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Nitrous oxide method of measuring cerebral blood flow during hypothermic cardiopulmonary bypass
I MacVeigh1, D J Cook, T A Orszulak
1Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota 55905, USA.
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 degrees, 32 degrees, and 27 degrees C using simultaneous direct (sagittal sinus outflow) and indirect (nitrous oxide washin) techniques. Animals underwent CPB with a whole blood prime and alpha-stat pH management.
Results:
In the absence of hemodilution, cerebral blood flow and oxygenation were reduced by approximately 38% and 55% at 32 degrees C and 27 degrees C, respectively, by both techniques. Direct and indirect methods showed an excellent correlation (R = 0.87) during CPB between 27.5 degrees C and 37.8 degrees 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.