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

Monitoring of brain tissue oxygenation (ptiO2) 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 ptiO2-autoregulation, defined as the ability of the brain to maintain ptiO2 despite changes in CPP, and to show the different states of ptiO2-autoregulation we found. Microcatheters to assess ptiO2 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 ptiO2 and CPP based on a data buffer consisting of 12 h. Depending on the linear regression slope (bptiO2 = delta ptiO2/delta CPP), we defined the state of ptiO2-autoregulation as present (0 < or = bptiO2 < or = 1/6), moderate (1/6 < bptiO2 < or = 1/3), impaired (bptiO2 > 1/3) or inverse (bptiO2 < 0). When ptiO2-autoregulation is present, an elevation in CPP is ineffective to raise ptiO2. In contrast, an increase in CPP elevates ptiO2 more pronounced in impaired than in moderate ptiO2- autoregulation, but decreases ptiO2 in inverse ptiO2-autoregulation. We conclude that online assessment of ptiO2-autoregulation gives valuable information on which patient will benefit from an increase in CPP and which CPP should be achieved to do so.