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Pharmacology > general anesthetics > Flashcards

general anesthetics Flashcards

1
Q

general anesthesia - definition

A
  • generalized, reversible CNS depression; all sensory perception is removed
  • only used to facilitate surgery/ surgical procedures; has no therapeutic or diagnostic purpose unto itself
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2
Q

5 progressive phases of anesthesia

A
  • sedation: pre-operative anxiolysis to facilitate induction
  • induction: sedation and rapid loss of consciousness
  • paralysis: total relaxation and loss of control of musculature with marked immobility; requires intubation
  • maintenance: with inhalation anesthetics
  • recovery: patients regain senses and muscle control
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3
Q

mechanisms of action

A
  • facilitate GABA: enhance the inhibitory effect of GABA binding to GABA-a; open Cl- channels, allows influx of Cl-; results in lowered membrane potential; makes it harder to depolarize and propagate an action potential
  • inhibit glutamate: inhibits the excitatory effects of glutamate binding to NMDA/AMPA receptors; allows influx of Na+ and Ca++ and efflux of K+; results in higher resting membrane potential / facilitates propagation of action potentials
  • facilitate 2-pore K+ channels: allows influx of Na+ and efflux of K+; results in overall lowered neuronal membrane potential; makes it harder to depolarize and propagate an action potential
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4
Q

4 stages of anesthesia: (list)

A

stage I: analgesia/ induction
stage II: excitement/ delirium
stage III: surgical anesthesia
stage IV: overdose/ medullary depression/ paralysis

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5
Q

4 stages of anesthesia: stage I

A

pt is conscious but drowsy. variable amnesia.

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6
Q

4 stages of anesthesia: stage II

A

dangerous stage due to risk of laryngospasm and vomiting; efforts made to limit this stage

  • pt experiences delirium; may exhibit violent combative beh; hyper-reactive / uncontrolled mvmts; elevated/irregular bp and resp rate
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7
Q

4 stages of anesthesia: stage III

A

ideal stage for surgery; no spontaneous mvmt, no effect (stable) on heart rate and MAP; further CNS depression results in progressive loss of muscle tone and reflexes

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8
Q

4 stages of anesthesia: stage IV

A

loss of spontaneous respirations, profound drop in bp, death

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9
Q

IV anesthetics (list of 5)

A
  • used as induction agents or for pre-procedural anxiolysis
benzodiazepines (GABA-a receptor)
barbiturates         (GABA-a receptor)
etomidate            (GABA-a receptor)
propofol               (GABA-a receptor)
ketamine              (NMDA receptor)
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10
Q

midazolam

A
  • short-acting benzodiazepene

- for anesthesia induction or conscious sedation

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11
Q

lorazepam

A
  • intermediate-acting benzodiazepene
  • pre-op sedative
  • amnestic
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12
Q

diazepam

A
  • long-acting benzodiazepene
  • pre-op sedative
  • long half life due to active metabolites
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13
Q

flumazenil

A
  • benzodiazepene antagonist used for reversal or overdose
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14
Q

thiopental

A
  • most common barbiturate for induction
  • no reversal agent
  • short onset of action and duration
  • facilitates GABA activity, also depresses brainstem activity

side-effects:

  • severe post-op n/v (treat with serotonin antagonist)
  • ** no increase in ICP / specific indication for head trauma
  • profound respiratory depression
  • dose-dependent decrease in MAP
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15
Q

etomidate

A
  • induction agent favored for pts at risk for hypotension (elderly, other pts with limited cardiac reserve)
  • short onset of action and duration
  • increases affinity of GABA for its receptor
  • ** no effect on BP
  • minimal effect on heart and respiration
  • greater margin of safety than barbiturates, greater post-op n/v than barbiturates
  • pain on injection (use with lidocaine)
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16
Q

propofol

A
  • most common induction agent
  • facilitates action of GABA
  • ** rapid onset 30 sec
  • ** rapid recovery 4-8 min
  • side-effects: ** anti-emetic effect, cardiac depression, hypotension, impaired baroreflex, pain on injection (use with lidocaine)
  • fospropofol: inactive, pro-drug form of propofol, converts to propofol in vivo
17
Q

ketamine

A
  • NMDA receptor antagonist
  • dissociative anesthetic best suited for asthma pts, children undergoing short and painful procedures
  • pt may appear conscious with eyes opened but is unable to respond to sensory stimuli
  • can be administered IV, IM, PO, PR

side-effects: effective analgesic; bronchodilation, **hypertension, increased HR and CO, increased cerebral blood flow and ICP; post-op hallucination, vivid dreams, excitation, NO pain with injection (no need for lidocaine)

18
Q

inhalational anesthetics (list of 4)

A
  • used for maintenance of anesthesia only
  • excreted by expiration
  • very dangerous / very small therapeutic index
  • very steep dose-response curve
  • NO antagonist

nitrous oxide (non-halogenated)
desflurane (halogenated)
sevoflurane (halogenated)
isoflurane (halogenated)

19
Q

Minimum Alveolar Concentration (MAC)

A
  • describes the potency of inhalational anesthetics
  • MAC of 1 (vol %) = minimum concentration preventing muscular response to a standard surgical incision in 50% of unparalyzed patients
  • low MAC = high potency
  • high MAC = low potency
20
Q

factors that increase MAC

A
  • these factors make the pt LESS sensitive to inhalational anesthetics

hyperthermia (greater than 42C)
drugs that increase CNS activity (catecholamines)
chronic ethanol use
pregnancy

21
Q

factors that decrease MAC

A
  • these factors make the pt MORE sensitive to inhalational anesthetics

hypothermia
advanced age (30% fatality in pts > 80 yrs)
acute ethanol intoxication
second gas effect (when two inhaled anesthetics are mixed, both become more potent)

22
Q

factors that do NOT effect MAC

A 
gender
height
weight
duration of anesthesia
thyroid gland dysfxn
23
Q

nitrous oxide (N2O)

A
  • non-halogenated
  • NMDA antagonist
  • very high MAC 105% (even if given at 100%, half of pts will still not lose muscular response to surgical incision; would have to be given with hyperbaric technique to achieve no muscular response in 50% of patients to increase the concentration sufficiently. because inhaled anesthetics must be mixed with minimum 20% oxygen to support life, N2O can never be given alone, only used with other inhalational anesthetics to achieve potency via second gas effect)
  • ** does not trigger malignant hyperthermia
  • will increase BP, CO when mixed with halogenated inhalational anesthetics
  • will decrease BP, CO when mixed with opioids
24
Q

halogenated / “volatile” inhalational anesthetics (characteristics)

A
  • MOA: activation of GABA-a and two-pore K+ channels

side-effects:

  • dose-dependent drop in BP
  • moderate bronchodilation & skeletal muscle relaxation
  • respiratory depression
  • can affect pregnancy/ crosses placenta; increased miscarriage rates in female OR workers
  • ** can trigger hyperthermia (treat with DANTROLENE)
25
Q

desflurane

A
  • halogenated inhalational anesthetic

- rapid onset, rapid recovery

26
Q

sevoflurane

A
  • halogenated inhalational anesthetic

- rapid recovery, no tachycardia

27
Q

isoflurane

A
  • halogenated inhalational anesthetic

- most common inhalational anesthetic used globally

Pharmacology (15 decks)

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