VALIDATION OF XE-133 CLEARANCE AS A CEREBRAL BLOOD-FLOW MEASUREMENT TECHNIQUE DURING CARDIOPULMONARY BYPASS

Xe-133 clearance to measure cerebral blood flow (CBF) was examined in 10 dogs during cardiopulmonary bypass. As a reference method, a continuous Kety-Schmidt technique (CBF(KS)) with Xe-133 as indicator was used. Extracranial tissue was removed to directly place the Xe-133 detectors on the skull, and the head was covered with a 3 mm lead shield to minimize contamination of the Xe-133 clearance curve with extracranial radiation. Xe-133 detectors for the Kety-Schmidt technique were embedded in a shielded brass block to minimize interference with radiation from the animal's body. Xe-133 clearance data were analyzed using stochastic (CBF10, CBF15, and CBF(INF)) and initial slope methods (CBF(IS)), and the results were compared with CBF(KS) using linear regression. CBF15 and CBF(INF) yielded similar CBF values as CBF(KS) (CBF(KS) = 0.97 . CBF15 - 2.08, r = 0.92, p < 0.01; CBF(KS) = 1.13 . CBF(INF) - 1.21, r = 0.92, p < 0.01). CBF10 slightly overestimated CBF(KS) but still showed a close correlation to CBF(KS) (CBF(KS) = 0.89 . CBF10 -2.58, r = 0.92, p < 0.01) and CBF(IS) considerably overestimated CBF(KS) (CBF(KS) = 0.60 . CBF(IS) - 1.27, r = 0.87, p < 0.01). With extracranial contamination of the Xe-133 clearance curve minimized, all Xe-133 clearance techniques used to measure CBF were consistently related to CBF(KS) in a constant, significant manner. Xe-133 clearance therefore is a valid method to assess CBF during cardiopulmonary bypass.