Subjective and Objective Sensory Responses to Inhalation of Nitrous Oxide and Methoxyflurane

Abstract

An investigation, in volunteers, into the sensory effects of nitrous oxide and methoxyflurane showed that the subjective changes of reduction in visual awareness and heightened auditory awareness were not supported by objective measurement. Vision remained normal until the subjects became unresponsive, whilst hearing was in fact diminished. The analgesia produced by nitrous oxide was late in appearance relative to the other sensory changes and it disappeared very rapidly upon recovery. In contrast, analgesia appeared early with methoxyflurane and persisted well into the recovery period. The principal changes found were alterations in orientation in space, of intellectual attitudes, of mood and of emotional attitudes. The emotional attitudes were easily disturbed by extraneous noise or conversation and the need for a quiet approach not only to the induction of anaesthesia but also to the recovery from anaesthesia is stressed.

STOP!: a randomised, double-blind, placebo-controlled study of the efficacy and safety of methoxyflurane for the treatment of acute pain

“…There is also evidence that methoxyflurane provides analgesia that is greater than or equal to that of Entonox 22. In a prospective, randomised, crossover study that compared nitrous oxide with Penthrox in 20 dental patients,23 there were minimal adverse effects with either gas, with the number of AEs similar between treatments.…”

Review article: Efficacy and safety of methoxyflurane analgesia in the emergency department and prehospital setting

“…Unlike most other anaesthetic agents, methoxyflurane possesses powerful analgesic properties 23,24 . It has a high blood gas partition coefficient of 13, which is potentially beneficial in providing analgesia after cessation of inhalation 25,26 …”

“…Comparative data with other current analgesic and sedative agents are limited. Two studies, in 1973 26 and 1975, 20 compared nitrous oxide and methoxyflurane. The methods of administration and doses used, as well as the study designs, render it difficult to interpret the results in light of current practice.…”

“…The methods of administration and doses used, as well as the study designs, render it difficult to interpret the results in light of current practice. In one study, the dose of methoxyflurane was between 0.35% and 1%, with the end‐point being loss of consciousness 26 . In the other study, 25% nitrous oxide was compared with 0.35% methoxyflurane; however, there is no record of the duration of inhalation or resultant dose 20 …”

“…23,24 It has a high blood gas partition coefficient of 13, which is potentially beneficial in providing analgesia after cessation of inhalation. 25,26 It is contraindicated in renal impairment, diabetes or with concurrent enzyme-inducing drugs or tetracycline. It should not be used in those with a history of…”