Ether is far from toxic. It is not directly carcinogenic like benzene or hexane, and does not have toxic metabolites like chloroform or toluene. Most of it is not metabolised at all, and at body temperature it is actually a gas (boils at 35C), so it leaves the body via the breath, skin, and sweat. What little is metabolised, is turned into ethanol. A bigger risk is if it catches fire, or getting frostbite from its evaporative cooling.
The amount of ether vapor for anesthesia is
1.4 - 1.7 g/L air in arterial blood. Recreational effects can be achieved with much less, though.
As far as I can tell, Ki values for most volatile anesthetics are not known, partially from the difficulty of getting an accurate measurement when it's always evaporating, and the difficulty in metering it accurately into solution. Even stuff like ether has a high vapor pressure, if you spill some it will immediately vaporise. Think butane. (Most of these anesthetics don't dissolve all that well in plain saline either.)
That's not to say there's not a potency scale. Most of the anesthetics have their potency directly related to their ability to dissolve in fat.
There are no values in the Ki database and the Nature Medicine paper on nitrous oxide has it as percent of a gas mixture they bubble through the cell culture (super accurate), not moles like one would expect.
The wiki article on
Theories of general anesthetic action is real good.
I think the two main targets are GABA receptors and NMDA receptors. Most of the anesthetics seem to be more selective for NMDA than GABA though (nitrous and xenon are). But it may also depend on the size and shape of the molecule - and whether or not it can hydrogen bond.
