Jugular venous bulb saturation (SjO2) is a measure of global cerebral oxygen delivery, and changes reflect cerebral blood flow and cerebral metabolic rate. Cerebral oxygen consumption is normally 35–40% and hence SjO2 should read 65–70% however, it cannot detect regional cerebral ischaemia. Reading less than 54% suggest cerebral hypoperfusion, and high levels
may be because of reduced oxygen extraction,hyperventilation and increased cerebral blood flow. There is a risk of artificial desaturation owing to disruption of the light intensity device.