The principle of near-infrared spectroscopy (NIRS) for cerebral oximetry monitoring during cardiac surgery is based on:
- A Measurement of cerebral oxygen partial pressure through transcranial arterial blood sampling
- B Doppler shift of transcranially transmitted ultrasound to measure cerebral blood flow velocity
- C Electroencephalographic changes in the beta frequency band reflecting cortical hypoperfusion
- D Differential absorption of near-infrared light by oxyhaemoglobin and deoxyhaemoglobin to estimate regional cerebral oxygen saturation (rSO2) ✓
Explanation
NIRS cerebral oximetry uses the differential absorption spectra of oxyhaemoglobin (OxyHb) and deoxyhaemoglobin (DeoxyHb) in the near-infrared spectrum (700–1000 nm). Photons penetrate the skull and brain cortex; the ratio of reflected light at different wavelengths yields the regional cerebral oxygen saturation (rSO2), which represents a weighted average of arterial, venous, and capillary haemoglobin saturation (~75% venous, ~25% arterial). A decline in rSO2 >20% from baseline or absolute value <50% during cardiac surgery or carotid endarterectomy prompts corrective action. Transcranial Doppler is the ultrasound-based method for cerebral blood flow velocity.
Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.
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