Pharm 101: Nitrous Oxide


Inhaled anaesthetic

  • Incomplete gaseous inhaled anaesthetic
    • Have high vapour pressures and low boiling points
    • Gas form at room temperature
  • Minimal Alveolar Concentration (MAC) > 100%
    • MAC is the anaesthetic concentration that produces immobility in 50% of patients exposed to a noxious stimulus
  • Mechanism of action not fully understood, thought to potentiate GABA-A receptors
  • Absorption through gas exchange in alveoli
  • Not metabolised
  • Low solubility, reaches high arterial tension rapidly
    • Low Blood:Gas partition coefficient 0.47
  • Rapid equilibrium in brain and fast onset of action
    • Rapid onset and recovery
Organ system effects
  • CNS:
    • Analgesia
    • Euphoria
    • Increased cerebral blood flow and ICP
  • CVS:
    • Dose-dependent myocardial depression
    • Preserved CO due to simultaneous sympathetic nervous system activation
  • Respiratory:
    • Bronchodilation
  • Renal:
    • Reduction in both GFR and renal blood flow, overall increase in filtration fraction
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MBBS CCPU (RCE, Biliary, DVT, E-FAST, AAA) Rob is an Emergency Medicine Advanced Trainee based in Melbourne, Australia. He has special interests in medical education, ECG interpretation, and the use of diagnostic and procedural ultrasound in the undifferentiated and unwell patient.

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