Cerebral Oximetry

Question 1

Key points

Answer 1

• Cerebral oximeters enable continuous
non-invasive monitoring of cerebral oxygenation.

• Cerebral oximeters utilize similar
physical principles to pulse oximeters.

• Cerebral oximeters use the Beer–Lambert law
and spatial resolution to provide
estimates of cerebral haemoglobin oxygen saturation.

• Baseline cerebral oximetry values
should be obtained before induction of anaesthesia.

• Cerebral oximetry values represent a balance between cerebral oxygen delivery and consumption

Question 2

Factors resulting in reduced cerebral oxygenation values

Answer 2

Cerebral blood flow:

Cardiac output
Acid–base status
Major haemorrhage
Arterial inflow/venous outflow obstruction

Oxygen content:
Haemoglobin concentration
Haemoglobin saturation
Pulmonary function
Inspired oxygen concentration

Question 3

Limitations in cerebral oximetry measurements

Answer 3

i) Blood from an extracranial source can create erroneously low measurement.

(ii) Electrosurgical equipment,
that is, diathermy,
can affect the accuracy of measurement

(iii) Cerebral oximeters only measure
regional cerebral oxygenation.
Large areas of the brain remain unmonitored

(iv) Cerebral oximeters are unable
to identify a cause for the desaturation