**2. Changes in cerebral blood flow during CPB with extracorporeal pump**

The brain weighs about 2% of total body weight. Cerebral blood flow accounts for 10 to 15% of cardiac output. Cerebral blood flow in normothermia is 50 millilitres (ml)/100 grams (g) of tissue per minute (min) and oxygen consumption is 3.5 ml/100 g tissue / min. Cerebral circulation is unusual in its self-regulating ability performed through the arteries of medium and large size. The ability for self-regulation acts at between 50 and 155 millimetres of mercury (mm Hg) for systolic blood pressure in normal conditions, but below 50 mm Hg brain irrigation is directly dependent on the amount of flow to this area. In cases of severe hypertensive disease or cerebral vascular disease, the lower limits can be much higher (Sotaniemi et al., 1986, Caplan et al., 1999).

At normothermia, there is permanent neurological damage when there is a cerebral perfusion defect or flow is less than 125 ml/min for more than 7 minutes. Vascular territories with little reserve, such as the border zones of cerebral arteries, the spinal cord and basal ganglia are the most sensitive and most affected by a situation of ischemia. The hippocampal cells and cerebellar Purkinje cells are also particularly sensitive to ischemia.

Fig. 2. Cannulation in ascending aorta and right atrium in preparation for using cardiopulmonary bypass. Similarly, the coronary sinus is cannulated to administer cardioplegic solution

The average cerebral blood flow in adult CPB is 25 ml/100g/min, which is approximately 6% of systemic flow. The ability for self-regulation with normotension persists, even in cases of hypothermia, ranging between 50 and 155 mm Hg. A decrease below 40 mm Hg may cause a significant decrease in cerebral oxygen delivery.
