We read with keen interest the pragmatic study by Myles et al.  1and wish to congratulate the authors for their outstanding work. Despite the concerns regarding its adverse effects, nitrous oxide has actually had a central position in anesthetic practice primarily because it is inexpensive, widely available, and has a long-standing safety profile. The most obvious advantage of using nitrous oxide is that it allows a dose reduction of other anesthetic agents and opioids, which translates into less cardiovascular depression and significant cost reduction (which are particularly important in the developing countries). Nitrous oxide is not associated with nephrotoxicity or hepatotoxicity and is safe to use in patients susceptible to malignant hyperthermia. It possesses an analgesic property that all modern anesthetics lack and is short acting, with quick onset and offset of action. In fact, inhalation of nitrous oxide has also been found effective in reducing pain associated with injection of propofol,2which is fast replacing thiopentone as an induction agent. There has been concern regarding disadvantages of nitrous oxide, such as megaloblastic anemia, teratogenicity, neurotoxicity, increased intracranial pressure, myocardial ischemia, increased pulmonary arterial pressure, immunosuppression, postoperative nausea and vomiting, risk of hypoxia, and expansion of air-filled spaces. But the suggestions to retire nitrous oxide from its current position have gained more impetus by the advent of newer, shorter-acting agents, particularly remifentanil, and newer inhaled anesthetics, and growing interest in total intravenous anesthesia, rather than by appreciation of its own toxicity. In this context, the scenario in the developing world is still very different from the developed world, where most newer agents, including remifentanil and desflurane, are still not available. Even not-so-new agents such as sevoflurane are available in limited centers. Above all, the costs of anesthetic agents, including propofol, are significant concerns. While most of the Western world has already bid farewell to halothane, it is still widely used (in combination with nitrous oxide) in most third-world countries. In recent years, the use of nitrous oxide has decreased significantly in Western countries, and many anesthesiologists prefer not to use it at all. We believe that nitrous oxide, like any other drug used in anesthetic practice, has its own advantages and disadvantages. Although there are specific situations where it should be avoided, we believe that not only should its routine use be questioned, but also its routine avoidance! We are also concerned about the routine use of 100% oxygen because the anesthesia trainees need to develop confidence using lower oxygen concentrations, which they might have to use in certain specific situations, such as laser surgeries. We opine that nitrous oxide is a useful agent that should remain freely available for anesthesiologists to use judiciously like all other agents, and we fear that newer generations of anesthesiologists might not have enough experience with judicious use of laughing gas because of the lack of its use during their training.

*All India Institute of Medical Sciences, New Delhi, India. drhh_dash@yahoo.com

Myles PS, Leslie K, Chan MTV, Forbes A, Paech MJ, Peyton P, Silbert BS, Pascoe E, ENIGMA Trial Group: Avoidance of nitrous oxide for patients undergoing major surgery: A randomized controlled trial. Anesthesiology 2007; 107:221–31
ENIGMA Trial Group
Sinha PK, Neema PK, Rathod RC: Effect of nitrous oxide in reducing pain of propofol injection in adult patients. Anaesth Intensive Care 2005; 33:235–8