Re: How does an anesthetic act so fast when introduced into a vein?

Well observed....
You're right in stating that anesthetic efeect is linked with blood 
velocity. Basically, the onset of anesthesia is mediated by two factors:

1) blood velocity: given that anesthetic effect is located on the brain, 
you have to bring the anesthetic solution from the vein (usually a 
forearm one)to the brain. In normal conditions, this needs a few seconds, 
but during cardiac diseases such as cadiac failure, it is usual to note a 
longer delay. By the way, during the 30's and 40's, before doctors had 
sophisticated devices at hand, cardiologists injected a bitter substance 
in the vein, and closely noticed the "arm-tongue circulation time" wich 
was the delay before the patient experienced a bitter taste. This gave 
an approximate value of cardiac output (the longer the delay, the lower 
the cardiac output)....

2)as important as the first one is the anesthetic substance delay of 
action,wich is the time needed to enter the brain and act. Present 
pharmacological research is focused on "very short acting" substances. 
You inject, and your patient "sleeps" immediately, and awakes very 
quickly. very useful, you will be free of delayed effects, such as 
persistent sleepiness or drowsiness hours after anesthesia was stopped. 
On the other hand, you need electronic syringes with variable output to 
deliver on a continuous basis your anesthetic, in order to keep your 
patient sleeping during the whole procedure. 21'st century anesthesia 
tends to be a "on-off" anesthesia, free of late effects.

Now, to answer your question, you have to keep in mind that anesthetic 
substances act on the immediate past memory. I mean that when you awake 
from your anesthesia, you won't remember the procedure (of course!), but 
not only the procedure. You will have forgotten the seconds before you 
fell asleep (your immediate memory). It's like on your computer. Your 
long-term memory (your name, what you learned at school, and so on) is 
stored on your "hard disk" and you can access it immediately. Your short-
term memory is stored in your "RAM" and you choose what you save (e.g., 
you don't remember all the people you met in the previous day). 
Anesthesia is like switching your computer off without saving.

When you had anesthesia, here's what happened: your anesthetist injected 
the hypnotic, and you were able to count from & to (probably) 9 OR 10. 
Then you fell asleep, and lost your immediate memeory. When you woke up, 
you remembered only that you counted from 1 to 3 or 4.

Hope this helps

Luc

Luc Ronchi
Ped Anesthesia
Hopital de Saint Nazaire (France)