L-arginine reactivity in cerebral vessels after severe traumatic brain injury

Objectives: Traumatic brain injury (TBI) causes an early reduction of cerebral blood flow (CBF). The purpose was to study cerebrovascular endothelial function by examining the reactivity of cerebral vessels to L-arginine. Methods: Fifty-one patients with severe TBI were prospectively studied by measuring cerebral hemodynamics before and after the administration of L-arginine, 300 mg/kg at 12 hours and at 48 hours after injury. These hemodynamic measurements, using transcranial Doppler techniques, included internal carotid flow volume as an estimate of hemispheric CBF, flow velocity in intracranial vessels, CO ₂ reactivity, and dynamic pressure autoregulation using thigh cuff deflation and carotid compression methods. Changes in the hemodynamics with L-arginine administration were analyzed using a general linear mixed model. Results: L-arginine produced no change in mean arterial pressure, intracranial pressure, or brain oxygenation. Overall, L-arginine induced an 11.3% increase in internal carotid artery flow volume (P=0.0190). This increase was larger at 48 hours than at 12 hours (P=0.0045), and tended to be larger in the less injured hemisphere at both time periods. The response of flow velocity in the intracranial vessels was similar, but smaller differences with administration of L-arginine were observed. There was a significant improvement in CO₂ reactivity with L-arginine, but no change in dynamic pressure autoregulation. Discussion: The low response of the cerebral vessels to L-arginine at 12 hours post-injury with improvement at 48 hours suggests that dysfunction of cerebrovascular endothelium plays a role in the reduced CBF observed after TBI.