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 (UWA) CCPU Emergency Medicine Trainee with interests in medical education, ECG interpretation, and the use of point-of-care ultrasound in the undifferentiated patient. Co-author of the LITFL ECG Library | Twitter

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