The role of diffuse correlation spectroscopy and frequency-domain near-infrared spectroscopy in monitoring cerebral hemodynamics during hypothermic circulatory arrests

Objectives: Real-time noninvasive monitoring of cerebral blood flow (CBF) during surgery is key to reducing mortality rates associated with adult cardiac surgeries requiring hypothermic circulatory arrest (HCA). We explored a method to monitor cerebral blood flow during different brain protection techniques using diffuse correlation spectroscopy (DCS), a noninvasive optical technique which, combined with frequency-domain near-infrared spectroscopy (FDNIRS), also provides a measure of oxygen metabolism.

Methods: We used DCS in combination with FDNIRS to simultaneously measure hemoglobin oxygen saturation (SO₂), an index of cerebral blood flow (CBF_i), and an index of cerebral metabolic rate of oxygen (CMRO_2i) in 12 patients undergoing cardiac surgery with HCA.

Results: Our measurements revealed that a negligible amount of blood is delivered to the cerebral cortex during HCA with retrograde cerebral perfusion, indistinguishable from HCA-only cases (median CBF_i drops of 93% and 95%, respectively) with consequent similar decreases in SO₂ (mean decrease of 0.6 ± 0.1% and 0.9 ± 0.2% per minute, respectively); CBF_i and SO₂ are mostly maintained with antegrade cerebral perfusion; the relationship of CMRO_2i to temperature is given by CMRO_2i = 0.052e^0.079T.

Conclusions: FDNIRS-DCS is able to detect changes in CBF_i, SO₂, and CMRO_2i with intervention and can become a valuable tool for optimizing cerebral protection during HCA.