Differences in tissue oxygenation and changes in total hemoglobin signal strength in the brain, liver, and lower-limb muscle during hemodialysis

Near-infrared spectroscopy has been used to measure regional saturation of oxygen (rSO₂) based on the total hemoglobin (t-Hb) signal strength. To date, few studies have investigated the changes of systemic oxygenation and t-Hb signal strength during hemodialysis (HD). This study aimed to (1) monitor rSO₂ and t-Hb signal strength in the brain, liver, and lower-limb muscle during HD and (2) clarify the differences in rSO₂ and t-Hb signal strength in each compartment. Fifty-three patients receiving 4-h HD were included and divided into three groups according to the compartments in which tissue oxygenation was measured as follows: brain (n = 44), liver (n = 42), and lower-limb muscle (n = 40). The rSO₂ and t-Hb signal strength was monitored using an INVOS 5100c (Covidien Japan, Tokyo, Japan). The rSO₂ levels were significantly lower in the brain than in the liver from HD initiation to the end (HD initiation: rSO₂ in the brain and liver, 46.5 ± 1.3 and 52.4 ± 1.7%, respectively, p = 0.031). Furthermore, compared to the t-Hb signal strength ratio [value at t (min) during HD/initial value before HD] in the brain during HD, there were significant increases in the liver and lower-limb muscle, respectively. In conclusion, deterioration of cerebral oxygenation was remarkable compared to the hepatic oxygenation in HD patients. Our results, which revealed significant differences among the t-Hb signal strength ratios in the brain, liver, and lower-limb muscle during HD, might reflect the non-uniform body-fluid reduction within systemic tissues induced by ultrafiltration.