Inhaled Anesthetics

Question 1

describe 6 factors affecting equilibration (onset) times of inhaled anesthetics

Answer 1

distribution (Fa=Fi)

lung uptake

tissue uptake

solubility

cardiac output

arterio-venous concentration gradient

Question 2

define potency (MAC) of inhaled anesthetics

Answer 2

equilibrium concentration required to prevent movement to skin incision at 1 ATM in 50% of px

Question 3

list 3 factors that increase MAC requirements

Answer 3

hyperthermia

elevated CNS catecholamine NT release (anxiety)

chronic alcoholism

acute amphetamine use

hypernatremia

Question 4

list 3 factors that decrease MAC requirements

Answer 4

hypothermia

pregnancy

shock

increasing age

acute alcohol ingestion

CNS depressant drugs

chronic amphetamine use

Question 5

describe the probable mechanism of inhaled anesthetic action

Answer 5

ligand-gated ion channels are the most likely target

Question 6

describe clinical effects of inhaled anesthetics on organ systems other than the CNS

Answer 6

decreased BP

decreased myocardial function

increased HR

decreased O2 consumption by muscles

faster respiratory rate

lower tidal volume of breath

Question 7

when does equilibrium occur? what is the tissue conc at equilibrium?

Answer 7

when alveolar concentrations equal inspired concentrations (what is breathed in is what is breathed out - takes many hours, usually do not reach it)

max conc exists in the tissues

Question 8

determinants of rate of rise of lung concentrations

Answer 8

inspired gas partial pressure

ventilation rate

functional residual capacity (FRC)

Question 9

what happens when there is an increase in the inspired anesthetic concentration? What law is this?

Answer 9

increased rate of induction by increasing the rate of transfer into the blood

Fick’s law: flux = (C1-C2) x (area x permeability / thickness) - concentration gradient is proportional to diffusion across a membrane, which is inversely related to the thickness of the membrane

Question 10

minute alveolar ventilation is another word for

Answer 10

ventilation rate

Question 11

how does functional residual capacity affect induction time of inhaled anesthesia?

Answer 11

increased FRC slows the flow of agent into the lung, so induction time is increased (slowed)

Question 12

why does increased FRC increase the induction time?

Answer 12

the increased volume of lung that must be filled to obtain the effect

Question 13

although Fa rises by inspired conc, MAV, and FRC, the rise of concentration is slowed greatly by…

Answer 13

LARGE amount of TISSUE UPTAKE (including blood)

Question 14

3 primary determinants of tissue uptake

Answer 14

solubility of the agent

pulmonary blood flow (i.e. cardiac output)

arterio-venous concentration gradient (in the lung)

Question 15

a ratio that describes the solubility of an agent in the body

Answer 15

blood/gas partition coefficient (B/G)

Question 16

a larger B/G partition coefficient…

Answer 16

increases blood uptake and decreases alveolar concentration, which SLOWS induction (due to greater tissue uptake)

Question 17

problems associated with more soluble agents dissolving easily in the blood

Answer 17

increased equilibration times

reduced ability to exit the blood (blood holds the agent)

reduced ability to enter the brain and other tissues

Question 18

halothane has a higher partition coefficient, so its induction time…

Answer 18

is slower than other drugs with lower B/G, and its slower to come off of

Question 19

describe pulmonary outflow (cardiac output) as it pertains to equilibration time

Answer 19

increases in cardiac output DECREASES rate of alveolar concentration rise, and SLOWS equilibration time

Question 20

clinical importance of cardiac output in an ER situation

Answer 20

low cardiac output of a victim combined with low blood volume could give tragic effects of regular anesthesia dose, due to preferential blood shunting to the brain!

Question 21

as cardiac output increases, induction time..

Answer 21

increases (is slowed)

Question 22

increased tissue uptake effect on blood concentrations

Answer 22

decreases blood concentrations, which increases blood uptake from the lungs

Question 23

increased solubility of an agent

increased CO

increased AV conc gradient

ALL have what effect on equilibration time?

Answer 23

increase equilibration time (slow induction)

Question 24

ligand-gated ion channel examples that are the most likely targets of MOA of inhaled anesthetics

Answer 24

nicotinic ACh recpetors

5HT receptors

amino acid receptors esp GABA

Question 25

most prevalent transmitter in mammal CNS

Answer 25

GABA - inhibitory function in central coordination of excitability, motor, and autonomic activity

Question 26

what happens at the GABA receptor when GABA binds?

Answer 26

Cl- influx, membrane hyperpolarizes, neuronal excitability is reduced

Question 27

how do drugs enhanve GABAa current?

Answer 27

increasing Cl- influx, channel open frequency, and channel open duration

Question 28

where do inhaled anesthetics bind to GABA receptors? So, are they agonists or antagonists?

Answer 28

bind at sites distinct from GABA binding sites, so they are GABA agonists

Question 29

problems with GABA theories

Answer 29

GABAa activity is inhibited at high anesthetic conc

other GABAa agonists give anxiolysis (inhaled agents do not)

GABAa ANtagonists have little effect on inhaled agents

Question 30

effect of hyper/hypo thyroidism on MAC

Answer 30

no effect

Question 31

inhaled anesthetics effect on renal blood flow, glomerular filtration rate, hepatic blood flow, uterine smooth muscle,

Answer 31

decreased consistently

Question 32

effect of N2O on nausea and vomiting

Answer 32

increased

Question 33

what affects potency?

Answer 33

disease state, other meds, etc

Question 34

list of inhaled anesthetics

Answer 34

desflurane

sevoflurane

isoflurane

halothane

nitrous oxide