Could laughing gas prevent PTSD?

People who go through extreme and harrowing events often develop a condition called post traumatic stress disorder, or PTSD. Sufferers describe recurrent intrusive flashbacks of the event that can sometimes leave them feeling suicidal. But might a dose of laughing gas, nitrous oxide, given after a traumatic event, lower the risk of PTSD? Naked Scientist Georgia Mills spoke with UCL's Ravi Das who has evidence to suggest that it might...

Ravi - We were specifically looking at nitrous oxide because we know that one of the way it acts is at a certain brain receptor that's critical in memory formation, and one of the main things that we think contributes to PTSD is the formation of these kind of traumatic memories that can resurface and cause these intrusive thoughts, and images, and flashbacks which are kind of the cardinal symptom of PTSD.  People can have the experience of being back at the time of the trauma, kind of context and situation free and re-experiencing that event. So it's really unpleasant.

Georgia - How did you test this?  I'm guessing you couldn't actually give people PTSD? That sounds slightly unethical.

Ravi - Yes, that wouldn't have been a real hit with the ethics board. So we've got a kind of laboratory model of a very weak form of PTSD, if you will, and it's used by quite a few labs.  Basically, it involves showing healthy volunteers a really unpleasant film and what you see is, over the course of a week if you get people to keep track, they'll experience these involuntary memories about aspects of the film which tend to be images of some of the nasty things that have happened, and they'll just pop into people's minds in an involuntary way and those are what we call intrusive memories.  So we show people this film and then measure over the following week how many times they're experiencing these.  We gave people either nitrous oxide gas, which is the same form that you'd get in the NHS (it's a product called entonox), so it's mixed with oxygen and it's a lot safer than the gas canisters that people use recreationally.  So they got that or a matched kind of normal air from a canister and they breath that for half an hour and then we assessed for the following week of how many of these intrusive thoughts they had.

Georgia - Now, I've not seen this film but I did look it up on line and I read a couple of reviews, and one of them called it cinematic torture.  They said "I've yet to meet anyone who's not been deeply affected by this movie if they were brave enough, or stupid enough, to watch it."  Your poor test subjects...

Ravi - There's a problem with doing any studies that try to model something that's inherently unpleasant in that you have to, within ethical bounds, give people something quite unpleasant to do. Yes, I did feel terrible for the participants while they were having to watch it.

Georgia - Did you watch it?

Ravi - Yes, because much of the time you were sitting in the room with the participants awkwardly knowing what they were having to go through.  Yes, I have to say I agree with some of the reviewers -  it is one of the worst things I've ever seen.

Georgia - And with the participants who got either this nitrous oxide mix or the control, which was air, what difference did you find with their feelings about the film?

Ravi - What we hypothesised was that given this receptor that nitrous oxide blocks is really important in the shift, the transfer of information from short term memory to long term memory. So we thought that it would prevent some of those memories stabilising and weaken them and what we saw is that by the second day, the people in the nitrous oxide group had greatly reduced in their number of intrusive memories about the film but the normal air group hadn't, and it wasn't until about four days later that we saw a significant reduction in those that had the normal air.  But it was basically straight after sleeping in the nitrous oxide group and we know that sleep is also really critical for this kind of stabalisation of memories into the long term.  So nitrous oxide seems to have interfered with that kind of sleep dependent stabalisation of the memories.

Georgia - Has nitrous oxide been tested in the field? Do we know if this works in the real life events that might cause PTSD?

Ravi - It's really interesting because it is used on the NHS currently in paramedic teams as a pre-hospital anaesthetic so it might be having unforeseen consequences already for people who are receiving it.  They might have already gone through a traumatic experience; we don't know currently whether that's subsequently affecting their memories.  And one of things we're interested in doing is looking to see if we can start monitoring situations where people have received it before being admitted to hospital versus people who haven't.  But in terms of, I'm thinking maybe military application, all this is dependent, obviously, on our results being replicated in a clinical example but, because it is easy to administer, it's portable, it's very safe, and once people stop breathing it it stops having an effect very quickly.  I don't see why it couldn't be miniaturised and used as a first line prophylactic type of intervention following traumatic events - yes.