Nitrous

Re: Nitrous

Evelyn Barbour-Hill — Fri, 21 Nov 2014 20:15:18 GMT

[quote user="Andrew Mellor"]

Only down side I did find - we had a tiny leak in our pipeline and it was giving everyone nasty headaches but as soon as discovered and fixed we were fine.

Hope this helps

[/quote]

https://www.youtube.com/watch?v=E9Tb4TMibk0&feature=related

Re: Nitrous

Andrew Mellor — Fri, 21 Nov 2014 19:03:06 GMT

[quote user="John Flynn"]

Do you use it?

If so, when?

If not, anti- or indifferent?

[/quote]

Yes I use it , we are a nurse training practice and they study at myerscough college , 20-30 nurses per class and ours for the memorable past 7-8 years have been the only ones to actually have and use nitrous.

we use it on anything that will be asleep longer than 15 minutes ( tend to allow pure o2 for the first 5 and last 5 minutes or so ) and have always found great benefits in reduction of pain and muscle relaxation compared to those that do not have it. Locums often get really jumpy as they so rarely if ever use it.

I would say on average 1% reduction in isoflurane once settled on nitrous.

We never use it on GDV's Intestinal FB'S etc anything with a potential gas filled viscus.

Only down side I did find - we had a tiny leak in our pipeline and it was giving everyone nasty headaches but as soon as discovered and fixed we were fine.

Hope this helps

ps I too use 1:1 in a rebreathing circle but honesty we never use closed so it is partial rebreathing only. 2 parts nitrous to 1 o2 in non-rebreathing

Re: Nitrous

Evelyn Barbour-Hill — Fri, 21 Nov 2014 14:48:32 GMT

[quote user="Anthony Todd"]

[quote user="Evelyn Barbour-Hill"]Don't those have any kind of unmixupable safety device?[/quote]

Whoops, yes there is but different size so no confusion possible...

http://www.frca.co.uk/article.aspx?articleid=100154

[/quote]

Oh yes, what we used to call bull-nose connectors.

That's a very modern article, it mentions helium but not cyclopropane!

Re: Nitrous

Anthony Todd — Fri, 21 Nov 2014 04:36:11 GMT

[quote user="Evelyn Barbour-Hill"]Don't those have any kind of unmixupable safety device?[/quote]

Whoops, yes there is but different size so no confusion possible...

http://www.frca.co.uk/article.aspx?articleid=100154

Re: Nitrous

Evelyn Barbour-Hill — Thu, 20 Nov 2014 23:16:08 GMT

[quote user="Anthony Todd"]

[quote user="Evelyn Barbour-Hill"]It applies for any size cylinder [/quote]

Er, not the ones that screw directly in the top, usually bigger which may be why the poster is confused....

[/quote]

Oh, I stand corrected. Don't those have any kind of unmixupable safety device?

Re: Nitrous

Anthony Todd — Thu, 20 Nov 2014 19:35:11 GMT

[quote user="Evelyn Barbour-Hill"]I've always understood that 5mls per minute per kg is the very minimum.[/quote]

This was the best reply I got a while ago:

Subject: RE: Fresh gas flow / Anaesthetic circuits

1. So no one can tell me the O2 requirements per Kg per min.?

Minimum O2 requirement for a dog/cat is 6.6ml/kg/min. Therefore, it's recommended to use at least double, or 15ml/kg/min. for a totoal rebreathing system. If using a partial rebreathing system, 25ml/kg.min. (minimum setting should be 500 ml/min.)

The tidal volume is calculated at 10 to 20 mL/kg of body weight. ... Donna Knitter (philadelphia)

Re: Nitrous

Anthony Todd — Thu, 20 Nov 2014 19:28:56 GMT

[quote user="Evelyn Barbour-Hill"]It applies for any size cylinder [/quote]

Er, not the ones that screw directly in the top, usually bigger which may be why the poster is confused....

Re: Nitrous

Anthony Todd — Thu, 20 Nov 2014 19:26:08 GMT

[quote user="robloxley"]My experience suggests that if they are light and you tug on the ovary they start taking rapid, SMALL breaths (as also demonstrated by the capnograph trace) and thus take on less anaesthetic gas?[/quote]

So they never go deeper unless you change the inspired anaesthetic concentration, no matter how long you wait??

You may well be right, all I can say is, with a Stephens, they deepen nicely but I haven't had experience with other systems.

We never had to alter the setting once they were initially deep, on the iso or whatever.

It may be that your experience coincides with the wearing off of the induction agent which did happen with us until we realised what was going on.

Quite often with thio, our usual inducer, we found that we could almost do a whole B/S without going off pure O2 [

[I was never that quick....]

Re: Nitrous

Gillian Mostyn — Thu, 20 Nov 2014 17:29:10 GMT

[quote user="Evelyn Barbour-Hill"]

It's a good system.

We've been here before.

[/quote]

lol... genuinely wouldn't know!

Re: Nitrous

Evelyn Barbour-Hill — Thu, 20 Nov 2014 17:21:15 GMT

[quote user="Gillian Mostyn"]Have never used (or even seen in use) an in-circle vaporiser![/quote]

It's a good system.

We've been here before.

Re: Nitrous

Gillian Mostyn — Thu, 20 Nov 2014 17:18:52 GMT

ok, fair enough, I can understand that.

Have never used (or even seen in use) an in-circle vaporiser!

Re: Nitrous

Evelyn Barbour-Hill — Thu, 20 Nov 2014 16:57:43 GMT

[quote user="Gillian Mostyn"]

Erm... I was under the impression that with every breath the anaesthetic gas goes in AND OUT of the blood very readily - and will basically equalise the concentration of anaesthetic gases in the alveolus and surrounding blood capillaries. Thus increased resp rate will have little impact on the concentration of the anaesthetic in the blood - which will only increase if you increase the concentration in the inspired air.

Or am I wrong??????

[/quote]

Sort of.

With an in-circle vaporiser the rate of vaporisation depends upon the rate of flow of oxygen over it. Increase rate or depth of respiration, increase rate of vaporisation, increase concentration of anaesthetic in the gas in the circuit.

Re: Nitrous

Gillian Mostyn — Thu, 20 Nov 2014 16:52:16 GMT

Or am I wrong??????

Re: Nitrous

Evelyn Barbour-Hill — Thu, 20 Nov 2014 16:50:23 GMT

[quote user="Anthony Todd"]Sorry, this only applies to E cylinders [I think] ie the ones that you can clamp onto the trolley. If you look on the side of the valve there are holes for the pins on the attaching clamp and they should match....[/quote]It applies for any size cylinder , any gas. Oxygen, nitrous oxide, carbon dioxide, cyclopropane: each has a different pattern of pin holes on the valve, matching pins on the machine clamp. For pretty obvious reasons.

Sawing pins off is criminally dangerous.

[quote user="Anthony Todd"]When you are using an in circle system the O2 needed is [from memory] 20mls/Kg so the flow and therefore the O2 needed is really low, as is the amount of anaesthetic agent needed, but in-circle vapourisers have gone the way of flared trousers, more's the pity, IMO.[/quote]

I've always understood that 5mls per minute per kg is the very minimum.[quote user="Anthony Todd"]

but in-circle vapourisers have gone the way of flared trousers, more's the pity, IMO.

[/quote]

No, I haven't worn flares for 41 years.

Re: Nitrous

Rob Loxley — Thu, 20 Nov 2014 16:28:47 GMT

[quote user="Anthony Todd"]

If you pull on the ligament and the animal is too light it will hyperventilate; this will ,in itself, deepen the animal and often leads to a period of apnoea in my hands [and with a Stephens, I know, I know] .This should happen with any inhalation system making any setting adjustment unnecessary

[/quote]

My experience suggests that if they are light and you tug on the ovary they start taking rapid, SMALL breaths (as also demonstrated by the capnograph trace) and thus take on less anaesthetic gas?

Re: Nitrous

Anthony Todd — Thu, 20 Nov 2014 10:15:54 GMT

[quote user="John Flynn"]am I missing something here?[/quote]

Whether the vapouriser is in or out of circuit makes no difference. With each breath the patient is taking in some molecules of anaesthetic agent, the deeper the breaths and the frequency of breaths determine the amount of agent. [think beer or wine, same principle]

Watch the depth and frequency of respiration when you pull on the ligament and note how the "minute volume" increases massively, count to 20 and see it settle down. Can't comment on ADE but with the Stephens, once on maintenance the changes in minute volume via rate and depth of respiration kept the animal nicely asleep.

[quote user="John Flynn"]This happens most often by an inexperienced operative[/quote] et seq

Too true and a bloody nightmare to get them either asleep or breathing again!!

[quote user="John Flynn"]the "benefits" seem pretty limited and debatable.[/quote]

Apparently so, trouble is the Stephens and probably the ADE was too simple and anaesthetists seemed to love making anaesthesia as complicated as possible; some wanted to design a machine themselves.

They all seem to trade simplicity against theoretical advantage.

They love having a machine with enough dials and levers to land on the moon and the idea that the animal itself via minute volume can control it's own anaesthetic depth suggests they aren't really needed.....

[quote user="John Flynn"]I don't quite understand what the pins are [/quote]

Sorry, this only applies to E cylinders [I think] ie the ones that you can clamp onto the trolley. If you look on the side of the valve there are holes for the pins on the attaching clamp and they should match....

When you are using an in circle system the O2 needed is [from memory] 20mls/Kg so the flow and therefore the O2 needed is really low, as is the amount of anaesthetic agent needed, but in-circle vapourisers have gone the way of flared trousers, more's the pity, IMO.

Re: Nitrous

John Flynn — Thu, 20 Nov 2014 04:28:21 GMT

[quote user="Anthony Todd"]it will hyperventilate; this will ,in itself, deepen the animal[/quote]

[quote user="Anthony Todd"]This should happen with any inhalation system making any setting adjustment unnecessary.[/quote]

I understand how this happens with vapourizer-in-circuit systems such as the Steven's, but I'm not convinced that hyperventilation would significantly deepen anaesthesia with vaporizer-out-of-circuit circles such as the Humphrey's ADE or non-rebreathing circuits - am I missing something here?

[quote user="Anthony Todd"]Chasing anaesthetic depth by adjusting the %age etc. IMO [sorry Arlo] is very difficult having watched nurses and vets flailing around like one-armed paper hangers and ending up with the animal either waking up or not breathing at all.[/quote]

This happens most often by an inexperienced operative when the dial is adjusted on a vapourizer-out-of-circuit system and an instant magical effect is expected with no consideration for actually filling the circuit with the dialled percentage, particularly if the dialled percentage is increased and the bag is then filled with oxygen from the emergency-oxygen-button rather than increasing the fresh gas flow (I've seen this done on occasions back in my locum days).

[quote user="Anthony Todd"]Adding another "drug" to a satisfactory and familiar anaesthetic protocol seems unnecessary to me, even if it has apparent benefits.[/quote]

I see your point, and the "benefits" seem pretty limited and debatable. As far as I can see, we're principally talking weak analgesia from NMDA antagonism - I would suspect that 1mg/kg ketamine intramuscularly at induction would achieve the same "benefit" with much less fuss, although one could argue that turning a knob up and down again with a reasonably rapid on-off effect is not a lot of fuss if you're used to it.

I'd just been intrigued by the discussion on merits/demerits in the human field (there was an editorial in the same edition of Lancet I mentioned previously that was rather scathing of the continued use, in some quarters, of such an outdated anaesthetic) and wanted to explore what modern day veterinary applications might be - I saw that Hall & Clarke still discuss its use in a generally positive light (but without the "real-world" application situations that you get from a forum like this) in their latest addition of "Veterinary Anaesthesia" and thought I might be missing a trick worth re-exploring.

[quote user="Anthony Todd"]By the way, just make sure the pins on your machine haven't been sawn off or you may attach the nitrous to the O2 feed, which has happened.........[/quote]

Warning heeded! At last annual service (a couple of weeks back) I asked the engineer if I could connect a nitrous cylinder and he said yes, but if you can extrapolate on details of the problem you saw (I don't quite understand what the pins are that might have been sawn off or the connection of this to the oxygen feed) then I can double-check the same thing doesn't happen to me... I'll certainly check that the oxygen and nitrous knobs do what I'd expect if I connect a cylinder having been warned of this issue.

Re: Nitrous

Anthony Todd — Wed, 19 Nov 2014 10:34:08 GMT

[quote user="Virginia Campbell"]You get some though who look and sound fine till you give a little tug on the first ligament then it transpires that they are too light.[/quote]

I'm surprised nobody has picked this up. If you pull on the ligament and the animal is too light it will hyperventilate; this will ,in itself, deepen the animal and often leads to a period of apnoea in my hands [and with a Stephens, I know, I know] .

This should happen with any inhalation system making any setting adjustment unnecessary.

Chasing anaesthetic depth by adjusting the %age etc. IMO [sorry Arlo] is very difficult having watched nurses and vets flailing around like one-armed paper hangers and ending up with the animal either waking up or not breathing at all.

Adding another "drug" to a satisfactory and familiar anaesthetic protocol seems unnecessary to me, even if it has apparent benefits.

By the way, just make sure the pins on your machine haven't been sawn off or you may attach the nitrous to the O2 feed, which has happened.........

Re: Nitrous

Rob Loxley — Tue, 18 Nov 2014 19:41:39 GMT

We have the charts laminated next to the machine. Worth remembering if you've a sidestream sampling capnograph to add that to the flow, as they can become a significant extra when you're on a lowflow system

Re: Nitrous

John Flynn — Tue, 18 Nov 2014 19:28:59 GMT

Thanks, Rob, that's REALLY helpful

Appreciate you taking the time to track down that link and post it here

Re: Nitrous

Rob Loxley — Tue, 18 Nov 2014 13:32:36 GMT

current recommendations here: http://www.edu.anaequip.com/?wpdmact=process&did=Mi5ob3RsaW5r

Re: Nitrous

John Flynn — Tue, 18 Nov 2014 07:20:44 GMT

Thanks Virginia,

what flow-rates do you use with the ADE system? Does it vary with weight of dog or are the recommednations fixed for the circle?

I have a rather ageing ADE system but can't find instructions anymore... I've decided to trial some nitrous myself but want to make sure I'm not doing anything dangerous in the process.

Re: Nitrous

Virginia Campbell — Fri, 14 Nov 2014 11:20:29 GMT

[quote user="John Flynn"]How does the use of nitrous affect the flow rates (if it does at all) that you use on the ADE system? I [/quote]Sorry for late reply.

I leave the flow rate the same but as per instructions with the ADE, I just use nitrous and oxygen 1:1 maximum rather than 2:1.

Re: Nitrous

Arlo Guthrie — Wed, 29 Oct 2014 11:34:34 GMT

[quote user="Bob Russell"]Nothing wrong with robust discussion but use of smilies and horrible 'IMO' etc do soften comments even if people hate them![/quote]

Agree absolutely Bob. In particular about the use of IMO. I prefer the longhand version, but whichever you choose, saying 'in my opinion' is, I dunno, a tad more humble than not expressing the recognition that a) it is only opinion and you may be wrong, and b) other people have opinions too.

Re: Nitrous

Bob Russell — Wed, 29 Oct 2014 10:19:44 GMT

Actually reading the phrasing carefully someone who is reluctant or scared to use it and use that as an excuse to 'see no need for it' probably is a fool!

More important for people to put forward experiences and arguments both for and against its use.

Nothing wrong with robust discussion but use of smilies and horrible 'IMO' etc do soften comments even if people hate them!