Continuous-wave near-infrared spectroscopy is not related to brain tissue oxygen tension

Near-infrared spectroscopy (NIRS) has gained acceptance for cerebral monitoring, especially during cardiac surgery, though there are few data showing its validity. We therefore aimed to correlate invasive brain tissue oxygen measurements (PtiO2) with the corresponding NIRS-values (regional oxygen saturation, rSO2). We also studied whether NIRS was able to detect ischemic events, defined as a PtiO2-value of < 15 mmHg. Eleven patients were studied with invasive brain tissue oxygen monitoring and continuous-wave NIRS. PtiO2-correlation with corresponding NIRS-values was calculated. We found no correlation between PtiO2- and NIRS-readings. Measurement of rSO2 was no better than flipping a coin in the detection of cerebral ischemia when a commonly agreed ischemic PtiO2 cut-off value of < 15 mmHg was chosen. Continuous-wave-NIRS was unable to reliably detect ischemic cerebral episodes, defined as a PtiO2 value < 15 mmHg. Displayed NIRS-values did not correlate with invasively measured PtiO2-values. CW-NIRS should not be used for the detection of cerebral ischemia.