Evaluation of splenic volume and oxygenation during hemodialysis

During hemodialysis (HD), the redistribution of blood from the hepatosplanchnic vascular bed to the central circulation is a key compensatory response to ultrafiltration. A major blood reservoir, the spleen can expel red blood cells into the circulation upon contraction. However, changes in splenic volume and oxygenation during HD have yet to be fully investigated.

Splenic regional oxygen saturation (rSO₂) was measured in 48 patients (33 men, 15 women) during HD using an INVOS 5100C oxygen saturation monitor (Covidien Japan, Tokyo, Japan). We assessed the spleen index by ultrasonography before and after the same HD session.

The splenic rSO₂ of patients undergoing HD was significantly lower than that of healthy controls (64.3 ± 13.4 vs. 87.0 ± 5.1%, p < 0.001). In contrast, no significant difference was detected between the pre- and post-HD values (64.3 ± 13.4 vs. 64.5 ± 13.6%, p = 0.890). The spleen index did not differ significantly between healthy control and pre-HD (31.3 [24-33] vs. 32.6 [23-40] cm², p = 0.416). However, the spleen index decreased significantly after HD (32.6 [23-40] vs. 28.1 [20-35] cm², p = 0.009). Multivariate regression analysis also showed that the pre-HD spleen index (standardized coefficient = -0.319), serum creatinine concentration (standardized coefficient = -0.492), and serum β2-microglobulin level (standardized coefficient = 0.344) were independently associated with changes in the spleen index.

In conclusion, splenic rSO₂ did not change significantly during HD, whereas the spleen index decreased. This reduction may reflect active splenic contraction, passive venous decongestion, or both.