Validation of 133Xe Clearance as a Cerebral Blood Flow Measurement Technique during Cardiopulmonary Bypass

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