Continuous Thermal Diffusion-Based Cerebral Blood Flow Monitoring in Adult Traumatic Brain Injury: A Scoping Systematic Review

Thermal diffusion flowmetry (TDF) is an appealing candidate for monitoring of cerebral blood flow (CBF) in neurocritical-care patients as it provides absolute measurements with a high temporal resolution, potentially allowing for bedside intervention that could mitigate secondary injury. We performed a systematic review of TDF-regional(r)CBF measurements and their association with (1) patient functional outcome, (2) other neurophysiological parameters, and (3) imaging-based tissue outcomes. We searched MEDLINE, EMBASE, SCOPUS, BIOSIS, GlobalHealth, and the Cochrane Databases from inception to October 2018 and relevant conference proceedings published over the last 5 years. Nine articles that explored the relationship between TDF-rCBF, mortality, and Glasgow Outcome Scale (GOS) or GOS-Extended (GOS-E) at various intervals were included. Despite being based on an overall weak body of evidence, our analysis suggests a link between sustained low or high CBF and poor functional outcome. Twenty-five studies reporting associations with neurophysiological parameters were included. The available data also point to an association between low or high TDF-rCBF and intracranial hypertension. TDF-rCBF appears to correlate well with regional brain tissue oxygenation measurements. We found no studies reporting on imaging-based tissue outcome in relation to TDF. In conclusion, despite being based on a relatively weak body of evidence, the available literature suggests a link between consistently abnormal TDF-rCBF values, intracranial hypertension, and poor functional outcome. TDF-rCBF also appears to correlate well with regional measurements of brain tissue oxygenation. Currently, such monitoring should be considered experimental, requiring much further evaluation prior to widespread adoption.