When a patient has an IV already infusing, you need to determine the medication dose the patient is receiving.  This may be done to verify the accuracy of the IV---is the patient actually receiving  the prescribed amount?  Sometimes the physician does not order a specific prescribed amount.  You may have an order such as "dopamine 400 mg/250 cc D5W titrated to maintain BP of 90-130 systolic".  In this situation, the nurse makes incremental changes in the IV flow rate, increasing and decreasing the flow rate as needed based on patient assessment data.  You want to be able to determine at any given point of time how much medication the patient is receiving as those changes are made.

Since this is a dose rate problem, the left hand side of the ratio should be the IV label information---how much medication in how many milliliters.  The mL/hr flow rate will go in the right hand side of the ratio and you solve for the medication dose per hour.  Additional steps may then be needed depending on the information asked for such as dose per minute or dose per kilogram per hour or per minute.


Example problem#1:  A patient has an IV of Heparin 50,000 units in 500 mL D5W infusing at 10 mL/hr.  How many units per hour of Heparin is the patient receiving?

Basic ratio:

     50,000 units  =    units
          500 mL            mL

When you "plug in" the 10 mL in the bottom on the right, put the per hour portion also.  When you put the per hour on the bottom, you must put it on the top.


     50,000 units   =   X units/hr
         500 mL             10 mL/hr


Cross multiply and solve for X.

         500 X  =  500,000

         500 X   =  500,000
          500         500

             X  =   1000 units/hr


Example problem #2:  You have an IV of Pronestly 1 g mixed in 250 mL of D5W infusing at 30 mL/hr.  What is the mg/min dose rate of Pronestyl?


     1000 mg   =    X  mg/hr
        250 mL       30 mL/hr

       250 X  =   30000

       250 X  =  30000
        250            250

          X  =   120 mg/hr

  You have determined the patient is receiving 120 mg/hr; however, you were asked for mg/min.  To go from hour to minutes, divide by 60.

    120 divided by 60 = 2.  Final answer is 2 mg/min.


Example problem #3:  During report a nurse tells you that a patient is receiving dopamine 8 mcg/kg/min.  When you go to assess the patient you find that the patient has an IV of dopamine 800 mg in 250 mL of D5W infusing at 25 mL/hr.  The patient weighs 180  pounds.  Was the nurse correct?

HINT:  In a problem such as this, do not start with what you were told.  Work with what you actually have and take the work to a level to match what you were told and then compare.  For example, in this problem you were told mcg/kg/min information.  Therefore, you will work your problem to the mcg/kg/min level and compare what you get to what you were told.


HINT:  If you will begin by determining the patient's weight in kilograms, then all subsequent steps can be performed without clearing your calculator.


     1  kg   =  X  kg
    2.2 lbs    180 lbs

     2.2 X  = 180

         X   =   81.8 = 82 kg  (PCC rule, weight over 100 pounds should have final answer to nearest whole number.)


    800 mg   =   X mg/hr
    250 mL      25 mL/hr


     250  X  =   20000

      250 X   =  20000
      250            250

        X  =  80 mg/hr

Remember you need to take this to mcg/kg/min to compare.   Convert mg to mcg with a three decimal  move to right = 80000 mcg/hr. 

To get to per minute dose, divide by 60.   80,000 divided by 60 =  1333.33 mcg/min. 

To get to the amount per kilogram, divide by the patient's weight in kilograms.  1333.33 divided by 82 =  16.26 mcg/kg/min. 

Now compare to what you were told.  The final answer to this problem would be "no, patient is receiving 16 mcg/kg/min". 

Remember you will not receive credit for just "yes" or "no" answers. Also, in this particular example, you would not receive credit for mg/hr or mcg/min comparisons.  You were told information in mcg/kg/min; therefore, you must work to the mcg/kg/min level to compare.