Inhalational Anesthetics

Question 1

Isoflurane: What is the MAC, what does it vasodilate?

Answer 1

Mac: 1.2, systemic and coronary vasodilator

Question 2

Advantages of iso?

Answer 2

Lowest cost
Not flammable
Minimal cardiac depression (CO is maintained by increase in HR
Reverses bronchospasm

Question 3

Disadvanctages of Iso, and what’s its blood and lipid solubility like? Coronary steal?

Answer 3

High blood and lipid solubility makes for a slower onset and emergence-which may be more of an issue in MO patients and long cases
Pungent odor-not good for inhalation
May produce tachycardia
Coronary steal: dilation of normal coronary arteries with resultant diversion of blood away from fixed stenotic lesion
not tolerated well in hypovolemia due to systemic vasodilation

Question 4

For poorly soluble anesthetics, an increase in Fa/FI depends very little on ______ _______

Answer 4

alveolar ventilation

Question 5

For soluble anesthetics, an increase in Fa/Fi depends heavily on:
What’s a soluble anesthetic?

Answer 5

For soluble anesthetic agents (ex. isoflurane), an increase in FA/Fi depends significantly on alveolar ventilation.

Question 6

Rate of uptake is dependent on:

Answer 6

1) alveolar ventilation rate 2) partial pressure of gas (concentration effect) 3) breathing system

Question 7

What are the partial pressures (aka blood gas coefficient) of the main 3 and nitrous?

Answer 7

Isoflurane: 1.46 (MAC 1.15%) – relatively dependent of alveolar ventilation rate
Sevoflurane: 0.69 (MAC 2.1-2.6%)
Desflurane: 0.42 (MAC 6-7.3%)
N2O: 0.46 (MAC > 760 mm Hg) – relatively independent of alveolar ventilation rate

Question 8

Explain blood/gas coefficient:

Answer 8

The blood/gas partition coefficient describes how the gas will partition itself between the two phases after equilibrium has been reached. For example: Enflurane has a blood/gas partition coefficient of 1.7. Therefore, if the gas is in equilibrium the concentration in blood will be 1.7 times higher than the concentration in the alveoli. Thus, it makes sense that a gas with a higher blood gas coefficient will require higher uptake of gas into the blood and induction will be slower.

Question 9

How does partition coefficient relate to lipophilicity, potency, and solubility

Answer 9

Higher partition coefficient = higher lipophilicity = higher potency = higher solubility
High solubility = more anesthetic needs to be dissolved = slower onset
MAC decreases as blood gas partition coefficient increases, generally speaking

Question 10

Sevo: how does it compare to iso and des with SVR?

Answer 10

less decrease in SVR

Question 11

Is sevo a mild myocardial depressant? Can it prolong QT? Explain nephrotoxicity? Sevo and carbon monoxide? Where does it fall on solubility spectrum? Sevo MaC:

Answer 11

Yes. Yes
Nephrotoxicity if given at flow rates less than 2-can from compound A.
Sevo can form CO during exposure to dry CO2 absorbents
Falls in middle of iso and des
Sevo MaC: 2.0

Question 12

Des: what does it require? Degrades to form:

Answer 12

requires a heated, pressurized vaporizer.

Degrades to form CO in extremely dry CO2 absorbers more than its counterparts

Question 13

N20 and concentration effect:

Second gas effect:

Answer 13

Combo of low solubility and high inhaled partial pressures. Increases blood concentration of N20 and speeds induction

Second gas effect: same principle as concentration effect
rapid diffusion of nitrous oxide from alveoli to blood increases alveolar concentration of volatile agent

Question 14

N20 and diffusion hypoxia:

Answer 14

occurs during emergence if low FiO2 is used. its the opposite of concentration effect-rapid diffusion of nitrous oxide from blood to alveoli decreases alveolar PO2

Question 15

Can nitrous cause combustion? What effect does nitrous have of cell function?

Answer 15

yes.

it can have a toxic effect-inactivation of vitamin B12, and effects on embryonic development