Inhalants

Question 1

Define saturated vapor pressure

Answer 1

When the pressure exerted by the gaseous molecules on the walls of the container is equal to the pressure of the liquid phase (when they are at equilibrium)

Question 2

Saturated vapor pressure depends on what two things?

Answer 2

The temperature and the agent; it is NOT affected by barometric pressure

Question 3

Define minimum alveolar concentration (MAC)

Answer 3

It is the measure of the anesthetic potency; it is at which 50% of patients don’t respond with a movement to surgical stimulation

Question 4

Surgical MAC and MAC*BAR are what MAC multiple?

Answer 4

Surgical: 1.2-1.4x MAC MAC (blunt autonomic response): >2x MAC

Question 5

Rank the inhalants by their MACs in dogs and cats

Answer 5

Lowest: Halothane < Iso < Sevo << Des <<< N2O

Question 6

What factors or conditions reduce the MAC?

Answer 6

Analgesic drugs, Ace, N2O, age, hypothermia, hypothyroidism, pregnancy

Question 7

Inhaled anesthetic concentration in the brain depends on what?

Answer 7

Alveolar concentration; thus if alveolar concentration rises fast, the anesthetic effect will be fast too

Question 8

If uptake of the anesthetic agent by circulation increases, the alveolar concentration ____, and the anesthetic effect ______

Answer 8

Drops; decreases

Question 9

After saturation of highly perfused tissues, alveolar concentration ___ arterial concentration ____ concentration in CNS

Answer 9

=, =, =

Question 10

Uptake is determined by what factor?

Answer 10

The solubility of the anesthetic agent (partition coefficient)

Question 11

The blood/gas partition coefficient tells you what?

Answer 11

The speed of partial pressure change; thus a low B/G coefficient = a fast change

Question 12

The olive oil/gas partition coefficient tells you what?

Answer 12

The potency of an inhalant anesthetic

Question 13

How does solubility relate to uptake?

Answer 13

Less soluble = less uptake = faster rise in alveolar concentration

Question 14

Rank the anesthetic agents by their rate of uptake (B:G)

Answer 14

Fastest: Des > N2O > Sevo > ISO > Hal

Question 15

At equilibrium, the _______ are the same, but _____ are usually different

Answer 15

Partial pressures; concentrations

Question 16

Why is it difficult to induce an excited patient with an inhalant?

Answer 16

B/c high cardiac output removes the anesthetic agent so quickly from the alveoli so the partial pressure in the alveoli does not have time to increase and neither does that in the blood

Question 17

In order to obtain a fast change in anesthetic plane, we need a fast rise in alveolar partial pressure. What 3 things do we need to achieve this?

Answer 17

High alveolar ventilation, low partition coefficient, low cardiac output

Question 18

Describe the difference between a gas and a vapor

Answer 18

• Gas
  
  • exist in gaseous form at room temp and sea level
  • can be given between 0-100%
• Vapor
  
  • gaseous state of a substance that is a liquid at room temp and sea level
  • needs a vape
  • max concentration depends on saturated vapor pressure

Question 19

Describe nitrous oxide

Answer 19

• Gas at room temp/sea level
• very high MAC - not hypnotic to animals
• reduces MAC when administered with O2 and halogenates
• acts as an NMDA antagonist when used as an adjuvant analgesic
  
  • Increases ICP, symp stim, myocardial depression

Question 20

Describe halothane

Answer 20

• Formulated with thymol to increase stability
• causes dose dependent resp depression, arrhythmias, and bradycardia
• can trigger malignant hyperthermia and produce hepatic damage
• potent (low MAC) and high B/G ratio (slow)

Question 21

Describe isoflurane

Answer 21

• Does not require preservative
• faster than halothane and less potent
• Marked dose dependent drop in BP and SVR, respiratory depression
• Little myocardial depression
• Does not sensitize myocardium to epinephrine-induced tachyarrhythmias (like hal)
• low rate hepatic metabolism
• can trigger malignant hyperthermia

Question 22

Describe sevoflurane

Answer 22

• Non-irritating for resp tract and non-pungent odor
• faster induction and recovery than Iso (lower partition coefficient)
• causes dose-dependent CV and resp depression
• 5% hepatic metabolism —> free floride
• Reacts with soda lime to form Compound A (nephrotoxic in rats)

Question 23

Describe desflurane

Answer 23

• due to low solubility —> very fast induction and recovery
  
  • ​can be blunted by co-administration of over drugs
• causes dose dependent CV and resp depression
• Sudden arousal when moving animals from OR to recovery
• Pungent odor —> airway irritation, breath holding, salivation (not ideal for mask induction)
• Very expensive
• Decomposes to carbon monoxide when using dry soda lime

Question 24

Which is the cheapest: Iso, Sevo, or Desflurane?

Answer 24

Iso < Sevo <<< Des

Question 25

Which drug has the lowest partition coefficient?

Answer 25

Des < Sevo << Iso

Question 26

What are some examples of scenarios when using a less soluble agent might be preferable?

Answer 26

• Horses having colic surgery
• Septic patients
• C-sections

Question 27

T or F: all volatile inhalation anesthetics cause dose dependent and drug specific changes in cardiovascular performance

Answer 27

True; the mechanisms often include direct myocardial depression and a decrease in sympathoadrenal activity (reduction of SVR) —-> decr MAP

Question 28

Which inhalant is the most depressing to cardiac output?

Answer 28

halothane

Question 29

Describe the respiratory effects caused by inhalant anesthetics

Answer 29

• Dose-dependent respiratory depression
• Reduction in total volume (shallow breath) followed by reduction of resp rate
• Depression of hypercapnia and hypoxemia respiratory drive
• Bronchodilatory effects

Question 30

Describe the CNS effects caused by inhalants

Answer 30

• Dose dependent depression
• Decrease cerebral metabolic rate
• Increase cerebral blood flow and ICP

Question 31

Define cerebral perfusion pressure

Answer 31

• the driving pressure for brain perfusion
• = difference between mean arterial blood pressure (MAP) and intracranial pressure

Question 32

Halogenates can do what to cerebral auto regulation?

Answer 32

Blunt it (especially >1 MAC)