Module 3 Flashcards
When discussing inhalational agents, what is the relationship between a higher blood/gas partition coefficient and its’ lipid solubility?
Higher lipophilicity
Involves both pharmacodynamic and kinetic factors.
Other factors such as co-morbidities play a role in dosing.
In GENERAL dosing should be reduced by 50-60%
Elderly Dosing
Administered via lungs
Kinetics are the same as for any drug
Other factors may come into play
Inhalation agents
Factors determining partial pressure gradiant necessary for establishment of anesthesia: Transfer of inhaled anesthetics from Anesthetic Machine to Alveoli
- Inspired partial pressure
- Alveolar ventilation
- Characteristics of anesthetic breathing system
Factors determining partial pressure gradiant necessary for establishment of anesthesia: Transfer of inhaled anesthetics from Alveoli to Arterial Blood
- Blood-gas partition coefficient
- Cardiac output
- Alveolar-to–venous partial pressure difference
Factors determining partial pressure gradiant necessary for establishment of anesthesia: Transfer of inhaled anesthetic from Arterial Blood to Brain
- Brain-blood partition coefficient
- Cerebral blood flow
- Arterial-to-venous partial pressure difference
When a gradient is established between your machine and the patient via the lungs, the lungs in turn…..
Equilibrates with the blood, which in turn will equilibrate with brain causing the desired effect
Most important factor in determining potency of inhalation agents
Blood-gas partition coefficient
Function of solubility of the agent in blood and is a measure of how quickly the inhalation anesthetic equilibrates between the lungs and blood and ultimately the target site in the brain
Blood-gas partition coefficient
Blood-gas partition coefficient is _________ proportional to induction rate, the higher the number the longer the induction and thus the longer the emergence
INVERSELY
In the case of inhalational agents, what is the relationship between a higher lipophilicity and agent potency?
Higher potency
With inhalational agents, the higher the blood/gas partition coefficient in the agent the _________ the solubility.
Higher
Inhalational agents with high solubility have _________ uptake/onset of anesthetic effect
Slower onset/uptake
A high blood/gas partition coefficient generally would mean a ________ MAC (Mean Alveolar Concentration).
Low MAC.
When considering the effects of inhalational agents on induction it is helpful to consider that what is happening in the lungs is likely happening in the _________.
Brain
A mnemonic that identifies inhaled anesthetics in order of highest blood/gas partition-lipophilicity-solubility- and therefore slowest uptake.
“HI-SE” (H-alothane, I-soflurane, Se-voflurane) Not included are Desflurane and N20, in that order.
Name inhaled anesthetics in order of fastest uptake.
N20, Desflurane, Sevoflurane, Isoflurane, Halothane (“HI-SE” in reverse)
In reference to the elimination rate with inhaled anesthetic agents, the higher the plasma drug concentration the _________ the rate of elimination is.
Faster
Inhaled anesthetic agents follow what type of pharmacokinetics?
First-order
Order of recovery times from inhaled anesthetics from fastest to slowest.
Desflurane-Sevoflurane-Isoflurane-Halothane. “HI-SE” in reverse. (inverse relationship between partition coefficient and uptake and recovery)
Increased cardiac output does what to the speed of induction?
Slows it down with all inhaled anesthetics.
How does hypothermia affect inudction with inhaled anesthetics?
Slows induction.
How does a high minute ventilation affect inhaled anesthesia induction?
Makes for a faster induction
What is the MAC and blood:gas coefficient for N20?
104%, 0.47
What is the MAC and blood:gas coefficient for Desflurane?
6%, 0.45
What is the MAC and blood:gas coefficient for Sevoflurane?
2%, 0.65
What is the MAC and blood:gas coefficient for Enflurane?
1.7%, 1.8
What is the MAC and blood:gas coefficient for Isoflurane?
1.4%, 1.4
What is the MAC and blood:gas coefficient for Halothane?
0.75%, 2.3
What is Pharmacodynamics?
the branch of pharmacology that studies the relationship between drug concentration at the site of action (receptor) and the resulting physiologic effect as well as any adverse effects
Defined as the biological and physiologic effect of a drug (what the drug does to the body).
Pharmacodynamics
A macromolecular complex which acts as the site of action for a drug. It is also a protein located on the cell surface that interacts with the cellular environment.
Receptor
The effective dose in 50% of the population.
ED50
The concentration (blood) at which an individual experiences 50% of the drug’s effect
EC50
An index for estimation of drug dosage which can treat disease effectively while staying within the safety range.
Therapeutic window (or pharmaceutical window)
What is the expression for Therapeutic Window
LD50/ED50