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

133 Xe 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 133 Xe as indicator was used. Extracranial tissue was removed to directly place the 133 Xe detectors on the skull, and the head was covered with a 3 mm lead shield to minimize contamination of the 133 Xe clearance curve with extracranial radiation. 133 Xe detectors for the Kety–Schmidt technique were embedded in a shielded brass block to minimize interference with radiation from the animal's body. 133 Xe clearance data were analyzed using stochastic (CBF 10 , CBF 15 , and CBF INF ) and initial slope methods (CBF IS ), and the results were compared with CBF KS using linear regression. CBF 15 and CBF INF yielded similar CBF values as CBF KS (CBF KS = 0.97 · CBF 15 − 2.08, r = 0.92, p < 0.01; CBF KS = 1.13 · CBF INF − 1.21, r = 0.92, p < 0.01). CBF 10 slightly overestimated CBF KS but still showed a close correlation to CBF KS (CBF KS = 0.89 · CBF 10 − 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 133 Xe clearance curve minimized, all 133 Xe clearance techniques used to measure CBF were consistently related to CBF KS in a constant, significant manner. 133 Xe clearance therefore is a valid method to assess CBF during cardiopulmonary bypass.