General Anesthetics

Question 0

Isoflurane

Answer 0

• Halogenated ether inhaled anesthetic
• Solubility: relatively low solubility (requires lower dose to dissolve in blood)
• Elimination: via lungs
• Mechanism of Action: unclear; increased threshold for neuronal firing
• CV effects: myocardial depressants (decreased contractility)
  
  • Minor compared to others
  • Decrease MAP by vasodilation (Decreased SVR)
  • Increased HR
• Respiratory: decreased tidal volume, increased respiratory rate, decrease in minute ventilation
  
  • Decreased response to PaCO2
  • Response to hypoxia decreased
  • Airway irritation
• Brain: decrease metabolism but increase blood flow
• Kidney: decreased blood flow, decreased GFR, impaired Autoregulation
• Liver: decreased blood flow, change in LFT

Question 1

Halothane

Answer 1

• Inhalation Anesthetic: most widely used
• Halogenated hydrocarbon
• Solubility: relatively high solubility (requires higher dose to dissolve in blood)
• Elimination: via lungs
• Mechanism of Action: unclear; increased threshold for neuronal firing
• CV effects: myocardial depressants (decreased contractility) & catecholamine sensitization (predisposes to arrhythmias)
• Respiratory: decreased tidal volume, increased respiratory rate, decrease in minute ventilation
  
  • Decreased response to PaCO2
  • Response to hypoxia decreased
• Brain: decrease metabolism but increase blood flow
• Kidney: decreased blood flow, decreased GFR, impaired Autoregulation
• Liver: decreased blood flow, change in LFT
  
  • Possible Hepatotoxicity

Question 2

Desflurane

Answer 2

• Halogenated ether inhaled anesthetic
• Solubility: Low solubility (requires low dose to dissolve in blood)
  
  • Fast induction and fast elimination
• Requires special vaporizer
• Elimination: via lungs
• Mechanism of Action: unclear; increased threshold for neuronal firing
• CV effects: myocardial depressants (decreased contractility)
  
  • Decreases MAP by vasodilation (Decreased SVR)
  • Increases HR
• Respiratory: decreased tidal volume, increased respiratory rate, decrease in minute ventilation
  
  • Decreased response to PaCO2
  • Response to hypoxia decreased
  • Airway irritation
• Brain: decrease metabolism but increase blood flow
• Kidney: decreased blood flow, decreased GFR, impaired Autoregulation
• Liver: decreased blood flow, change in LFT

Question 3

Sevoflurane

Answer 3

• Halogenated ether inhaled anesthetic
• Solubility: low solubility (requires low dose to dissolve in blood)
  
  • Fast induction/elimination/change in concentration
• Elimination: via lungs
• Mechanism of Action: unclear; increased threshold for neuronal firing
• CV effects: myocardial depressants (decreased contractility)
  
  • Decreases MAP by vasodilation (Decreased SVR)
  • Decreased cardiac output
  • No change in HR
• Respiratory: decreased tidal volume, increased respiratory rate, decrease in minute ventilation
  
  • Decreased response to PaCO2
  • Response to hypoxia decreased
• Brain: decrease metabolism but increase blood flow
• Kidney: decreased blood flow, decreased GFR, impaired Autoregulation
• Liver: decreased blood flow, change in LFT
• Toxicity: possible fluoride toxicity if low carrier gas flow used

Question 4

Nitrous Oxide

Answer 4

• Non-halogenated inhaled anesthetic
• High MAC (>100%) requires high concentrations
• Solubility: low solubility (requires low dose to dissolve in blood)
  
  • Fast on/off/change
• Elimination: via lungs
• MOA: unclear; increased threshold for neuronal firing
  
  • NMDA receptor antagonist may enhance analgesia
• CV effects: minimal b/c sympathomimetic effects counter
• Respiratory: decreased tidal volume, increased respiratory rate, decrease in minute ventilation
  
  • Decreased response to PaCO2
  • Response to hypoxia decreased
• Brain: decrease metabolism but increase blood flow
• Kidney: decreased blood flow, decreased GFR, impaired Autoregulation
• Liver: decreased blood flow, change in LFT
  
  • Possible Hepatotoxicity

Question 5

Barbiturates

Answer 5

• Thiopental injection anesthetics
• MOA: CNS depression via GABA-A activation
• Ultra short acting
• Highly lipid soluble: rapidly passes BBB
• Duration: short acting
• Dose dependent decreases in SVR, MAP, & CO
  
  • Due to venodilation decreasing preload
• Respiratory depressant
• Cerebral metabolic O2 consumption & blood flow decreased
  
  • ICP decreased
• Highly protein bound

Question 6

Etomidate

Answer 6

• Carboxylated imidazol IV anesthetic
• MOA: CNS depression via GABA-A activation
• Rapid on/off
• Minimal CV & Respiratory effects
• Side effects: adrenocortical supression
  
  • myoclonic movements
  • Post-op nausea & vomiting
• No analgesic effects

Question 7

Propofol

Answer 7

• phenol derivative IV anesthetic
  
  • Physiologic effects similar to barbiturates
• MOA: CNS depression via GABA-A activation
• Profound respiratory depressant
• Decrease in MAP via decreased SVR
• Route of Administration: continuous infusion
• Metabolism: fast via extra hepatic sites
• Amnestic, anti-emetic
• No analgesic properties

Question 8

Opioids

Answer 8

• IV anesthetics: fentanyl, sufentanil, remifentanil
• MOA: act on Mu, kappa, & delta receptors
  
  • Hemodynamically stable: minimal circulatory deterioration
• Side effects: dose dependent respiratory depression
  
  • potential chest wall rigidity

Question 9

Benzodiazepine

Answer 9

• IV anesthetic: Midazolam
• MOA: GABA-A receptor mediated inhibition of neurotransmission
• Used for anxiolytic & amnestic effects
  
  • pre-op or intra-op
• Water soluble & relatively short half life
• Benzo antagonist: flumazenil

Question 10

Ketamine

Answer 10

• Phencyclidine derivative producing dissociative anesthesia
  
  • Catatonia, amnesia, analgesia
• MOA: inhibits NMDA receptors
• Side effects: CV stimulation via sympathomimetic effects
  
  • If no catecholamines, then myocardial depressant
  • increases cerebral metabolic rate & blood flow
  • Minimal respiratory depression