Basic Pharm of Inhaled Anesthetics

Question 1

What does MAC stand for?

Answer 1

Minimum Alveolar Concentration

Question 2

Define 1 MAC.

Answer 2

The concentration at which 50% of patients will not move in response to surgical stimuli.

Question 3

True/false. MAC is directly proportional to potency and lipid solubility.

Answer 3

False. MAC is INVERSELY RELATED to potency and lipid solubility. increased MAC=decreased potency and lipid solubility.

Question 4

What is the MAC value of Halothane?

Answer 4

0.7

Question 5

What is the MAC value of Isoflurane?

Answer 5

1.2

Question 6

What is the MAC value of Enflurane?

Answer 6

1.7

Question 7

What is the MAC value of Sevoflurane?

Answer 7

1.9

Question 8

What is the MAC value of Desflurane?

Answer 8

6

Question 9

What is the MAC value of Nitrous Oxide?

Answer 9

104

Question 10

Which gases are worst for the environment?

Answer 10

Desflurane and Nitrous Oxide

Question 11

What is the oil:gas coefficient?

Answer 11

reflects the tissue affinity for an inhaled anesthetic. Measure of potency.

Question 12

What things cause need for more gas?

Answer 12

increased CNS catecholamines/anxious/stressed, hyperthermia, chronic ETOH use, hypernatremia, hypokalemia, young age

Question 13

What things cause need for less gas?

Answer 13

CNS depressants, hypothermia, advanced age, anemia, hypotension, hypoxia, hypercarbia, hyponatremia, increased Mg/Ca/K, pregnancy, acute intoxication.

Question 14

What is MAC-awake?

Answer 14

0.3 MAC; 50% of subjects respond to command as long as no other meds on board.

Question 15

What is MAC-BAR?

Answer 15

“block adrenergic response;” 1.1-1.5 MAC; blocks response to incision

Question 16

____% decrease in MAC per decade of age regardless of volatile anesthetic.

Answer 16

6

Question 17

Describe the Meyer-Overton Hypothesis.

Answer 17

potency of anesthetics relates to their lipid solubility, anesthetic molecules dissolve into CNS membranes, disrupting their effect. *most widely accepted.

Question 18

Describe the Mullin’s Critical Volume Hypothesis.

Answer 18

Volume expansion, pressure reversal; CNS cell membranes expand with general anesthetic agents which distorts channels responsible for maintaining membrane potential and generating action potentials; increased ambient pressure reverses general anesthetics.

Question 19

What are the 4 determinants of uptake?

Answer 19

inspired concentration
partial pressure (alveolar gradient
solubility
blood flow

Question 20

Define alveolar partial pressure.

Answer 20

Determines the partial pressure of anesthetic in the blood and ultimately the brain–>clinical effect

Question 21

What is Henry’s Law?

Answer 21

amount of gas which will go into a solution is proportional to the partial pressure of that gas. External pressure has very little effect on the solubility of liquids and solids but solubility of gas increases as PP of the gas above a solution increases.

Question 22

How does temperature affect partial pressure?

Answer 22

lower temps, more gas will dissolve; lower temp=slower induction; cold liquids hold more gas.

Question 23

True/false? Lower blood/tissue solubility=faster induction.

Answer 23

true. less gas dissolved, so alveolar concentration higher and induction faster.

Question 24

Define blood-gas partition coefficient.

Answer 24

Ostwald coefficient for blood-gas: describes the SOLUBILITY of inhaled general anesthetics in blood; the ratio of the conc. in blood to the conc. in gas that is in contact with that blood when partial pressure in both compartments is equal.

Question 25

Order the gases from lowest to greatest solubility.

Answer 25

Desflurane, nitrous oxide, sevoflurane, isoflurane, enflurane, halothane.

Question 26

True/false. Higher cardiac output speeds up induction time.

Answer 26

False, higher output pulls agents out of alveoli reducing PP, moving further from equilibrium causing slower induction time.