Dopamine is a challenge to calculate for any Paramedic student. The big problem that students have is that Dopamine must be calculated. So the first thing to know is that Dopamine is based on μg/kg/min.
For the first example we will use:
• 400 mg of Dopamine
• 500 cc bag (either NaCl or D5W depending on protocol/system)
• 75 kg patient
• Dose of 5 μg/kg/min
You should first notice there is an issue with the Dopamine in this example. Its units are in mg but the equation is in μg. This is easy to fix; multiply 400 x 1,000 (or just add three zeroes to the end of 400). Now we have 400,000 μg.
When giving any medication, we need to know the concentration of the drug we are giving. To find this take the amount of Dopamine we are going to give (400,000 μg) and divide it by the amount of fluid we have on hand (500cc). This comes out to 800 μg/cc. So in one cc of fluid we have 800 μg of Dopamine.
So lets rewrite the equation into something that we can plug into our phone/calculator that we may have on scene with us. First rewrite the dose of Dopamine. Get rid of the /’s and replace them with x. So our new equation should look something like this: μg x kg x min. Now, to get this new equation to work, we need to add one little thing: /concentration.
Our final equation should now be μg x kg x min / concentration. In other words; the dose we want to give, multiplied by the weight of the patient in kilograms, multiplied by our drip set (which will be 60 drips in one minute), divided by the concentration that we calculated earlier (800 μg/cc). Lets plug everything in:
5μg x 75kg x 60drips/min / 800μg/cc
This may look a little bit confusing so lets drop the units and we get:
5 x 75 x 60 / 800
And the final answer is 28.125 drips/min. In other words you give this patient 28.125 drops every minute or 0.46875 drops every second. Lets make life easy and do some rounding. So you would give about 28 drops per minute, which would equate to about 1 drop every 2 seconds.
Lets take a look at another example.
• 250 mg of Dopamine
• 100 cc bag
• 125 kg patient
• Dose of 10 μg/kg/min
- First we need to get our Dopamine in the right units. 250mg x 1000 = 250,000 μg.
- Now find the concentration. 250,000 μg / 100cc = 2,500 μg/cc.
- Remember the new equation? Here it is again μg x kg x min / concentration.
10 x 125 x 60 / 2,500
- And we get 30 drips/min.
So lets say that as you were checking out your ambulance for the day and you forgot to stock your 60 drip sets and on your first call you need to give Dopamine. Now what do you do. We will use the following parameters:
• 400 mg of Dopamine
• 250 cc bag
• 125 kg patient
• Dose of 15 μg/kg/min
- First get the units correct: 400mg x 1,000 = 400,000 μg.
- Next find the concentration: 400,000 μg / 250cc = 1,600 μg/cc
- Use the new equation, but with one thing different. Instead of 60 replace it with the drip set you are using (e.g. 10 or 15 in most cases).
- 15 x 125 x 15 / 1,600 = 17.578125 drips per minute using a 15-drip set. We can round this to 18 drips per minute.
Lets take a look at one more example.
• 400mg of Dopamine
• 500 cc bag
• 150 kg patient
• Dose of 12 μg/kg/min
- First get the units correct: 400mg x 1,000 = 400,000 μg
- Next find the concentration: 400,000 μg / 500cc = 800 μg/cc
- Use the new equation: 12 x 150 x 60 / 800 = 135 drips/min
In this last example your bag will pretty much be running wide open to meet the needs of the patient. This should demonstrate how important it is to use a medication pump, because all the calculations can be performed for you.
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