Flashcards in Inhalant Anesthetics Deck (79)
Why use inhalant anesthetics?
1. Predictable effects
2. Rapid adjustment of anesthetic depth
3. Minimal metabolism
- Low blood gas PC (0.47)
- Mild analgesic
- Accumulation in closed gas spaces
Expensive, used mostly experimentally
Anesthetic vapors dissolve in liquids and solids
Equilibrium is reached when the PP of the anesthetic is the same in each phase (pressure, not number of molecules)
Expression of solubility
Concentration ratio of an anesthetic in the solvent and gas phases, describes the capacity of a given solvent to dissolve an anesthetic
Blood-gas partition coefficient
Most clinically useful number
Describes amount of anesthetic in the blood vs. alveolar gas at equal partial pressure
What does the pressure of anesthetic in the alveolar gas represent?
Brain concentration- location of effect
T/F: Anesthetic in blood is pharmacologically active?
Most to least soluble anesthetics
Low blood-gas PC
1. Less anesthetic dissolved in the blood at an equal PP
2. Shorter time required to attain PP in brain
3. Shorter induction and recovery
Clinically more useful
High blood-gas PC
1. More anesthetic dissolved in the blood at an equal PP
2. Longer time required to attain PP in brain
3. Longer induction and recovery
Not very clinically useful
Effect of solubility on recovers
The lower the solubility, the faster the recovery
Order of inhalant uptake
Vaporizer > breathing circuit > alveoli > arterial blood > brain
Partial pressure in the brain is roughly equal to...
Partial pressure in the alveoli
Ways to increase partial pressure in the alveoli
1. Increase anesthetic delivery to alveoli
2. Decrease removal from the alveoli
Increased alveolar delivery
1. Increase inspired anesthetic concentration
2. Increase alveolar ventilation
How do you increase inspired anesthetic concentration?
1. Increase vaporizer setting
2. Increase fresh gas flow
3. Decrease breathing circuit volume
How do you increase alveolar ventilation?
1. Increase minute respiration
2. Decrease dead space ventilation
Decrease removal from alveoli
1. Decrease blood solubility of anesthetic
2. Decrease cardiac output
3. Decrease alveolar-venous anesthetic gradient
The higher the inspired pressure the more rapidly alveolar pressure approachs inspired pressure
As uptake into blood decreases, inspired pressure can...
A ____ inspired pressure is required at the beginning of gas anesthesia to quickly increase____
High, alveolar pressure
Requres decrease in alveolar concentraions
Anesthetic elimination is most effected by:
1. Anesthetic solubility
2. Alveolar ventilation
(same that effect alveolar concentration)
How do you quickly decrease alveolar concentration?
1. Turn off vaporizer
2. Disconnect patient and flush O2
3. Turn up O2 rate- dilutes the circuit
4. Increase ventilation (IPPV)- increase fresh gas to alveoli
Definition: Minimum Alveolar Concentration (MAC)
Minimum alveolar concentration of an anesthetic that prevents movement in 50% of patients exposed to noxious stimulus
Relationship between MAC and potency of an anesthetic
High MAC = low potency
T/F: Alveolar concentration is NOT the same as the vaporizer setting
How is MAC measured?
Percent of agent in expired gas