I started in a lab fairly recently that uses lots of blood/serum for assays. When each study is terminated, the mice are given a lethal dose of xylazine and ketamine and then opened up for visualization of the heart/aorta/etc when they become non-responsive. The tech in the lab had determined that by using an insulin needle and syringe inserted into the right side of the mouse's heart, he could remove nearly a mL of blood before any clotting- thus yielding plenty of material for later assays. It is an excellent way to get lots of blood, but my concern is that the insulin syringe shears the RBCs and contributes to hemolysis. I'm also concerned that if I wanted to use the blood for flow cytometry assays, the small needle size would create problems for cells. I have tried several larger needles with less luck. I need to be able to perfuse via the heart after withdrawing as much blood as possible too, so what is the best way to get both outcomes- plenty of non-hemolyzed blood to use for downstream assays and also a clean aorta after perfusion? Thanks!