Application of near infrared spectroscopy for monitoring of cerebral oxygenation during cardiopulmonary bypass

Near-infrared spectroscopy is an inexpensive technology that offers noninvasive monitoring and diagnoses. The principle of NIRS is that each chromophore has its own characteristic absorption spectrum. The oxy- and deoxyhemoglobin have different absorption spectrums so that light can be used to calculate their concentration in the tissue. In the 700–1,000 nm region, there is a “spectroscopic window” that only a few chromophores strongly absorb light. Absorption and scattering by other tissues such as water, lipids, skin and bone remain relative constant during monitoring period. Combining with clever optical probe arrangement, the original as well as the modified Beer-Lambert law can be applied to quantify the concentrations or ratio of oxy- and deoxyhemoglobin (HbO₂ and Hb).; Based on the principle, we have designed and built an NIRS monitor with the objective of overcoming the shortcomings of current NIRS instruments. This dissertation presents the result of our study on patients undergoing cardiac surgery using the NIRS monitor of our own design for non-invasive continuous monitoring of cerebral oxygenation. Particularly, we evaluated the correlation of NIRS parameters with the measurements of variables related to bypass. The most significant finding from the study is that the patients who failed to return to HbO₂-Hb baseline 20 minutes after coming off CPB have about 8 times greater risk of 6 week post operative cognitive deficit than those who returned to baseline. Our data suggest that there is substantial number of patients suffered from worsening cerebral oxygenation during CPB, indicating the occurrences of mismatch of cerebral oxygen supply over demand. More importantly, we have found that there are significant correlations between the worsening of cerebral oxygenation with post-operative cognitive deficit.; In summary, we have demonstrated that NIRS is a very useful technology to monitor cerebral well-being during critical procedures such as cardiac surgery with CPB. Its application should help to shed light on the understanding of the mechanisms of CNS dysfunction after CPB.