Weight does calculation

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blachatch

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Is there an easy somewhat fail proof weight based does calculation? This seems to be hanging me up pretty good in class, I am not to good at math AT ALL:unsure: No drip doses yet just IV push.
 
Dimentional analysis ftw
 
I am not sure what exactly you are asking...

For a simple weight based dose calculation, the dimensional analysis should look something like this:

(Dose / 1 kg) x (Patient weight / 1) x (med concentration- ml/mg)

Each of the items in parenthesis should be written as a fraction, as in (dose over 1 kg) I would have tried to write it that way for you but I can't get the formatting to show it here.

So, if you want to administer 0.05 mg/kg of morphine to a patient weighing 83 kg, and the morphine has a concentration of 10 mg/ml, filling in the blanks, it would look like this:

(0.05 mg / 1 kg) x (83 kg / 1) x (1 mL / 10 mg)

Cancel your units first to make sure you have the dimensions set up appropriately, and then multiply through and divide. Check to make sure your answer is reasonable, and you should be good to go.

ALWAYS carry your units. It is easy to get sloppy and drop the units, but especially when you are learning, it will bite you every time!

If you have to convert a problem like this between pounds and kg, just know your conversion factor for either or, and plug it in wherever you like, taking care to make sure you have the correct dimensions in the numerator or denominator as appropriate, and you are good.

If you need some more help, don't hesitate to ask. I kind of enjoy DA...believe it or not.
 
I've always used one calculation for IV push doses as well as drip calculations.

(Dose) X (weight[kg]) X (drip set) ÷ concentration(amount of drug per mL)

If the drug is not weight based then take the weight integer out of the equation.

If it is not given by cc per hour then take the drip set out of the equation.

This equation will work with any drug anytime.
 
Another question does dose x volume/concentration always work? My instructor said not to use that equation but everytime I use it I get the right answer..:unsure:
 
lightsandsirens5 said:
Repetition. And lots of it.
Click to expand...

Once you pick one. Practice it regularly. Don't just cram for the exam and fail to look at it again until you need it. I try to do some drug calcs every week. Its really really simple maths and its never hard to practice, but in the heat of the moment, at 5 in the morning, when someone sows the seeds of doubt in your mind, you appreciate having it burnt into your mind.

Then check, cross check and cross check again. My personal policy is to do it myself, have my partner do it independently to me, then to cross check that against a chart where possible.

I was recently a job where we were doing an unfamiliar calculation for an pressor, so all three of did the calculation separately, then did it again 10 mins later before we switched the infusions.
 
WTEngel said:
I am not sure what exactly you are asking...

For a simple weight based dose calculation, the dimensional analysis should look something like this:

(Dose / 1 kg) x (Patient weight / 1) x (med concentration- ml/mg)

Each of the items in parenthesis should be written as a fraction, as in (dose over 1 kg) I would have tried to write it that way for you but I can't get the formatting to show it here.

So, if you want to administer 0.05 mg/kg of morphine to a patient weighing 83 kg, and the morphine has a concentration of 10 mg/ml, filling in the blanks, it would look like this:

(0.05 mg / 1 kg) x (83 kg / 1) x (1 mL / 10 mg)

Cancel your units first to make sure you have the dimensions set up appropriately, and then multiply through and divide. Check to make sure your answer is reasonable, and you should be good to go.

ALWAYS carry your units. It is easy to get sloppy and drop the units, but especially when you are learning, it will bite you every time!

If you have to convert a problem like this between pounds and kg, just know your conversion factor for either or, and plug it in wherever you like, taking care to make sure you have the correct dimensions in the numerator or denominator as appropriate, and you are good.

If you need some more help, don't hesitate to ask. I kind of enjoy DA...believe it or not.
Click to expand...

Anything over 1 is that number.
 
blachatch said:
Is there an easy somewhat fail proof weight based does calculation? This seems to be hanging me up pretty good in class, I am not to good at math AT ALL:unsure: No drip doses yet just IV push.
Click to expand...

I feel your pain.
 
blachatch said:
Another question does dose x volume/concentration always work? My instructor said not to use that equation but everytime I use it I get the right answer..:unsure:
Click to expand...

It'll work but not with weight based doses or with drip rates. I use formula I gave you on each and every drug calculation. One formula that works each and every time.
 
I have been practicing everyday and I am starting to feel comfortable with it. It just takes practice.. But im sure once I have a patient in front of me ill draw a blank on what to do:P
 
MSDeltaFlt said:
It'll work but not with weight based doses or with drip rates. I use formula I gave you on each and every drug calculation. One formula that works each and every time.
Click to expand...

Once I get the weight into kilos and get my basic dose can't I use that calculation? It seems to be working for me? I know the drips wont work for that calculation.
 
blachatch said:
Once I get the weight into kilos and get my basic dose can't I use that calculation? It seems to be working for me? I know the drips wont work for that calculation.
Click to expand...

Use whatever works for you, dude. I personally like the philosophy of "if one will do it all, why learn others". That's all.
 
For IV push medications I too use the dose x vol / concentration. It is simple and easy to remember.

For example, you want to give 80mg of Lasix:

You take your dose (80mg) x vol in the vial (4mL) and divide by the total amount/concentration of the drug in the vial (40mg).

80mg x 4mL / 40mg = 8mL.

I don't agree with your instructor when he said don't use this formula. Use it! It doesn't get any easier than this.

Don't be intimidated by weight-based calculations. You just simply have to multiply the dose by the weight in kgs. Once you do that, use the formula above.

For example, you want to give D10 to a pediatric patient. The dose is 2mL/kg and the child weighs 8kg. Just take 2mL x 8kg = 16mL. That is how much you give without even needing to use the formula above.

Another example, you want to give fentanyl which is 1mcg/kg. Your patient weighs 25kg. So the dose you want to give is 25mcg which you now can plug into the above formula.

dose (25mcg) x vol (2mL) / concentration (100mcg) = 0.5mL


Versed. 0.1mg/kg. Kid weighs 15kg = 1.5mg.

dose (1.5mg) x vol (5mL) / concentration (5mg) = 1.5mL

Always remember too that with drugs in a 1:1 concentration no calculation is needed. We carry Versed 5mg/5mL. How ever much we need to give is how much we draw up. I know that seems obvious but for new people starting out its worth mentioning.
 
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