Extended essay for the IB on Anaesthetics

**gullie** · 16-08-2008, 08:08 PM

Hello everyone!

My younger brother is doing his extended essay on anaesthetics. His aim is: To compare the effectiveness of various general anaesthetics on open and closed circulatory systems. His Extended Essay subject is Biology.

He will be using the anaesthetics: chloroform (tetrachloromethane), halothane, isoflurane, triochloroethylene.

His first question is: do any of you have access to values on the time taken to render a patient (human) unconscious and the length of unconsciousness by each of the anaesthetics listed above? We realise that chloroform is not used in surgery but he's still going to be using the anaesthetic.

His other question is: What kind of things could he talk about in his extended essay? Biological, not Chemical aspects including effects on the nervous system etc. What factors should he be looking for during the experiment besides what's stated in the aim?

Thank you! We really do appreciate it!

**Dr Noodle** · 17-08-2008, 01:16 AM

Sorry to sound preachy but is part of the point of this essay to demonstrate his research skills? Asking outright on a forum doesn't really constitute research IMO.

**gullie** · 17-08-2008, 05:02 PM

Hehe actually, no, he needs literature values for closed circulatory systems (humans/mammals etc.) but he doesn't have access to the right sources. He's done the other research. And he asked the other question, what else he could talk about etc. to see if there's anything he's forgotten.

He's going to email the local hospital and some chemical firms to see if they can provide him with the values. ^_^

**andy2** · 21-08-2008, 12:16 AM

The first thing I would do is question your choice of anaesthetic agents - you have three largely obsolete anaesthetics in there (chloroform and Trilene are pretty much never used these days, ether is still in some 3rd world nations and would be a better choice as an 'exemplar' inhalational anaesthetic), Halothane is also seldom used these days - isoflurane and some of the newer halogenated hydrocarbons -sevoflurane and desflurane - would be more up to date.

In terms of the info you are after, you'll need to do some reading about the agents but the hint about speed of onset (and offset) is the solubility of the agent. The duration of action depends on the speed of offset - but in reality patients are kept anaesthetised by having a continuous flow of the anaesthetic agent for the duration of anaesthesia (although for the slow offset agents one can stop administering anaesthesia some time before the end of the operation).

In terms of reading good places to start would be Anaesthesia UK :Inhalational agents

Books with good explanations include:

Pharmacology for Anaesthesia and Intensive Care by Tom E. Peck and Sue Hill

and Fundamentals of Anaesthesia by Colin Pinnock

(both a pretty pricey, especially the second one - your local hospital may have a library you could use).

Finally, you've taken on a subject which even many entry level anaesthetists find conceptually quite challenging- it would certainly be worth finding a tame anaesthetist to talk to about this. You could try asking the anaesthetic department of your local hospital if you could arrange a visit and take it from there.

**gullie** · 21-08-2008, 01:58 AM

My little brother read somewhere that people mainly mix sevoflurane and desflurane together to obtain a 'modern' anaesthetic. Or can he use them separately? I think so, but he still insists on asking.

He also didn't choose more of the 'modern' anaesthetics for a couple reasons: they need to be liquid at room temperature, he couldn't find information on sevoflurane and desflurane on the internet, and one of the main points of this experiment is to compare the effects on open and closed circulatory systems.

He thanks you all for your help,

I thank you, too! ^_^

**andy2** · 21-08-2008, 07:29 PM

No, no one mixes inhalational anaesthetic agents together - although it is not uncommon to use one agent for induction of anaesthesia and another for maintainence (e.g. use sevoflurane for induction as it is pleasant to breath and rapidly induces anaesthesia, before converting to isoflurane for maintainence of anaesthesia as it is a lot cheaper but less good for induction).

The boiling point will tell you which agents are liquid at room temperature - most are, although desflurane has a low boiling point (about 24 degrees if I recall correctly) and so requires a special type of vaporiser. Fully open systems (e.g. a Schimmelbusch mask) are now only found in museums in the developed world although you may find the odd person using these in developing world countries.
Generally speaking these days semi-closed or fully closed systems are used - see Anaesthesia UK :Breathing circuits