Induction Agents Flashcards
what is the pH of thiopental? Is it a good medium for bacteria?
10.5. No, too basic
How long is thiopental good for if it is in a refrigerator? Room temp?
indefinately if in the fridge. 7 days room temp
What are carbon 2 derivitives of thiopental useful for?
more useful as a sleep aid
What are carbon 5 derivatives of thiopental useful for?
anticonvulsant properties
Name 2 disadvantages of the high pH of thiopental?
burns when injected and when given with acidic drugs will form a precipitate. Therefore it may require a separate IV.
how is thiopental supplied?
anhydrous powder
what is the mechanism of action of thiopental?
Thiopnetal binds at the GABA site and at a distinct binding site at the GABAa receptor and increases the time the Choride channel is open.
Thiopental also decreases sympathetic transmission
Are barbituates lipid soluble?
Yes. High lipid solubility allows them to get into the brain quickly. UPtake in the brain takes place in 30 seconds
What percent of thiopentol is bound to protein in the blood stream.
80%
how long does redistribution of barbs take?
5-8 minutes
what is an IV induction dose of thiopental?
3-5 mg/kg (Jenn said she didn’t care if we know this number)
What is the onset and duration of thiopental?
onset: 30-40 seconds with a peak at 1 minute and duration of 5-8 minutes
Where is thiopental metabolized? Is this a fast or slow process?
metabolized relatively slowly by the liver. this can lead to the “hangover”
Does thiopental have active metabolites?
yes–pentobarbital
how is thiopental eliminated?
renal
Which is metabolized faster: thiopental or methohexital?
Methahexitol
What are the clinical uses of barbituates?
Induction of anesthesia and treatment of increased ICP
How do you calculate cerebral perfusion pressure?
MAP - ICP (CVP can be substituted for ICP if you don’t have an ICP monitor) normal value is 80-100 mm Hg
Which receives more blood flow white or gray matter?
Gray matter performs the cortical activity and receives 80% of the blood flow. White matter is more associated with structural integrity and receives 20% of blood flow
How much can the metabolism of the brain we suppress with anesthesia?
60% of the brain’s energy consumption is associated with electrophysiological function. This can be suppessed. The remaining 40% is for homeostatic functions and cannot be suppressed
how does a decrese in brain activity affect blood flow?
A decrease in brain activity will lead to a decrease in cerebral blood flow. An increase in brain activity will lead to an increase in blood flow.
Name 5 factors that can decrease cerebral blood blow
Anesthetic Drugs, temperature, PaCO2, PaO2, cerebral metabolic rate
At what temperature will the bare minimum O2 be consumed by the brain?
18C. Temperature can lead to lower oxygen consumption in the 40% of the brain that anesthetic drugs can’t
Which drug increases cerebral metabolic O2 requirements?
Ketamine
Does cerebral protection work for global ischemia?
NO. It is good for focal ischemia. Examples include corotid endarterectomy, thoracic aneurysm resection, and cerebral aneurysm clipping
What are cardiovascular side effects of thiopental?
Decrease SBP (vasodilation) with reflex tachycardia
how does thiopental cause heat loss?
Vasodilation
With a low does of thiopental, is laryngospasm possible?
yes
Why would you choose benzos over thiopental?
Benzos have a more specific action
Thiopental has a lower therapeutic index than benzos
Thiopental use results in tolerance than benzos
Besides how they compare to benzos what are reasons to avoid thiopental?
HANGOVER High risk for drug interactions High incidence of abuse Paradoxical excitement instead of sedation no skeletal muscle relaxation Acute intermittent porphyria
What is an absolute contraindication to thiopental?
Acute intermittent porphyria
What happens with prolonged infusions of thiopental?
Thiopental has a context sensitive half life and may take a long time to wake up when infusions are given over a long time
What is acute intermittent porphyria?
Deficiency in the ability to make heme due to a mutation in the porphobilogen deaminase enzyme. barbituates exacerbate this problem
What are the symptoms of porphyria?
abdominal pain urine retention or dark urine paresthesia proximal motor weakness Increased catecholamine anxiety, agitation, hysteria hyponatremia
Can you use benzos with acute intermittent porphyria?
Yes
Which is more lipid soluble: methohexital or pentothal?
Methohexital
What is the IV induction dose of Methohexital? Rectal?
1-1.5 mg/kg. 20-30 mg/kg
What is a common side effect of methohexital?
hiccups
what are the components of propofol?
1% propofol 10% soybean oil 2.25% glycerol 1.2% purified egg phosphatide 0.005% disodium edetate (preservative good for 6 hours)
Which component of propofol is responsible for bacterial growth? burning?
bacterial growth–soybean oil
burning–glycerol
how does propofol work?
decreases the rate of dissociation of GABA from the GABAa receptor, thereby increasing the duration of the GABA-activated opening of the chloride channels
What is the induction dose of Propofol?
1-2.5mg/kg IV
What is the onset and duration of propofol?
onset-30 second with a peak around 90-100 seconds. Duration is 5-10 minutes (dose dependent)
What is the distribution half life of propofol?
2-8 minutes
Where is propofol metabolized?
70% liver
30% lungs
HOw do renal and liver dysfunction affect the effects of propofol?
Doesn’t. propofol wears off due to redistribution
Does propofol cross the placenta?
Yes, but there are no ill effects on the baby
How should you change the dose of propofol for elderly patients?
Decrease. the decrease in SVR may be more dramatic
What are the effects of propofol on the brain?
decreased CMRO2 Decreased CBF Decreased ICP Amnestic EEG--burst suppression
Why do you have to use caution when using propofol for decreased CMRO2 or ICP?
Can also decrease MAP leading to a decreased Cerebral perfusion pressure. Oftentimes in this case propofol can be given with norepi
What are effects fo propofol on the pulmonary system?
RR and Vt,
Bronchodilation
Hypoxic pulmonary vasoconstriction left intact
What is hypoxic pulmonary vasoconstriction?
Physiologic function where pulmonary arteries constrict in areas of hypoxia, redirecting blood flow to areas of the lungs with higher oxygen concentration. Propofol does not affect this function.
What hapatic and renal effects does propofol have?
None. may turn urine green if used for long periods of time in ICU
What causes allergy in propofol?
it is likely due to the propofol molecule itself, not egg
Is propofol good for a mapping siezure activitiy?
no, may suppress this activity
What is an IV sedation dose of propofol?
25-100mcg/kg/min
What is a GA TIVA dose of propofol?
100-200mcg/kg/min
Why might you use a low dose of propofol as as an adjunct to a volatile anesthetic?
as an anti emetic
Why can you only use propofol for 3 days in ICU?
Lipids in propofol may lead to hyperlipidemia
Why should propofol be avoided in septic patients?
these patients already have a low BP and are vasodilated
Is etomidate lipid soluble?
It is water soluble at an acidic pH, but when you inject it, it becomes lipid soluble in the body
T or F. Etomidate is 45% glycerol
False. 35%
How does etomidate work?
GABA activation
Depresses the reticular activating system
T or F. Etomidate is a racemic mixture.
T
What is the onset and duration of Etomidate?
Onset 30 second, peak 1 minute
Duration 3-5 minutes
How much etomidate is protein bound?
75%
What is the elimination half time of Etomidate?
2.6 hours
how is etomidate metabolized and eliminated?
Etomidate is mainly metabolized by hydrolysis in the liver to an inactive metabolite.
It is eliminated mostly by the kidneys with a small portion in bile.
What effects does etomidate have on the CNS?
decreased CBF and CMRO2 (35-45%_
Similar EEG pattern to thiopentol, but with an increase in excitatory spikes on EEG (may decrease seizure threshold), use etomidate with caution in seizure patients
What are the CV effects of etomidate?
minimal CV response
How does etomidate effect ventilation?
No decrease in etomidate
What are the side effects of etomidate?
Pain Myoclonus Adrenocortical suppression--etomidate reversibly inhibits 11-beta hydroxylase, an enzyme in the important for steroid production. Cortisol levels can be decreased after only 1 dose. Hiccups Increased risk of PONV
What are the clinical uses of etomidate?
Cardiac challenge
Hypovolemia
Mask ventilation
What class of drug is Ketamine?
Phencyclidine
Where does ketamine work?
not on GABA
Works on NMDA, Opioid, MAO and muscarinic receptors
What is the onset and duration of ketamine?
Onest: IV: anesthetic effect 30 seconds IM anesthetic effect 3-4 minutes Duration: IV: 5-10 minutes IM: 12-25 minutes
What is the solubility and protein binding of ketamine?
high lipid solubility, with limited protein binding
What is the elimination time of ketamine?
2.5 hours by the kidneys
How is Ketamine metablolized?
by hepatic enzymes.
it has an active metabolite: norketamine–possibly give ketamine analgesic effect?
What are subanesthetic infusion rate ketamine?
0.1mg/kg/hour up to 0.5mg/kg/hour
What kind of pain is ketamine better for?
Somatic pain>visceral
What is an IV induction dose of ketamine?
1-2 mg/kg (30-60 seconds to loss of consciousness)
What is IM induction dose of ketamine?
4-8 mg/kg
How does ketamine affect the CNS?
ICP increases
CBF and CMRO2 increased
EEG increased
SSEP ok for monitoring
How does Ketamine affect ventilation?
NO ventilatory depression
Increased secretions (muscarinic)
decreased bronchomotor tone
Bronchodilator
How does ketamine cause its CV effects?
Impairs MAO leaving more catecholamines
What are the CV effects of ketamine?
Increases blood pressure (systolic>diastolic) Increases HR INcreases cardiac output Myocardial depressant may cause cardiac rhythm disturbances
What are factors that may increase the chance emergence delirium?
> 15 yo
girls>guys
prior use
psychiatric disorders
What prevents emergence delirium?
Benzos
