Interstitial fluid shifts to plasma compartment during blood donation

A vasovagal reaction (VVR) occurs in 0.8% to 0.9% of voluntary blood donors in Japan. However, they generally tolerate the acute loss of 400 mL of whole blood rather well, perhaps because several circulatory defense mechanisms compensate for the loss. This study aimed to determine the extent to which an interstitial fluid shift contributes to the development of a VVR.

Blood hemoglobin (Hb) was measured upon admission, at venipuncture, and immediately after collecting 400 mL of whole blood from 736 donors. Shifted fluid volume was calculated using a formula that included Hb levels and estimated total blood volume.

By the end of blood collection, 188 ± 80 and 211 ± 82 mL of fluid, which is equivalent to almost half of the total amount of withdrawn blood, had entered the intravascular space in male and female donors, respectively. The difference between the sexes was significant despite the lower body weight and circulating blood volume of the female donors. Body weight increased, whereas age decreased the volume of shifted fluid in female donors.

Blood loss after donation is quickly compensated by an interstitial fluid shift into the intravascular space and may not be the only direct cause of VVR in the setting of a whole blood donation of 400 mL.