General Anesthetics

Question 1

Use of General Anesthetics

Answer 1

Should only be used for surgery

Question 2

What was used prior to general anesthetics?

Answer 2

ethanol, opiates, partial asphyxiation, cerebral concussion….ether and chloroform were also mentioned

Question 3

Name the characteristics of the ideal anesthetic

Answer 3

• balanced anesthesia
• loss of consciousness
• amnesia
• analgesia
• inhibition of reflexes
• muscle relaxation
• rapid onset
• rapid recovery
• pleasant experience
• No dangerous SEs (low respiration, hypothermia, nausea, vomiting)

Question 4

Describe Therapeutic Index of inhaled general anesthetics

Answer 4

TI is low, between 2-4. Lethal dose is near that of the therapeutic dose.

Question 5

Mechanism of action for Inhaled General Anesthetics

Answer 5

• inhibition of neuronal firing
• potentiation of inhibitory GABAergic neurons
• inhibition of excitatory glutaminergic neurons
• cortex most sensitive, then thalamus

Question 6

Factors influencing potency for inhaled G.A.s

Answer 6

• in general, the more lipid soluble is the drug, the more potent it is
• MAC = minimum alveolar concentration, same as ED50
• the lower the MAC, the more potent is the drug

Question 7

Describe speed of induction and speed of recovery for inhaled G.A.s

Answer 7

speed of induction is related to solubility of agent in blood. The more soluble it is in the blood, the slower the onset. A high blood / gas coefficient means that it is more soluble in blood and thus, has a slower induction.

In general, recovery from G.A. is symmetrical with induction

Question 8

What is blood / gas coeff of NO?
Describe characteristics of NO, including MAC.
Describe blood solubility.
What occurs after repeated exposure?

Answer 8

• NO is a gas at room temp. has a blood/gas coeff of 0.5 = relatively insoluble in blood = rapid onset
• MAC > 100% = not very efficacious

NO has a rapid induction (low blood solubility), rapid recovery, good analgesic, very low potency, no amnesia, and since it is not soluble in blood, it tends to enter body cavities as a gas and cause px discomfort

repeated exposure: megaloblastic leukemia, leukopenia

Question 9

Name the halogenated hydrocarbons, their use and the consequence of repeated exposure

Answer 9

Used to maintain anesthesia, once induced.

Isoflurane: MAC = 1.4% and b/g coeff = 1.4

desflurane

sevoflurane

-increased incidence of liver disease can result from repeated exposure

Question 10

Name the 5 IV G.A.s from lecture

Answer 10

etomidate
ketamine
methohexital
midazolam
propofol

“eating ketamine murdered master of pop”

Question 11

How is methohexital administered? Name the class of drug and mechanism of action.

Answer 11

It is administed IV. It is a barbituate. It binds to and activates GABAergic neurons. Its action is terminated by redistribution from brain.

Question 12

Describe propofol and its mechanism of action

Answer 12

It killed the king of pop!
It is the most commonly used parenteral anesthetic
It acts to increase GABAergic activity

Rapid onset, short duration, antiemetic effects

Question 13

Ketamine is an analog of what?

Describe characteristics of ketamine and mechanism of action.

Answer 13

analog of phenylcyclidine (aka PCP) is known on the street as angel dust.

causes dissociative amnesia = profound amnesia / analgesia

• short induction
• short duration
• binds to receptor which inhibits glutamate neurons
• can cause hallucinations in px emerging from anesthesia

Question 14

Describe etomidate. Whats it do?

Answer 14

Activates GABA receptors, high TI, very rapid analgesic - “conscious sedation”

has some post op nausea

Question 15

Talk to me about MidazoLAM. That ending doee.

Answer 15

Benzodiazepine. binds to benzodiazepine receptors and enhances activity of GABAergic neurons.

Could be used in procedures such as colonoscopies for its amnesia effects.