Veronica says,
*************************************
Therefore, suggesting pumping for 12 hours is in accordance with ICRP
guidelines. Storing >milk and using after at least 12 hours is also reasonable
(since half life is 6 hours, in 12 >hours the Tc99m has practically
dissapeared
from the milk).
************************************
This recommendation puzzles me just a little bit. Tom Hale suggests that
waiting 5 half lives assures that the substance has virtually disappeared from
the milk, but you are saying that waiting 2 half lives is sufficient? That
would be much nicer for moms, but is this only for Tc99m or would it be for all
radioactive substances?
Please correct my thinking here, because I'm obviously missing something.
Let's say (for ease of illustration) that there are 100 units of whatever that
gets into the milk. The half life is 5 hours. That means, in 5 hours, 50
units will be left (or there will be 100 units, but they will be half as strong).
In 10 hours (2 half lives) there will be 25 units, or the 100 units will have
only 25% of their original strength. In 15 hours, another half will
disappear -- down now to 12.5; in 20 hours, we are down to 6.25, and by the time we
get to 25 hours (5th half life) we are down to 3.125.
I realize that is extremely simplistic, but that's about how I've thought of
it, and it fits what Tom has said about 94% gone in 4 half lives, and 97% gone
in 5 half lives.
Or are we saying that any substance, as long as it is only 25% of the
original strength would be OK?
***********************************
Jan Barger, RN, MA, IBCLC, RLC
Wheaton, Illinois
www.lactationeducationconsultants.com
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