Cerebral perfusion pressure and intracranial pressure are not surrogates for brain tissue oxygenation in traumatic brain injury

Objective: Utilization of brain tissue oxygenation (pBtO(2)) is an important but controversial variable in the treatment of traumatic brain injury (TBI). We evaluated the correlation between pBtO(2)/CPP and pBtO(2)/ICP and determined the parameter most closely related to survival. Methods: Consecutive, adult patients with severe TBI and pBtO(2) monitors were retrospectively identified. Time-indexed measurements of pBtO(2), CPP and ICP were collected and correlation coefficients were determined. Patients were then stratified according to survival and pBtO(2), CPP and ICP values were compared between groups. Results: There were 4169 time-indexed data points (i.e., pBtO(2) with respective CPP and ICP values) in 15 patients. The cohort consisted of a mean age of 37 +/- 17 years, ISS of 27 +/- 7 and GCS of 4.5 +/- 1.5. Survival was 53% (8/15). In a normal regression models, neither the ICP (p = 0.58) nor the CPP (p = 0.71) predict pBtO(2) significantly. There was a significant difference in pBtO(2) in survivors (31.5 +/- 3.1 vs. 25.2 +/- 4.8, p = 0.010) but not in CPP or ICP. Survivors had a lower proportion of time with pBtO(2) < 25 mmHg [20% (3.4-44.6) vs. 40% (16.2-89), p = 0.049]. In contrast, survivors had a greater proportion of time with CPP < 70 and no difference in the proportion of time with and ICP > 20. Conclusions: CPP and ICP should not be used as surrogates for pBtO(2) since cerebral oxygenation varies independently of cerebral hemodynamics and pressures. Brain tissue oxygen monitoring in patients with TBI provides unique information regarding cerebral oxygenation the utility of which remains to be fully described. Significance: CPP and ICP are not surrogates for pBtO(2). Brain tissue oxygenation monitoring provides unique information for the treatment of traumatically injured patients. (C) 2011 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.