Cerebral oximetry is a noninvasive measurement of brain tissue
oxygenation using near infrared spectroscopy. It can be used to
show local brain tissue hypoxia or asymmetry in saturation between
the two sides of the brain potentially indicating unilateral blood
- ▪ Near infrared spectroscopy: Light of multiple wavelengths
(690-1100 nm) is passed through multiple tissue layers (skin, bone,
brain) and reflected photons are measured by a receiver.
- ▪ Chromophores: Transmitted photons at certain wavelengths
are absorbed by chromophores (ie, hemoglobin) in the tissue and
the absorption will be a function of the degree of oxygen saturation of
- ▪ Low-intensity, near infrared light is transmitted
through a “source” applied (typically) to the forehead
of a patient.
- ▪ Reflected/Transmitted light is measured at a point,
approximately, 4 cm from the transmitter (Figure 17-1).
- ▪ Transmitter-receiver pairs are typically applied to each
side of the forehead allowing comparison between left and right
frontal lobe perfusion (Figure 17-2).
Diagram showing transmission of near
infrared light and the arc it takes through brain
Oximetry pads applied to right and left forehead permitting
comparison of oxygenation in north hemispheres.
Clinical Pearls and Pitfalls
- ▪ Transmitters
and receivers should not be placed over skin with hair follicles
(even shaven) because the follicles can absorb and alter light.
- ▪ Transcranial
oximetry readings do not measure blood flow or oxygen uptake, and
normal values may occur in the presence of active pathology if the
pathology is not perfusion related.
- ▪ Cerebral
oximetry shares many of the principals and applications of pulse
- ▪ Electrocautery,
movement, lead placement problems, and ambient light can all interfere
with cerebral oximetry.
Casati A, Spreafico E, Putzu M, Fanelli G. New technology for
noninvasive brain monitoring: continuous cerebral oximtery. Minerva