It is this ratio which reveals the cerebral oxygen saturation. NIR is a new technique with several technical pitfalls. In order to understand this monitoring technique one must first have knowledge of the blood supply to the brain. The brain is supplied with oxygenated blood via the internal carotid arteries. Once blood from these vessels has perfused the brain the blood is drained back to the heart in the internal jugular veins.
Monitoring is the assessment of the amount of oxygen dissolved in the internal jugular vein.
This is the amount of dissolved oxygen in the blood returning from the brain which was not used by the brain. As such SjvO2 monitoring records the balance of the supply of oxygen available to the brain and the brain's demand for oxygen. For example, a low SjvO2 value indicates that the brain needs more oxygen. This is a dangerous situation since without oxygen brain tissue dies. Jugular venous oxygen saturation is monitored by the placement of a fiber-optic catheter into the internal jugular vein.