Comparison of brain tissue and local cerebral venous gas tensions and pH

Neurosurgical monitoring devices have recently become available which are capable of measuring cerebral tissue gas tensions and pH. Brain tissue sensors have not been conclusively demonstrated to correlate with other measurements of regional cerebral gas tensions or pH. The present study was undertaken to correlate sensor values for pO2, pCO2 and pH with blood samples taken concurrently from local cerebral veins. Adult mongrel dogs were anesthetized and a craniotomy was performed. A small gyral vein was isolated and cannulated. Adjacent to the venous catheter tip, a Neurotrend brain tissue probe was inserted in an intracortical location. Each subject received a sequence of manipulations in inspired oxygen and end tidal carbon dioxide conditions. Under each experimental condition, samples of arterial and gyral venous blood were obtained and blood gas analysis performed. Concurrent brain probe measurements of tissue pO2, pCO2 and pH were recorded. Statistical analysis determined that local tissue and cerebral venous blood values for pO2, pCO2 and pH were highly correlated (R(s) = 0.62-0.82; p < 0.001). This indicates that there exists a confirmable monotonic relationship between tissue values and conditions in the post-capillary venous bed. Tissue sensors such as the Neurotrend probe can offer reliable trend indications in brain tissue gas tensions and pH.