Continuous postoperative ICBF monitoring in aneurysmal SAH patients using a combined ICP-laser Doppler fiberoptic probe

Cerebral vasospasm remains the principal cause of morbidity and mortality following successful clipping of intracranial aneurysms. Current management often requires subjective judgments concerning presumed abnormalities of cerebral blood flow. In this study, a combined intracranial pressure (ICP)-laser Doppler flowmetry (LDF) fiberoptic probe that permits continuous monitoring of local cerebral blood flow (ICBF) was used in the postoperative management of 20 aneurysm patients. Using this probe, ICBF was simultaneously recorded and integrated on a real time basis with other physiological parameters, including ICP, systemic arterial pressure, pulmonary arterial pressure, central venous pressure, and pulse oximetry. The combined probe also provided the ability to obtain precise and detailed information concerning the presence or absence of cerebral autoregulation and CO₂ vascular reactivity, and allowed calculation of the cerebral vascular resistance. Continuous monitoring of ICBF in this manner complemented by transcranial Doppler and angiographic data permitted early detection of cerebral ischemia, helped to differentiate cerebral ischemia from edema and hyperemia, was useful in titrating blood pressure and fluid management, provided direct feedback about the effectiveness of instituted therapies, and determined early on when medical management was of no avail and that interventional neuroradiology was indicated. Evidence is presented that the presence of angiographic vasospasm and increased velocities on TCD do not always correlate with ischemia in the microcirculation and that direct measurements of ICBF are often at variance with calculations of cerebral perfusion pressure (CPP).