Factors affecting the topography of nitrous oxide-induced neurological complications

The factors underlying the topography of nitrous oxide (N₂O)-induced neurological complications are unknown.

We included all consecutive patients admitted to the university hospital of Marseille for N₂O-induced neurological complications in a prospective observational study. Patients underwent neurological examination, spinal cord magnetic resonance imaging, and nerve conduction studies within the first 4 weeks after admission.

In total, 61 patients were included: 45% with myeloneuropathy, 34% with isolated myelopathy, and 21% with isolated neuropathy. On multivariable analysis, the odds of myelopathy were associated with the amount of weekly N₂O consumption (~600 g cylinder per week, odds ratio [OR] = 1.11, 95% confidence interval [CI] = 1.001-1.24). The extent of the myelopathy (number of vertebral segments) was correlated with the number of ~600-g cylinders consumed weekly (ρ = 0.40, p < 0.005). The odds of neuropathy were associated with the duration of consumption (per month; OR = 1.29, 95% CI = 1.05-1.58). Mean lower-limb motor nerve amplitude was correlated with the duration of consumption (in months; ρ = -0.34, p < 0.05).

The odds of myelopathy increased with the amount of N₂O consumption, and the odds of neuropathy increased with the duration of N₂O exposure, which suggests distinct pathophysiological mechanisms underlying these two neurological complications.