Nitrous oxide in 2010: who will have the last laugh? (Part 1)

Towards Quantum-Chemical Modeling of the Activity of Anesthetic Compounds

The modeling of the activity of anesthetics is a real challenge because of their unique electronic and structural characteristics. Microscopic approaches relevant to the typical features of these systems have been developed based on the advancements in the theory of intermolecular interactions. By stressing the quantum chemical point of view, here, we review the advances in the field highlighting differences and similarities among the chemicals within this group. The binding of the anesthetics to their partners has been analyzed by Symmetry-Adapted Perturbation Theory to provide insight into the nature of the interaction and the modeling of the adducts/complexes allows us to rationalize their anesthetic properties. A new approach in the frame of microtubule concept and the importance of lipid rafts and channels in membranes is also discussed.

Subacute combined degeneration of the spinal cord following nitrous oxide anesthesia: A systematic review of cases

OBJECTIVE

Vitamin B12 deficiency can lead to subacute combined degeneration (SCD). Nitrous oxide (N₂O) is an anesthetic which oxidizes the cobalt ion of vitamin B12, interfering with its function as a coenzyme. In this study, we conduct a systematic review of reported cases of SCD following nitrous oxide anesthesia.

PATIENTS AND METHODS

A comprehensive search of multiple databases was conducted, and information about patient characteristics, symptomatology, clinical work-up, and treatment was extracted from eligible articles. Univariate analyses were performed to identify predictors of poor neurological recovery following SCD.

RESULTS

32 studies, reporting 37 cases of nitrous oxide-induced SCD, were included through the screening process. These cases included 21 male patients and 16 female patients, with an average age of 50.4 years (SD 17.6). An etiology for subclinical B12 deficiency was determined in 30 reports; of these, 25 were due to vitamin malabsorption secondary to a gastrointestinal disorder. Duration of nitrous oxide exposure was described in 19 reports, and ranged from 30 min to 11 h. Univariate analysis failed to find an association between post-operative recovery and age (p = 0.60), sex (p = 0.46), positive MRI findings (p = 0.47), post-operative serum B12 (p = 1.00), post-operative hemoglobin (p = 0.18), type of surgery (p = 0.58), or post-operative high mean corpuscular volume (p = 0.13).

CONCLUSION

In patients with postsurgical myelopathy, surgeons should evaluate B12 status and consider the possibility that nitrous oxide could cause a subclinical B12 deficiency to become overt, particularly in patients with malabsorptive GI comorbidities. Treatment with B12 in this population can result in significant improvement of neurological function.