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June 1975

Hypocapnia and Intracranial Volume-Pressure Relationship: A Clinical and Experimental Study

Author Affiliations

From the University Department of Neurosurgery, Institute of Neurological Sciences, Glasgow, Scotland. Dr. Rowed is now with the Sunnybrook Medical Centre, Toronto, and Dr. Leech is now at Royal Perth Hospital, Perth, Western Australia.

Arch Neurol. 1975;32(6):369-373. doi:10.1001/archneur.1975.00490480035003

The effect of induced hypocapnia was observed, during intraventricular pressure monitoring, in five patients with chronically increased intracranial pressure (ICP) and in five baboons with acutely raised ICP. The volume-pressure response (VPR) was used as a measure of intracranial elastance (inverse compliance), an index of residual compensatory capacity. The VPR is the acute increase in mean ICP that occurs in response to a constant volume increment to ventricular cerebrospinal fluid.

In the patients, hypocapnia produced a decrease in the VPR that was proportional to the decrease in ICP; in the baboons, ICP was substantially decreased with minimal change in the VPR. Both observations indicate that hypocapnia, though it decreases ICP, does not selectively decrease intracranial elastance. This may be a limiting factor in the use of hypocapnia in the management of raised ICP.

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