I read with interest the article of Myles et al.  1and the accompanying editorial by Hopf.2Hopf celebrates the article by Myles et al.  and suggests that it “… is likely to have a major impact on clinical practice in anesthesia.” She even confesses to having stopped using nitrous oxide nearly a decade ago because of the importance of high tissue oxygen in preventing wound complications.

According to Hopf, there are two main reasons for avoiding nitrous oxide: (1) It produces postoperative nausea and vomiting; and (2) it prevents using 80% oxygen, which Hopf suggests also reduces nausea and vomiting, and even more importantly might reduce surgical site infection.

I recently published a letter3expressing my doubts about the benefits of 80% oxygen, caused by the inconsistency of the results of trials, the lack of clinical benefit, and most importantly, the inexistence of data evaluating more moderate oxygen concentrations (45–60%).

It is true that nitrous oxide produces postoperative nausea and vomiting, but it also happens for halogenated inhaled anesthetics, so you would not get any benefit from substituting halogenated anesthetics for nitrous oxide except the possibility of applying 80% oxygen. However, it is quite mystifying to read articles from the same authors who found 80% oxygen halving nausea and vomiting in the past,4stating now that it is of no benefit.5Finally, a recent clinical trial6shows that 80% oxygen is useless for preventing nausea and vomiting.

I personally still use 50% nitrous oxide plus 50% oxygen plus sevoflurane widely, and it is true that I might prevent some nausea and vomiting by substituting propofol for sevoflurane and nitrous oxide. But any real clinical benefit from substituting 80% oxygen for 50% oxygen is still unclear.

The two studies that found benefit from using 80% oxygen used 30% oxygen as control group, and these authors have surprisingly concluded that we should accept a linear clinical benefit beginning at 30% oxygen and ending at 80% oxygen. At the moment, this linear benefit is unproven, so it is surprising to read Hopf’s suggestion that the study of Myles et al.  could accelerate the process to accept 80% oxygen as standard practice. Moreover, Myles et al.  did not find an independent effect of oxygen concentration in the nitrous oxide–free group.

I must join Hopf’s residents in challenging the medical community to substitute evidence-based treatments for personal options.

Hospital General Universitario de Elche, Elche, Alicante, Spain. gtorcam@hotmail.com

1.
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
2.
Hopf HW: Is it time to retire high-concentration nitrous oxide? Anesthesiology 2007; 107:200–1
3.
Tornero-Campello G: Hyperoxia to reduce surgical site infection? Anesthesiology 2007; 106:632
4.
Grief R, Laciny S, Rapf B, Hickle RS, Sessler DI: Supplemental oxygen reduces the incidence of postoperative nausea and vomiting. Anesthesiology 1999; 91:1246–52
5.
Organ-Sungur M, Sessler D, Kranke P, Apfel C: Supplemental oxygen does not reduce postoperative nausea and vomiting: A systematic review of randomized controlled trials (abstract). Anesthesiology 2005; October:A626
6.
Turan A, Apfel CC, Kumpch M, Danzeisen O, Eberhart LH, Forst H, Heringhaus C, Isselhorst C, Trenkler S, Trick M, Vedder I, Kerger H: Does the efficacy of supplemental oxygen for the prevention of postoperative nausea and vomiting depend on the measured outcome, observational period or site of surgery? Anaesthesia 2006; 61:628–33