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

Abstract 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 ptiO 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 (bptiO 2 = ΔptiO2/ΔCPP), we defined the state of pti 2O-autoregulation as present (0≤bptiO2≤1/6), moderate (1/6 < bptiO2≤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.