Impact of hypoxemia on the performance of cerebral oximeter in volunteer subjects.

Adverse neurological events during hypoxic episodes in high-risk patients or in patients not thought to be at risk while undergoing procedures increase morbidity and mortality. The ability to reliably monitor cerebral oxygenation could serve as an indicator for the need of therapeutic intervention and it's overall effect. This study was designed to verify the reliability of the only commercially available continuous noninvasive monitor, the INVOS 3100 (Somanetics Corp., Troy, MI), in subjects with varying levels of hypoxemia. Six adult volunteer subjects were enrolled. After placement of electrocardiogram (EKG), noninvasive blood pressure (NIBP), pulse oximeter (SpO2), cerebral oximeter (rSO2), a 20 g radial artery catheter, and a 4 F oximetric jugular bulb catheter, the subjects were given hypoxic mixtures to breathe to varying levels of desaturation. Arterial and mixed venous blood was drawn for blood-gas analysis at each level of O2 saturation. The cerebral hemoglobin saturation value from the cerebral oximeter was compared to the combined brain saturation using the formula: estimated field saturation between the light source and the detector (fSO2) = 0.25 x the arterial oxygen saturation (SaO2) + 0.75 x the jugular bulb venous oxygen saturation (SjvO2), (fSO2 = 0.25 SaO2 + 0.75 SjvO2). Statistical analysis demonstrated a correlation of 0.67 between rSO2 and fSO2 and a bias of -3.1% with a precision of 12.1%. Minimal bias of 0.38% and precision of 6.22% were calculated for transitional error. We concluded from the study that rSO2 may serve as a reliable indicator of changes in brain oxygenation induced by hypoxemia.