Nitrous Oxide Method of Measuring Cerebral Blood Flow During Hypothermic Cardiopulmonary Bypass

Background. Determination of cerebral blood flow and oxygenation is a means of evaluating our cardiopulmonary bypass (CPB) practice. Because much of CPB is hypothermic, our measurement technique must be valid over a range of temperatures. In this study we evaluate the validity of N2O washin for measurement of cerebral blood flow and oxygenation at three temperatures. Methods. Cerebral blood flow and oxygenation were measured in 7 dogs undergoing CPB at 37°, 32°, and 27°C using simultaneous direct (sagittal sinus outflow) and indirect (nitrous oxide washin) techniques. Animals underwent CPB with a whole blood prime and α-stat pH management. Results. In the absence of hemodilution, cerebral blood flow and oxygenation were reduced by approximately 38% and 55% at 32°C and 27°C, respectively, by both techniques. Direct and indirect methods showed an excellent correlation (R = 0.87) during CPB between 27.5°C and 37.8°C (21 paired measurements). Conclusions. This investigation demonstrates that the correlation between a direct measure of global cerebral blood flow and that obtained by the N2O saturation method is excellent during CPB over the range of common CPB temperatures.