CONTINUOUS MONITORING OF CEREBRAL PERFUSION BY THERMAL CLEARANCE

Currently, no commercially available system exists to continuously mon itor the effective tissue perfusion within the parenchyma of the brain . While several methods exist for accurately measuring cerebral perfus ion; among them: xeonon-133 clearance, hydrogen clearance and radiolab eled microsphere injection; none of these methods provides continuous monitoring. The Cook Incorporated VH8500 Volumetric Hyperthermia Treat ment System (Bloomington, IN, USA) was initially developed to treat br ain tumours by maintaining constant, moderate hyperthermia within a de fined tissue volume over an extended duration. The system continuously adjusts the power applied to heating elements in order to maintain a constant temperature within the treatment volume. Because tissue perfu sion is a primary factor responsible for removing heat from tissue, mo nitoring the amount of power applied to the heating elements allows on e to continuously estimate tissue perfusion in the vicinity of the hea ting elements. In the current study, regional blood flow in the vicini ty of heater/sensor catheters implanted in the brain parenchyma of thr ee dogs was estimated by the VH8500 tissue perfusion algorithm and dir ectly measured with radioactive labeled microspheres. The accuracy of the perfusion estimate (Thermal Perfusion Index) was evaluated by comp aring these values. A range of blood flow was achieved in each animal by infusing nitroprusside. It was found that with the perfusion estima tion algorithm of the Cook Incorporated VH8500 Volumetric Hyperthermia Treatment System as it is currently implemented, the Thermal Perfusio n Index tended to underestimate regional perfusion as measured with ra dioactive microspheres, but the relationship was nearly linear. Thus, the system currently tracks changes in regional blood flow. Such conti nuous measurement of parenchymal brain tissue perfusion would have bot h clinical and research applications for a variety of head trauma reco very and neurosurgical monitoring situations. Especially if research d emonstrates that changes in regional brain perfusion predict detriment al changes in neurologic function before they become irreversible.