Volatile agents

Question 1

What does Xenon have a faster onset time than?

Answer 1

Due to low blood:gas partition coefficient
Sevo
N2O
Desflurane

Question 2

What anaesthetic drugs are structural isomers?

Answer 2

Iso & Enflurane

Question 3

What is the pseudo-critical temp of Entonox?

Answer 3

-7 degrees
- 30 when delivered via pipeline

Question 4

What is Isoflurane?

Answer 4

Halogenated ethyl methyl ether

Question 5

What are the effects of Isoflurane?

Answer 5

• Inc RR & PaCO2
• Dec minute vol
• Pungent smell
• BronchoD
• Red SVR, CO & myocardial contractility
• Reflex tachy
• Red Cerebral O2 requirement
• Inc CBF

Question 6

What is coronary steal?

Answer 6

Seen with isoflurane
Normally responsive coronary arterioles are dilated & divert blood away from areas supplied by unresponsive diseased vessels = ischaemia

Question 7

Which gases can cause CO build up?

Answer 7

Isoflurane
Enflurane
Desflurane

Question 8

What is Sevo?

Answer 8

Polyfluorinated isopropyl methyl ester

Question 9

What are Lewis Acids?

Answer 9

Any substance that can accept an electron pair

Question 10

What is a complication of Sevo storage? How is it stopped?

Answer 10

• 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

Question 11

What are the effects of Sevo?

Answer 11

• Depress ventilation: Inc PaCO2 & dec MV
• Reduced Cerebral/SVR & BP
• Normal contractility

Question 12

How is Sevo metabolised?

Answer 12

P450

Question 13

What are the causes of Sevo toxicity?

Answer 13

• Compounds A, B, C, D, E formed when around CO2 absorbents
• A & B in higher quantities

Question 14

What is Halothane?

Answer 14

Halogenated hydrocarbon
Unstable when exposed to light
Corrodes certain metals

Question 15

What is Halothane stored with and why?

Answer 15

0.01% Thymol
Prevent liberation of free Bromine

Question 16

What are the effects of Halothane?

Answer 16

• Inc RR
• Normal PaCO2
• BronchoD
• Reduced CO by inc vagal tone & myocardial depression
• Inc CBF = Inc ICP

Question 17

How is Halothane metabolised?

Answer 17

• 25% oxidative metabolism by P450
• Reductive metabolism produces F- when liver becomes hypoxic

Question 18

What is Halothane toxicity?

Answer 18

1) Reversible, subclinical due to hepatic hypoxia
2) Fulminant hepatic necrosis, Trifluoroacetyl chloride binds to hepatic proteins

Question 19

What are risk factors for Halothane hepatic toxicity?

Answer 19

• Multiple exposures
• Obesity
• Middle age
• Female

Question 20

What can be seen on an EEG when using Enflurane?

Answer 20

3Hz spike & wave pattern
Consistent with grand Mal activity

Question 21

What is the boiling point of Desflurane?

Answer 21

23.5 - extremely volatile

Question 22

What are the indications for Desflurane?

Answer 22

Prolonged surgery
Bariatric surgery

Question 23

What are the effects of Desflurane?

Answer 23

• Above 1 MAC: Tachy & HyperT
• Reduced Cerebral/SVR
• Inc PaCO2 & MV

Question 24

What is Xenon?

Answer 24

Inert, odourless gas
Produced by fractional distillation of air

Question 25

What are the effects of Xenon?

Answer 25

• Slows RR
• Inc TV
• Inc airway resistance at higher Concs
• No effect on contractility
• Inc CBF
• Significant analgesic properties

Question 26

How is Xenon removed from the body?

Answer 26

Via the lungs

Question 27

Which volatiles cause the most and least cerebral dilation?

Answer 27

Most: Halothane
Least: Sevo

Question 28

What are the MAC values for the volatile anaesthetics?

Answer 28

Halo: 0.75
Iso: 1.17
En: 1.6
Sevo: 2.1
Des: 6.6
NO: 104