Central Nervous System

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XQWCat
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Central Nervous System
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2013-12-01 00:00:42
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Agents acting on the Central Nervous System in VETC 220
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  1. types of CNS agents (general)
    • tranquilizers (sedative-hypnotic)
    • anesthetic
    • analgesic
    • Primarily decrease CNS activity.
  2. Sedative
    • depresses CNS
    • decrease motor activity
    • calm, quiet, unconcerned with surroundings
  3. Hypnotic agent
    • depresses CNS
    • produces drowsiness
    • facilitates onset and maintenance of sleep
  4. tranquilizer
    • older term
    • produces tranquil and calm feeling.  
    • Depresses CNS
  5. Major tranquiliers (sedative-hypnotic agents)
    • strong, inital sedative-hypnotic effects.  
    • Phenothiazine derivatives.  
    • Acetylpromazine/acepromazine (alpha 1 blocker, causing vasodilation and hypotension)
    • Blocks dopamine receptors in brain
  6. acetylpromazine (acepromazine)
    • sedative-hypnotic agent (tranquilizer), neuroleptic
    • depresses CNS
    • Phenothiazine derivative
    • alpha 1 blocker causing vasodilation and hypotension
    • Antiemetic due to blocking dopamine at CTZ
  7. neuroleptic
    • produces sedative effect by depressing brian stem and connections to brain.  
    • Does not effect coordinated motor activity so animal can be roused
    • Acepromazine (acetylpromazine)
  8. acepromazine contraindications
    • hypovolumia
    • hypotension
    • history of seizures
    • Stallions
  9. Effects of acepromazine
    • mild histamine receptor block (antipuritic)
    • mild muscarinic receptor block (antichoinergic, possible constipation)
    • NO analgesic
  10. adverse effects of acepromazine
    • protrusion of penis in large animals, can last 2 hours or lead to swelling and paralysis or retractor muscle)
    • Prolaps of membrana nictitans in horses and d/c ("ace eyes")
    • aggressiveness due to CNS stimulation
  11. Neurotransmitters in CNS
    as many as 50, both excitatory and inhibitory
  12. Excitatory neurotransmitters _______________ post-synaptic membrane
    depolarize
  13. inhibitory neurotransmitters ______________ post-synaptic membrane
    hyperpolarize
  14. benzodiazepine effects and list
    • minor tranquilizers.  Schedule IV substances
    • Sedative-hypnotic, seizures, muscle relaxant, appetite stimulant (cats)
    • hold open chloride channel on GABA receptor to increase hyperpolarization
    • diazepam
    • midazolam
    • alprazolam
  15. diazepam
    • Valium, minor tranquilizer benzodiazepine.  
    • sedative-hypnotic, seizure therapy, muscle-relaxant, appetite stimulant in cats.  
    • Plateau effect--cannot cause medullary paralysis.
    • hold open chloride channel on GABA receptor to increase hyperpolarization
    • IV administration, SLOW (propylene glycol causes hemolysis)
    • Don't administer IM, could cause tissue irritation, pain, unpredictable absorption
  16. midazolam
    • Versed, minor tranquilizer benzodiazepine.  
    • sedative-hypnotic, seizure therapy, muscle-relaxant, appetite stimulant in cats.
    • Plateau effect--cannot cause medullary paralysis.
    • hold open chloride channel on GABA receptor to increase hyperpolarization
    • IV, IM, IN
    • causes sedation, ataxia, and sternal or lateral recumbancy
    • cheaper, water soluble, no propylene glycol, 2x potency and greater affinity for benzo-receptor than diaz.
  17. adverse effects of midazolam
    • dysphoria and excitement
    • more common in cats than dogs, and when administered alone.
  18. Alprazolam
    • Xanax, minor tranquilizer benzodiazepine.  
    • sedative-hypnotic, seizure therapy, muscle-relaxant, appetite stimulant in cats.  
    • Plateau effect--cannot cause medullary paralysis.
    • hold open chloride channel on GABA receptor to increase hyperpolarization
  19. Phases of CNS depression
    • 1. sedation, disinhibition, anxiolysis, possible muscle relaxation and anticonvulsant
    • 2. Hypnosis
    • 3. Anesthesia
    • 4. Medullary depression
    • 5. Coma
    • 6. Medullary paralysis
  20. Plateau effect of benzodiazepines
    • work within first 4 phases of CNS depression (sedation, hypnosis, anesthesia, medullary depression).
    • Cannot cause medullary paralysis alone
    • Minimal cardio effects
  21. additive CNS depression
    • pharmacodynamic effect of tranquilizers, etc. 
    • 2+2=4
  22. synergistic CNS depression
    • pharmacodynamic effect of tranquilizers, etc.  
    • 2+2=5+
    • Can also cause unpredictable paradoxical effects like excitement or aggression
  23. GABA
    • gamma aminobutyric acid
    • major inhibitory neurotransmitter in CNS
    • Enhanced by benzodiazepines (holds open chloride channel to increase hyperpolarization)
  24. Diazepam storage and handling
    • don't mix in syringe (pharmaceutic), could precipitate
    • CRIs must be used within 3 hours due to plastic
    • store in original container, away from light
    • may absorb into plastic (depends on temperature, concentration and flow rates)
  25. adverse effects of diazepam
    • paradoxical excitement, esp in young, healthy animals
    • chronic use in cats (>2 days), liver dysfunction
    • Excessive affection from friendly cats
  26. anxiolytic effects
    • removes anxiety
    • sometimes anxiety is all that is stopping aggression
    • any sedative could cause aggression
  27. Benzodiazepine receptor antagonist
    • flumazenil.  Competitive reversal.
    • Contraindicated where benzo's are stabilizing life-threatening conditions
    • Adverse effects include abstinence syndrome in dogs and seizures, VD, ataxia in humans. 
    • Keep it in the vein (inflammation and necrosis)
    • No oral administration.
  28. abstinence syndrome
    symptoms that occur in cold-turkey stop from drug dependancy. Usually opposite effect from dependent drug.
  29. Flumazenil
    • benzodiazepine receptor antagonist.  Competitive reversal.
    • Contraindicated where benzo's are stabilizing life-threatening conditions
    • Adverse effects include abstinence syndrome in dogs and seizures, VD, ataxia in humans. 
    • Keep it in the vein (inflammation and necrosis)
  30. Barbiturates
    • Sedative-hypnotic agents that reach all phases of CNS depression (dose-dependant, can cause medullary paralysis and death).
    • Tranquilizers, anesthetic agents, anticonvulsants, euthanasia
    • All come from barbituric acid
  31. 2 ways barbituates work in brain
    • 1.prevent calcium from going into cell and stimulating neurotransmitter (NorEpi or glutamate) release (inhibit excitatory)
    • 2.hold Chloride channel open to hyperpolarize (GABA) (enhance inhibitory)
  32. How propofol works in brain
    • Not sure how it causes CNS depression.  
    • Potentiates GABA: holds Chloride channel open to hyperpolarize and increase inhibitory.
  33. How dissassociative anesthetics work in brain
    block glutamate in NMDA channel, keeping it open, letting chloride in and hyperpolarizing (inhibitory)
  34. Long-acting barbituates
    • Phenobarbitol (Luminol)
    • Schedule IV
    • 8-12 hour duration
    • anticonvulsant
    • adverse include PU/PD, polyphagia, sedation and ataxia. Some diminish.  
    • oral or IV
    • Oxybarbituate
  35. Phenobarbital
    • Long-acting Barbituate (Luminol)
    • Schedule IV
    • 8-12 hour duration
    • anticonvulsant
    • adverse include PU/PD, polyphagia, sedation and ataxia. Some diminish.  
    • oral or IV
    • Oxybarbituate
  36. Pentobarbital
    • Short-acting barbituate
    • Schedule II
    • 45-90 minutes
    • anesthetic agent, anticonvulsant, euthanasia (most common). 
    • Slowly IV to prevent apnea/respiratory arrest (keep in vein, necrosis)
  37. Short-acting barbituate
    • Pentobarbital
    • Schedule II
    • 45-90 minutes
    • anesthetic agent, anticonvulsant, euthanasia (most common). 
    • Slowly IV to prevent apnea/respiratory arrest (keep in vein, necrosis)
  38. Adverse effects of pentobarbital
    • dose-dependant CNS depression
    • NARROW safety margin (2-2.5x dose is lethal)
    • Reflex tachycardia fixes most, but hypotension for full 45-90 minutes
    • decreases heart rate
    • decreases stroke volume
    • decreases cardiac output
    • decreases blood pressure
    • respiratory depression
    • apnea
  39. Euthanasia including schedule of control
    • Pentobarbital
    • fatal depression of medullary respiratory and vasomotor centers.  
    • Schedule II by itself (sleepaway)
    • Schedule III combined with others (Beuthanasia-D Special combined with phenytoin-anticonvulsant)
    • Blue or pink dyes so unmistakable.
  40. Storage of euthanasia drugs
    • store away from therapeutic agents
    • may not be administered to food animals
    • extreme care in handling
    • avoid contact with open wounds
  41. ultrashort-acting barbiturates
    • sodium thiopental (Pentothal)
    • Schedule III
    • 5-30 minutes
    • induce anesthesia
    • Extreme caution in IV administration, highly alkaline, stay in vein (pain, tissue necrosis, sloughing)
    • Give a little fast, rest slow (too slow = excitement, too fast = apnea)
    • truth serum
    • Highly lipid-soluble, in and out of CNS then redistributed into fat, so be aware in skinny animals like greyhounds, could OD
  42. sodium thiopental
    • ultra-short acting barbituate (Pentothal)
    • Schedule III
    • 5-30 minutes
    • induce anesthesia
    • Extreme caution in IV administration, highly alkaline, stay in vein (pain, tissue necrosis, sloughing)
    • Give a little fast, rest slow (too slow = excitement, too fast = apnea)
    • truth serum
    • Highly lipid-soluble, in and out of CNS then redistributed into fat, so be aware in skinny animals like greyhounds, could OD
  43. Contraindications and adverse effects of sodium thiopental
    • sighthounds due to redistribution of fat (they have none).  Their biotransformation is very slow due to some missing enzymes.  Prolonged recovery, risk of OD.
    • Rapid IV can cause apnea, significant vascular dilation (hypotension) and hypoglycemia (idiopathic).
    • dose-dependant respiratory depression
    • apnea
    • cardiac arrhythmias
    • decreased cardiac output
  44. Sodium thiopental and glucose
    • Hypoglycemia is an idiopathic effect.  
    • If given glucose, can get re-sedation/anesthetation.  Random effect.
  45. Propofol
    • Not a barbituate, not currently controlled
    • 2-8 minutes
    • Induction and maintenance of anesthesia, sometimes CRI
    • Highly lipid soluble, fast recovery, rapid tissue redistribution, rapid hepatic biotransformation (slower in sighthounds)
    • May be metabolized in other areas than liver as well, like lungs in cat.
  46. Danger of propofol
    • Vehicle contains no preservatives and supports bacterial growth.  
    • Aseptic technique, pull whole vial into sterile syringe and then use from there, less contamination.  
    • Lasts 6 hours after opening
    • reported to increase risk of post-op infections (new is better)
  47. Propofol administration and adverse affects
    • Give IV very slowly (60-90s) to avoid apnea
    • Milky, but still IV.  Okay out of vein.  
    • Causes apnea if too fast
    • causes hypotension (vasodilation)
    • HR effected much less than BP
    • Used to have propylene glycol, cause heinz body anemia in cats
    • used to grow bacteria, increase post-op infections
  48. Propofol syndrome
    • dogs, rare but lethal effect after CRI.  Metabolic acidosis, renal and cardiac failure, arrhythmias, rhabdomyolysis (breakdown of skeletal muscle).  
    • Propofol disturbs mitochondrial metabolism (we think)
    • Septic animals and neonates more at risk.
  49. Suggestions for propofol admin
    • pre-oxygenate and start on fluids first (for apnea and hypotension)
    • give 1st 3rd slowly, then titrate.  Watch hypotension and breathing closely.
  50. Dissociative Anesthetic
    • cyclohexamines.
    • Ketamine and Tiletamine
    • Schedule III
    • dissociative anesthesia characterized by skeletal muscle rigidity, sedation with sensory sensitivity, emergence phenomena during recovery
    • Block NMDA receptor to prevent modulation
  51. barbituate metabolism
    • Metabolized by P450 in liver, eliminated by kidney.  
    • Don't give with a P450 inhibitor to avoid increasing dose/effect.  
    • Monitor liver in long-term pheno
  52. Emergence phenomena
    vocalizing, thrashing, restlessness and anxiousness occurring during recovery from dissociative anesthetic agents
  53. Nocioception and its 4 components
    • processing of a noxious stimulus through thalamus into cortex, resulting in the perception of pain by the brain.  
    • Components: transduction (trauma converted to electrical impulse), transmission (on one of the three fibers), modulation, perception
    • Can cause neuroplasticity (body trying to protect itself)
  54. Neuroplasticity
    • changes in neurosystem response, the body trying to protect itself.  
    • Peripheral sensitization
    • central sensitization
    • combination (results in increased magnitude and duration of pain)
  55. central neuroplasticity
    • spinal wind-up pain.  
    • Includes secondary hyperalgesia, spontaneous pain and allodynia
  56. Primary hyperalgesia
    form of sensitization.  When you cut yourself in the same spot twice, it hurts more the second time
  57. secondary hyperalgesia
    • part of spinal wind-up/central sensitization.
    • expansion of receptor field until areas that aren't damaged start to hurt (cut your finger, thumb hurts)
  58. allodynia
    • part of spinal wind-up/central sensitization
    • hypersensitization where normal stimulus becomes painful.
  59. NMDA receptor
    • nocioception transmitted from sensory afferent neurons to nociresponsive neurons in spinal cord via NMDA receptors.  
    • Influence modulation and allow spinal wind up pain in surgery.  
    • Blocked by dissociative anesthetic agents
  60. 3 types of fibers in nocioception transmission
    • A-delta: inital sharp pain
    • C: throbbing sensation
    • A-beta: lowers threshold of pain
  61. amantadine
    oral NMDA blocker for chronic pain like osteoarthritis.  Dissociative anesthetic
  62. Ketamine and adverse effects
    • NMDA receptor antagonist in spinal cord
    • Sub-anesthetic doses to reduce spinal "wind-up" pain.
    • IM injection painful but may be absorbed from oral and/or ocular mucous membranes
    • Adverse effects: increased heart rate, CO and BP, apneuistic breathing pattern, increased salivation and respiratory secretions, seizures
  63. apneuistic breathing pattern
    • prolonged inspiration and rapid expiration.  
    • Seen in ketamine
  64. contraindications in cyclohexamines
    • head trauma, seizure history, myelography, CSF tap, brain or spinal surgery
    • Never give alone to horses due to emergence phenomena
    • hyperthyroid cats (already have increased sympathetic tone)
    • Liver and kidney problems (metabolism)
    • New Zealand white rabbits (death)
  65. Recovery from cyclohexamines
    • Excited or violent recoveries common.  Usu given with sedative-hypnotic to prevent this. 
    • Bizarre behavior, exaggerated sensory responses, tremor, possible seizures
    • Closely monitor to prevent self-injury
    • Hyperthermia in some cats within 1-4 hours
  66. Alfaxalone
    • IV anesthetic in small animals, not yet approved in US, negligable analgesic properties.  
    • Binds GABA receptors, increases neuronal transmembrane Cl- transport to cause hyperpolarization
    • Metabolized in liver, excreted in fecal and renal
    • respiratory depression and apnea with rapid IV administration (better with pre-med IM)
    • Recover to sternal recumbency 60-80
    •  minutes at usual doses
    • not for neonates
  67. alpha-2 adrenergic receptors
    • found in CNS and PNS, Pre- and post-synaptic receptors
    • Presynaptic inhibits norepi release (blocks Ca channels and negative feedback loop)
    • Postsynaptic cause vasoconstriction and platelet aggregation in liver cells, platelets and vascular smooth muscle
  68. Alpha-2 adrenergic receptor agonists
    • Selective for a2, but some a1 occurs.  
    • Causes sedation-hypnosis, muscle relaxation and ANALGESIA.
    • Synergistic with opioids
    • pre-oxygenate
    • Xylazine, dexmedetomidine, medetomidine
  69. alpha-2 adrenergic receptor agonist mechanism, adverse effects
    • Biphasic CV response (initial vasoconstriction, increasing BP, followed by vasodilation, lowering BP)
    • Decreased conduction can cause bradycardia and AV block.
  70. alpha-2 adrenergic receptor agonists and anticholinergics
    • Use together is controversial
    • Anticholinergics can be administered 10 minutes before dexmedetomidine, but not during or after.  Could cause secondary tachycardia, prolonged hypertension and cardiac arrhythmia.
    • Not evaluated in cats.
  71. Xylazine
    • a2 adrenergic agonist with most a1 activity.  Used in large animals (cows are very sensitive, 1/10 dose, pigs need 2-3x)
    • Causes emesis in 50% of dogs and 90% of cats
  72. dexmedetomidine
    • a2 adrenergic agonist causing sedation, analgesia and emesis (cats)
    • Sudden stimuli causes aggressive defense response
    • can be absorbed through skin, eyes and mouth
    • Causes bradycardia
    • reversed with atipamezole
  73. yohimbine
    • a2 adrenergic antagonist
    • reverses xylazine
  74. tolazoline
    • a adrenergic receptor antagonist
    • reversal for xylazine.  Best in ruminants.  Non-selective, so a1 and a2
  75. atipamezole
    • antisedan
    • most specific a2 adrenergic antagonist.  
    • Reverses dexmedetomidine and medetomidine.
  76. Doxapram (Dopram)
    • Stimulates all levels of CNS, usually used to stimulate respiration: 
    • general anesthesia
    • neonates (dystocia or C-section)
    • Larpar (diagnose laryngeal paralysis)
  77. Doxapram contraindications and adverse effects
    • not to be used as substitute for CPR
    • not for mechanical ventilation
    • Can cause arrhythmias, hypertension, seizures
    • Labeled IV, but sublingual for neonates
  78. Opioid clinical uses and examples
    • produce sedation and analgesia, reduce anxiety and fear
    • Control II
    • Used in: analgesia*, general anesthesia (reduce anesthesia requirement in CRI), sedation, chemical restraint (morphine, hydromorphone, oxymorphone, fentanyl) 
    • antitussive (receptor in cough center, Codeine, hydrocodone, dextromethorphan), antidiarrheal, emetic (Loperamide, apomorphone)
  79. opioid receptors and reversals
    • Mu: pain-regulating area of brain and spinal cord (analgesia, euphoria, respiratory depression, hypothermia, physical dependence). Addiction receptor
    • kappa: cerebral cortex and spinal cord (analgesia, sedation, miosis)
    • Delta: modified Mu receptor (analgesia, increased appetite, immunomodulation)
    • Reversed by naloxone (antagonist)
  80. adverse effects and contraindications of opioids
    • adverse: potent respiratory depressant (Mu worst)
    • thermoregulatory center in brain (panting)
    • GI (vomiting, defecation, constipation)
    • Excitatory effects, especially in cats and horses
    • hyperthermia in cats
    • Contra: head trauma (resperatory depression, increased CO2, increased cranial pressure)
    • impaired hepatic blood flow (metabolism of opioids)
    • use with caution in respiratory disease
  81. Naloxone
    reverses opioids
  82. Butophanol
    • Mixed opioid
    • Kappa agonist, mu partial agonist/antagonist
    • Class IV controlled substance
    • sedation, antitussive, a tiny bit of pain.
    • Minimal respiratory depressive or cardiac effect
  83. Buprenorphine
    • Mu partial agonist, kappa antagonist
    • Class III
    • Potent analgesic (ceiling effect, dose-dependant), poor sedative
    • Safer than pure Mu
  84. Inhalant anesthetics
    • produce and maintain general anesthesia by depressing respiratory system (dose dependent, lower CO and arterial BP
    • Dose related decrease in renal blood flow and GFR
    • Depression of liver function and hepatocellular disease
    • vaporizer converts from liquid to gas, delivered to lungs
    • absorbed from alveoli into blood and delivered to CNS
    • Rapid induction and recover, unconsciousness, analgesia and muscle relaxation
    • Little biotransformation, enter and leave through lungs so not really metabolized
  85. minimum alveolar concentration
    • Lower MAC = more potent
    • alveolar concentration of inhalant anesthetic that prevents gross purposeful movement in 50% of patients in response to standard pain stimulus. 
    • measure of potent
  86. Partition coefficient
    • lower number = faster agent
    • (more soluble, more in blood so less particles make it into brain (sand vs sugar in the coffee cup)
    • Ratio of the number of molecules of an anesthetic agent that exist in two places (blood/gas)
    • indicates solubility of an agent
    • correlates with speed of induction/recovery
  87. vapor pressure
    • higher number = greater volatility
    • indicates how volatile an agent is and maximum concentration 
    • precision vaporizers
  88. Partial pressure of inhalant anesthetics
    • Proportional in alveolar and brain.  Depends on amount of agent delivered to lungs vs amount removed
    • Increase delivery by increase vaporizer, oxygen flow, minute ventilation or decrease dead space
    • Removal by solubility, molecular weight, partial pressure difference, alveolar surface, CO
  89. Halothane
    • First used in humans in 1957
    • 60-80% eliminated unchanged through exhalation (rest p450 liver elimination)
    • Dose-related CNS depression untl respiratory and cardiovascular collapse (medullary paralysis)
    • sensitizes heart to catecholamines
    • Hepatic dysfunction (mild and transient with hypoxia or halothane hepatitis, hypersensitivity, often fatal)
  90. Halothane hepatitis
    severe, often fatal response to halothane.  Metabolites set off hypersensitivity reaction
  91. Isofluorane
    • One of least soluble of inhalant agents, so very rapid induction and recovery
    • Allows stable heart rhythm and has less effect on CO, modulated by IV fluids
  92. Sevoflurane
    • Good choice for mask induction, little odor and even faster than isofluorane (induction and recovery)
    • Primary indication in high-risk small animal patients
  93. "mimetic"
    "like", mimics.  Parasympathomimetic, like PNS effect
  94. "lytic"
    not like.  Parasympatholytic = like sympathetic
  95. neuroleptic
    • Produce sedative effect by depressing brain stem and connections to brain.  
    • Does not effect coordinated motor activity, animal can be roused
    • major tranquilizers like acepromazine (phenothiazine derivatives)
  96. paraphimosis
    penis prolapse in horses and large animals, happens in acepromazine, contraindicated in stallion.  Can become permanent.
  97. amitriptyline
    tricyclic antidepressant given to cats with chronic cysto problems, inappropriate urination
  98. cyclohexamines
    • dissociative anesthetics (NMDA blockers)
    • ketamine, tiletamine
    • Schedule III
    • muscle rigidity, sedation with sensory sensitivity. 
    • emergence phenomenon

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