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.

The Cause of, and Solution to, All Life’s Problems

I wandered into the TV room and sat as my family watched the old, 1978 version of Battlestar Galactica.  The scene on the bridge was tense, as some poofy-haired guy wandered up to the admiral and reported, “Sir!  An incredible number of Cylons are approaching!”, at which line we all burst into laughter.  “Incredible number?”  Of what possible help could that report be?  “Perhaps we should formulate an unbreachable defense!”  Tactically, it would be better to have an actual count, right?

And so it is for EMS.  We don’t say, “Doc, the patient BP is high!” – it’s 180/110, or whatever.  Pulse isn’t “Racing!”, it’s 120.  We use actual numbers because they suggest what our treatment should be, and by comparing them afterward allow us to know if our treatment is working.

Now, we’ve been saddled with some useless numbers – GCS for instance, of which I’ve written previously.  But there’s always been a number I’ve wanted, something I think an ED, ICU, or floor could really use – and despite looking everywhere I couldn’t find it, until I got a Christmas present.

In school one of the instructors told us that one of the first things a doc will do, on entering a patient room, is glance at the Foley bag (if there is one).  For those unfamiliar, a Foley is a bag used to drain urine.  A catheter is inserted into the patient’s urethra and threaded into the bladder.  A small balloon on the catheter tip is inflated with saline, making it too big to slide back out again.  The distal end of the tube connects to a clear bag, which is hung on the side of the bed.  The bag has a provision for emptying it without removing the catheter from the patient’s bladder, and the whole setup can be left in place for days at a time.  This is usually not a field procedure in our area, but other parts of the country, where transports are long, might do so.

The three things a doc is usually looking at are:  Volume (amount of urine), Color, and Flocculence (stuff floating it).

So, Volume.  When the catheter is first inserted, there should be some urine output.  Over time, of course, the bag fills – the bags are of different capacities, but in general one or two liters.  If the patient has had a Foley for a while, and the bag isn’t filling, that’s a Bad Thing – kidneys might not be working.  If that’s what you see, ask the RN when the bag was last emptied.  If it’s not been emptied by the nursing staff, and it’s only a few milliliters full, you may be seeing kidney failure.

Flocculence is usually Bad.  It’s appearance varies – I’ve seen what look like soggy cornflakes floating in the urine – but it can be sediment-like or a simple cloudiness.  Flocculence implies bacteria, usually – UTI, bacterial infection of the kidneys, that sort of thing, but can be other material I’m sure.

And Color.  This is where I wanted a number. Generally, urine should be clear or pale if the patient is adequately hydrated.  Urine is of less volume, but a darker color, if the patient is underhydrated – the urine is more concentrated because the body is trying to conserve what little water it has.  Conversely, if you see a patient whose Foley is filled to the brim with clear liquid, chances are they’re way overhydrated, although this can be on purpose if they’re flushing his kidneys.

Rhabdomyolysis is the breakdown of muscle tissue, from trauma or burns, sometimes stroke.  It releases a red-pigmented chemical which can overwhelm the kidneys and turns the urine copper- or red-colored, or dark.

We can go on, but basically the point is that the color of the urine can be indicative of underlying processes, and this would be good information to have.  And rather than running to Commander Adama on the bridge of the Galactica and shouting like a goof, “Sir, the patient’s urine is really messed up!”, it would be nice to quantify it somehow.

Enter Christmas, for which I received a startup Home Brewing kit.  What fun!  And in learning all I could about this fun and rewarding hobby, I came across something called the SRM.

The SRM is the Standard Research Method, a scale of color.  In Europe they use something called the European Brewing Convention or EBC – same colors, different numbers.

There are hundreds if not thousands of types of beer, and interestingly they range from Clear, through straw colors (pale yellow), to amber, all the way to very, very Black.  Just like urine.  And there’s a number for each of these.  The SRM ranges from 0 through 40;  here’s an example, shamelessly pick-pocketed from the Web:

EBC and SRM scale

I believe that with some minor tweaking, or perhaps simply expanding the scale, this might serve the purpose of quantifying urine color.  Is this a desirable thing?  I think so.  Charting over time that the patient’s urine changed from SRM 12/S (with sediment) to SRM 6/C (clear of sediment) is showing progress, that kidney function is moving in the right direction.  The other way, not so much, the patient’s condition is deteriorating.

Anyway, there it is.

MedMath: Parkland Formula Trick

A colleague was recently lamenting to DTs his lack of real-world experience with algebra, which he had not used since high school.

Normally, this is not an issue, but there are circumstances where we in EMS need it. One such is the Parkland formula, which determines the fluid resuscitation requirements of a burn victim.

For those whose algebra is dusty, as is mine, it can look more daunting than it should. The DTs solution is (as usual) to CHEAT. Since it’s hard to cheat mathematically, we can instead make the Damned Thing less frightening. Same crap, basically, but off comes the mask, turning the Scooby-Doo ghost into Old Man Jenkins.

In Stephen J. Rahm’s Paramedic Review Manual for National Certification – a highly recommended resource for anyone seeking to refresh and review – we find the following, shamelessly reprinted example:

“A 39-year-old man, who weighs approximately 160 pounds, was trapped inside his burning house and sustained full-thickness burns to approximately 40% of his body. On the basis of the Parkland formula, how much IV crystalloid solution should he receive within the first hour?

a. 620 mL

b. 700 mL

c. 730 mL

d. 815 mL”

Notice that you are not given the Parkland formula. If you are in an NREMT testing situation, you won’t have any handy-dandy reference guides either. So how do we work this?

The Answers section of the book reminds us that the Parkland formula is: 4 mL x patient’s weight in kilograms x percentage body surface burned. This gives us the total volume of fluid to be delivered in a 24-hour period. We are further reminded that 1/2 of the total should be given over 8 hours, and the remaining fluid delivered over 16 hours.

THIS I gotta REMEMBER? And this STILL doesn’t answer the above question. How much should we be giving in the FIRST hour?

THE HARD, TRADITIONAL WAY

160 pounds needs to be turned into kilograms, but we do this all the time for meds and know to divide by 2.2, giving us 73 kg (actually 72.7; we round up.) Plugging in the numbers, the Parkland formula looks like this:

4 mL x 73 (kg) x 40 (% BSA) = TOTAL FLUID.

Not to muddy the water, but the formula only wants the “40” of 40%. In other words, multiplying 4ml x 73 kg x 40% (which is 0.40) is incorrect.

We do the math and get 11,680 mL as the total fluid the patient needs. He needs 1/2 of that, though, over the first 8 hours. So we divide 11,680 by 2 = 5,840.

The Question, though, is how much he should receive in the FIRST hour. The FIRST hour is part of the FIRST EIGHT hours, isn’t it? So we just need to divide the 5,840 by eight to find out how much fluid per hour. 5,840 / 8 = 730.

IF we remember the Parkland formula and IF we have a scratch pad and pencil, or calculator, we can easily (albeit, “eventually”) figure the answer is C, 730 mL.

THE HARD EXPLANATION OF THE EASY WAY

Algebra, as we in EMS use it, has three main components: Constants, Variables, and Operators.

Operators are the mathematic symbols – “+” (plus), “-” (minus), “/” (divide by), that sort of thing. We can flip-flop these sometimes to make problems more understandable. 8 x 1/2 = 8 x 0.5 = 8 / 2.

Variables are, as the name implies, variable. This is the bit that changes from problem to problem in the test. The patient’s weight, for example, won’t always be the same, nor will the percentage of BSA burned.

And then there are the Constants. Constants are the actual numbers. A “1” or a “2” or a “27”.

In the Parkland formula:

4 mL x patient’s weight in kg x BSA burned %

we have one constant, 4 mL. But is that true? We actually have a couple of invisible constants. The answer to the above math gives us the 24-hour fluid volume. It should REALLY read:

24 HOURS OF FLUID = (4 mL x Kg x BSA%)

and we know that we give half of that volume over the first eight hours. To express that algebraically, we can multiply by 1/2 or (my personal preference) divide by 2:

FIRST 8 HOURS = (4 mL x Kg x BSA%) / 2

One of the neat things we can sometimes do with algebra is simplify things. Notice that there are two numbers in the above example: 2 and 4. These are constants; they won’t change. As such, we can go ahead and “do the math” with those two numbers. We can lose the 2 by dividing by 2. That changes the 4 as well (4 / 2 = 2). The following is the EXACT SAME FORMULA:

FIRST 8 HOURS = (2 mL x Kg x BSA%)

But we want the amount to give in the first hour. “8 hours” is too much. We can turn that “8 hours” into “1 hour” by dividing by 8, but we have to do so on both sides of the equal sign:

8 HOURS / 8 = (2 mL x Kg x BSA%) / 8

or

1 HOUR = (2 mL x Kg x BSA%) / 8

Again, to the right of the equal sign, both the “8” and the “2” are constants. We can do the math on those guys to get (2 / 8) = 0.25

1 HOUR = (0.25 mL x Kg x BSA%)

To me, though, dividing by a whole number seems easier than multiplying by a decimal, so we’re going to switch the above around a bit:

1 HOUR = (Kg x BSA%) / 4

Whether you want the 24-hour value, the 8-hour, or a single hour, the patient’s weight and BSA% don’t change. To make the formula even less intimidating, we can multiple those two together, turn them into a single number and be done with it.

JUST THE EASY WAY – SYNOPSIS

When testing, especially when you aren’t allowed to reference the formula, just remember that “PARKLAND IS 4″.

Figure out your patient weight and burn area – sorry, you need to do this with each problem. But once that is out of the way, remember: Times 4 is the total fluid. Divided by 4 is the amount for each hour, for the first eight hours.

A 39-year-old man, who weighs approximately 160 pounds, was trapped inside his burning house and sustained full-thickness burns to approximately 40% of his body. On the basis of the Parkland formula, how much IV crystalloid solution should he receive within the first hour?

a. 620 mL

b. 700 mL

c. 730 mL

d. 815 mL

Weight has to be in Kg, not pounds, so 160 / 2.2 = 72.7 or 73 kg. We multiply that by the BSA%, 40, to get a number we’ll call THISPATIENT. For this question, THISPATIENT is (73 x 40) or 2920.

Parkland volume to give each hour for first eight hours, in mL = THISPATIENT / 4 (example: 2920 / 4 = 730)

Total Parkland volume to give a burn patient, over 24 hours, in mL = THISPATIENT x 4 (example: 2920 x 4 = 11680)

Remember that for the first 8 hours you give HALF THE TOTAL, and HALF OF FOUR IS 2:

Parkland volume to give over first eight hours, in mL = THISPATIENT x 2 (example: 2920 x 2 = 5840)

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