11 INHALATION ANAESTHETICS/ IV ANASTHETICS

Question 1

What is one understood mechanism of action of volatile anaesthetics

Answer 1

Possibly due its lipophilic properties. Causing non-specific expansion of lipid bilayer and consequent disruption of receptors/ ion channels

Question 2

Describe the current thinking on mechanism of action of volatile anaesthetics

Answer 2

Though to enhance GABA activity (inhibitory NT). Multisite vs. unifying hypothesis.

Question 3

Define ‘MAC’

Answer 3

A means of describing potency and dose. 1 MAC = minimum alveolar concentration to produce immobility on standard surgical stimuli (forearm incision) in 50% of patients. The more potent the drug the lower the MAC. Usually described as a percentage of alveolar gas.

Question 4

What are some covariates that increase MAC

Answer 4

Young age, hyperthermia, heavy alcohol, hyperthyroid, drugs that are stimulants (amphetamines)

Question 5

What are some covariates that decrease your MAC

Answer 5

Old age, hypothermia, hypothyroid, drugs such as opioids/ depressants, pregnancy, Low 02

Question 6

Describe the pharmacodynamics of volatile anaesthetics

Answer 6

Hypnosis, immobility, amnesia, decrease cerebral metabolic rate for 02, increase cerebral blood flow and intracranial pressure, lower bp, vasodilation, resp depression, bronchodilation. Also reduce portal blood flow and renal blood flow.

Question 7

Describe NO

Answer 7

Nitrous oxide. Rapid onset, low potency, analgesic, many adverse effects.

Question 8

What are the modern agents

Answer 8

Methyl ethyl ethers

Question 9

Describe isoflurane

Answer 9

Pungent, potent, medium onset, cardiac stability

Question 10

Describe sevoflurane

Answer 10

Good for induction of children, non pungent, intermediate potency.

Question 11

Describe desflurane

Answer 11

Pungent, intermediate potency, ideal for long surgeries.

Question 12

Name three methyl ethyl ethers

Answer 12

Isoflurane, sevoflurane, desflurane.

Question 13

Describe the concept of balanced anaesthesia and the components/ drugs that encompass it

Answer 13

Hypnosis/ amnesia (iv/ inhalation anaesthetics)

Autonomic areflexia (opioids)

Immobility (NMB)

Question 14

Name five types of IV anaesthetics

Answer 14

Barbituates, phenols, imidazoles, phenycyclidine derivatives, benzodiazepines

Question 15

Describe the mechanism of action of IV anaesthetics

Answer 15

Like inhalation anaesthetics mechanism not well understood. Thought to a) enhance GABA–> prolong Cl- current, hyper polarisation.
b) bind to PCP receptor and antagonise glutamate/ suppress excitation.

Question 16

General pharmacokinetics of IV agents

Answer 16

highly lipid soluble and cross BBB. Acts on Vessel Rich Group organs. Then redistribute into fat and muscle. Metabolism slow.

Question 17

Describe and give and example of brabituates

Answer 17

Thiopentone. Rapid onset, slow clearance, metabolised in liver, some decrease in peripheral resistance and BP, res depression and loss of airway reflexes. Used in emCS

Question 18

Describe and give examples of phenols

Answer 18

Propofol. Rapid onset and offset. Fast clearance. Used in maintanence infusion. Causes resp depression and decreased BP.

Question 19

Imidazoles

Answer 19

Etomidate. Good cardiovascular stability, rapid clearnace, causes adreno cortical inhibition. Causes myoclonus, epileptogenic.

Question 20

Benzodiazapams

Answer 20

Midazolam. Anti epileptic. Slow onset and offset limits use.

Question 21

Phencyclidine

Answer 21

Ketamine. Outlier- instead of GABA agonist, supresses excitation (glutamate at NMDA receptors). Has analgesic effect. Maintains airway reflexes, and res drive. Increases cerebral metabolic rate o2, CBF and ICP. complicated by dysphoria/ nightmares.