General anesthetics Flashcards
(56 cards)
What is MAC?
This is the minimum alveolar conc. that prevents movement in response to surgical stimulation in 50% of subjects
- it is an indicator of gas potency
- indicated by how lipophillic it is as well as how fast the mechanism of action works in the brain
- Faster mechanism of action and high lipophillicy would have the lowest MAC and considered the most potent drug!
Would a smaller MAC be more lipophilic or less?
More lipophilic
What does 1.04 MAC mean?
It means you need 104% of the drug in the body to get it to knock you out. Thus you would need another drug to get you knocked out.
What are the 5 general effects of GA?
Amnesia
SKM relaxation
inhibition of autonomic reflexes
Analgesia
Unconsciousness
- none of the currently available GA’s can cause all 5 and only 5 alone.
- we rely on IV and inhaled drugs- a balance between to the two
What is an ideal drug?
rapid, smooth loss of consciousness, rapidly reversible upon discontinuation and a wide margin of safety (LARGE Therapeutic index)
What is conscious sedation?
Drug induced alleviation of anxiety and pain and….
smaller doses of sedative medication (altered level of consciousness)
- patient will maintain patent airway and is responsive to verbal commands
Name some common drugs that can cause conscious sedation?
Diazepam Midazolam Propofol Benzos and opioids - benefit is there are rapidly reversible
What drug would you use to reverse opioids?
Naloxone
What drug would you give to reverse benzos?
Flumazenil
What is deep sedation?
Similar to light state general anesthesia
- There is a gray medium between deep sedation and GA
- may be even indistinguishable from GA
What are two ways which GA works?
- Enhance inhibitory activity
2. inhibition of excitatory activity
How does GA target and act on enhancing inhibitory activity?
- Either through chloride channels
- pump Cl- into cell to make it stay at resting membrane potential
- do so through GABAa and glycine - or through K+ channels
- Postsynaptically it hyper-polarizes
- pre it hyperpolarizes and thus no NT’s are released
How does GA target and act on inhibition of excitatory activity?
- inhibits release of glutamate via AMPA and NMDA
- how ketamine and NO works - via Nicotinic and muscarinic receptors
- through ACh
- nicotine can modulate amnesia and analgesia
What are the volatile anesthetics?
Halothane, enflurane, isoflurane, desflurane and sevoflurane
- low VP and high BP
What are the gaseous anethetics?
NO
- high VP and low BP
What are the factors controlling uptake of inhaled anesthetics?
- Inspired conc and ventilation
- Solubility
- Alveolar-venous partial pressure difference
What 2 parameters determine how quickly the alveolar conc changes?
- inspired conc or partial pressure (how much is given)
2. Alveolar ventilation (how big the breath is)
What is the partial pressure alveoli ratio?
Alveolar conc (FA)/(FI) inspired conc. - significance being that the closer this number is the one the faster anesthesia will occur during inhaled induction
What is the partioning coefficient?
Blood:gas (Otsward coefficient)
- basically how fast the drug can pass from the gas of lungs to the blood
- the higher solubility in the blood would indicated a higher B:G ratio and would cross the blood/gas barrier easier.
How would you compare solubility to B:G to FA/FI?
The higher the solubility the faster it crosses the B:G barrier and the greater number of B:G
- This means it will take longer to reach FA/FI to reach equilibrium because so much is lost to the blood right away.
- So higher solubility means higher B:G and means longer time to reach high conc. in the blood and the anesthetic agent is the brain can rise no faster than it does in the blood.
- Lower B:G thus means faster onset of anesthetics
What does a B:G of 1.7 mean?
Means that at equilibrium there is 1.7x more drugs in the blood than in the gas. Since B:G is high its soluble and would take longer to have its effects.
What is henry’s law?
Number of gas molecules that enter a liquid equilibrium is reached is determined by the solubility of the gas in the liquid.
- as pressure decreases the amount of gas dissolved in a liquid decreases
What is the alveolar venous partial pressure difference?
Dependent mainly on the uptake of the anesthetic by the tissues, even non neuronal tissues
- influences by tissue:blood coefficients
How does tissue:blood coefficient affect induction of anesthesia?
The more soluble the drug is in tissues, the highly perfused tissues will take that drug and will have less venous partial pressure of the drug.
- thus the longer it will take to reach FA/FI
