DEATtt subsequent to initially successful cardiac re~uscilation is no~ uncommonly reported. Fatalities are primarily "related tOocentra lo-nerVous system damage. Too often the cycle of hypoxia, cardiac arrect, circulatory arrest, central nervous system damage, cerebral oedema, hypoxia, becomes irreversible, despite successfully resuscitated cardiac and circulatory haemodynarnics. The introduction of deliberately induced controlled availability of an intravenous urea preparation have with two valuable adjuncts in the management of the I: On a physiologieo-pharmacological basis they are appl these patients. It is well documented that hypothermi~ ments of central nervous system tissues and allows thei oxygen supply. This is desirable "in patients with rece tral nervous system. Urea has been shown tO rec sure and cerebral oedema. These two techniques, then, would appea~ useful in the reversal or arrest of the grave hypoxic q conditions for recovery of hypoxic damage to centra We have had this hypothesis substantiated by our cli: Table I summarizes six selected case reports, i application of these principles, as a guide to a method after'cardiac arrest.

RESEARCH in the past twenty years has contributed significantly to the basic unders.tanding and management of diverse problems in various aspects ol~ clinical medicine. Not the least of these have been advances in anaesthetic techniques, equipment, and available agents which now make possible the contemplation and execution of surgery on "bad risk" patients under such deliberately altered conditions of body economy as hypothermia and extracorporeal circulation. Under such conditions the possibility then arises that the side-effects of a compound or group of compounds may have much more significance than previously. The introduction of curare into clinical anaesthesia in 1942 by Griffith and Johnson ~ has led to a steadily increasi.ng use of muscle relaxants. A voluminous literature has developed rel!lting to their ,node of action both clinically; and in the laboratory, and a review of these agents in man has been recently prepared by Foldes.-~ It is well acc6pted that some patients exhibit an abnormal response to relaxant administration, the most vexing and probably the most familiar being that of prolonged hypoventilation or apnoea. Having excluded such causes of respiratory failure as hyperventilation with suppression of the Hering-Breuer reflex, hypocarbia secondary to hyperventilation, gross hypoventilation with carbon dioxide narcosis, respiratory depression secondary to hypnotics, depleted plasma pseudocholinesterase, electrolyte imbalance, and obvious overdosage of relaxant with prolonged myoneural block, there remains a group in which no ready cause is apparent and where a direct central effect of relaxants might be considered. The purpose of the present study was to assess the central activity of five muscle relaxants in healthy dogs under conditions which excluded all of the abovementioned factors. METHOD The investigation of the central action of drugs makes it necessary to separate the central from peripheral effects of the injected agent. To accomplish this, the classical isolated-head technique described by tteymans and L~/don ~ and Heymans and Heymans 4 was used. The method utilizes the cardiovascular system of one *A preliminary report of this work was presented at the 1960 Fall Meeting of the American Society for Pharmacology and Experimental Therapeutics (Hersey, L. W., The Pharmacologist 2:86 [1960]). tAwarded British Oxygen Canada Prize 1961. :

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