SummaryThirty-two patients were randomly allocated to be anaesthetised either with nitrous oxide or xenon. Those who received nitrous oxide required significantly more fentanyl peroperatively. Arterial blood pressure and heart rate were adequately controlled during surgery in both groups. Plasma noradrenaline and prolactin increased peroperatively in both groups, but plasma adrenaline and cortisol, which increased in the nitrous oxide group, did not change in the xenon group. Growth hormone was below control in those given xenon, but not in the nitrous oxide group, while dopamine remained unchanged in both groups. Postoperative plasma concentrations of noradrenaline, adrenaline, cortisol and prolactin (in both groups) and dopamine (in the nitrous oxide group) were elevated, and slowly returned to control. No differences were seen between the two gases in effects on plasma sodium and potassium. Xenon, because of its favourable haemodynamic, neurohumoral and antinociceptive properties, deserves a more prominent place in anaesthetic practice than it has so far occupied.
The effects of nitrous oxide-induced cobalamin inactivation on homocysteine and folate metabolism have been investigated. Plasma levels of cobalamin, folate, homocysteine, and methionine were determined in 40 patients before and after operation under nitrous oxide anesthesia (range of exposure time, 70 to 720 minutes). Twelve patients anesthetized with total intravenous anesthesia served as control subjects (range of exposure time, 115 to 600 minutes). Postoperative plasma levels of folate and homocysteine increased (p less than 0.001) up to 220% and 310%, respectively, in nitrous oxide-exposed patients, whereas plasma levels of methionine decreased (p less than 0.025). Response occurred after 75 minutes of nitrous oxide exposure. The percentage increase of plasma folate and homocysteine correlated significantly with exposure time (p less than 0.025 and p less than 0.0001, respectively). In eight patients receiving nitrous oxide anesthesia plasma homocysteine levels had not returned to preoperative levels within 1 week (p less than 0.01). Urinary excretion of folate and homocysteine increased during and after nitrous oxide exposure (p less than 0.01 and p less than 0.002, respectively) and correlated with exposure time (p less than 0.01 and p less than 0.005, respectively). It can be concluded that disturbance of homocysteine and folate metabolism by nitrous oxide develops with little delay and return to normal levels requires several days. Elevation of plasma homocysteine levels may therefore be used for monitoring nitrous oxide-induced cobalamin inactivation.
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