Entonox (BOC Healthcare [20]), a gaseous mixture of 50% nitrous oxide (N₂O) and 50% oxygen (O₂), is a patient‐controlled, inhaled analgesic that is used for the short‐term relief of acute pain (Young et al. [201]). Nitrous oxide is a colourless, sweet‐smelling gas with powerful analgesic properties and is supplied in premixed cylinders (Brown and Sneyd [31]). The gas is inhaled and self‐administered by the patient using a demand valve system attached to a face‐mask or mouthpiece (Collins [41]). The nitrous oxide component of the gas acts as a powerful analgesic, producing similar physiological effects to opioids, while the oxygen component has an anti‐hypoxic effect (Bonafé‐Monzó et al. [24]).