MULTIPARAMETRIC CONTINUOUS MONITORING OF BRAIN METABOLISM AND SUBSTRATE DELIVERY IN NEUROSURGICAL PATIENTS

Brain function and tissue integrity are highly dependent on continuous oxygen supply and clearance of CO2. Aerobic metabolism is the major e nergy source to normal brain, however, during hypoxia and ischemia, la ctate accumulation may sometimes he seen, indicating anaerobic glycoly sis after severe head injury. Current monitoring techniques often fail to detect such events which can affect substrate delivery to the inju red brain. We have recently adapted a method for continuous monitoring of brain tissue pO(2), pCO(2), pH and temperature, using a single sen sor The multiparameter sensor is inserted into brain tissue, via a new three lumen bolt, together with a standard ventriculostomy catheter a nd a microdialysis probe. The system has been left in place as long as needed, but never more than 7 days. All readings were compared to cli nical parameters, and outcome. Stable measurements could be obtained i n the first group of 20 patients, after calibration and rigid fixation , using the new bolt. Severely head injured patients had brain oxygen levels of less than 25-30 mmHg for the first hours after injury. There after two patterns could be seen. Patients with favorable outcome had a slow increase in brain oxygen, and brain CO2 decreased to normal val ues, as long as the cerebral perfusion pressure (CPP) was kept above 7 0 mmHg. However, in those patients with secondary ischemic events, and bad outcome, a further decline in brain oxygen to anaerobic levels (< 20 mmHg) was seen. For these patients, both decreased and increased b rain CO2 levels could be seen. Brain CO2 levels of 90-150 mmHg were co nsistently seen after brain death. Brain pH was inversely related to b rain CO2 for all patients. Brain glucose and lactate in patients with poor outcome were 639 mu M I-1 330, and 1642 mu M I-1 +/-788, whereas patients with good outcome had brain glucose levels of 808 mu M I-1 32 1 and lactate levels of 1007 mu M I-1 +/-417. Extended neuromonitoring using a combined sensor for brain oxygen, CO2, pH and temperature mea surements, as well as a microdialysis probe for glucose and lactate an alysis may optimize the management of comatose neurosurgical patients in the future, by allowing a fuller understanding of dynamic factors a ffecting brain metabolism.