so on.  Again, not many systems ask “What is the patient’s mean arterial pressure?”  If you want to ballpark it, though, Systolic/10 + Diastolic is probably an easier way to go.

So, there it is.

Extending the Art

We each do what we can.  Current backing signals are:

Backing - turn left

Direct the rear of the vehicle to the left

and

Backing right

Direct the rear of the vehicle to the right

And of course,

Backer stop

Stop.

But I have developed a new signal – quite accidentally, just wasn’t thinking actually.  Think of pantomiming “the Bunny hop”:  Hands in front, making little “wave” motions up and down, while you jump:

Speed bump

You are about to go over a speed bump.

It looks really stupid, but your driver will laugh, and some days that’s what ya need.

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