Cerebral Oximetry in Cerebral
After Cardiac Arrest
A. Ahn, J. et al.
Mohamed A. Kotb
Lecturer of Anesthesia, ASU
Pathophysiology of Post-CPR state
• Cardiac arrest represents a state of generalized whole-body
ischemia resulting from either a no-flow or a low-flow state
that culminates in inadequate organ perfusion and oxygen
delivery (DO2) leading to cellular damage and death.
• On-going inflammatory responses and cellular damage
continue even after return of spontaneous circulation (ROSC),
and are confounded by the problem of ischemia-reperfusion
injury because of a combination of neurological and cardiac
• Limitation in current practice is the inability to measure and
optimize end-organ perfusion in real-time due to lack of a
clear physiological marker to guide the quality of care to vital
organ and in particular brain perfusion.
• Adjustments in CPR could then improve coronary and
cerebral perfusion and ultimately outcome.
Monitoring during CPR
• End tidal carbon dioxide (etCO2):
proposed recently as a general marker of effective overall
circulation and perfusion as well as ROSC during cardiac
arrest, but does not indicate the quality of cerebral perfusion
• Electroencephalogram (EEG) :
Used during procedures such as cardiac and neurosurgery as
an indicator of cortical activity.
limitations during CPR:
-No real-time DO2 and brain tissue perfusion.
- Technical limitations.
• Bispecteral Index: Unreliable ,movement artifacts
Cerebral Oximetry:a Prognosticator and RealTime Marker of Cerebral Perfusion During CPR
• works by non-invasively transmitting and detecting
harmless near-infrared light through sensors that are
placed on the patient’s forehead, and is not
susceptible to motion artifact.
• Cerebral oximetry relies on near-infrared
spectroscopy (NIRS), which is based on the Beer
• Since 70–80 % of blood in the measured areas of
brain tissue is venous, these data represent mainly
cerebral venous saturation . normal range-60-80% .
Why we chosen NIR light ?
Penetrate the biological tissue deeper
Property : Oxygenated hemoglobin and deoxygenated
hemoglobin both absorb light differently in this
At 780 nm, deoxygenated blood has a higher
absorption, whereas at 830 nm, oxygenated blood has
a higher absorption.
Comparison between NIRS and Pulse oximetry
Different wavelengths are used in both these techniques
NIRS is far more penetrating effect than Pulse oximeter because sources of light is in NIR wavelength
NIRS characterize more chromophores than Pulse oximeter
NIRS - assessment of all the vascular compartments
(Arterial, Venous and capillary).
• Pulse oximeter - only
compartment by time
Measure hemo dynamics, metabolic and fast neuronal
responses to brain activation
Measure relative changes in pulsatile components of
the cerebral blood flow and cerebral blood volume .
Used in patients with low perfusion states an. It gives
exact oxygen level in the blood.
Reliable and commonly used to monitor
systemic oxygen supply only.
Pulse oximeter utilizes the arterial
oscillations to extract arterial oxygen
• saturation SaO2 and does not exploit all of
the information from the heartbeat
Validation Studies of Cerebral Oximetry Using
NIRS :Baseline Variables
• Different body positions: no effect except in high
ICP, decrease cerebral DO2 and perfusion.
• Age, Hb concentration, and sensor location did alter
• Gender, weight, height, and head size: Did not impact on
• Hyperbilirubinemia may directly alter cerebral
oximetry readings and interfere with cerebral
oxygen saturation in patients with icterus.
The Effect of Oxygen, Carbon Dioxide, Sedatives
and Neuromuscular Blocking Drugs on NIRS
• CO2: CBF and perfusion are linearly related to PaCO2;
cerebral VD occurs during hypercapnia and VC during
• O2: Cerebral oximetry values decrease following induced
hypoxia. The administration of oxygen increases mean
• The administration of sedatives, general anesthetics and
MR will enhance O2 effect, that could have a significant
impact on preserving neuronal tissue lying at the
ischemic threshold following cardiac arrest and in other
brain injury states.
The Effect of Low Cardiac Output and
Hypothermia on NIRS
• NIRS has been validated in both low cardiac output states
• Reduced COP decreases systemic DO2, which leads to
increased brain oxygen extraction and lower cerebral oxygen
saturation as measured using NIRS.
• Hypothermia is another factor that independently affects
cerebral metabolism and the balance between oxygen supply
and demand leading to increased cerebral oxygen saturation
because of reduced cerebral metabolism and oxygen uptake.
Application of NIRS During Cardiac Arrest
• NIRS has been used extensively in patients with
different medical specialties including neurology and
neurosurgery, trauma, vascular and cardiac surgery.
• There have been few studies of cerebral oximetry
during cardiac arrest. These studies indicate that
cerebral saturation may correlate with outcome .
• Cerebral oximetry using NIRS may prove
to be a valuable real-time monitor of the
quality of CPR, and in particular cerebral
resuscitation. It may also provide data that
can contribute to prognostication in
• Further studies are needed to understand
the utility of this technology during CPR
and in the post resuscitation period.