On the Way to Paramedic in Northern VA
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Sunday, November 16 2008
My Thanks

A couple of posts back (and a long, long time ago) I put up a quick method I'd stumbled upon for calculating dopamine drips. The comments I received on that post were so well thought-out and pertinent that I thought I'd make them into their own post.

I have noticed, in looking back over old posts, that the HaloScan system must do a "purge" now and then since old comments seem to be missing, and I didn't want these lost.

And a BIG thanks to those who pointed out my "800mg in 250ml" typo - yes, that should be "400mg in 250ml", and I promise I'll put the thing up again shortly. Along with a kind of neat Palm PDA database for drug flashcards, a link to a Palm DB with useful EMS phrases in Arabic, Chinese, Creole, Farsi, French, German, Greek, Hindi, Italian, Japanese, Korean, Polish, Russian, Spanish, Urdu, and Vietnamese which, quite frankly, is still "in progress" but sharable, and, hopefully, some stories.

Yeah, been busy.

DTs

James wrote:

Hey awesome stories - I love it!!

That constant error of 6.67% is because you're dividing by 5, which is also multiplying by 0.2, instead of 0.1875. The 6.67 comes from the % difference between these.

The 0.1875 comes from 5*60/1600 = 0.1875 which comes from (5mcg/kg) x (1ml/1600mcg) x (60min/hour).

0.1875 = 3/16.... so you could multiply the pt's weight (kg) by 3, then divide by 16, that'll give you the EXACT amount.. but easy at 2am? maybe not..

but i'm confused if 800mg in 250ml is 1600mcg/L ?

but I think your trick is good enough for me!

cheers

Crystal wrote:

Can you change it on the page to the correct mix of 400 mg in 250 mL please? I wanted to use your page to show somone this method, but that error is too big for me to use, plus anyone who doesn't do the math could make the mistake if they tried to use the method. . .I did the math (to make sure I was right) others might not.

Marcus wrote:

So I have a way to correct your numbers, but first a note, as pointed out above, you gave the right number for the standard concentration, but the wrong numbers for the standard admixture, all these numbers are predicated on 400mg/250ml (1600mcg/ml). (And, I can't fault you, when I reread this prior to posting, I noticed I had put the numbers in backwards.)

So, for cardiac dosing, again, as noted above, if you reduce the equation, you wind up with 3*kg/16=ml/hr, thus kg*(3/16)=mg/hr, but if you take that 3/16 and get the inverse, 16/3=5.33 repeating, thus kg/5.33 repeating=ml/hr. If you shave that down to just kg/5.33~mg/hr, you wind up with a very small margin of error (It increases as the weight increases, but for a 300lb pt, you are less than 1 gtt/hr off, assuming a 60 drop set.) I don't think the most anal retentive person in the world can fault that, not to mention set a drip set that finely. (And if you have a pump in your ambulance, I hate you.)

Alright, well that's great and all, but what about renal dosing? Seems like there ought to be an easy way to figure that as well, and sure enough, there is. Doing the math again, it reduces to 3*kg/40=ml/hr=kh*(3/40)=kg/13.33 repeating~kg/13.33. Now using kg/13.33 gives you an even better error rate, less than .16 gtts/hr for a 300lb pt!

For vasopressor dosing, the math runs (9*kg)/16=ml/hr=kg*(9/16)=kg/1.77 repeating~lg/1.77. Unfortunately, this gives a much larger error rate...all the way up to a bit over 20 gtts/hr for our 300lb pt. I still don't think that on my best day I ever set a drip set that accurately.

All of these numbers are put together in a fancy shmancy table available in both html and

*snip*

I was too verbose, it cut me off.

In any case, you can also get the table as an Excel document.

Finally, I just thought that I would note that I was most of the way through some engineering degrees before I found EMS.

EMS geeks unite!


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Posted Friday, December 19 2008 14:34  Site Meter