Pharmacology of nitrous oxide

For more than 150 years clinicians have been using nitrous oxide (N2O) without fully understanding the pharmacological mechanisms of its analgesic and anaesthetic actions. Recent studies have helped to clarify the analgesic mechanisms of N2O but the mechanisms involved in its anaesthetic action remain less clear. Findings to date indicate that N2O induces opioid peptide release in the brain stem leading to the activation of descending noradrenergic neurones, which results in modulation of the nociceptive process in the spinal cord. Several receptor–effector mechanisms including dopamine receptors, α2 adrenoceptors, benzodiazepine receptors and -methyl- -aspartate (NMDA) receptors have been implicated although the relationship of one with the other is not known.