Intracranial Pressure Changes Following a Bolus Infusion of Mannitol at Various Levels of Pa CO2 in Normal Dogs and Dogs with Experimentally Induced Intracranial Hypertension

Abstract

Ever since hyperosmotic agents, and in particular mannitol, were first introduced for clinical use, the mechanism by which they reduce intracranial pressure (ICP), increase cerebral perfusion pressure, and enhance cerebral blood flow (CBF) has remained controversial (Brown et al, 1979). Caution has recently been urged regarding the use of mannitol during states of raised ICP and impaired autoregulation such as occur following head injury. The reason for this concern is that in patients with normal ICP, acute increases in ICP have been noted during and after administration of hyperosmotic agents (Cottrell et al., 1977). Researchers have therefore suggested (but not demonstrated) that in patients with elevated ICP, mannitol, by increasing cerebral blood volume (CBV) early in the infusion, may in fact transiently aggravate intracranial hypertension. On the other hand, hyperventilation is well known to cause cerebral vasoconstriction via a decrease in PaCO2, thereby decreasing CBF and CBV, and hence ICP. The present study was therefore undertaken to compare the effects on ICP of a bolus infusion of mannitol at various levels of PaCO2 in two groups of dogs: those with induced intracranial hypertension and those without. The study was approved by the MNI Animal Care Committee.