A clinical study of cerebral circulation during extracorporeal circulation

The objective of this study is to clarify the relationship of cerebral blood flow to extracorporeal circulation flow and mean arterial pressure during nonpulsatile extracorporeal circulation under moderate hypothermia. Cerebral blood flow was determined by an argon saturation and desaturation method after that of Pevsner and colleagues with a mass spectrometer in 21 adult patients undergoing cardiac operations. Cerebral blood flow was 25, 33, 35, and 42 ml/100 gm/min, ranging from 19 to 50 ml/100 gm/min, at extracorporeal circulation flow rates of 40, 50, 60, and 70 ml/kg/min, respectively. Cerebral blood flow increased proportionally to extracorporeal circulation flow. Cerebral blood flow scattered almost transversely to mean arterial pressure and was 31 ml/100 gm/min in a hypotensive group (mean arterial pressure 34 to 50 mm Hg) and 34 ml/100 gm/min in another group (mean arterial pressure 51 to 94 mm Hg). Mean arterial pressure did not significantly influence cerebral blood flow. Cerebral oxygen consumption did not remarkably decrease and remained in the reasonable range when cerebral blood flow was 23 to 40 ml/100 gm/min. Subsequently, we assumed that the average cerebral blood flow value of 25 ml/100 gm/min at an extracorporeal circulation flow rate of 40 ml/kg/min also would be in the safe range. All of the patients are living without cerebral complications. We conclude that (1) cerebral blood flow was extracorporeal circulation flow dependent and (2) cerebral blood flow in the safe range was maintained even in the hypotensive range, provided the extracorporeal circulation flow rate was 40 ml/kg/min or higher.