Evidence that nitrous oxide can maintain anaesthesia after induction with barbiturates

Blakemore, C, Donaghy, M J, Maffei, L, Movshon, J Anthony, Rose, D and Van Sluyters, Richard C.

Published in Journal of Physiology, vol.237(2), pp. 39-41P, 1973.

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    • Three cats were prepared under short acting barbiturate methohexital: approximately 30 mg/kg, given i.v., as required, over about 1.5 hr). Each cat was then paralyzed by continuous infusion of gallamine (7.5 mg/kg.hr) and artificially ventilated with 80% N 2O/19% O 2/1% CO 2. The electroencephalogram, electrocardiogram and expired P(CO 2) were monitored throughout the ensuing neurophysiological experiment. Maximum P(CO 2) was held at 4%. Apart from a reduction in E.E.G. spindling there was no discernible change throughout the 30-32 hr of the experiments. Even a firm pinch to the forepaw failed to desynchronize the E.E.G. However, desynchronization did occur if the concentration of N 2O was reduced to 65% but did not if it was raised again to 80%. After 28-29 hr relaxant infusion was stopped: 1-2 hr later each cat was able to breathe the N 2O mixture for itself. In this unparalyzed state the animals were still adequately anesthetized, having very little spontaneous movement and only a weak withdrawal reflex. Finally, after 30-32 hr, a light dose of methohexital (3 mg/kg) did not affect the E.E.G. although larger doses did cause barbiturate spindling.
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