Volatile agents Flashcards
What does Xenon have a faster onset time than?
Due to low blood:gas partition coefficient
Sevo
N2O
Desflurane
What anaesthetic drugs are structural isomers?
Iso & Enflurane
What is the pseudo-critical temp of Entonox?
-7 degrees
- 30 when delivered via pipeline
What is Isoflurane?
Halogenated ethyl methyl ether
What are the effects of Isoflurane?
- Inc RR & PaCO2
- Dec minute vol
- Pungent smell
- BronchoD
- Red SVR, CO & myocardial contractility
- Reflex tachy
- Red Cerebral O2 requirement
- Inc CBF
What is coronary steal?
Seen with isoflurane
Normally responsive coronary arterioles are dilated & divert blood away from areas supplied by unresponsive diseased vessels = ischaemia
Which gases can cause CO build up?
Isoflurane
Enflurane
Desflurane
What is Sevo?
Polyfluorinated isopropyl methyl ester
What are Lewis Acids?
Any substance that can accept an electron pair
What is a complication of Sevo storage? How is it stopped?
- When Conc of H2O added < 100ppm, attack by Lewis acids at ether/halogen bonds
- Hydrofluoric acid released = toxic
- Stored at 300ppm H20 = inhibitor of Lweis acids
What are the effects of Sevo?
- Depress ventilation: Inc PaCO2 & dec MV
- Reduced Cerebral/SVR & BP
- Normal contractility
How is Sevo metabolised?
P450
What are the causes of Sevo toxicity?
- Compounds A, B, C, D, E formed when around CO2 absorbents
- A & B in higher quantities
What is Halothane?
Halogenated hydrocarbon
Unstable when exposed to light
Corrodes certain metals
What is Halothane stored with and why?
0.01% Thymol
Prevent liberation of free Bromine
What are the effects of Halothane?
- Inc RR
- Normal PaCO2
- BronchoD
- Reduced CO by inc vagal tone & myocardial depression
- Inc CBF = Inc ICP
How is Halothane metabolised?
- 25% oxidative metabolism by P450
- Reductive metabolism produces F- when liver becomes hypoxic
What is Halothane toxicity?
1) Reversible, subclinical due to hepatic hypoxia
2) Fulminant hepatic necrosis, Trifluoroacetyl chloride binds to hepatic proteins
What are risk factors for Halothane hepatic toxicity?
- Multiple exposures
- Obesity
- Middle age
- Female
What can be seen on an EEG when using Enflurane?
3Hz spike & wave pattern
Consistent with grand Mal activity
What is the boiling point of Desflurane?
23.5 - extremely volatile
What are the indications for Desflurane?
Prolonged surgery
Bariatric surgery
What are the effects of Desflurane?
- Above 1 MAC: Tachy & HyperT
- Reduced Cerebral/SVR
- Inc PaCO2 & MV
What is Xenon?
Inert, odourless gas
Produced by fractional distillation of air
What are the effects of Xenon?
- Slows RR
- Inc TV
- Inc airway resistance at higher Concs
- No effect on contractility
- Inc CBF
- Significant analgesic properties
How is Xenon removed from the body?
Via the lungs
Which volatiles cause the most and least cerebral dilation?
Most: Halothane
Least: Sevo
What are the MAC values for the volatile anaesthetics?
Halo: 0.75
Iso: 1.17
En: 1.6
Sevo: 2.1
Des: 6.6
NO: 104
