Jugular Venous Oximetry (JVO)
-It provides
insight into the metabolic and oxygenation state of the brain.
-It provides
information about the balance of oxygen supply and demand, for a larger portion, if
not the complete brain.
Indications:
-During cardiopulmonary bypass
-Neurosurgery
-After
traumatic brain injury.
Figure 1: JVO Catheterization Technique |
Technique:
-A catheter is
inserted into the jugular vein in a retrograde fashion (using Seldinger’s
technique) so that its tip sits at the base of the skull in the jugular bulb.
This allows continuous pressure monitoring as well as intermittent withdrawal of
a jugular venous blood sample for gas analysis (Fig. 1).
-Continuous
monitoring: This can be achieved using an oximetry catheter inserted via a conduit
sheath.
-Confirmation
of location: can be made with a lateral cervical spine x-ray (Fig. 2).
Figure 2: JVO Catheter Lateral Cervical Spine X-Ray |
Identification
of the dominant Jugular vein:
For the best
representation of the metabolic state of the brain, the catheter should be
placed in the dominant jugular vein, most commonly the right side. Confirmed
by:
-In patients
who have had a cerebral angiogram, the venous phase of the study will provide
information on dominant venous drainage.
-The
intra-arterial contrast will drain almost exclusively through one jugular vein,
regardless of the side of injection.
-Side dominance
can also be predicted using ultrasound where the dominant vein may be larger.
In the absence of this information, the right side is preferred.
The pressure gradient between the jugular venous pressure and the central venous pressure:
-Pressure
transduction of the jugular bulb catheter allows comparison with the central
venous pressure to rule out potential venous obstruction.
-In a supine
patient with a neutral neck position, there should be no pressure gradient
between the tip of the jugular bulb and the central venous catheter.
-Although rare,
a significant gradient (> 4 mmHg) can occasionally develop during positioning
if there is significant twisting or bending of the neck.
-This gradient
indicates venous obstruction, potentially causing brain edema or ischemia.
-The head
should be repositioned until the gradient resolves.
Interpretation of blood gas analysis of jugular venous blood sample:
-The saturation
of jugular venous blood (SjvO2) demonstrates whether cerebral blood
flow (CBF) is sufficient to meet the cerebral metabolic rate for oxygen (CMRO2)
of the brain (Lower values of SjvO2 reflecting greater uptake by the brain and therefore less blood flow).
-It is
essential that blood samples from the retrograde catheter be drawn slowly to
avoid contamination from non-cerebral venous blood.
-A normal value
is between 65-75 %. Desaturation (SjvO2 < 55 %) indicates impending
cerebral ischemia (e.g., caused by hypotension, hypocapnia, increasing cerebral
edema).
-In traumatic
brain injury, SjvO2 below 50% for more than 10 min. is undesirable
and associated with poor outcomes. However, it has low sensitivity, (a relatively
large volume of tissue must be affected, approximately 13 % before SjvO2
levels decreased below 50 %).
-Intraoperative
hyperventilation will lower SjvO2 as it decreases CBF.
-In the setting
of a non-traumatized brain that is exposed to moderate hyperventilation for the
duration of a neurosurgical procedure, the acceptable level for SjvO2
is unknown.
-In the absence
of other demands, it is reasonable to guide intraoperative hyperventilation by
maintaining SjvO2 > 50%.
-Measurement of
simultaneous arterial and jugular venous samples allows the determination of
lactate output from the brain, the presence of which indicates the occurrence of anaerobic
metabolism.
Disadvantages & Limitations:
-It is a global
monitor that could easily miss small areas of regional ischemia.
-If CBF & O2
consumption both decreased (e.g., in severe brain injury, SjvO2 may
be unchanged.