THE EFFECT OF ANOXIA ON THE ACTION OF NITROUS OXIDE IN THE NORMAL HUMAN SUBJECT

¹ From the Departments of Pharmacology and Anesthesia, University of Wisconsin School of Medicine, Madison

The sensory threshold for pain and the appearance of amnesia and unconsciousness were used as criteria of depression in a comparative study of the effects of different degrees of anoxia on the action of 30 per cent nitrous oxide in a group of normal subjects.

Exposure for fifteen minutes to oxygen at 66 mm. did not appreciably modify the action of nitrous oxide, as judged by the above criteria, although subjective recovery was delayed, generalized fatigue and hemicrania being prominent symptoms, a fact which is suggestive of a causal relationship between anoxia and postanesthetic "sickness."

A five-minute period of inhalation of oxygen at 45 mm. with nitrogen produces amnesia during the last minute in most subjects. A definite summation of depressant action with that produced by nitrous oxide occurs at this pressure of oxygen, as judged by the appearance of unconsciousness and the occurrence of amnesia, although in those subjects who retained consciousness the pain threshold did not appear to be elevated above the nitrous oxide level.