Math Problem

nurse4theplanet, RN · Jan 20, 2007

100mg/hr

mg = 1 G | 1000mg

---- ---- --------

hr 10hr | 1 G

1 Gram is equal to 1000 mg. If you are giving 1000mg over 10 hours then your are giving 100mg an hour.

notaclue · Jan 20, 2007

Wow - thank you for your SUPER fast response! I understand it now -

Daytonite, BSN, RN · Jan 20, 2007

hi, notaclue!

sorry it took me so long to post my answer for you. i only have dial up service and i was having a problem staying connected to the internet.

i like to use dimensional analysis which is also called the factor label method. in this, you are creating a series of fractions (or ratios) which you are multiplying together. these fractions include numbers along with labels on them, such as 1 gram ("1" is the number and "gram" is the label) and 10 hours ("10" is the number and "hours" is the label). the idea is to manipulate the numerators and denominators of the fractions in order to cancel out the labels on the numbers so you are left with only the labels you want on the final answer. a "gram" in the numerator can be canceled out by a "gram" in the denominator. got the idea?

in the problem you've posed, you want your final answer to have the label of mg/hr on the final answer with mg in the numerator and hr in the denominator. this is how you set the problem up by dimensional analysis. i leave you to actually work the math.

1 gram

/10 hours

(dose desired)

x 1000 mg

/1 gram

(conversion factor - you have to convert from grams to mgs and this fraction is actually an "identity" and equal to the number "1")

=

100 mg/hr

(after performing the math and canceling out the repeated labels)

please note that the information about 500ml is not necessary to use in calculating your answer to this problem. now, if the problem had asked you how many ml of the iv solution per hour the patient will receive, then your calculation would be much different and you would need to include the information about the 500ml in your calculation.

hope that helps. welcome to allnurses! :welcome:

Scrubz · Jan 21, 2007

Hi -
Can someone help me figure out this problelm - and may I be so bold as to ask how you got your answer, THANK YOU
One g of aminophylline is added to 500 mL NS. The order is to infuse the IV over 10 hours. Calculate the mg/hr that the patient will receive.

You're looking for mg/hr, so you really don't need to know that the solution you're adding it to contains 500mL. I mean, it's important, but not for the sake of figuring out mg/hr. You're giving 1g, which the same as 1000mg, and the IV is going to be infusing for 10 hours. So if you're giving 1000mg over a period of 10 hours, that's 100mg per hour because 1000/10 is 100.

notaclue · Jan 21, 2007

Thank you all for your help -

My very 1st nursing test is tomorrow!!

Drug Calculations

Daytonite, BSN, RN · Jan 21, 2007

Good luck on your test! Remember to read each problem carefully. Look at the last words of the problem and determine what it is that the problem is asking you to find. You can almost always use, or adapt for use, the old "dose desired divided by the dose on hand" formula and use tricks you learned in basic algebra to manipulate the numbers. Go to factor labeling and dimensional analysis when you have to apply conversion factors and manipulate the fractions to make your final answer have the labels in the numerator and denominator as you want them.