Lecture 12 - Anestethics

Question 1

How do local anesthetics work

Answer 1

• block vg Na+ channels in nerves and other tissues

- acts at a site within the channel: access to this site is intracellular so LAs must first cross the cell membrane

Question 2

Physiochemical properties of LAs

Answer 2

• LAs are weak bases -> poorly water soluble and unstable
• when combined with strong acid they form water soluble and stable salts
• non ionised form of LA crosses the membrane
• ionised form binds to the sodium channel

Question 3

Hydrophilic pathway of LA

Answer 3

• non ionised form crosses the membrane
• ionised form binds to channel
• channel needs to be open for binding to occur -> ude dependent

Question 4

Hydrophobic pathway

Answer 4

Only 10 % of LA work with that

- not use ependent

Question 5

Method of anesthesia: Surface (spray)

Answer 5

• nose, mouth, cornea

- eg: Lignocaine

Question 6

MEthod of anesthesia: infiltration

Answer 6

• minor surgery

- eg: most drugs

Question 7

Method of anesthesia: IV regional

Answer 7

• limb surgery

- eg: Lignocaine, prilocaine

Question 8

Method of anesthesia: Nerve block

Answer 8

• use: surgery, dentistry

- eg: most drugs

Question 9

Method of anesthesia: spinal, inject into subarachnoid space

Answer 9

• use: Major surgery when GA cannot be used

- eg: lignocaine

Question 10

MEthod of anesthesia: epidural

Answer 10

• use: major surgery or childbirth

- eg: mainly lignocaine and bupivacaine

Question 11

Speed of onset of LA is determined by

Answer 11

• degree of ionisation (pKa)

Question 12

Duration of action is determined by

Answer 12

• protein binding to Na+ channel (increases duration)

- vascularity at the site of action (decreases duration)

Question 13

Advantages of vasoconstrictors in relation to LA

Answer 13

• reduce blood flow -> increase duration of action
• minimise dosage
• decrease toxicity

Question 14

Toxicity due to LA

Answer 14

• toxic effect related to action: CNS (initial stimulation followed by depression)
• cardiotoxicity: profound bradychardia
• allergic reactions

Question 15

GA: Premedication

Answer 15

• relieve anxiety
• produce sedation and amnesia
• relieve pain
• reduce secretion
• reduce nausea and vomiting
• neuromuscular blockade

Question 16

Fours stafes of anesthesia

Answer 16

• analgesia
• excitement
• surgical anesthesia
• medullary depression

Question 17

Intravenous GA: THIOPENTAL

Answer 17

• ultra short, fast acting barbiturate
• loss of consciousness in 10-20 sec, regained in 2-3 min
• hangover for 24hr
• adverse effects: laryngeal spasm, cardiac and respiratory depression, hypersensitivity

Question 18

Intravenous GA: Midazolam

Answer 18

• benzodiazepine, water soluble
• slow onset of recovery
• less risk of of respiratory, cardiovascular depression

Question 19

Intravenous GA: propofol

Answer 19

• may be used alone for short procedures
• acts in 30 sec
• no hangover, and little to no nausea
• cardiac and respiratory depressant`

Question 20

Inahalation GA

Answer 20

• Halothane: associated with hepatotoxicity, cardiovascular and respiratory depression (bradychardia + arrythmia)
• isoflurane: tends to cause hypotension but less cardiodepression
• Desflurane and sevoflurane: faster induction and recovery
• Nausea and vomiting concern for all

Question 21

Sedative effects of GA

Answer 21

• occur early on at low doses

- act on prefrontal cortex

Question 22

Loss of consciousness effect

Answer 22

• occurs at higher doses

- acts on thalamus

Question 23

Effects on CNS

Answer 23

• enhance inhibition (via GABA receptor potentiation)
• inhibit excitation (block NMDA receptors)
• reduce excitation (open K+ channels)