Effect of experimental brain injury on blood pressure, cerebral sinus pressure, cerebral venous oxygen tension, respiration, and acid-base balance

✓ Changes in the blood pressure, cerebral sinus pressure, cerebral venous oxygen tension, acid-base balance, respiratory frequency, and respiratory minute volume were studied in the rabbit after a lethal cold injury to the brain. About half of the animals responded to the injury with a quick rise in cerebral sinus pressure and in its relation to blood pressure (CSP/BP); in the other half, cerebral sinus pressure and the CSP/BP ratio rose more slowly. Changes in the CSP/BP ratio correlated well with criteria for changes in respiratory performance. The changes in cerebral venous oxygen tension were reasonably uniform: a dip during freezing, an overshoot to a mean of 1.6 times the original level (about 30 mm Hg) immediately after injury, a gradual return to the pretraumatic level, and then a drop to lower levels. The brain injury led to a respiratory alkalosis that became more pronounced the longer the animals lived. Considered with CSP/BP ratio, respiratory reaction to the brain injury may provide an early and accurate prognosis. The fact that at the time of death the cerebral perfusion pressure was still within a range believed safe for the brain shows that an actual brain injury, in addition to raised intracranial pressure, is important in such experiments and emphasizes the inappropriateness of comparing levels of intracranial pressure raised by a variety of methods.