Flashcards in Pharm- 16 Deck (68)
What is P(CNS)?
CNS Partial pressure --> the level of the anesthetic in the CNS
Can you measure P(CNS) directly?
So how can you measure P(CNS)?
What is P(Alv)?
The partial pressure of the anesthetic in the lungs. basically the balance between the anesthetic delivered to the alveoli and the loss from the lungs (to blood + tissues)
So how does anesthetic get into the tissues from the alveoli space (generally)?
down a concentration gradient cuz theres a crap ton in the alvoli and nothing in the tissues
And how does the anesthetic get out of the tissues and back into the lungs?
remove the anesthetic from the lungs --> moves down its concentration gradient back ot to the lung space
WHat is the minimum alveolar concentration (MAC)?
It's the P(alv) that results in the lightest possible anesthesia. basically the point in which anesthesia is induced.
True or false: a lower MAC means an lower potency of anesthesia.
FALSE. lower MAC = higher potency. takes less partial pressure to cause anesthesia.
What is AP50?
the partial pressure where analgesia (no pain) results in 50% of pts
Define: this is the partial pressure where movement is lost in 50% of pts when cut during surgery
What is the analgesic index?
Ratio of MAC to AP50
If there is an increase in analgesic index, is there an increase or decrease in the partial pressure of anesthetic needed to gain anesthesia than that required for surgical anesthesia?
What is the therapeutic index?
(MAC is the same as the ED50 for nongaseous things)
Do you want the therapeutic index to be high or low? Why?
High because you want a high LD50 (only kills pts at a very high conc) and you want a low MAC (drug works at a lower conc)
What is the danger of some analgesics which have a lot therapeutic index?
Respiratory depression + cardiac arrest
Why must the dosing must be very accurate for analgesics?
There are no antagonists to their actions. To get rid of it if you OD you just need time and ventilation lol. Call an MD.
What exactly is the LD50?
lethal dose in 50% of subjects
What is the ED50/MAC?
the effective dose that gives desired effect in 50% of pt
What is the meyer overton rule?
Greater the lipid solubility (greater oil/gas coefficient) of anesthetic in olive oil = greater its potency
What is the oil/gas partition coefficient good at showing?
predictor of how soluble an anesthetic is in olive oil- essentially defines the potency (larger coefficient = more soluble = more potent).
What is the solvent/gas partition coefficent good at predicting?
predictor of how soluble an anesthetic is in a solvent (blood and plasma). High coefficient = more soluble
What is the diffusion of the anesthetic dependent on?
this is proportional to the tissue area as well as the partial pressure difference between the alveoli and the capillary beds
What is the role of perfusion of the anesthetic?
capillary beds then deliver the O2 + anesthesia to cells in body. THIS IS THE RATE LIMITING STEP.
What is the anesthetic flow rate?
the rate at which the blood perfuses the tissue and anesthetic reaches tissue
Why do you need do some changes for a fat person vs a muscular person as far as dosages of anesthetics?
i. Fat pt is going to have a lot of volume (fat) therefore he will store a more lipid soluble anesthetic MUCH more than a muscular patient.
ii. This means that the anesthetic will affect him much more as well as he will be MUCH slower to recovery and for the anesthetic to leave his body
What is the time constant for anesthetics?
If you increase the flow rate, you will decrease the time it takes to equilibrate between blood and tissue (faster) and vice versa
How well are anesthetics delivered to well-rich groups?
• CNS + visceral organs
• Low capacity for anesthetic + high blood flow for delivery
How well are anesthetics delivered to muscle groups?
• Muscle + skin
• High capacity + moderate blood flow = longer equilibrium time
How well are anesthetics delivered to fat groups?
• High capacity for anesthetic + low flow for delivery = extremely long equilibrium time