[N2O-induced acute funicular myelosis in latent vitamin B 12 deficiency]

The neurotoxicity of nitrous oxide ("laughing gas") had already been observed in 1956 when using N2O in the long-term sedation of tetanus patients. In 1967 Parbrook described leukopenic effects during long-term exposure to N2O. It was only in 1978 that further studies were conducted on myeloneuropathies and myelodepression under the influence of N2O. The basic cause is vitamin B12 deficiency and the irreversible oxidation of coenzyme B12 by N2O. Between 1986 and 1995 eight cases of acute funicular myelosis associated with latent vitamin B12 deficiency subsequent to nitrous oxide anaesthesia were reported. In our hospital, two further patients now have this disease. Two observations must be emphasised when assessing the 10 patients mentioned above: 1. There was no long-term exposure to N2O (> 6 hrs); the periods of anaesthesia were between 1.5 and 3.5 hrs. 2. Vitamin B12 deficiency was not known preoperatively, and there was no marked pernicious anaemia, so that the only pointers to the risk patients were supplied by the mean corpuscular haemoglobin (MCH) and the mean corpuscular volume (MCV) of the blood picture.