Although considerable attention has been directed towards the elucidation of the patho-physiologic factors observed when the body temperature is lowered, there has been a relative paucity of investigation in the area of tissue oxygen tension. The lack of such information is understandable, in view of the difficulties imposed by a direct approach, and the inherent inaccuracies of an indirect approach.
Previous investigations in our laboratory on animals and humans have indicated that continuous quantitative oxygen tension measurements of the cisternal or ventricular cerebrospinal fluid could be easily accomplished using a platinum microelectrode. Furthermore, it was observed that the oxygen tension of the cerebrospinal fluid quickly reflected changes in arterial poe, cerebral blood flow, and cerebral metabolism 1. Since the cerebrospinal fluid appeared to be in dynamic equilibrium with the brain and its circulation, it was thought that some advance in the knowledge of the oxygen tension changes of the central nervous system, during hypothermia, might accrue from the application of this technique. Methods Experiments were performed on 31 mongrel dogs, weighing an average of 13.8 kg. A total perfusion pump oxygenator technique was used to minimize the variable of cardiac output so that temperatures down to 10~ could be more easily explored. To decrease the effects of anesthesia on cerebral metabolism and normal vasomotor activity, the animals were intubated under light thiamylal sodium (Surital) anesthesia. During the period of preparation, the animals were immobilized with intramuscular suceinyl choline and mechanic~ily respirated.