Anesthetic Pharmacology 2 Flashcards
Pharmacokinetics of inahlation
Absoprtion phase - uptake
Metabolic - biotransformation
Excretion - elmination
NO and xenon are true gases but all others are vapors of volatile liquids
Volatile anesthetics
Exist in liquid form in ambient pressure and temp
Vapor pressure
If system is in closed container, will equilibrate between liquid and gas phases
Boiling point
Point at which VP exceeds atmospheric temp
How is anesthetic effect acheieved
Deliver a specific PP of agent to the brain
All phases are minimal relative to rate at which delivered or removed from the lungs
INhaled anesthetics transferred
From lungs to blood to brain…all pressures will equilibrate
Anesthetic inhalation…how do we control
Plasma and tissues havbe low capacity to absorb the inhaled relative to amount we can deliver to lungs…allows use ot rapidly change concentration in BS and brain
Anesthetic uptake
Rate of rise of partial pressure of the inhalational agfent at the alveolus (Fa/Fi) correlates best with onset
Blood gas sloubility best used to describe the speed of onset
Low blood gas solubility causes a fadster rise in Fa/Fi and induces faster anesthesia
Low, medium and high solubility
Low - desflurane, sevoflurane
Med - isoflurane
High - halothane
If you want to increase speed of induction
CHoose low solubility agent
Increase inspired ocncentration
Increase minute ventilation (hyperventilation)
How to induce a child
Mix sevoflurane and N2)
Turn dials to maximum
Crying baby helps speed up
Anesthesia termination
Biotransformation plays little role in termination of anesthesia
Halothane is major exception and up to 20% is biotransforemd in liver
Effects are primarily terminated by excretion (nearly exclusively throug hthe lungs)
Wakeup occurs when
PP of volatile agents drops below MAC(awake)
Depot
Amount of anesthetic abosrbed in fat once the vaporizer has been turned off and inspired concentration drops
Speedy wake up
Choose low blood/gas solubility agent
Low fat solubility
Increase minute ventilation
MAC
Minimuum alveolar concentation
Analogous to ED50 for an IV drug
Alveolar conetration at one atmosphere that prevents movement in response to a surgical stimulus in 50% of patients
MAC is a measure of
Potnecy
Halothane Isoflurane Sevoflurane Desflurane N2O
MAC aware
MAC awake
MACBAR
.4XMAC
.25XAMC
1.5XMAC
Most anesthesiologists use
1.3-1.4 MAC (MAC95%)
MAC values are additivie
Increase MAC
NT levels (cocaine, MAOI, meth, ephdrine, lveodopa)
Hyperthermia
Chronic EtOH abuse
Hypernatremia
Factors that decrease MAC
Age EtOH intoxication Hypothermiaa/thyrodism/tnesion/oxia Pregnancy Opiodis
N2O
Very low potency
MAC greater than atmospheric pressure
Very rapid
Could cause megaloblastic anemia
Methionine synthase inhibition
Reduced homocysteine production
N2O rapidly discojntinued
iffusion hypoxia
Rapid elmination reduces amount of oxygen in alveolus
Desaturation during awakening
Desflurane
Fluorinated mehtyl ethyl ether
Very low B/G solubility (rapid onset)
Very low fat solubility (rapid elimination)
Very high VP (specialy designed vaporizer)
Desflurane side effects
Small of immune-mediated hepatotoxicity
Some tachycardia and hypertension
Sevoflurane
Methyl isopropyl ether
Low blood/gas solubility (fast onset)
Sweet smelling (good for mask induction)
Sevoflurane biotransformation and side effect
Release of inorganic fluoride ions and compound A which may lead to kidney injury
Also with heat generating reaction in certain situations
Isoflurane
High potency
Intermediate blood gas solubility
Stable for long periods of time
Smells bad
Halothane
Not avbailbale in US
Malignant hyperthermia
Severe and sustained muscular contractions
Auto dom
Avoid triggering agents
Tx with dantrolene and aggressive ocoling
