CNS NTs Flashcards
Anatomy for Glutamate:
Relay neurons all levels and some inter neurons
What are the receptors for Glutamate?
NMDA
AMPA
Kainate
Metabotropic
What is the mechanism for NMDA (glutamate)?
Excitatory: increase cation conductance (Ca)
What is the mechanism for AMPA (glutamate)?
Excitatory: increase cation conductance
What is the mechanism for Kainate (glutamate)?
Excitatory: increase cation conductance
What is the mechanism for metabotropic (glutamate)?
Inhibitory of presynaptic: decrease Ca and cAMP
Excitatory: decrease K and increase IP3 and DAG
What is the anatomy for glycine?
Spinal interneurons and some brainstem interneurons
What is the receptor for glycine?
Glycine
What is the mechanism for glycine?
Inhibitory: increase Cl
What is the anatomy for GABA?
Supraspinal and spinal interneurons pre and post synaptic
What are the receptors for GABA?
GABAa
GABAb
What is the mechanism for GABAa?
Inhibitory: increase Cl
What is the mechanism for GABAb?
Inhibitory in presynaptic: decrease Ca
Inhibitory in postsynaptic: increase K
What anesthetics use the receptor GABAa?
Barbiturates (enhance) Propofol (enhance) Etomidate (enhance) Benzodiazepine (enhance) Inhaled agents (enhance)
What anesthetics use the receptor glycine?
Barbiturates (enhance)
Propofol (enhance)
Etomidate (enhance)
Benzodiazepine (enhance)
What anesthetics use the receptor NMDA?
Ketamine (inhibit) Inhaled agents (N20) (inhibit)
What anesthetics use the receptor nACh?
Barbiturates (inhibit)
Ketamine (inhibit)
What anesthetics use the receptor K+ channels?
Inhaled agents (enhance)
Calming and drowsiness, decreases activity, moderates excitement, calms patient
Sedation
Produces drowsiness and facilitates the onset and maintenance of a state of sleep
Hypnosis
Global but reversible CNS depression resulting in loss of response to and perception of external stimuli “deafferentation”
Not all agents produce identical state
Collection of changes in behavior and perception – anesthetic state is:
•Amnesia
•Immobility to noxious stimuli
•Attenuation of autonomic response to noxious stimuli
•Analgesia
•Unconsciousness
Anesthesia
Potential other effects of drugs?
Amnesia Analgesia Anticonvulsant Muscle Relaxation Respiratory Depression
What are the different drug classes (6)?
Benzodiazepines Non-bz sedative hypnotic drugs (z drugs) Barbiturates Melatonin Congeners IV Anesthetics Inhaled Anesthetics
What is the triad of GA?
Unconsciousness
Analgesia
Muscle Relaxation
What can IV agents be used for (5)?
Sedation-based anesthesia
Monitored anesthesia care (regional or local + sedation)
Conscious sedation (small doses used to alleviate anxiety)
Deep sedation
Light state of GA
What comes with light state of GA?
Loss of protective reflexes
Inability to maintain patent airway
Lack responsiveness to surgical stimuli
IV Anesthetics characteristics of each agent (7)
Induction Analgesia Sedation/antianxiety Hypnosis Amnesia Muscle Relaxation Anesthesia
Non-anesthesia drugs side effects of induction (5)
Apnea CV Hiccups Movement Pain - site of injection
Non-anesthesia drugs side effects of recovery (3)
Nausea
Vomiting
Restlessness
What is GABA?
Inhibitory CNS NTs
What kind of structure is GABAa receptor?
Pentameric with subunits alpha, beta, and gamma
What subunits of GABA is major isoform?
2 alpha1
2 beta2
1 gamma2
Where is the binding site for GABA?
Between alpha1 and beta2
Where is the binding site for BZ?
Between alpha1 and gamma2
What else is barbiturates known as?
Methohexital (brevital)
Thiopental (pentothal) and Thiamylal are no longer in US
Mechanism of action for barbiturates?
Enhance GABA (Cl) Increase duration of GABA -High doses activate Cl and depress glutamate binding to AMPa receptor
What do barbiturates substitutions affect?
Hypnotic potency and anticonvulsant activity
What activity does phenobarbital affect?
Anti-convulsive
What is thiopental, thiamylal activity?
Greater potency
More rapid onset
Shorter duration fo action compared to pentobarbital
How are barbiturates absorbed?
IV
Rectally in peds
What kind of distribution are barbiturates?
High lipid solubility
How fast does plasma:brain equilibrium occur in barbiturates?
Rapidly, onset within 30 sec
How is barbiturates diffusion to other tissues limits duration of induction?
Waken in about 20min
How do you dose elders with barbiturates?
Reduce induction does due to slower redistribution and longer duration of action
How is repeated doses (or continuous infusion) affected with barbiturate?
Saturate peripheral compartments and minimize the redistribution effect (increasing duration of action)
Does continuous infusion prolong the half life?
Yes
How should barbiturates be mixed with other solutions?
Alkaline solution to make soluble
What happens with barbiturates when mixed with drugs that are weak bases (rocuronium, lidocaine, labetalol, morphine)?
Precipitation
Barbiturate Pharmacodynamics to CNS (5)?
Onset 10-20sec; bolus lasts about 8-20min (half life 3-12hr)
Constrict cerebral vasculature (decrease CBF and ICP)
Decrease cerebral oxygen
Potent antibonvulsant (phenobarbital)
Lower pain threshold (hyperalgesic effect)
Involuntary muscle movements (excitatory with induction (methohexital))
Barbiturate Pharmacodynamics to CV (5)?
Peripheral vasodilation (small decrease in BP)
Negative inotropic effects
Venous vasodilation (peripheral pooling, decrease preload (CO&BP))
Vagolytic compensatory responses (HR&contractility)
Caution in patients without adequate baroreceptor responses (decrease BP&CO) (hypovolemia, beta blocker, CHF)
Barbiturate Pharmacodynamics to respiratory (3)?
Depression (medullary center, decrease response to CO2&O2)
Don’t completely suppress airway reflexes (muscarinic nerve stimulation-atropine and thiopental to avoid bronchospasm
Apnea, bronchospasm (asthma), hiccup, laryngospasm
Barbiturate Pharmacodynamics to histamine release?
May cause hypotension, tachycardia
Caution in asthma patient
Rare allergic reactions
Does barbiturates have muscle relaxation?
No
Additional info about Barbiturate Pharmacodynamics?
Pain on injection
No analgesia
Renal/hepatic - no short term toxicities
Contraindicated in acute intermittent porphyria
What is porphyria?
Neurological disease cause by inadequate porphyria metabolism
-rate limiting step in haem synthesis (ALA synthetase)
What is porphyrins?
Highly reactive oxidants
Cause toxic neurological sequelae
What drug is barbiturates being replaced by?
Propofol
Thiopental (4)
Primary use was in induction
Used alone for short procedure with no pain
Promote sleep for local anesthesia
Critical care uses: ICU sedation, increased ICP, epileptic
When is methohexital used?
For ECT or epilepsy-related surgical procedures
What interactions should be considered for dose reduction in barbiturate?
Combo with opioid
alpha2 adrenergic agonist
Benzodiazepine
Acute ethanol
What patients should be considered for dose reductions with barbiturate?
Anemia Low protein Decreased CO Shock Elderly
What drugs are under benzodiazepines (BZ)?
Diazepam
Lorazepam
Midazolam
BZ mechanism of action (5):
Interaction with GABA (inhibitory, Cl)
GABA inhibition at all levels (spinal cord to cerebral cortex)
Increase efficiency of GABA by increasing frequency of Cl challenge openings
Do NOT substitute for GABA, must be present
Do NOT directly activate GABA receptor (bind to BZ receptor)
What is BZ’s receptor competitive antagonist?
Flumazenil
What structure is BZ?
Heterocyclic ring with varied substituents that impact potency and metabolism (diazepine ring)
What does BZ water solubility affect?
Parent earl preparations
What does BZ lipid solubility impact?
CNS onset
What are the kinds of formulations for BZ?
P.O., IM, IV administration
How long is diazepam and lorazepam P0 onset?
1-2 hr
What is midazolam for PO administration?
Syrup
What kind of absorption do you get from IM diazepam?
Painful and erratic
What kind of absorption do you get with IM lorazepam and midazolam?
Well absorbed and peak in 90min (lorazepam) and 30min (midazolam)
What is the only IV BZ for induction and how is its onset?
Midazolam and among BZ shortest onset (but still longer compared to other classes of agents)
-diazepam and others can be given IV but not used for induction due to delayed onset
BZ lipid solubility distribution from highest to lowest:
M > D > L
Distribution of BZ to brain - time to onset highest to lowest:
L > D > M
- L slowest CNS uptake and onset
- BZ have slower onset for induction vs propofol