Characterization of Focal Brain Tissue Water Measurements in Human Traumatic Brain Injury

Abstract

Cerebral edema is a major cause of morbidity in patients with severe traumatic brain injury (TBI). Intraparenchymal thermal conductivity-based probes that measure local cerebral blood flow can measure percent brain tissue water (%BTW) content, but such measures have been insufficiently characterized in patients with TBI. We retrospectively reviewed physiologic data from patients with severe TBI treated at our institution (2014-2016) who underwent cerebral blood flow monitoring. Sixteen patients underwent focal %BTW measurements at a 15-minute sampling rate. %BTW measurements showed characteristic temporal profiles, with a mean time to peak of 3.7 ± 1.7 days. The mean minimum and maximum %BTWs were 71.0 ± 3.9% and 82.7 ± 7.4%, respectively (overall mean %BTW, 77.0 ± 2.9%). Intracranial pressure (ICP) values of 22 mm Hg (the current treatment threshold for patients with trauma) corresponded to 75.8 ± 5.4 %BTW. Repeated measures correlation showed that %BTW is negatively correlated with serum sodium concentration (r= -0.3; P < 0.001) and weakly positively correlated with ICP (r= 0.08; P= 0.01) and regional cerebral blood flow (r= 0.06; P < 0.001). These effects were consistent in a multivariable model including time from injury. In the best model, time was modeled as a quadratic term because the %BTW followed a parabolic trajectory. %BTW may be a clinically useful, real-time measurement of cerebral edema in patients with TBI. It is closely associated with the serum sodium concentration and follows a characteristic temporal course with characteristic trajectory and stability over time.