Maintenance Agent

Question 1

What are the common inhalants used in veterinary industry ?

Answer 1

Isoflurane and sevoflurane

Desoflurane is available but expensive

Question 2

What us the goal of using inhalants?

Answer 2

To keep inhalant concentration to a minimum in order to Minimise adverse effects

Question 3

What are the three main physical properties of inhalants?

Answer 3

1) Vapor pressure
2) Solubility
3) Minimum alveolar concentration (MAC)

Question 4

Vapor pressure of inhalant

Answer 4

Measure of its ability to evaporate
Expressed as a percentage of barometric pressure at sea level (760mmHg)
-High vapor pressure = more molecules available at gaseous phase
-Higher the saturated vapor pressure, the greater the concentration fo inhalant delivered to patients

Question 5

Vapor pressure of isoflurane vs sevoflurane

Answer 5

Saturated vapor pressure of Isoflurane = 240mmHg at 20C
Saturated vapor pressure of sevoflurane = 160mmHg at 20C
Hence Isoflurane is easier to vaporize than sevoflurane

Question 6

Solubility and partial coefficient (PC) of an inhalant

Answer 6

Defined as the amount of inhalant vapor that is dissolved within a solvent at equilibrium. 
Partial coefficient (PC) is a ratio describing its solubility in a specific solvent such as oil, tissue or blood. 
Blood to gas PC tells us about the speed of anesthetic induction and recovery as well as how fast the anesthetic depth can be changed.

Question 7

Agent that us highly soluble

Answer 7

• Will have a high blood to gas PC
• The more soluble an agent (therefore higher blood to gas PC) = the longer it will take for induction, recovery and depth changes to occur

Question 8

Isoflurane vs sevoflurane blood:gas PC

Answer 8

Isoflurane 1.5, sevoflurane 0.68

Hence sevoflurane has a quicker induction and recovery time than Isoflurane

Question 9

How are inhalants taken up within the body?

Answer 9

They move along partial pressure gradients, NOT concentration gradients

Question 10

Minimum Alveolar Concentration (MAC)

Answer 10

The concentration of inhalant that prevent gross, purposeful movement in 50% of patients exposed to noxious stimulus.

Surgical MAC: 1.5 x MAC

A measure of inhalant potency
-The lower the MAC, the more potent the inhalant

Question 11

What factors will decrease MAC?

Answer 11

• Use of premedication
• Injectable anesthetic and intraoperative CRIs
• Local/regional blocks
• hypoxemia
• low PCV(<10%)
• geriatric patients
• hypothermia
• pregnancy
• hepatic, cardiovascular and respiratory diseases

Question 12

What factors will increase MAC?

Answer 12

• Mask or chamber inductions
• Hyperthermia
• Increase levels of catecholamines

Question 13

MAC of isoflurane vs sevoflurane

Answer 13

MAC of Isoflurane is 1.3% in dogs and 1.6% in cats
MAC of sevoflurane is 2.4% in dogs and 2.6% in cats
-Sevoflurane is less potent than isoflurane
-needs a higher vaporizer setting for maintenance