Taking Blood

by Isabel Perez-Cruz

He looked at me as if I was crazy, and I don't blame him. I was really mortified by doing this procedure to the small mouse. "Him," my colleague, was an expert technician. He actually had been a surgeon in his native China and he moved with ease in our small operating area for animals. I asked him why he found this simple. I was trying to get a blood sample from some mice. Sounds easy? Well, a mouse happens to be a very small animal when it comes to blood sample. The max you can get from the whole animal is 1 Ml. That means about 1/5 of a teaspoon when you bleed the animal blank. It can be gross to think about that, but bottom line: it's not much blood.

My blood sample (I was not trying to suck all the blood out of the animal) would be about 200 microlitres. A really precious little drop. Just one drop! From that one little drop, I was hoping to get so much information: stain the cells from the drop, wash the drop, spin the drop, pass it through a system of laser to detect the fluorescent dye I had added to the by-then diluted drop. But that wee drop was costing me too much stress.

How do you get a drop of blood from a mouse? Punch him in the snout? There are several methods depending on the amount of blood you need, and they are, in decreasingly gross order: the orbital sinus technique (inserting a needle behind the eye), into the jugular vein, a cardiac puncture, or a tail vein puncture. I have tried the last horrifying two. I actually succeeded in avoiding drawing blood from the eyes by actively designing experiments that would give me other options. I knew I just could not do such a thing. I remember my good friend coming back from the animal room with a rack of small tubes with precious drops of blood in each. After I asked him what procedure he had performed, he told me "eye". I never saw my friend the same way again. At that moment he looked like a cold-blooded villain without a heart. I am talking about my very good friend! But the idea of him immobilizing an animal and taking a sample from its eye was beyond my limits of acceptance.

My drop of blood would come from the tail. A very thin vein supplies blood to the mouse's tail. Not that other veins are thick, but when you are trying to insert a thin needle into an apparently thinner vein... well, you wish you were working with bigger animals, bigger veins, or that you were a surgeon from China. To get the blood, you immobilize the animal with a small cage that leaves the tail outside. Because the vein compresses with cold and distends with heat, the procedure is done under a lamp. The lamp was where my ordeal begun.

The lamp was damn hot and I felt an enormous amount of heat on my hands. I began to wonder how much heat this small animal could take without thinking he was a bad mouse in life and now must be in Hell. I "shielded" the body of the animal with pieces of ready-cut cardboard that I brought in my lab coat.

Then, there was attempts number 1, 2, 3 to get the needle into the vein. The skin is quite translucent in the tail and you can easily see the blue vein. But inserting the needle right in the middle of it? Not so easy. Just when you try to poke the needle in, the vein disappears. So you do it "blind." After seeing where the vein is, you insert the needle knowing you won't see the vein again. Then you try to pull the syringe to get the drop. Most of the time (at least in my hands): nothing. Then you try again. Nothing.

I tried one more time, sweat on my forehead. You guessed it. Nothing. The truth of the matter is that by then I was as distressed as the mouse. I was feeling that the mouse was too hot, too thirsty, and hated getting pinched repeatedly while being immobilized. I could really feel his pain. I wanted it to be over, but I needed his drop of blood!

My Chinese colleague would have been finished taking all the samples by this time. He couldn't care less about the comfort of the mouse. One day, after repeated failed attempts on my part, he looked at me and bluntly asked, "Why can you not do it?" I told him I was feeling bad for the mouse. I was actually thinking of giving it some pain medication! I'm glad I didn't mention this last part, because my colleague looked at me perplexed. " I also worry that the animal is suffering," he said. "But he will be fine!" he added. I knew the mouse would recover and be ready for another blood take in a week. Maybe he would not even remember. But at that moment, all I could think about was its pain.

To relieve the mouse and myself I indeed had started thinking of pain medication. I could bring some baby Tylenol and give him few drops before or after the procedure. Of course, I was facing the problem of the dose. How much to give him? I could use the same dose recommendations given for a child, but extrapolate to grams instead of kilograms. There. Problem solved. However, there were other problems. How could I give him Tylenol? Why would he take it? Do I use a dropper or a syringe and force the liquid into the mouse (for his own good)? But then I faced the biggest question of all: What if this affects my experiment? What if this Tylenol modifies the response I am trying to study, changes the number of cells, affects its liver, or does something else? I thought about all this terrible possibilities and the way to get around them. But I was not certain that pain medication given to a mouse in pain would not affect my experiment, my months-long experiment. I considered some other worthless pain relief-things, along with more effective shades and even a secretary-desk fan to cool off the mice. But the only thing that stood to the scientific questioning of "can this affect the experiment" was a simple, lonely and quiet piece of sterile gauze, and press it on it's tail.

I was actually never able to drain the blood from most of my mice, so I had to ask my generous Chinese colleague to ("please") do it for me. I was amazed to see his hands moving with ease and certainty. As he manipulated the mouse, put it in the immobilizing cage, cleaned the tail with alcohol, inserted the needle and got the blood. Next mouse.

I was left to press the tail with the gauze, and put on a -- yes -- band-aid. To this moment I remember how difficult was to go down to the animal room carrying the tube-track with all those tiny tubes to be filled, with the syringes and needles. How good it felt when my co-worker agreed to help (always asking me if I wanted to try, and me always saying next time).

I am glad that I finally stopped working with mice. That type of work is extremely valuable, but for some people like me, it is plain impossible.


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