What is the reason for measuring SjvO2 (Jugular Venous Oxygen Saturation)?
 

Answer:

Similar to Measuring Mixed Venous Oxygen Saturation (SjvO2), Jugular Venous Oxygen Saturation (SjvO2) is a measurement of the amount of oxygen in the venous blood taken from a catheter inserted into the jugular venous bulb (usually a double or triple lumen catheter).  This reflects the amount of oxygen left over after the brain has used what it needs.  If SjvO2 falls below normal, it suggests that the brain is having to extract a higher percentage of oxygen than normal to meet its needs.   This indicates that the amount of oxygen being delivered to the brain is inadequate.  A rise in SjvO2 above normal may indicate that the brain is unable to extract oxygen.  In brain death, where no oxygenated blood reaches the brain, the SjvO2 would equal the SaO2 (arterial saturation).
 

Jugular venous oxygen saturation (SjvO2) is a measurement of the amount of oxygen left in the venous system after the brain has removed the oxygen that it needs.  Measured as the percentage bound to hemoglobin, it provides information about the adequacy of the brain's oxygen delivery.

Normal SjvO2 is 55-75%.  If the SjvO2 falls below this level, it suggests that the blood flow to the brain is not enough to meet the brain's oxygen requirements, causing the brain to EXTRACT a greater percentage of oxygen from the blood. 

When treating patient's with raised intracranial pressure, one goal is to reduce the amount of blood flow to the brain, as a strategy for decreasing the volume in the intracranial compartment. While reducing blood flow (e.g. HOB elevated 30o, hyperventilation), it is important to keep blood flow high enough to perfuse the brain.  SjvO2 monitoring can help identify when the brain blood flow is too low, identified by a fall in SjvO2 below normal. 

SjvO2 monitoring can assist in determining the most suitable blood pressure for patients with a neurological insult.  With neurological injury, it is often difficult to know whether hypertension is harmful (by increasing the blood flow and cerebral blood volume), or life-saving (by maintaining the cerebral perfusion pressure).  If the blood pressure is adequately perfusing the brain, the SjvO2should be within normal limits.  A fall in SjvO2 could occur if the BP is too high (increasing the ICP and therefore, reducing cerebral perfusion pressure) or too low (decreasing cerebral perfusion pressure).

A rise in SjvO2 can also be important.  If the brain injury becomes so severe that the brain is unable to extract oxygen, the SjvO2 will rise.  In brain death, when the brain is no longer capable of extracting any oxygen, the SjvO2 will equal the SaO2.

Limitation 
One limitation of SjvO2 monitoring can be that the results reflect oxygen extraction on one side of the brain, depending upon catheter placement.  A trend of the changes is important.

Catheter
A double or triple lumen catheter is used, connected to a pressurized system to maintain patency.

Sampling
Draw SjvO2 sample from the distal tip of the catheter.  Send to lab as per venous blood gas sample. ENSURE LAB DIFFERENTIATES SPECIMEN FROM THE MIXED VENOUS GASES.

Record results on the hemodynamic graphic record to avoid confusion with mixed venous results.