Augmented Creatinine Clearance in Traumatic Brain Injury

Hypertonic saline and/or norepinephrine infusion are routinely used to achieve a desired cerebral perfusion pressure (CPP) in the management of traumatic brain injury (TBI). We hypothesized that creatinine clearances (CrCls) would be significantly augmented in this setting. This was an observational cohort study in TBI patients older than 16 years with normal serum creatinine concentrations, requiring maintenance of CPP. Eight-hour urinary CrCl collections were performed while on and off active management. Demographic data, use of vasoactive medications, fluid balance, feeding regimen, and hemodynamic variables were recorded throughout the study period. Augmented CrCl was defined as >150 mL/min/1.73 m(2) in women and >160 mL/min/1.73 m(2) in men. Twenty patients were enrolled, and augmented clearances were demonstrated in 17 (85%). The mean maximum CrCl was 179 mL/min/1.73 m(2) while receiving CPP therapy (95% confidence interval [CI], 159-198), returning to a mean of 111 mL/min/1.73 m(2) (95% CI, 91-131; P < 0.001) when measured after discharge from the intensive care unit. The mean CrCl in the intensive care unit while not receiving CPP therapy was 150 mL/min/1.73 m(2) (95% CI, 134-167; P = 0.03). The mean time to reach peak CrCl while receiving active treatment was 4.7 days (95% CI, 3.0-6.4). In a multivariate analysis, norepinephrine use, saline loading, mean arterial blood pressure, and central venous pressure were associated with augmented CrCl on the day of measurement. Augmented CrCls are common in TBI patients receiving active management of CPP and persist even after discontinuation of such therapy. Further work is needed to clarify the impact of such clearances on renally excreted drugs in this setting.