Cerebral circulation after head injury

Abstract

A considerable body of evidence suggests that posttraumatic disturbances of the cerebral circulation contribute to poor neurological outcome after blunt head injury, especially when regional cerebral blood flow (rCBF) falls to the ischemic range (below 17 ml/100 gm/min). Cerebral infarction concentrated in the arterial boundary regions has been described in patients who died. Since arterial boundary zones are the cortical areas most susceptible to cerebral ischemia, the authors have investigated the relationship between neurological outcome and the anatomic pattern of rCBF values in the acute phase. The bolus-injection xenon-133 washout technique was used to measure rCBF in 35 regions of the hemisphere during the 1st week after head injury. Eighty-eight hemispheres were studied in 80 patients whose Glasgow Coma Scale (GCS) score was less than 8 on admission to the neurosurgical department. A characteristic pattern of rCBF was found in patients who later died of neurological complications, or who survived in a persistent vegetative state, with low flows in regions conforming to the arterial boundary zones. These patients also had lower average global cerebral blood flow (CBF), GCS scores, and cerebral perfusion pressure compared with those who recovered, with or without neurological deficits; the latter group had an rCBF pattern similar to that of normal individuals. There was little change in the GCS score between the time of hospital admission and CBF measurement, suggesting that the major neurological injury had occurred prior to admission. It was not possible to determine whether boundary-zone ischemia preceded neurological deterioration, but the rCBF pattern of boundary-zone flow deprivation was clearly related to poor neurological outcome. These observations suggest that elevated intracranial pressure and arterial hypotension were important etiological factors. Measures to protect regional cerebral perfusion should be instituted as early as possible after injury, preferably before the patient reaches the hospital.

Induced Hypotension and Brain Ischaemia

“…Furthermore, more recently it has become clear that there are differences in the autoregulation curve between different hypotensive drugs, with nitroprusside (NTP) being associated with the greatest leftward shift on the curve (Stoyka and Schutz, 1975;Michenfelder and Theye, 1977;Maekawa, MtDowall and Okuda, 1979). \ Autoregulation is often impaired in areas of brain pathology, for example around traumatic brain contusions, tumours and in areas of cerebral vasospasm (Palvogyi, 1969;Overgaard and Tweed, 1974;Enevoldsen and Jensen, 1978). In such cases, cerebral perfusion decreases with any reduction in arterial pressure and it has been suggested that critically low perfusion may occur at greater arterial pressures in the absence of autoregulation.…”