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OB/Gyn Math

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by kas1965 kas1965 (New Member) New Member

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I start OB tomorrow and the math is freaking me out. Is there anywhere out there that shows me how to figure out lbs/oz to grams and kg and also percent loss of a newborn. example is baby lost 7% of birth weight of 3648 gm. How much do they now weigh in gr, kg, lbs. This math stuff always stresses me out and this is not anything I recall learning so far.

Thanks!:uhoh21:

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This is the exact same math that you need to use for your medication calculations, just simple math/algebra will work. Nothing more is needed, not even a calculator if you do not have one with you.

Take each problem and go thru it one step at a time. What is 7% of that weight that you listed? Subtract that from the number, and then convert that to pounds and ounces.

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The percentage part is easy.

Subtract the % change (in this case 7) from 100 = 93

Multiply the original weight by .93

3648 X .93= 3392.7

To change to pounds 3392.7 grams /1000= 3.3927 kilograms X 2.2= 7.46 lbs

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Daytonite has 40 years experience as a BSN, RN and specializes in med/surg, telemetry, IV therapy, mgmt.

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well, first of all, stop freaking out. nurses don't freak out. they use their brains and any resources they can get their hands on to find answers. do you have a nursing drug reference or a medical dictionary? check the appendices in those and in your nursing textbooks for a table of weight or volume equivalents. you'd be surprised what the appendixes of some of your books have. if they don't have conversion tables in them there is a website called convert me.com where you can get these: http://www.convert-me.com/en/

1 kg = 2.2 pounds

1 kg = 1000 grams

1 kg = 32 ounces (actually 32.15 ounces if you're a purist)

1 ounce = approx 30 gram (actually 31.1 grams if you're a purist)

1 ounce = 30 ml (or cc's)

1 liter = 1000 ml

1 pound = 454 grams (actually 453.59 grams if you're a purist)

1 pound = 15 ounces (14.583 ounces if you're a purist)

with those conversion factors you should be able to convert a baby's weight and their feeding formulas.

baby lost 7% of birth weight of 3648 gm. how much do they now weigh in gr, kg, lbs. this problem is asking "what is 7% of 3648 grams. give your answer in grams, kg and pounds."

whenever you see a word problem asking for a percentage of something you are looking at a multiplication problem. expressing the answer in grams, kg or pounds involves applying a conversion factor to the final answer. all of this can be easily accomplished using dimensional analysis (factor label method), like this:

7/100
(percentage) x (of)
3648 grams/1
(baby's weight)
=
255.36, or 255
grams
(rounded off). that is the 7% weight loss. to find the baby's weight
now
, subtract that from the starting weight so that
3648 grams
(starting weight)
-
255
(7% weight loss)
=
3393 grams
(current weight)

to convert to kg:

3393 grams/1
(baby's current weight)
x 1 kg/1000 grams
(conversion factor)
=
3.393 kg

see if you can do the conversion to pounds.

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Thank you all. I think the biggest problem is no one ever explained how we do these. Math always raises my stress level, so this is once a semester as we take a test everyone. It really really helps seeing it broken down for me.

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