VictorJohn Harding
1921 The Lancet  
belly were not relaxed; with 2 litres, finally reduced to 1 litre per minute, the belly wall became softer, and the legs showed much less resistance to flexion or extension ; tail wagging and vocal breathing ceased. 'The pads were sweating and slightly blue in colour. When the mask was taken off the animal staggered drunkenly, but quickly recovered. We then tried 8 parts N2O to 1 part O2. With a ventilation of 3 to 3½ litres per minute the breathing was slow and deep, the pads bluish and
more » ... g, the abdomen softer, but the recti contracted in response to a touch. With 2 litres per minute asphyxial breathing occurred and the belly was soft. When the mask was removed the animals were unconscious, with blue lips and dilated pupils, but recovered quickly after a few breaths of pure air. Results in a Pressure Chamber. Having shown that cats cannot be deeply anoesthetised by N20 until asphyxiation is partly induced, we next tried the same mixture-viz., 8 parts N20 to 1 part O2 in the pressure chamber at the Lister Institute, for the use of which we are indebted to the Director, Prof. C. J. Martin. The method of administration was exactly the same, except that we took the cats and the bag containing the mixture into the chamber, and did not begin the administration until the air pressure had been raised till it stood at plus 7 lbs.-i.e., at about 1 t atmospheres in place of 1 atmosphere. The partial pressure of N20 was thus raised from eight-ninths to twelve-ninths of 760 mm. Hg, that is, from 675 mm. Hg to 1013 mm. Hg, and that of oxygen from one-ninth to one-and-a-halfninths of 760 mm. Hg, that is, from 84 mm. Hg to 126 mm. Hg. The partial pressure of oxygen in pure air at sea level is one-fifth of 760 mm. Hgi.e., 152 mm. Hg. So that the effect of the extra half atmosphere of pressure was to raise the partial pressure of N2O notably, and, at the same time, to make that of oxygen much nearer to that in the air of the plains, and equal to that in the air of an alpine health-resort. Be it noted that the anaesthetic is
doi:10.1016/s0140-6736(01)32190-6 fatcat:tfde45o2tzcz3lvk6d3zhlojoa