Lecture 54: General Anesthetics

Question 1

General anesthesia is used

Answer 1

For procedures that require loss of consciousness; immobility despite painful stimulation

Question 2

What is the surgical plane and one goal of anesthesia

Answer 2

Surgical plane = Level III EEG; goal is to minimize time at levels I & II

Question 3

What four things would an ideal anesthetic do? What do we have to do to achieve these effects?

Answer 3

1. Loss of consciousness, 2. Analgesia, 3. Paralysis, 4. Amensia; no ideal anesthetic, must blend drugs = balanced anesthesia

Question 4

What drugs as used as adjuncts in anesthesia?

Answer 4

Sedative-hypnotics, opioids, NM blockers

Question 5

Advantage of an inhaled anesthetic

Answer 5

Rapidly titrate depth of anesthesia

Question 6

Advantage of intravenous anesthetic

Answer 6

Better tolerated at induction (no mask)

Question 7

Three examples of high potency inhaled anesthetics we need to know (+ one from LC) and the molecule they’re derived from

Answer 7

Sevolurane, isoflurane, desflurane* (halothane**); ether

Question 8

One example of low potency inhaled anesthetic

Answer 8

N2O*

Question 9

How are inhaled anesthetics thought to work (2)

Answer 9

Enhance inhibitory ligand-gated channels (GABAa, glycine in SC) and inhibit excitatory ligand-gated channels (AMPA, NMDA, nAChR)

Question 10

What is the limit on volatile anesthetic concentration?

Answer 10

Vapor pressure of the liquid

Question 11

Define MAC; how is MAC expressed and how would you describe a certain dose?

Answer 11

Minimum Alveolar Concetration: median value of the minimum effective concentration to suppress movement in standardized incision, expressed a % and dose given as MAC multiples

Question 12

Describe lipid solubility and anesthetic potency. What key drug has the highest oil:gas ratio?

Answer 12

Oil : gas partition coefficient –> greater oil solubility (larger coefficient), lower the MAC; Isoflurane

Question 13

Higher blood solubility means you need more/less molecules to get anesthetic to brain

Answer 13

More

Question 14

Describe blood solubility and rate of equilibrium. What drug has very low solubility?

Answer 14

Lower the solubility, the faster the induction; N2O

Question 15

What is the effect of ventilation on induction rate? Biggest effect on what type of anesthetic?

Answer 15

Increased ventilation speeds induction; those w/ high solubility

Question 16

Anesthesia is maintained at what MAC multiple? What if its used for induction?

Answer 16

1.3 - 1.4x MAC; higher MAC (maybe 3-4x MAC)

Question 17

Name and describe two considerations for NO (one when NO is turned on and one when it’s turned off)

Answer 17

1. Turn on: Trapped air space, due to N2O moving into blood faster than N2 leaves; 2. Turn off: Diffusion hypoxia, due to N2O flooding alveoli, terminate with 100% O2

Question 18

Why would you want to deliver NO with other inhaled anesthetics. Name the effect.

Answer 18

Second gas effect: N2O creates alveolar “vacuum” which increases respiration, quickening induction of all inhaled anesthetics

Question 19

All high-potency agents do what to blood pressure, GFR, pCO2?

Answer 19

Decrease; decrease; increase

Question 20

Describe N2O’s BP/pCO2 effects

Answer 20

N2O does not decrease BP and is less likely to increase pCO2

Question 21

When used with what, what SE of inhaled anesthetics can occur? Treatment?

Answer 21

Malignant hyperthermia; Dantrolene

Question 22

What is the most widely used induction agent. Receptor? Advantage? SEs?

Answer 22

Propofol*; GABA; rapid onset; decreases BP/respiratory depression

Question 23

Explain why Propofol’s half life increases with length of administration

Answer 23

Obeys two-compartment kinetics: the fast phase involves distributing the drug into poorly perfused tissues and the slow phase involves hepatic elimination; injection favors fast phase while infusing favors slow phase

Question 24

Name another common infused anesthetic and its advantage over Propofol

Answer 24

Etomidate*; does not cause cardiopulmonary SEs

Question 25

What is the mechanism of ketamine? What state does it produce? SEs?

Answer 25

Inhibits excitatory glutamate signaling via NMDA receptors; dissociated anesthetic state; sympathetic: increased HR/BP/bronchodilation