Nitrous oxide abuse direct measurement for diagnosis and follow-up: update on kinetics and impact on metabolic pathways.

Recreational use of nitrous oxide (N 2 O) has become a major health issue worldwide, with a high number of clinical events, especially in neurology and cardiology. It is essential to be able to detect and monitor N 2 O abuse to provide effective care and follow-up to these patients. Current recommendations for detecting N 2 O in cases of recreational misuse and consumption markers are lacking. We aimed to update current knowledge through a review of the literature on N 2 O measurement and kinetics. We reviewed the outcomes of experiments, whether in preclinical models ( in vitro or in vivo ), or in humans, with the aim to identify biomarkers of intoxication as well as biomarkers of clinical severity, for laboratory use. Because N 2 O is eliminated 5 min after inhalation, measuring it in exhaled air is of no value. Many studies have found that urine and blood matrices concentrations are connected to ambient concentrations, but there is no similar data for direct exposure. There have been no studies on N 2 O measurement in direct consumers. Currently, patients actively abusing N 2 O are monitored using effect biomarkers (biomarkers related to the effects of N 2 O on metabolism), such as vitamin B12, homocysteine and methylmalonic acid.