I am not sure what you want to measure, and so not sure why you need a
confocal.  The vessel diameter?, local blood flow?  Cross-sectional dimensions?
 
   If you just need to make the plasma fluorescent, use a high molecular weight
dextran or ficoll labeled with FITC.  Very bright and if the MW is greater than
150K, there will be virtually no leakage to the tissue during short experiments
(up to 60 min, maybe).
   If you really want to estimate blood flow, I suggest that you look up papers
by Ingrid Sarelius or Brian Duling as a starting place for fluorescence methods
to monitor blood flow.  One of the techniques that was developed called for
labeling a population of red cells (can be easily obtained and separated from
blood) with a fluorescent dye.  A sample of "glowy" cells is reintroduced to
the animals blood and used as flow markers.  Then the movement of individual
cells during a video recording can be used to estimate blood flow.  Numerous
automations have been developed and I suppose numerous statistical estimations
have been published.  Other methods depend on the appearance of a dye front
injected at a distant site.  Relative changes will be fairly easy to document;
accurate estimates will require a little sophistication.
 
Roger    [log in to unmask]