Lecture 5: Non-barbiturates Flashcards
What is the drug name of propofol? Where does that abbreviation come from?
Diprivan
2,6 diisopropynlphenol
In an aqueous solution, propofol is:
insoluble
What percentage of the white solution that you inject into your patient is actually propofol?
1%
Mechanism of action for propofol?
It works similarly to barbiturates; it decreases dissociation of GABA to its receptor, so keeps Cl- channels open to hyperpolarize cell and decrease neurotransmission.
Distribution half-life of propofol?
2-8 minutes
Why must you stop propofol infusions after three days?
Lipids build up in circulation to cause hyperlipidemia
Why can propofol cause green urine?
Thiol ring
Why don’t patients wake up feeling hungover on propofol like they do on thiopental?
The half life of propofol is so short, meaning that by the time the drug as redistributed in the tissues, prompting the patient to wake up, the vast majority of the drug has already been excreted from the body.
Although propofol is principally metabolized by the liver, what proportion of a dose is metabolized in the lung via first-pass metabolism?
30%
Why do patients wake up so quickly on propofol?
Redistribution to tissues with no GABA receptors
How should you adjust your propofol doses in patients with liver or kidney failure?
No need to adjust; effect is redistribution-dependent, not metabolism-dependent
How much less propofol do elderly patients require? Why?
25-50% less because they have a smaller central distribution volume and decreased clearance
Does propofol have any effect on the fetus of a pregnant mother?
While propofol does cross the placenta, it doesn’t have any effect on the fetus d/t its mechanism of metabolism.
Ideally, propofol induces a decrease in CBF and CMRO2, but it doesn’t affect ICP. However, at what point are we concerned propofol’s effect on ICP?
If ICP increases too high, our brains will compensate by decreasing CBF and decreasing MAP; therefore, there will be a decrease in CPP.
What is an appropriate dose for a GA TIVA? How can we ensure that TIVA level is sufficient
100-200 mcg/kg/min
Use a BIS to ensure sufficiency
What are some less common uses of propofol?
1) Antiemetic effect
2) Antipruritic effect
3) Anticonvulsant effect
4) Attenuation of bronchoconstriction
In what way does proprofol have an anticonvulsant effect?
It decreases dissociation of GABA, an inhibitory neurotransmitter–therefore, it decreases excitatory activity that brings about seizures
Etomidate is like midazolam in solution in that:
it is water soluble, but when it sees physiological pH, it becomes lipid soluble
Why is etomidate so painful upon injection?
Its composition is 35% glycerol–burns when it hits the blood.
How much more glycerol does etomidate contain than propofol?
17x more in etomidate than in propofol
Of the racemic mixture that etomidate exists as, how many isomers are active?
Only one
What is the reticular activating system and how does etomidate affect it?
It’s the part of the brainstem that mediates awareness, and etomidate suppresses it, causing you to go to sleep.
In addition to affecting the RAS, etomidate also works on:
GABA and GABA receptors
Onset, peak, and duration of etomidate?
Onset: 30 sec
Peak: 1 minute
Duration: 3-5 minutes
What proportion of etomidate will be bound to protein within the body?
78%
What is the half-life of etomidate?
2.6 hours
What type of metabolism does etomidate undergo? Where? By what enzymes?
Hydrolysis in the liver by plasma esterase and cyt P450
How is etomidate eliminated?
Via the kidneys
By what percent does etomidate decrease CBF and CMRO2?
35-45%
Why do we not use etomidate on seizure patients while we are mapping seizures out?
Etomidate causes excitatory spikes in EEG that resemble those that a seizure would produce. May ruin data.
What do we mean when we claim that etomidate is cardiovascular stable?
We mean that it produces minimal cardiovascular effects; while there are still effects, they are not nearly as severe as those of propofol.
Does etomidate suppress ventilation?
Yes.
Which induction drug produces myoclonus? What is myoclonus?
Etomidate; myoclonus is brief, involuntary twitching of a muscle or a group of muscles–larger movement than fasiculations
By what mechanism does etomidate suppress adrenocortical activity?
It inhibits 11-beta hydroxylase enzyme, which is integral to corticoid synthesis
How many doses of etomidate required to suppress adrenocortical activity?
One dose
Why is etomidate a good choice for septic patients?
They are already so vasodilated that propofol would only potentiate the cardiovascular issues they have.
Which induction drug is a derivative of PCP?
Ketamine
What class of drug is ketamine?
Phencylclidine
What receptors are ketamine’s main targets?
1) NMDA
2) Opioid receptors (analgesic effect)
3) MAO
4) Muscarinic (causes salivation)
How do we avoid emergence delirium in our patients who receive ketamine?
Administer a sub-anesthetic dose and use in conjunction with other drugs, like propofol
What kind of receptor is an NMDA receptor? How does ketamine affect it?
NMDA receptor = glutamate receptor
Ketamine prevents receptor from binding to glutamate.
Which induction agent is most beneficial in post-thoracotomy phase?
Ketamine
Unlike all other induction drugs, ketamine does not:
act on GABA receptors
Ketamine inhibits MAO, which causes:
increased levels of serotonin and dopamine in the brain.
Onset and duration of IV ketamine?
Onset: 30 seconds
Duration: 5 - 10 minutes
Onset and duration of IM ketamine?
Onset: 3 - 4 minutes
Duration: 12 - 25 minutes
Elimination time of ketamine:
2.5 hours
Where is ketamine metabolized? By?
In the liver by cyt P450
What is the metabolite of ketamine? Active or inactive?
Norketamine; active
How is ketamine eliminated from the body?
Renal
How does low-dose ketamine affect somatic vs. visceral receptors?
Why the difference?
While low-dose ketamine seems to relieve both pain and intensity in visercal receptors (located in thorax, abdomen, etc.), it seems to only alleviate pain–not intensity–in somatic areas of the body (musculoskeletal areas). This is likely because NMDA receptors play different roles in these tissues.
How does low-dose ketamine compare to morphine in epidural/spinal situations?
10,000x less potent than morphine
When used for epidurals and spinals, what receptors does ketamine target?
Mu receptors
How long does it take for a patient to lose consciousness with IV ketamine?
What about IM?
IV ketamine: 30 seconds
IM ketamine: 2-4 minutes
What is ketamine’s effect on CMRO2 and CBF?
Increases them both
What is ketamine’s effect on ICP?
Increases ICP
In terms of EEG, what effect does ketamine produce?
Excitatory
What induction drug can be used for somatosensory evoked potential (SSEP) monitoring?
ketamine
In what way does ketamine increase secretions?
Increases activity of salivary and tracheobronchial mucus glands
Ketamine can have antagonistic effects on muscarinic receptors. How does this effect blood pressure, heart rate, and cardiac output?
It increases them
Why shouldn’t you use ketamine unopposed in a bad heart?
It is a myocardial depressant
How do you prevent emergence delirium in patients?
Use benzos w/ ketamine
Who are most likely to develop emergence delirium?
1) Kids
2) Women
3) Pyschiatric patients
In what patients would ketamine be a good choice?
1) Children
2) Asthmatics
3) Patients w/ chronic pain
In what patients would ketamine be a poor choice?
1) Patients w/ increased ICP
2) Patients w/ increased IOP
3) Patients w/ ischemic heart disease (as sole agent)
4) Patients w/ vascular aneurysm
5) Psychotic patients
What percent of a dose of ketamine is bound to protein?
27%
Duration of ketamine?
10-15 min
Duration of propofol?
4-8 min
Duration of etomidate?
4-8 min
What class of drug is dexmedetomidine?
short-acting alpha-2 agonist (sympathomimetic)
Which non-barbiturate possesses anxiolytic, anesthetic, analgesic, and hypnotic properties?
Dexmedetomidine
Why isn’t dexmedetomidine often used for MACs?
Slow onset
Bolus dose of dexmedetomidine?
1 mcg/kg over 10 minutes
Why must we dose slowly when dosing dexmedetomidine?
Can cause bradycardia and hypotension
What is the infusion rate of dexmedetomidine?
0.2 - 0.7 mcg/kg/hr
If patient presents with Addison’s disease, which non-barbiturate is contraindicated?
Etomidate b/c patient already has low levels of steroids
