Help with ICVC injections!!!!

Dag Stenberg stenberg at cc.Helsinki.FI
Thu Oct 13 14:20:56 EST 1994


Philippe Lebrun (plebrun at minf.vub.ac.be) wrote:
> 	Sorry, I didn't mean completely rigid, but rather stiff enough to
> resist expanding under pressure, like PE. I think silastic might be a little
> weak, depending on the length you use.

Well, we use PE because it is readily available even in our remote and
backward region. However, there is PE of varying dimension: for the cat,
only the thick-walled variety is OK, like I.D. 0.38, O.D. 1.08, whereas
for the rat, tubies like I.D. 0.58, O.D. 1.00 is quite useful. 
  The dead volume is of importance, naturally. If you want to inject
something like 5 microliters, and the substance is expensive, and you do
not want to fill the complete infusion system with about 0.5 milliliters
of solution, the trick is to fill your syringe and tubing with let us
say water, then suck up 3-5 milli_meters_ of air into the tube, and
lastly the substance to inject from a droplet on a glass (yes, I know
that the smallest droplet possible is about 25 ul). Now, you set
up your infusion pump (or, in the case of a very small Hamilton syringe,
you do it by hand), and eject your 5 ul. Your drug will be ejected into
the ventricle, and the air bubble prevents your drug from mixing into
the water and disappearing that way. The air bubble will also make it
possible to observe the movement of fluid, in case you do not have the
infusion pump. If you are injecting small volumes with a small syringe, 
the pump is not obligatory; however, if injecting something over a 
time of more than 5 minutes, an infusion rate of 1 ul/min starts to 
toll patience excessively, and, indeed, if the volume to be injected 
and syringe has to be large, you cannot achieve it without a pump.

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Dag Stenberg     MD PhD                    stenberg at cc.helsinki.fi
Institute of Biomedicine		   tel: int.+358-0-1918532
Department of Physiology                   fax: int.+358-0-1918681
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FIN-00014 University of Helsinki,Finland   
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