Pharmacology of Inhalant Anesthetics Flashcards
What makes inhalant anesthetics unique from other drugs?
- Administered & eliminated through the lungs
- onset & offset does not depend on liver or kidney function
- predictable & rapid titration of anesthesia
- requires a specialized device for delivery
What is the anesthesia triad?
Anti-nociception > Unconsciousness > Muscle relaxation
When and what were the first inhalant anesthetics used?
1840; Chloroform, diethyl ether, nitrous oxide
How many inhalant agents are used in vet med and what are they?
4; Isoflurane, Desoflurane, Sevoflurane, and Nitrous oxide
Why are physiochemical characteristics important?
- determines actions & safety
- determines how they are supplied & delivered
- determines how they interact with other substances within the anesthetic machine
- determines equipment used for delivery
- determines uptake, distribution, & elimination
What are some organic compounds for inhalant agents?
Modern inhalants: isoflurane, sevoflurane, desflurane
What’s an example of an inorganic compound in inhalant agents?
Nitrous oxide
Modern inhalants are ______ and have an _______
Halogenated; ether bond
What is halogenation?
Addition of Cl, Br, or F
What are the effects of halogenation?
-decreases reactivity, increases potency, makes inhalants non-flammable, toxicity still possible (esp. with F)
What is the effect of the ether bond in inhalants?
Makes them less arrhythmogenic
What are the properties determining how inhalants are administered?
-vapor pressure -boiling point -liquid density/specific gravity
What are the properties determining how inhalants travel around the body?
- solubility
- blood:gas partition co-efficient
What does the change in the state of matter depend upon?
Molecular motion and degree of intramolecular attraction
Define gas
an agent that exists in gaseous form at room temperature and atmospheric pressure
Example: Nitrous oxide
Define vapor
Gaseous state of an agent that exists as a liquid at room temperature and atmospheric pressure -example: isoflurane, sevoflurane, desflurane
Inhalants existing as a ____ still have the same physical properties as a _____ when it exists in its ____ form
Vapor
Gas
Gaseous
What is partial pressure?
The pressure an individual gas exerts on the walls of a closed container; it is an absolute value
What is Dalton’s Law of Partial Pressure?
The total pressure of a mixture of gases is equal to the sum of the partial pressure of all the gaseous substances present
What are 3 ways to quantify inhalants?
- pressure (mmHg)
- concentration (%) - most often
- mass (grams or milligrams)
Inhalant concentration changes relative to the concentration of what?
The whole gas mixture
- vol% changes relative to atmospheric pressure
- vol% may be different in various body compartments while partial pressure is the same if the inhalant agent is in equilibrium b/t body compartments
How would you calculate the percent of an agent to be used in a vaporizer, given the total pressure and the alveolar pressure of that agent?
(Alveolar pressure (Pa)/total pressure)x100 = % of that gas
Ex:
Total pressure = 760 mmHg
Pa of ISO = 15 mmHg
15mmHg/760mmHg x 100 = 2%
Define vapor pressure
The pressure vapor molecules exert when the liquid and vapor phases are in equilibrium
Define saturated vapor pressure
Maximum concentration of molecules in the vapor state that exists for a given liquid at a given temperature
