Cerebral blood flow and metabolism during open-heart surgery.

, , 633-638. Changes in cerebral blood flow and metabolism were investigated in 30 patients during the first five minutes of cardiopulmonary bypass. The ratio of blood flow to oxygen uptake (the cerebral blood flow equivalent or CBFE) rose by 54% and this change could not be attributed to simultaneous variations in arterial carbon dioxide tension, haematocrit or temperature. A modified thermovelocity technique was used to assess changes in blood flow in the internal jugular vein in 12 of the 30 subjects. The method suffers from a number of serious limitations, but the evidence suggests that there was a reduction in cerebral blood flow at the onset of bypass in more than 50% of the patients studied. The fall was associated with a particularly marked reduction in systemic blood pressure and occurred in spite of high overall flow rates from the oxygenator. It is argued that the findings indicate considerable depression of cerebral metabolism, which may be due to the decreased oxygen availability consequent upon haemodilution and hypotension and which may contribute to neurological damage in some patients.