NITROUS OXIDE—TIME TO SAY GOODBYE!

Abstract

Nitrous Oxide, our old companion is in usesince long. Its two properties analgesia andreduction in MAC of inhalational agent make ita powerful tool in anaesthetic practice.Importance of nitrous oxide can be judged fromthe fact that sizable percentage of anaesthetistswill cancel the elective list if nitrous oxide isnot available!Widespread and prolonged use ofnitrous oxide has brought into focus certain sideeffects. There is almost consensus that chancesof postoperative nausea and vo miting areincreased with intraoperative use of nitrousoxide.Nitrous oxide has been blamed forincreased pulmonary artery pressure, pulmonaryhypertension leading to right heart failure insome cases. Increase in volume and pressure inclosed spaces including intracuff pressure ofcuff endotracheal tubes is long known toanaesthetist.Nitrous oxide has been implicated infew cases of postoperative blindness whichresolved spontaneously. The tag of increasedincidence of spontaneous abort ion andteratogenic effect remained unresolved issue sofar. Nobody paid much attention to all these sideeffect because advantages of nitrous oxideoutweigh its disadvantages.There is a major safety concern in use ofnitrous oxide.1 There are occasional reports ofadministration of hypoxic gas mixture to thepatient leading to hypoxic brain damage andsome occasions leading to death. Reports arefew and far apart but they make big heading inmodern day press.This was all good when anaesthesia wasimportant contributor to overall surgicalmortality. Occasional reports of hypoxicmixture.1–3 administration and death in few caseswere ignored on ground of acceptable mortality.At that time (1960) anaesthesia was fourth incauses of direct maternal death in confidentialenquiry into maternal and child health.4 Nowanaesthesia is among uncommon causes inrecent reports. General mortality in anaesthesiain ASA 1 and 11 cases is in the tune of1:250000. This exactly is number of cases whichone can maximally perform in h is/heranaesthetic carrier (more than 13 cases per dayfor carrier span of 50 years without having anybreak!). So there is no margin of error as faryoung and fit patients are concerned.Nitrous oxide has been the cause ofdeath in six cases between 200 4–2006 inGermany, Austria, and Switzerland. There istendency toward underreporting of less severcases and in developing countries even deathdue to nitrous oxide remain unreported in someoccasions.5 The problem is much morewidespread than that normally reported in thepress.Two main reasons for use of nitrousoxide—analgesia and reduction MAC ofinhalational agent—can conveniently beachieved by alternate means. Wide range ofanalgesic drugs are available, concepts ofbalanced and multimodal analgesia has broadenour analgesic options.Reduction in MAC can be achieved byabove mentioned analgesic options and/or use ofwide range of benzodiazepines. Do we requirereduction in MAC with new inhalational agentsis another question? It was in era of halothanewhen reduction in MAC was safety concern.Halothane is gradually fading away from thescene and new inhalational agents are much lessarrhythmogenic.Disaster involving nitrous oxide usuallyoccurs in scenario of repair of existing gassystem or instalment of new gas system. Fillingof wrong gas, cross connection, disconnectionand failure of oxygen-nitrous proportion devicecan happen in routine daily life.1,6Keeping in view safety achieved bypresent day anaesthesia practice, nitrous oxide ismajor safety hazard and its use in operatingtheatres should be discontinued.7Possible contenders to replace nitrousoxide are many, two are most promising,Medical Standard Air and Entonox. Advantagesand disadvantages of each are beyond the scopeof this article.