Significance and Limitation of Transcranial Doppler (TCD) Ultrasonography in Evaluation of Intracranial Hemodynamics in Severe Head Injury

Abstract

Intracranial hemodynamics were studied in 36 patients with diffuse (n=16) and focal brain injuries (n=20) and also in experimental animals, with extradural balloon inflation, by use of TCD ultrasound. The mean flow velocities in the basal cerebral arteries commonly decreased on the side of hematoma depending on intracranial pressure (ICP) elevation and cerebral perfusion pressure (CPP) reduction in focal brain injury. The pulsatility amplitude between the systolic and diastolic flow velocities (S/D ratio) was then increased significantly. The decrease of the flow velocities and increase of S/D ratio returned to normal after treatment. The mean flow velocity of the middle cerebral artery and blood flow in the internal carotid artery exhibited the flow patterns which change correlatively depending on ICP and CPP in monkey models of acute intracranial hypertension. The flow velocities transiently increased bilaterally within several days after injury and there was no difference between the right and left side in diffuse brain injury. The velocities remained high even when the ICP increased and the CPP decreased. The result in focal brain injury therefore represents compression ischemia in the hemisphere due to increased cerebrovascular resistance. In patients with diffuse brain injury, however, hemodynamic events are more complex than those in focal brain injury. The flow velocities in diffuse brain injury may represent hyper or hypoperfusion states or arterial narrowing due to associated diffuse axonal injury, diffuse cerebral swelling or traumatic subarachnoid hemorrhage. Noninvasive study by use of TCD ultrasound can thus provide valuable informations on variant hemodynamic phenomena in patients with diffuse and focal brain injuries. But many complicated factors must be considered in the interpretation of TCD data in diffuse brain injury.