lecture 14 Flashcards
what is MAC
minimum alveolar concentration
the alveolar concentration of gas at which 50% of patients do not respond to a surgical stimulus
the MAC for NO is 1.04 atm or 104% - so patients would need to breathe pure NO for 50% of them to fail to respond to a surgical stimulus
a complete _ produces: unconsciousness unresponsiveness amnesia immobility autonomic stability
Diethyl ether is example but has drawback of being very flamable
anesthetic
modern general anesthesia tends toward using a combo of drugs, taking advantage of the best aspects of each
general anesthetics contain other drugs
_ minimize salivation, laryngospasm (block vagal stim) reflex bradycarda
antimuscarinics
general anesthetics contain other drugs
preop pain relief, sedation, amnesia, anxiety
various analgesics
general anesthetics contain other drugs
reduce anesthetic requirement, provide analgesia
NO and/or opioids
general anesthetics contain other drugs
paralyze skeletal muscle - not diaphragm
anti-nicotinics
there is a very strong correlation between solubility in olive oil and anestheic potency
anesthesia begins when the anesthetic reaches a critical concentration in membrane lipids
MOA of general anesthesia
membrane lipid based theories of anesthesia
direction action on lipids leads to indirect actions on proteins tickness, volume, curve, etc
General anesthetics block _ better than blocking axonal
Local - block axonal Na channels
synaptic transmission
block many different ligand activated ion channels
LA- voltage-gated
what sort of proteins are the likely targets of general anesthesia
GABA receptors - ligand activated ion channel
and non ligand gated CNS ion channels
big hyperpolarization receptor
bottom line - they interfere with the fxn of many proteins of neurochemical interest - definitive target unknown
GABA receptor is in neuronal membrane - Cl-
4 bindings sites for _ _ _ and one for GABA binding
ethanol
barbiturate
benzodiazepine
GA binds to proteins, _ is target
unknown target forsure
many proteins
are APs or synaptic transmission generally more sesitive to GA
synaptic transmission
pre and post have both been seen
Have to produce sedation but keep doing brain functions
Consciousness seems to be more affected than like the heart
Produces the sedation effect - but heart keeps going and organs keep fxn regularly
_ part of the brainstem - deals with consciousness and we block it with anesthesai - sedatio
Reticular activating formation
major center for consciousness and alertness
we are depressing its activity - unconsciousnes ensues
Neurophysiological mechanisms of GA
reicular formatuion is depressed
anesthetics exert _ effects on other structures, such as the thalamus/hippcampus
this loop essential to maintain conscious
direct effects
many believe the thalamocortical loop is essential to maintain conscoious
_ system affected by GA
involved in memory
anesthetic-induced amensia - can’t sense the lost of time - lost sense of tiem
limbic system
depth of GA
- analgesia (induction) - loss of pain sensation
- excitement
- surgical anesthesia - unconsciousness
- medullary paralysis - death
4 stages
we want state 3 as rapidly as possible
IV drug
Binds at the PCP site blocking NMDA- angle dust - cyclopine
Produces a different kind of anesthesia - called dissocaitive anesthesia - analgesia and amensia with minial resp effect
Quick
Might use with cardiac arrest patients, eldery, low BP very unstable hypotension
Some people have hard time coming out of the effects
ketamine
Barbiturate IV
similar to thiopental but 2.5x more potent, faster acting, shorter duration of action
sleep time 5-7 min
methoxhexital - barb
good for dentist
IV barbiturate
ultra short acting, induction phase
causes unconsiousnce 30sec-1min (60% to brain)
then distrubutes 5-10 min and come back
thiopental - truth serum 5-10min
replaced by propofol - also a barb
what class
single injection can induce anesthesia
also used as maintenance (total IV anesthesia)
respiratory depression major adverse effect
IV barbiturates
rapid distribution vein to brain
reduced cardiac depression - adverse affect
no risk of maligant hyperthemia
no risk of doctor exposure to volatile anesthetics
which class
act as CNS depressants
by potentiating the activitiy of the GABA-A
activating Cl channels (hyperpolarizing post synaptic membrane)-thus providing an inhib influence on synaptic channel
barbituates
pre and post synaptic
makes gaba work better
Barbs act by binding to GABA receptors - potentiate GABA make it work a little better
They are not inhibitors - they bind to the GABA receptors (inhib influece, have a postive effect on a negative receptor)
volatile anesthetics
we want low _ and low _
low MAC and low blood:gas coefficient
bloodgas - determines onset and revocery time
MAC - olive oil - little of drug to produce effect
NO has low bloodgas - induction and recovery fast, but high MAC - not potent, does not produce full surgical anesthesia
MOA
Volative
BARB
Ketamine
volative - unknown
BARB- potential GABA
ketamin - PCP dissociative anesthesia
