Intracranial pressure reserve testing. Initial clinical observations.

Sequential subdural injections of fluid through an intracranial pressure (ICP) monitoring cup catheter have been employed to measure "ICP reserve" in a series of 136 determinations in 30 patients over a total of 155 days of recordings. This dynamic method of quantitating the brain's ability to adapt to increased intracranial volume tests the brain's compensatory mechanisms over a five-minute time span. The test, incorporating several safety features, has been found to be reliable, safe, and well tolerated. A series of observations have been made using this test in patients with subdural drains and in response to fluid, mannitol, and dexamethasone therapy. Deteriorating ICP reserve gave early warning of the need for reoperation for postoperative hematoma, massive brain swelling, or cystic reaccumulation. Intracranial pressure reserve testing also quantitated the evolution of postoperative brain edema. Changes in ICP reserve could be detected as much as 48 hours before changes in baseline ICP and as much as 72 hours before clinical deterioration was evident.