Jugular Bulb Venous Oxygen Saturation

Jugular bulb venous oxygen saturation (SjvO₂ ) is thought to be a measure of the degree of oxygen extraction by the brain and represents the balance between cerebral oxygen supply and demand. As CBF decreases or demand increases without a flow increase, oxygen extraction increases, and SjvO₂ falls. Conversely, when flow increases or metabolic demand decreases without a fall in flow, extraction decreases, and SjvO₂ increases. Interpretation of the absolute value of SjvO₂ is difficult if clinical circumstances are not clearly defined. For example, an increase in SjvO₂ may be an ominous sign if the increase is caused by a fall in metabolism associated with cellular death.

SjvO₂ can be measured by placing a sampling catheter or a fiberoptic catheter (for continuous monitoring) into the jugular bulb through the internal jugular vein or through a peripheral arm vein. In most clinical studies, SjvO₂ measurements of below 50% are thought to indicate cerebral ischemia. Because venous blood in the jugular vein drains from a large portion of the brain, SjvO₂ must be considered a monitor of global cerebral oxygenation. There is also significant variability from patient to patient about which areas of the brain are drained by which jugular vein. Focal areas of cerebral ischemia may therefore go undetected.

SjvO₂ monitoring has been used most extensively in the intensive care unit to monitor patients with severe head injury and has been used to guide blood pressure and ventilatory management to optimize blood flow. This monitoring technology has had a major effect on ventilatory management of the head injured patient and has significantly reduced the routine use of hyperventilation in neurosurgical patients.^{[236] [237] [238] [239]} Its use to guide intraoperative management that may affect CBF has been described during carotid endarterectomy, craniotomy for neoplasms and vascular anomalies, and CPB procedures.^{[240] [241] [242] [243] [244] [245]} Although it is used routinely in some neurosurgical centers, it has not yet gained widespread clinical acceptance as a routine monitor of neurologic well-being intraoperatively during procedures placing the CNS at risk.