Characterization of cerebral hemodynamic phases following severe head trauma: hypoperfusion, hyperemia, and vasospasm

Abstract
✓ The extent and timing of posttraumatic cerebral hemodynamic disturbances have significant implications for the monitoring and treatment of patients with head injury. This prospective study of cerebral blood flow (CBF) (measured using 133Xe clearance) and transcranial Doppler (TCD) measurements in 125 patients with severe head trauma has defined three distinct hemodynamic phases during the first 2 weeks after injury. The phases are further characterized by measurements of cerebral arteriovenous oxygen difference (AVDO2) and cerebral metabolic rate of oxygen (CMRO2). Phase I (hypoperfusion phase) occurs on the day of injury (Day 0) and is defined by a low CBF15 calculated from cerebral clearance curves integrated to 15 minutes (mean CBF15 32.3 ± 2 ml/100 g/minute), normal middle cerebral artery (MCA) velocity (mean VMCA 56.7 ± 2.9 cm/second), normal hemispheric index ([HI], mean HI 1.67 ± 0.11), and normal AVDO2 (mean AVDO2 5.4 ± 0.5 vol%). The CMRO2 is approximately 50% of normal (mean CMRO2 1.77 ± 0.18 ...