Safety of inhalation of a 50% nitrous oxide/oxygen premix: a prospective survey of 35 828 administrations

Drug Saf. 2006;29(7):633-40. doi: 10.2165/00002018-200629070-00008.


Background: A 50% nitrous oxide/oxygen (N(2)O/O(2)) premix is widely used to alleviate pain or anxiety during brief care procedures in various medical domains. In some countries, recent changes in regulation status for medical gases state that they should be considered as drugs. Consequently, more valuable data gained from exhaustive clinical surveys are needed. This prospective study, conducted in the same conditions imposed for testing a drug, aims to analyse the factors that affect tolerance of the 50% N(2)O/O(2) premix in a wide range of clinical indications.

Methods: In a 4-year prospective survey, 35 942 data sheets were received from 191 French hospital paediatric (82%) and adult units (18%). Of these, 35 828 sheets were sufficiently complete to be included in the study. The number and the type of adverse events declared to the manufacturer were analysed.

Results: A total of 1581 (4.4%) adverse events were reported on 1384 data sheets, which were mostly gastrointestinal and neuropsychiatric disorders (86%). The main factors associated with adverse events were age, concomitant drug administration and longer duration of inhalation. Among the 27 (0.08%) reported serious adverse events, only 9 (0.03%) were possibly attributed to the N(2)O/O(2) premix. Among the serious adverse events that were not attributed to the gas, a concomitant drug association and insufficient patient surveillance occurred in 12 and 2 cases, respectively.

Conclusion: This survey confirms the pharmacological safety of the 50% N(2)O/O(2) premix in a wide variety of clinical indications and emphasises the need for rational training of medical personnel in its administration.

Publication types

  • Clinical Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Administration, Inhalation
  • Analgesics, Non-Narcotic / administration & dosage*
  • Analgesics, Non-Narcotic / adverse effects
  • Anesthetics, Combined / administration & dosage*
  • Anesthetics, Combined / adverse effects
  • Anesthetics, Inhalation / administration & dosage*
  • Anesthetics, Inhalation / adverse effects
  • France
  • Gastrointestinal Diseases / chemically induced
  • Humans
  • Nervous System Diseases / chemically induced
  • Nitrous Oxide / administration & dosage*
  • Nitrous Oxide / adverse effects
  • Oxygen / administration & dosage*
  • Oxygen / adverse effects
  • Pain / prevention & control
  • Prospective Studies


  • Analgesics, Non-Narcotic
  • Anesthetics, Combined
  • Anesthetics, Inhalation
  • Nitrous Oxide
  • Oxygen