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✓ Cerebral oxygen metabolism was studied in the dog at brain temperatures ranging from 37° to 8°C. As brain temperature decreased, the cerebral oxygen metabolism (CMRO2) decreased following the Arrhenius equation. The natural logarithm of the CMRO2 was a linear function of the reciprocal of the absolute (K) brain temperature. Oxygen metabolism, although much decreased, continued at very low brain temperatures. The CSF composition was unchanged after 1 hour at brain temperatures down to 10°C. Circulatory arrest for tolerable periods and longer caused changes only in the CSF potassium concentration. The interval between the onset of circulatory arrest and the beginning of the CSF K concentration increased with decreasing temperature and the rate of CSF K increase was increasingly slower at lower temperatures. At all temperatures the rate of CSF K changed gradually increased with time. The interval before the CSF K started to increase was dependent upon the amount of O2 available in the brain and the length of this interval was inversely proportional to the CMRO2. The amount of CSF K concentration was not clearly related to the tolerable periods of circulatory arrest, but at normal temperatures an obviously increased CSF K following a period of acute cerebral anoxia without CSF hemorrhage may indicate brain damage.

T O PROVIDE circulatory arrest in the brain during intracranial surgery, total body profound hypothermia has been successfully accomplished with extracorporeal circulat ion in a number of neurosurgical centers th roughout the world? ,4,G,7,9 Unfort una te ly , inherent in this techniquc are a t least ~ ma jo r l imitations: 1) the necessity of a prolonged period of systemic anticoagulat ion dur ing the cooling and rewarming phases which causes t roublesome bleeding during and af ter surgery; ~) the complexity of the m e t h o d itself which requires ~ well-trained surgical t eams and presupposes complete fami l ia r i ty with the pump-oxygena tor -hea t exchanger systems. Since the surgical target of cooling and ischemic ar res t is the brain itself and not the b o d y as a whole, we have become interested in overcoming the present l imitations of ext racorporeal ly-produced, profound hypothermia . Th is could be accomplished by selective cerebra l cooling via carotid perfusion during t e m p o r a r y arres t of the cerebral circulation b y occlusion of the extracranial cervical arter ia l sys tem. Uti l izing a simple a r te ry to a r te ry extracorporeal circuit to cool the brain alone would avoid cooling of the entire body and would thus eliminate the need for an oxygena to r and the mechanically controlled rew a r m i n g phase. In addition, the period of an t icoagula t ion would be significantly shortened and with the absence of the oxygenator , add i t iona l problems in blood coagulation would be obv ia ted? 's While we, as others, 2'1~ have demons t ra ted the feasibi l i ty of differentially reducing the bra in t empe ra tu r e in the experimental anim a l uti l izing direct cooling via the carotid ar te r ia l sys tem, this method to da te has en joyed only limited clinical application.

✓ Direct surgical repair of technically difficult or otherwise inoperable vascular lesions of the brain may become possible or safer using profound hypothermia and circulatory arrest. Most surgeons who use this technique establish extracorporeal circulation by cannulating the femoral vessels. To avoid difficulties associated with this closed chest method, a method was devised to establish extracorporeal circulation, profound hypothermia, and circulatory arrest by direct cannulation of the right atrium and aorta through the chest. This technique is described in a patient whose otherwise inoperable vertebral artery aneurysm was successfully treated. This approach is simple and offers several advantages over the closed chest method.

EPORTS by Drew, a Woodhall, ~t Neville, 7 Wertheimer] ~ Guiot, 4 Juvenelle, 5 Bucknam, 2 and BjSrk, 1 and their colleagues have mentioned the success of combining deep hypothermia with extracorporeal circulation and circulatory arrest in the treatment of certain surgical comtitions in which periods of circulatory arrest would facilitate surgical repair by affording a bloodless fiehl. The advantages gained from a relatively bloodless surgical field prompted our decision to employ this Inethod to operate on intraeranial vascular lesions. The technic for inducing profound hypothermia by the extraeorporeal circulation of blood, using the patient 's own lungs as lhe oxygenator, has been described in previous reports, a

E FFECTIVE hemostas is is usually attained by rout ine and standardized procedures. However , since the operat ive t r ea tmen t of highly vascularized lesions often requires addit ional hemostat ic measures, unique ad junc ts such as controlled hypotension 2,26,3~176 or hypo the rmic techniques 1'9'1~ have been employed. Indeed, hypotens ive agents have also been used in combinat ion with body-surface cooling, 1,12,1~,21,2s,31,32,4~ while the nervous system has been cooled topically, selectively, or indirectly. Moreover , var ious levels of hypothermia (or more precisely, brain temperatures), ranging f rom 35~ to 10~ have been used. In the lower ranges (or profound hypothermia) , extracorporeal circulation has been applied ei ther as a cardiac bypass , 14,1s, 22,29,33,34,38,42,a3.44,46 or for selective cooling, u, 19,20,24,25

o va interest in the application of deep hypothermia to neurologic surgery was stimulated by the success of this procedure in cardiovascular surgery. The method of Drew and associates was suggested to us by Kirklin. The Drew technic ~ was introduced in the Section of Neurologic Surgery of the Mayo Clinic on March 3, 1960. 9 From that date until December, 19613 the Drew technic was used in 18 cases. In January, 1963, we adopted a modification of the "closed-chest technic" described by Woodhall et al. l~ and Patterson and Ray. 6 Between January, 1963, until March, 1963, we employed the closed-chest technic of hypothermia in 36 cases. We have not, however, used these methods exclusively during the period under consideration. For instance, 45 intracranial aneurysms were treated by intracranial surgical procedures without the use of profound hypothermia, and some form of extracranial carotid ligation was used in 33 cases. In brief, 111 operations were carried out during this 3-year period, 44 with the adjunct of profound hypothermia and 67 by other methods. I t is of further interest that 69 patients were seen in our institution who died without having undergone a definitive surgical procedure, and necropsy in these instances revealed intracranial aneurysms, most of which had ruptured, causing the patient's death.