Inhalational anaesthetic agents

[SH4:p42; BH1:p47]

=== Unfinished ===

Transpose the tables when I get a chance.

Gases on the left hand side, and properties on top (to bring it in line with LAs, IV, and local)

 

All alkane (e.g. halothane) are proarrhythmic

Thus ether was used (not proarrhythmic)

 

 

 

======

History

• 1840s - Discovery of anaesthetic properties of diethyl ether, nitrous oxide, and chloroform
• 1930s - Discovery that fluorination of molecules decreased flammability and toxicity
• 1950s - First fluorinated agent (fluroxene) introduced

Introduction for clinical use

• 1951 - Fluroxene
• 1956 - Halothane
• 1960 - Methoxyflurane
• 1973 - Enflurane
• 1981 - Isoflurane
• 1992 - Desflurane
• 1994 - Sevoflurane

Overview

[SH4:p43]

• Only halothane and sevoflurane are not stable in soda lime at 40 degrees
• Halothane and sevoflurane are non-pungent
• Only halothane requires preservative

 

Inhalational anaesthetics

	Halothane	Enflurane	Isoflurane	Desflurane	Sevoflurane	N2O	Xenon	Comment
Blood:gas coefficient [SH4:p43]	2.54	1.90	1.46	0.42	0.69	0.46	0.115	Use this
Blood:gas coefficient [EEW1:p45]	2.4		1.4	0.45	0.65	0.46
Oil:gas coefficient [RDM6:p236]			90	18.7	53.4	1.4	1.9
Oil:gas coefficient [EEW1:p45]	224		98	19	47	1.4
MAC [SH4:p43]	0.75%	1.63%	1.17%	6.6%	1.80%	104%	63-71%	Use this
MAC [RDM6:p236]			1.15%	6%	1.71%	105%	71%
MAC [RDM6:p115]	0.74%	1.68%	1.15%	6%	2.05%	104%	71%
MW	197	184	184	168	200	44	131
Boiling point (degree Celcius)	50.2	56.5	48.5	22.8	58.5	-88.5	-108
Vapour pressure at 20C (mmHg)	244mmHg	172 mmHg	240mmHg	669mmHg	170mmHg	gas	gas

 

 

Simplied table of inhalational anaesthetics

	Halothane	Enflurane	Isoflurane	Desflurane	Sevoflurane	N2O	Xenon	Comment
Blood:gas	2.54	1.90	1.46	0.42	0.69	0.46	0.115	Xe = lowest,
Oil:gas	224		98	19	47	1.4		N2O less oil soluble, but more blood soluble than desflurane
MAC	0.75%	1.63%	1.17%	6.60%	1.80%	104%	71%	Hal = lowest, N2O > 100%
MW	197	184	184	168	200	44	131	S>H>E=I>D
Boiling point	50.2	56.5	48.5	22.8	58.5	-88.5	-108	Des = lowest, Iso = second lowest, Sev = highest
Vapour pressure at 20C	244 mmHg	172 mmHg	240 mmHg	669 mmHg	170 mmHg	gas	gas	Des = highest, Sev = lowest

 

 

 

 

 

Carbon monoxide production

Carbon monoxide is produced when inhalational anaesthetics degrades during interaction with the strong base in desiccated carbon dioxide absorber

• Desflurane produces the highest carbon monoxide
• Then enflurane and isoflurane
• Negligible with halothane and sevoflurane