Heparin drip 100 units/mL infusing at 130 mL/hr. Decrease rate by 1000 units/hr. Set IV rate at how many mL/hr to achieve the new dose?
To solve this you need to use a conversion factor. You are given this in the problem, which is 100 units/mL. In order words 100 units = 1 mL. You use the conversion factor in whatever order you need it to solve the problem because no matter what it equals 1. So you can write it as 100 units/1 mL or 1 mL/100 units - either way it equals 1. Just like another conversion factor - 60 mins/1 hr or 1 hr/60 mins.
So you first need to figure out how many units per hour are running CURRENTLY. Before the rate change. You have a heparin drip of 100 units/mL infusing at 130 mL/hr.
So you set it up with what you have - 130 mL/hr - now you use the conversion factor. You need to know how many UNITS
are running per HOUR
. So, you need to cancel out the mL. You can only cancel diagonally. mL are in the numerator of the 130 mL/hr, so you need mL in the denominator of the conversion factor. So it will be 100 units/mL (rather than 1 mL/100 units). So, now you can cancel out the mL in each fraction, and you are left with units in a numerator (of the conversion factor) and hr in the denominator (of the first fraction), which gives you what you need - units/hr. So, you calculate across the numerators and across the denominator (in this case isn't necessary), and you get 13,000 units/hr.
You now know you are running it at 13,000 units/hr currently. The order is to decrease rate by 1000 units/hr
. The units match up - you are running 13,000 units/hr
and you need to decrease by 1000 units/hr
So you take 13,000 units/hr - 1000 units/hr = 12,000 units/hr
So, you now know what you need the new infusion to run at with the adjustment for the decreased rate. But how do you get back to mL/hr?
You need to run it at 12,000 units/hr.
You have a heparin drip of 100 units/mL.
If you look at the units for these you have units/hr and units/mL. REMEMBER - You can only cancel out units diagonally. So how do you set up the problem?
You need mL/hr, so you need to be left with mL in the numerator of a fraction and hr in the denominator of a fraction. You have to cancel out the units from each fraction to be left with mL/hr. To get hr in the denominator, you need to set up the first fraction as 12,000 units/hr. Now, you need to cancel the units out (which is in the numerator), and you can only do this diagonally, so the next fraction will need units in the denominator. So, it will be mL/100 units.
Again, you calculate across the numerators and across the denominators, and are left with 12,000/100 = 120 mL/hr.
Hope this helps you see each step you need to go through.