Brain-kidney crosstalk in subarachnoid hemorrhage patients.

Background: A "crosstalk" between brain and kidney after Subarachnoid Hemorrhage (SAH) is suggested. A link can be the vascular autoregulation. It can be evaluated with cerebrovascular Pressure Reactivity index (PRx). It is not clear if augmented renal clearance (ARC) can be used as a marker of kidney dysregulation or if ARC is associated with brain autoregulation. Our aim was to evaluate correlation between ARC and PRx in SAH. Methods: Pilot study of SAH patients admitted to a Neurocritical Care Unit (NCCU), at tertiary Portuguese hospital, submitted to multimodal brain monitoring. Fifteen patients were included over a period of two years. Daily observations from 15 patients were analysed, during the first 14 days after admission. Creatinine clearance was measured (MCC) using plasma creatinine and urinary creatinine in a 6-hour urine collection. Multimodal brain monitoring data included intracranial pressure, cerebral perfusion pressure, optimal perfusion pressure (optCPP; CPP level which makes autoregulation working optimally) and PRx. Results: Fifteen patients were included. Median age was 58 and initial Glasgow Coma Score 13, Hunt and Hess classification was ≥3 in 66%, and Fisher was 4 in 100%. ARC is highly prevalent since the admission. There was a positive correlation between the number of days in ICU and CPP (R2=0.37), optimal CPP (R2=0.23), and PRx (R2=0.25), indicating loss of autoregulation over time. There was no significant association between ARC and preserved autoregulation (R2=0.05) suggesting that ARC is itself a manifestation of kidney dysregulation. ARC doesn't correlate with noradrenaline or fluid balance. In multivariate analysis only age has an impact on MCC, with MCC expected to decrease by 1.328 for one year of life. Conclusions: ARC is highly prevalent in SAH patients during the first two weeks after NCCU admission. Presence of ARC, evaluated with MCC, was not significantly associated with the presence of cerebral autoregulation.