Online assessment of brain tissue oxygen autoregulation in traumatic brain injury and subarachnoid hemorrhage

Monitoring of brain tissue oxygenation (p(ti)O(2)) enables early diagnosis of secondary cerebral ischemia and may guide a cerebral perfusion pressure (CPP) orientated therapy. The purpose of our study was to explain the concept of p(ti)O(2)-autoregulation, defined as the ability of the brain to maintain p(ti)O(2) despite changes in CPP, and to show the different states of p(ti)O(2)-autoregulation we found. Microcatheters to assess ;O-2 and intracranial pressure were implanted into cerebral 'tissue at risk' of patients suffering from traumatic brain injury or subarachnoid hemorrhage. By using a multimodal neuromonitoring setup and in-house built software we assessed and displayed online the relationship between p(ti)O(2) and CPP based on a data buffer consisting of 12 h. Depending on the linear regression slope (b(pti)O(2) = Delta(pti)O(2)/DeltaCPP), we defined the state of p(ti)O(2)-autoregulation as present (0less than or equal tob(pti)O(2)less than or equal to1/6), moderate (1/6<b(ptiO2) <= 1/3), impaired (b(ptiO2)<= 1/3) or inverse (b(ptiO2) < 0). When p(ti)O(2)-autoregulation is present, an elevation in CPP is ineffective to raise p(ti)O(2). In contrast, an increase in CPP elevates p(ti)O(2) more pronounced in impaired than in moderate p(ti)O(2)-autoregulation, but decreases p(ti)O(2) in inverse p(ti)O(2)-autoregulation. We conclude that online assessment of p(ti)O(2)-autoregulation gives valuable information on which patient will benefit from an increase in CPP and which CPP should be achieved to do so.