Pharm 101: Nitrous Oxide

Class

Inhaled anaesthetic

Pharmacodynamics

• 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

Pharmacokinetics

• 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

References

• Katzung BG. Basic and Clinical Pharmacology. 14e. 2018: 441-449