Pentothal/Brevital/Etom/Dex Flashcards
Intravenous Anesthetic Agent moa
It changes the level of consciousness (fast) by
depressing the reticular activating system
either by enhancing the inhibition
properties of GABA or inhibiting the NMDA
excitatory synapses.
What can be used as a TIVA when volatiles contraindicated?
IV anesthetic drugs
List 6 IV anesthetic agents that are APPROVED for GA
- propofol
- ketamine
- thiopental - pentathol
- methohexital
- etomidate
- benzos
What med is NOT approved for GA?
dextmetodine
Vessel-rich (brain, heart, liver, kidney,
endocrine) receives what % CO
75%
Lean muscle (muscle, skin) receives what % CO
19%
Fat receives what %
6%
vessel -poor (bone, ligament, cartilage)
0%
What is the primary mechanism for terminating central effects of IV induction agents?
redistribution from central compartment (brain) to the peripheral compartment (plasma/muscle)
describe the Redistribution – (alpha phase)
the plasma concentration of the drug has
declined to the point that the drug moves
out of the vessel-rich central group and is
then taken into the peripheral group
[termination of effect]
what is the Elimination – (beta phase)
involves metabolism and excretion
how long does it take for thiopental to reach equilibrium with skeletal muscles?
15 minutes
why do large or repeated doses of barbiturates produce a cumulative effect?
storage capacity of fat
What 4 things would make the ideal IV anesthetic (think effects)?
anticonvulsant
antiemetic
analgesic
amnestic
What is the only agent you can give ALONE as an anesthetic?
ketamine
Barbiturate – thiobarbiturate (sulfur)
Thiopental (Sodium
Pentothal)
what state accounts for bacteriostasis of pentothal?
alkaline - 2.5% sodium salt preparation is water-
soluble, but highly alkaline with a pH of
10.5
how long does pentathol last when reconstituted from powder form?
6 days at room temperature, 2 weeks
in refrig
what happens to pentathol if mixed with opioids,
catecholamines, and NMB, which are
more acidic in IV line?
significant precipitate forms. clear the line after giving
Is there pain upon injection of thipental?
no, unlike prop
MOA thiopental
Increases the duration of GABA activating its receptor
causing the chloride ion channels to remain open
longer, allowing increased influx, and causing the cell
membrane to be hyperpolarized and thus inhibited
thiopental Mimics GABA at its receptor to directly cause
chloride channels to open
what other receptors are activated with thiopen admin?
glutamate
adenosine
nACh
important concept to remember about GABA receptor?
multiple things can bind to it same time, so can have big synergism.
[ex: you give midazolam preop, wont have to give as much pentathol to induce]
cardiovascular effects of thiopental are overall…
minimal, compared to prop
Cards effect thiopental
transient decrease BP [rate of admin doesnt prevent]
increase HR
peripheral vasodilation
vasodilation of cutaneous and skeletal muscle blood vessels with admin thiopent can cause
heat loss and reduction in temp
what pt can thiopent be good for and why?
cards r/t arterial vasodilation
does thiopen cause histamine release?
yes and you will see greater drop in BP
thiopent Decreases the sensitivity of what to CO2?
medullary ventilatory center
how do respirations return with thiopent?
small TV and slow RR
what is interesting about resp reflexes with thiopent?
Reflexes remain intact with apnea, allowing
possibility of laryngospasm
what drug is recommended for insertion of LMA?
prop
how does thiopen effect CNS?
Decreases ICP by decreasing cerebral blood
volume and CMRO2 by 55% [best for cerebral protection]
explain what it means that demand
is less than supply in referring to cerebral protection with thiopen
The induced reduction in the cerebral
metabolic oxygen requirement is greater than
the decrease in cerebral blood flow
what types of cases are cerebral protection shown to be successful with pent?
Incomplete cerebral ischemia cases protection is successful. (CBP, hypotension,circ. arrest)
Global cerebral ischemia cases show no
protection. (cardiac arrest)
what does a dose 39.6 mg/kg of thiopent cause?
more use of inotropes due to a trash BP, found that hypothermia added same cerebral protection without problems
what weird syndrome can be exacerbated with thiop?
acute intermittent porphyria r/t the stimulation and increase in production of heme
can thiopen cross placenta?
yes, but 4 mg/kg is safe to give
what % is thiopen protein bound and what does that mean?
85% - only unbound drug is available to cross BBB and have effect, the more drug bound, the slower the diffusion rate of the drug
[lower dose in ppl low proteins]
what two patients do you decrease dose of thiopent?
elderly early pregnancy (7-13 weeks)
Barbiturate – oxybarbiturate – less lipid
soluble than thiopental
Methohexital (Brevital)
how long does methohex last once reconstituted?
6 weeks in refrig, unlike thio that lasts 2 weeks
MOA methohex
Increases the duration of GABA activating its receptor
causing the chloride ion channels to remain open
longer, allowing increased influx, and causing the cell
membrane to be hyperpolarized and thus inhibited
pethathol gives patients what type of effect after waking
hangover
compare metabolism of methohex and thiopen
Metabolism of methohexital occurs three
to four times faster than that of thiopental
due to the decreased lipid solubility,
which allows more methohexital to stay in
the plasma
the metabolism of methohex causes:
less hangover, rapid awakening, less accumulation
Disadvantage Methohexital
more excitatory activity –
myoclonus, hiccoughs (dd)
how to decrease excitatory activity of methohex?
opioids preop and dose of 1.0-1.5 mg/kg of methohexital
do NOT INFUSE - seizures
potency of methohex vs pentathol and why
More potent (2.5X) than thiopental due to higher % nonionized at blood pH of 7.4
does methohex cause histamine release?
no, thiopen does
CV effects methohex
similar to thiopental with
equivalent doses or maybe less
hypotension due to increase in HR is
better preserved
Chemically unrelated to any other IV anesthetic
Etomidate
etomidate contains a Carboxylated imidazole-containing compound which means
water-soluble at an acidic pH and lipid
soluble at physiologic pH
moa etomidate
mimics the inhibitory effects of
GABA by increasing the receptors affinity
to GABA; thus depresses the reticular
activating system
Unlike thiopental, etomidate has excitatory
activity to cause myoclonus in
30-60% of pts.
Myoclonus – 50-80% who don’t receive premedication ((fentanyl or benzo or sm dose of etomidate)
how does etomidate cause mycolonus?
disinhibition of subcortical structures that normally suppress extrapyramidal motor activity
Cardiovascular effects etomidate
[better than others]
15% decrease in MAP
minimal changes HR, SV, CO
decrease in svr
what patient is etomidate good for?
pts with poor left ventricle
Respiratory effects etomidate?
decreased TV, increased RR
less effect than barbs
when is etomidate advantageous
when spontaneous ventilation
is desired; apnea doesn’t always occur (however will become apneic when combined volatiles/opioids)
etomidate cns effects Similar to thiopental, but with a decrease of CMRO2 of
35-45%
who should you avoid etomidate with?
seizure patients
explain Adrenocortical suppression with etomidate
Causes an inhibition of the conversion of
cholesterol to cortisol (Inhibition of the
enzyme which performs 11-beta- enzyme reaction)
[decreased cortisol and aldosterone]
how long does adrenocortical supporession last with etomidate?
4-8 hours, up to 48 hrs
why is adrenocortical suppression significant with etom
Septic and bleeding patients need to have
appropriate stress response.
what enzyme is inhibited by etomidate
11-beta-hydroxylase
Metabolism etom compared to thiopen
by hepatic microsomal
enzymes and plasma esterases produces
clearance 5 times faster than thiopental
Alpha2-adrenergic agonist
Dexmedetomidine
Precedex
MOA dext
Hyperpolarization with efflux of K+
Reduced NE release due to presynaptic receptors
Decrease cAMP concentration by inhibiting adenylyl cyclase
what is key element of moa from anesth standpoint of dex?
neuronal hyperpolarization
dex causes Hypertension – r/t loading dose (don’t bolus) r/t
May have direct effect on alpha2B and
alpha2A receptors
Factors increasing risk of hypotension with dext?
High sympathetic tone
Diabetic, elderly, hypovolemic
Sedation and analgesia with little
depression of ventilation
Dexmedetomidine (Precedex)
whats cool about dext?
you can wean vent without titration, easily arousable
Dexmedetomidine (Precedex) Decreases MAC by
> 90%
Dexmedetomidine (Precedex) Approved for
infusions of 24 hours and
sedation cases
Alternative to ketamine for awake
fiberoptic intubations?
dext r/t antisialogue effects
dose of dext that decreased propofol infusion
and analgesia requirement
0.5 mcg/kg IV
how does dext Reduces shivering
inhibits central thermoregulatory control,
vasoconstriction – more susceptible to
hypothermia
Emergence delirium prophylaxis
dext
used as sedation
during surgery with subarachnoid block is
the main anesthetic and why
IV dexmedetomidine
No significant respiratory depression
Dependable, titratable intraoperative sedation
Wide safety margin
