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96 Cards in this Set
- Front
- Back
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The ideal anesthesia will do what?
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induce anesthesia rapidly and smoothly
analgesic amnesia minimal cardiovascular side effects minimal resp depression rapid emergence antiemetic |
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How do barbiturates work?
Mechanism of action |
Enhance effects of GABA, the primary inhibitory NT in the CNS
GABA increases transmembrane chloride conductance of post-synaptic cell memebran Results in hyperpolarization of the post-synaptic membrane making it more difficult for cell the have action potential |
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What is the complex network of neurons responsible for the general state of wakefulness?
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The reticular activating system which is overall depressed by barbiturates
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What do barbiturates bind to thus inhibiting neurotransmission of excitatory neurotransmitter glutamate?
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ionotropic glutamate
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Do barbiturates sometimes have an antianalgesia effect?
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yes, increased reaction to a painful stimuli(hyperalgesia)
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What are the two barbiturates Tim discussed?
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Sodium Thiopental(pentothal)
Methohexital(brevital) |
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Which of the above two is most commonly used?
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Thiopental(pentothal)
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Which one of the two barbiturates has the shortest duration of action?
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Methohexital(brevital)
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When might Methohexital(brevital) be used?
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ECT
Cardioversion AICD check |
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Thiopental(pentothal) is as potents resp depressant, True of False?
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True, reduces the sensitivity of central resp center to CO2
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What is the induction dose of Sodium Thiopental(pentothal)?
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3-5mg/kg
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What is the induction dose for Methohexital(brivital)?
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1-2mg/kg
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Both agents produce unconsciousness within how long?
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30-60 seconds
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What terminates the action of these barbiturates?
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Redistribution
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When will a patient return to consciousness after admin of a barbiturate?
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5-15 minutes
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Sodium Thiopental and Methohexital are highly lipid soluble, True or False?
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True, and this is what we want with IV drugs
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After administration of a barbiturate what happens with the drug?
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Rapidly equilibrates with organs that receive a high percentage of cardiac output, ie: vessel rich group
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IV drugs go directly into systemic circulation, true or false?
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True
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What is the vessel rich group?
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heart
lungs liver kidneys brain spinal core |
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How do IV drugs diffuse?
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down concentration gradient
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Once in plasma: brain equilibration is reached, the drug will diffuse out of the brain (VRG) and redistribute where?
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to less vascular tissues including the muscle group (MG), fat group(FG) and vessel poor group (VPG)
**This is redistribution** |
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Explain why are barbiturates short acting?
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Because of the rapid redistribution of the drug away from the brain
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What is termination of action of the barbiturates a result of?
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Redistribution
(following a single dose) |
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After repeated barbiturate doses or an infusion what will be MORE responsible for the patient awakening from the drug?
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1/2 life or metabolism
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With repeated doses or infusion what groups become saturated?
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Muscle and fat groups
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After a SINGLE dose explain distribution...
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Highly perfused VRG starts to take up drug and drop our plasma concentration which is when patient now asleep
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(After a single dose)
As the drug is taken up by the MG and FG it is being pulled out of VRG and now what is happening? |
the patient is waking up
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Why is Methohexital an exception when is comes to barbiturates being potent anticonvulsants?
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It is a metholated barbiturate, by having the methel group on its structure it confers to it some CNS excitatory behavior and EEG can resemble seizures
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Cerebral and CNS effects of barbiturates are...
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Potent anticonvulsants
No amnesia Potent vasoConstrictors -decrease cerebral blood flow -decrease ICP -decrease CMRO2 |
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Back to distribution of barbiturates, repeated doses or infusion will begin to saturate MG and FG and what happens to the concentration gradient?
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becomes more equal and does not leave the CNS
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Barbiturates can cause a "hangover" effect and increased PONV compared to propofol, true or false?
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True
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Cardiovascular effects
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Decreased blood pressure secondary to peripheral vasodilitation and decreased venous return
Decrease preload Venous pooling Cardiac output maintained due to baroreceptor mediated reflex increase in heart rate Minimal to no depression of myocardial contractility |
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But...beware the patient who is already cardiovascularly compromised...
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hypovolemic
acidotic cardiomyopathy You may see exaggerated BP drops in these patients |
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Barbiturate effects on the resp system include..
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Decreased response to hypercarbia
Decrease response to hypoxia Inductin dose will usually produce apnea |
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Benzodiazepines Mechanism of Action
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Like barbiturates they facilitate GABA in the CNS
GABA is the principal inhibitor neurotransmitter --inhibits normal neuronal outflow |
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Name the commonly used agents
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Midazolam(Versed)
Diazepam(Valium) Lorazepam(Ativan) |
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Clinical uses for benzos...
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Sedation/anxiolysis prior to surgery
Component of conscious or deep sedation for MAC cases Rarely used for induction of GA Sedation for kids preop 0.5 mg/kg po 20 minutes prior induction but remember this could delay wakening |
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With benzos like barbs what is responsible for awakening after a single dose?
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redistribution
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What is the half-life for diazepam?
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30 hours
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Diazepam's principle metabolite is desmethyldiazepam and what is its half life?
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48-96 hours
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Where are all benzodiazepines biotransformed and excreted?
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Biotransformed in liver and excreted in urine
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What two different concentration does Midazolam (versed) come in and you should be cautious..
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1mg/ml
5mg/ml |
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Benzodiazepines are potents anticonvulsants true or false?
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True, as effective as barbiturates
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Provide anterograde amnesia..explain
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Patients are amnestic to events after you administer it
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Benzodiazepines are Cerebral vasocondtrictors so what will this do the the CNS?
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Reduce cerebral blood flow
Reduce ICP Reduce CMRO2 |
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Benzodiazepines have minimal CV effects true or false
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True
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Do benzodiazepines have specific antagonist?
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Yes
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What is the most popular med used for induction of GA?
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Propofol
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Can you do a pure propofol anesthesia?
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yes
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What is uniquie about propofol?
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oil in water emulsion containing glycerol, and egg lecithin(egg yoke)
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Just avoid propofol in patients with egg allergy, true or false?
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True
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Propofol can cause pain on injection, true or false?
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True, use some lidocaine
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Propofol supports bacterial growth so how long is it good for once drawn up?
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6 hours
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Propofol has great antiemetic properties
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True
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onset of propofol?
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30-60 seconds
Fast like sodium thiopental |
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Duration of action of propofol
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2-8 minutes
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How is awakening accomplished with propofol?
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redistribution
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If doing a propofol infusion you will have longer to awake time why?
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because now MG and FG have become saturated
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Propofol has inactive metabolites and where is it metabolized and excreted?
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liver, urine
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Inductin dose of propofol
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1-3mg/kg
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Maint infusion for GA
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50-200mcg/kg/min
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Difference between sedated and general anesthesia?
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Sedated-maintains own airway
GA-will lose airway, no longer able to protect their own airway |
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Propofol and cerebral/CNS effects
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Cerebral vasoconstriction
-decreased cerebral blood flow -decreased ICP -decreased CMRO2 |
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Propofol decreases CMRO2 more than decreases cerebral blood flow, what does this mean?
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good thing because we want balance of supply/demand and remains in the positive
Dont want to reduce supply more than demand-would be a bad thing |
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Propofol is...
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Anticonvulsant
No analgesia Similiar degree of amnesia compared to midazolam |
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Propofol will cause decreased blood pressure more pronounced than with any other agent, true or false?
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True
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Why does propofol do this?
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Decreased SVR-vasodilitation
Decreased myocardial contractility Can have profound bradycardia and asystole |
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What doe propofol do to resp system?
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Profound resp depressane
Decreased response to hypercarbia Decreased respons to hypoxia Airway obstruction is common!! |
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Etomidate(amidate) Mechanism of action
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Facilitates effect of GABA
Depresses reticular activating system |
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Clinical uses for Etomidate
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Induction of GA
Procedural sedation -cardioversion -AICD -Out of OR intubation |
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Etomidate dose for induction of GA
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0.2-0.4 mg/kg
Concentration: 2mg/ml |
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What is the incidence of myoclonic activity after admininstration of Etomidate?
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30-60%
Tims says more like 100% |
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Pain on administration of Etomidate
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Worse than with propofol
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Etomidate has increased incidence of PONV when compared with what?
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Barbiturates
Etomidate will most likely produce PONV |
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Etomidate induction dose causes adrenocortical suppression true of false?
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True
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How does awakening occur with Etomidate?
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Redistribution
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How is Etomidate excreted
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In the urine
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What is unique about Etomidate?
or as Tim would say the KEY differences |
NO anticonvulsant properties
Cardiovascular stability |
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What makes Ketamine(Ketalar) different from other drugs we have talked about?
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Dissociative anesthetic
NO GABA |
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Would Ketamine be considered a "complete" anesthetic and why?
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YES!!!
Provides profound analgesic and excellent amnesia |
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What is dosing for Ketamine?
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1-2mg/kg IV for induction of GA
3-4 mg/kg IM for induction/sedation |
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Ketamine is a structural analogue of phencyclidine which is like what popular drug from the 70's?
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PCP
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Why has Ketamine received a "bad wrap"?
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emergence delirium, hallucinations and nightmares during emergence
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How may the bad side effects of Ketamine emergence be avoided?
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give a drug like Versed
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Ketamine awakening is achieved how?
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Redistribution
Metabolized by liver, extreted by kidneys |
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What are cerebral and CNS effects of Ketamine?
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increased CBF
increased ICP increased CMRO2 (opposite of the other drugs we have discussed) |
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What effects does Ketamine have on the CV system?
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Does NOT depress
Increased MAP Increased Heart rate Increased C.O. Increased myocardial oxygen demand |
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From table 6.2 Circulatory effects of Ketamine what % of increase is seen in HR, MAP and cardiac index
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Heart rate +33
MAP +28 Cardiac index +29 |
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Dexmedetomidine(Precedex) dose
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Load dose 1mcg/kg over 10 min
Infusion 0.2-0.7mcg/kg/hr |
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What are common side effects of Dexmedetomidine?
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hypotension
bradycardia-sometimes profound |
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Dexmedetomidine mechanism of action
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Highly selective and potent alpha-2 agonist
Works centrally & peripherally Negative feedback loop peripherally Decreased SNS outflow from brainstem |
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What are 3 effects of Dexmedetomidine Tim mentioned in class?
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1. decrease BP and HR
2. analgesia 3. sedation/anxiolysis |
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How is sedation/anxiolysis accomplished with Dexmedetomidine?
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binds to alpha 2 receptors in locus ceruleus and causes hyperpolarization of neurons in this area and thus causes sedation/anxiolysis
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How is agalgesia accomplished with Dexmedetomidine?
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binds to alpha 2 recepotors in dorsal horn of spinal cord
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How is MAC affected when using Dexmedetomidine?
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linear decrease in anesthetics because it causes sedation and anxiolysis
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What kind of emergence will you see with Dexmedetomidine?
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calm
you can extubate on this drug, no resp depression |
