5.0 General Anaesthetics

Question 1

Ether

Answer 1

• <b>Class</b> = Inhalation GA<br></br>- <b>Target</b> = ?<br></br>- <b>Mechanism</b> = Prevents cellular depolarisation<br></br>- <b>Steps</b>: <br></br>- <b>Info</b>: <br></br>-rate of induction of anaesthesia is dependent upon the blood:gas partition coefficient. Ether has a relatively high blood:gas partition coefficient (solubility in blood), and so its rate of induction is slow<br></br>-increasing the respiration rate, to increase the rate at which Ca is reached, increases the rate of induction. <br></br>-small and lipophillic

Question 2

Etomidate

Answer 2

• <b>Class</b> = Intravenous GA<br></br>- <b>Target</b> = Beta3 (or beta2) subunit of GABAa receptor<br></br>- <b>Mechanism</b> = Prevents depolarisation of cell<br></br>- <b>Steps</b>:<br></br>Potentiates current through receptor to promote hyperpolarisation and prevent depolarisation<br></br>- <b>Info</b>:<br></br>-metabolised more rapidly than thiopentone<br></br>-used for both the induction of anaesthesia

Question 3

Halothane

Answer 3

• <b>Class</b> = Inhalation GA<br></br>- <b>Target</b> = Glycine receptor, two-pore domain potassium channel, alpha unit of GABAa<br></br>- <b>Mechanism</b> = Prevents depolarisation<br></br>- <b>Steps</b>: <br></br>Potentiates glycine receptor and two-pore domain potassium channels to prevent cellular depolarisation <br></br>- <b>Info</b>:<br></br>Low blood:gas partition coefficient (solubility in blood) means that onset of anaesthesia is rapid. Increasing cardiac output to maintain the concentration gradient between the blood and aleolae can be used to increase induction rate

Question 4

Nitrous oxide

Answer 4

• <b>Class</b> = Inorganic gas GA (inhalation)<br></br>- <b>Target</b> = ?<br></br>- <b>Mechanism</b> = Prevents cellular depolarisation<br></br>- <b>Steps</b>: <br></br>- <b>Info</b>:<br></br>Used in maintenance of anaesthesia<br></br>Small and lipophillic<br></br>Very low blood:gas partition coefficient results in rapid analgesia. Increasing cardiac output increases the rate of induction<br></br>Lowest oil:gas partition coefficient means NO is not particularly potent, and so a high partial pressure is required for anaesthesia

Question 5

Propofol

Answer 5

• <b>Class</b> = Intravenous GA<br></br>- <b>Target</b> = Beta3 subunit of GABAa receptor<br></br>- <b>Mechanism</b> = Prevents depolarisation of cell<br></br>- <b>Steps</b>:<br></br>Potentiates current through receptor to promote hyperpolarisation and prevent depolarisation<br></br>- <b>Info</b>:<br></br>-metabolised more rapidly than thiopentone<br></br>-used for both the induction and maintenance of anaesthesia

Question 6

Thiopental (thiopentone)

Answer 6

• <b>Class</b> = Barbiturate (intravenous GA)<br></br>- <b>Target</b> = <br></br>- <b>Mechanism</b> = <br></br>- <b>Steps</b>: <br></br>- <b>Info</b>:<br></br>Very high lipid solubility<br></br>Injection → loss of consciousness in 20secs<br></br>Lasts for 5-10 minutes<br></br>Different redistribution phases<br></br>Offset of anaesthesia is due to redistribution phase (not elimination)<br></br>Prolonged use is dangerous: Large/repeated dose → plasma conc. after fast redistribution still > level needed for GA → prolonged anaesthesia