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Does anyone know if we can use the formula: ClCr = (140- age)* weight/70 or
85 for female
to estimate body weight of a patient ?
Because I know the daily creatinine clerance and I know the age.
So it could may be possible to estimate body weight.
But this formula has may be some restrictions ? (severity of the renal function)
My patients are staying in intensive care unit and it's not possible to
weigh these patients.
The estimation by staff was not practicable.
Thank you very much to answer.
----------------
Nicolas VAN BRANDT
Pharmacist
Lab. of Pharmacokinetics (Prof R.K. Verbeeck)
UNIVERSITY OF LOUVAIN
Av. E. MOUNIER, 73-55
1200 Brussels, Belgium, EUROPE
Belgium,
Europe.
vanbrandt.aaa.fatc.ucl.ac.be
from: "N. Van Brandt"
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ClCr = [(140-age)*(body mass)]/[SrCr*72]
Multiply by 0.85 for females.
This nomogram has a high correlation among the variables, so solving for
body mass would give a good estimate.
One would still have to consider the body *type*, ie, is the patient
obese (larger proportion of fat) or particularly lean (larger proportion
of muscle).
After estimating the mass, it would be a good idea to calculate lean body
mass, which would require knowing the height (or length, in this case) of
the patient, because on e of the factors determining the rate of
creatinine production is muscle mass--of two people weighing the same,
the one with a larger proportion of skeletal muscle would produce more
creatinine.
Randy Trinkle
Dept. of Pharmacy
Dawson Creek & District Hospital
Dawson Creek, BC
Canada
from: Randy Trinkle
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NICOLAS
It is certainly possible to obtain an ESTIMATE of weight (actually,
something closer to ideal weight). Remember, however, that the
coefficient of determination (r2) for this relationship is not more than about
0.7 and there will be fairly large error in the estimate. To the
best of my knowledge your question has not been answered
experimentally. Good luck!!
Michael Mayersohn
College of Pharmacy
University of Arizona
Tucson, Arizona 85721
MAYERSON.-a-.TONIC.PHARM.ARIZONA.EDU
P.S. I have GREAT memories of Chez Leon.
from: "N. Van Brandt"
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Dear Nicholas,
Regarding your question:-
>Does anyone know if we can use the formula: ClCr = (140- age)* weight/70 or
>85 for female
>to estimate body weight of a patient
>(snip)
>My patients are staying in intensive care unit and it's not possible to
>weigh these patients.>(snip)
I would think that formula relates to a normal population with normal renal
function. I would be very cautious about using it to estimate the weight of
patients in intensive care, many of whom have grossly impaired renal
function. If you think about anuria as being one extreme (a regular
situation in intensive care) the answer to the formula is a nonsense and a
patient who was almost anuric would weigh almost nothing. I think you should
look at some alternative ways to estimate weight.
Regards, Ken Newton.
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Hello,
I am a Pharm D. student from Idaho State University. Recently I completed a
calss on clinical research and design. This class included lots of
statistics and mathmatical models. One thing the professor pounded into our
heads is that when doing a linear regression, such as estimating CrCl from
weight and serum creatine, or estimating kel for aminoglycosides from CrCl,
YOU CANNOT GO BACKWARDS. Estimating CrCl from predictor variables like
weight and serum creatinine is good, but what area good predictor variables
for weight? Is the patient hypermetabolic, recieving adequate nutrition,
third spacing, recieving adequate hydration. There area a lot of variables
that go into why a patients weight may fluctuate, not just CrCl.
I work at a 250 bed tertiary care facility with about 35 ICU beds. I am not
sure what your facilitie's resourses are, but our beds are capable of
weighing the contents of the bed. thus the patient. Each day the nurse
pushes a button and the bed tells him/her the patients weight. I am sure
there is more to it than that, but it is a very good way to monitor a
patients weight.
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I guess the estimations by staff would be not less accurate than those
obtained via the formula.
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I would be hesitant to use such an estimator to go back to
establishing weight. It might be acceptable to establish a guess to
correlate with guesses of the staff. The degree of variability might
be as high as you could get from having two or three staff make an
educated guess. Good luck.
John E. Murphy, Pharm.D.
Professor and Head
Department of Pharmacy Practice and Science
(520) 626-5730 (P), (520) 626-7355 (FAX)
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