Changes in cerebral oxygenation and cerebral blood flow during hemodialysis - A simultaneous near-infrared spectroscopy and positron emission tomography study

Near-infrared spectroscopy (NIRS) is used to monitor cerebral tissue oxygenation (rSO(2)) depending on cerebral blood flow (CBF), cerebral blood volume and blood oxygen content. We explored whether NIRS might be a more easy applicable proxy to [O-15]H2O positron emission tomography (PET) for detecting CBF changes during hemodialysis. Furthermore, we compared potential determinants of rSO(2) and CBF. In 12 patients aged >= 65 years, NIRS and PET were performed simultaneously: before (T1), early after start (T2), and at the end of hemodialysis (T3). Between T1 and T3, the relative change in frontal rSO(2) (Delta rSO(2)) was -8 +/- 9% (P = 0.001) and -5 +/- 11% (P = 0.08), whereas the relative change in frontal gray matter CBF (Delta CBF) was -11 +/- 18% (P = 0.009) and -12 +/- 16% (P = 0.007) for the left and right hemisphere, respectively. Delta rSO(2) and Delta CBF were weakly correlated for the left (rho 0.31, P = 0.4), and moderately correlated for the right (rho 0.69, P = 0.03) hemisphere. The Bland-Altman plot suggested underestimation of Delta CBF by NIRS. Divergent associations of pH, pCO(2) and arterial oxygen content with rSO(2) were found compared to corresponding associations with CBF. In conclusion, NIRS could be a proxy to PET to detect intradialytic CBF changes, although NIRS and PET capture different physiological parameters of the brain.