How does chloroform cause unconsciousness?

We put Deeksha's question to resident chemist Ben Pilgrim...

Ben - The first thing to say is that the movies definitely have it wrong with regards to chloroform. Chloroform has been used as an anaesthetic for about 150 years and the kind of misconception that you have from watching movies is that by breathing a chloroform soaked rag you'll knock someone out within a second or so. This isn't the case, you need to be breathing it for several minutes in order to make someone pass out and they need to be breathing it constantly in order to keep them passed out. In fact, about 150 years ago, a famous medical journal, The Lancet, published a paper asking the criminal classes whether any one of them could divulge their supposed secret of being able to knock people out so quickly because it would be very, very useful for medicine. Needless to say, no-one has come forward to this date.

Chris - It was called a blow to the head probably, wasn't it, rather than chloroform! I think Queen Victoria was the first monarch to undergo a caesarean [section delivery]?

Ben - Yes for a couple of her last pregnancies. How does it work - this is something of debate and, indeed, in all anesthetics there is considerable debate about how they actually cause someone to pass out. Obviously they affect the nervous system. One idea is they affect the flux of potassium ions and this affects the body's response to nerves. Another idea is that the chloroform interferes with the cell membranes and slows down the passage of nerves which makes people less likely to feel pain. So there's a couple of ideas about how it might work. I should say, it was replaced because it was dangerous. Dangerous for a couple of reasons; one is actually you just breath too much of the gas in your lungs and this fills up your lungs and stops your lungs getting enough oxygen and so you just die from not having enough oxygen. But also, if you start fiddling around with the nervous system, then it can also cause people's hearts to fail because hearts rely on electrical impulses to work and if you mess around with that, you can die of a heart attack.

Chris - So don't do it is the bottom line, because people do abuse other kinds of solvents, like butane out of gas refills and glue - because there are solvents in there - all because they work the same way?

Ben - Yes, very dangerous to breathe in...