Experimental subarachnoid haemorrhage. Part II: extravasation volume and dynamics of subarachnoid arterial bleeding in cats.

The volume and dynamics of arterial subarachnoid bleeding in a cat were studied. Using an arterial shunt, blood was directed into the chiasmatic cistern. The blood flow and pressure in the shunt, as well as intracranial pressure, were registered. It was found that the bleeding is a biphasic event, lasting about 118 seconds. During the initial high flow phase, lasting 1/3 of the time of the bleeding, 2/3 of the extravasated blood fills the subarachnoid space. The resulting rise of intracranial pressure reduces the flow markedly. The average volume of extravasated blood was found to be 2.4 ml. The haemorrhage was arrested 25-60 seconds after the maximum ICP elevation was reached.