Hyperbaric pressure does not affect the analgesia produced by nitrous oxide in the mouse

Abstract

14: 48-9, 1987. Supported in part by NIH Grant GM 29628.The ability of increased pressure to reverse unconsciousness produced by administration of general anaesthetics (pressure reversal) has been well documented since its first description over 40 years ago) Anaesthetic actions amenable to pressure reversal include loss of the righting reflex in the mouse produced by both nitrous oxide 2 (25 ata of helium increased EDso by 15 per cent) and isoflurane 3 (12.5 ata was associated with a 27 per cent increase in EDso) recovery of swimming in tadpoles exposed to 0.25 per cent chloroform 4 (complete narcotic reversal was observed at a hydrostatic pressure of 34 ata), and inhibition of axonal transmission in the rat superior cervical ganglion s (35 ata reduced the inhibition produced by 2,4 per cent halothane by 30 per cen0. However, pressure does not antagonize all phenomena associated with general anaesthesia. For example, halothane's inhibition of synaptic transmission in the rat superior cervical ganglion is potentiated, rather than antagonized, by pressure; a decrease of five to ten per cent in post-ganglionic action potential is produced by 35 ata of helium, both in the presence and absence of halothane.5 Similarly, halothane's depression of the ciliary beat of Tetrahymena pyriformis is enhanced by 137 ata. 6 Recently, it has been reported that halothane's inhibition of the oxygen uptake of rat liver mitochondria 7 and intact green monkey kidney cells 8 is not reversed by 50 ata of hydraulic pressure.While there have been numerous studies of the action of pressure on anaesthetic-induced unconsciousness or loss of the righting refex, its effect on other components of general anaesthesia (such as analgesia or suppression of reflex activity) has not been examined. Accordingly, the following study was undertaken.Abbreviation: ata = atmospheres absolute. Ambient pressure is 1 ata = 101.3 kPa (760 mmHg; 14.7 lb. in -2) CAN J ANAESTH 1989 / 36:1 / pp40-3