Chapter 10: Pain assessment and management
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Related theory
Although the exact mechanism of action of nitrous oxide is unknown, its effects take place within the pain centres of the brain and spinal cord and are related to the release of endogenous neurotransmitters such as opioid peptides and serotonin and the activation of certain opioid receptors (Huang and Johnson [81]). N‐methyl‐D‐aspartate (NMDA) receptor currents are inhibited by nitrous oxide and it is known that these receptors are involved with many central nervous system pathways (Huang and Johnson [81]). The release of these neurotransmitters is thought to activate descending pain pathways that modulate pain transmission in the spinal cord (Huang and Johnson [81]). Pulmonary transfer of nitrous oxide is rapid, with onset of effect in seconds and full analgesic effect within 2–3 minutes (BOC Healthcare [18]). It is also rapidly eliminated from the blood, via the lungs, when inhalation ceases (Collins [41]).
Special precautions for storage
To ensure that Entonox is suitable for immediate use, cylinders of it should be maintained at a temperature above 10°C for at least 24 hours before use. If Entonox cylinders are allowed to get too cold (below −6°C), the nitrous oxide component of the gas will start to separate out of the gas mixture, changing the concentration of the gas delivered to the patient (BOC Healthcare [17]) – that is, the cylinders will initially deliver a high concentration of oxygen but then will deliver nearly pure nitrous oxide.
