Following Paul Myles’ paper in Anesthesiology in 2007 – that demonstrated bad outcomes in patients anaesthetised with nitrous oxide (click here), “experts” clamoured to demand that we stop using the stuff in our clinical practice. Their opinions were enhanced by the ENIGMA trial, that claimed increased risk of myocardial infarction in patients receiving nitrous (click here); following adjustment for the usual factors.  I have been personally accused of “poisoning” my patients by continuing to administer nitrous. Hence, it was with great relief that I read this paper (click here) in this month’s anesthesia and analgesia.
Turan and Colleagues evaluated almost 50,000 patients who had noncardiac surgery at the Cleveland Clinic over a 4 year period (2005 and 2009). Of the patients that had general anesthesia, 17,00 were given N₂O (45%) and 21,000 were not (55%). Of each group, 10,000 patients were propensity score-matched  on 30-day mortality and a set of 8 in-hospital morbidity/mortality outcomes.
The results were surprising. Patients that were given N₂O intraoperatively had decreased odds of 30-day mortality (odds ratio [OR]: 97.5% confidence interval, 0.67, 0.46–0.97; P= 0.02), compared with no nitrous. In addition, patients that received  had a17% (OR: 0.83, 0.74–0.92) reduced odds of experiencing major in-hospital morbidity/mortality than non-nitrous (P < 0.001). In particular, the risk of pulmonary complications with significantly lower in patients who received nitrous.(OR, 95% Bonferroni-adjusted CI: 0.59, 0.44–0.78).
Ok – so this was a propensity score analysis induced fluke – right? In the same issue of A&A we have a second paper that analysed the POISE trial outcomes (click here). 30% of the 6000 patients in the study received nitrous – and there was NO association between the gas and adverse outcomes. A fairly biased editorial in A&A, written with the help of Paul Myles, whose group is the only one that has demonstrated bad outcomes with nitrous, dismembers the Turan paper.
Nitrous oxide has been around for 160 years. I am not aware that there is a pandemic of death and MI amongst the patients of those of us who use the stuff. In any case, I think that this paper, at the very least, suggests that the jury is still out on the subject.