Journal of Neurology, Neurosurgery, and Psychiatry, 1995, Vol 58, 153-159
Cerebral blood flow and metabolism in children with severe head injuries. Part 2: Cerebrovascular resistance and its determinants
PM Sharples, DS Matthews and JA Eyre
Department of Child Health, University of Newcastle upon Tyne, UK.
It has been proposed that in children with severe head injuries the
cerebral circulation does not respond appropriately to normal physiological
control mechanisms, making children more susceptible than adults to low
cerebrovascular resistance, increased cerebral blood flow (cerebral
hyperaemia), and raised intracranial pressure. To investigate this issue,
122 serial measurements of cerebrovascular resistance in 17 children with
severe head injuries have been performed and related to cerebral perfusion
pressure, arterial CO2 (PaCO2), arterial oxygen content (AO2), and the
cerebral metabolic rate of oxygen (CMRO2). Cerebrovascular resistance
values (mean (SD) 1.54 (0.61) mm Hg.ml-1.100 g.min) were normal or raised
in most cases; 71 values (58%) were within the normal range, 39 (32%) above
the upper limit, and only 12 (10%) below the lower limit. There was a
significant correlation between cerebral perfusion pressure and
cerebrovascular resistance (r = 0.32, p = 0.0003), suggesting preservation
of pressure autoregulation. This correlation was absent in four of the five
children who died or survived with severe handicap. Analysis by multilevel
modelling indicated that, as in normal subjects, CMRO2, CPP, AO2, PaCO2,
and cerebrovenous pH were important independent determinants of
cerebrovascular resistance. The results indicate that normal
cerebrovascular reactivity is often preserved in children with severe head
injuries but may be impaired in the most severely injured patients.
