SPLANCHNIC ERYTHROCYTE CONTENT DECREASES DURING HEMODIALYSIS - A NEW COMPENSATORY MECHANISM FOR HYPOVOLEMIA

Splanchnic and splenic erythrocyte volumes decrease during postural ch anges and exercise to help maintain central blood volume and cardiac o utput. The contribution of this compensatory mechanism to hemodynamic stability during dialysis has not been studied, however. In 8 ESRD pat ients, age 51.0 +/- 4.5 years old, we measured changes in the splanchn ic/splenic erythrocyte volume during dialysis by tagging the patients' erythrocytes with technetium and following abdominal radioactivity ov er time. Splanchnic radioactivity decreased to 90.2 +/- 3.8% (mean +/- SEM) of the baseline value after 2 hr of accelerated fluid removal (3 .7 +/- 0.4 liters) during dialysis (DUF), while it remained relatively unchanged after two hours of dialysis without fluid removal (DD) [106 .5 +/- 2.3%, P (DUF vs. DD) 0.03]. Splenic radioactivity decreased to 89.2 +/- 5.0% of the initial value during DUF versus 103 +/- 3.5% duri ng DD, but the decrease was noted only during the last 30 minutes of D UF and did not attain statistical significance. Autonomic nervous syst em integrity was measured by the spontaneous variation of the R-R inte rval during deep respiration (E/I ratio) and by the Valsalva ratio. Th e mean E/I and Valsalva ratios in the eight patients were 1.13 +/- 0.0 3 (+/- SEM) and 1.42 +/- 0.1 respectively, suggesting reasonably adequ ate autonomic nervous system functioning. The results suggest that con traction of the splanchnic, and possibly the splenic, vascular beds oc curs during fluid removal associated with hemodialysis. The resultant addition of erythrocytes to the circulation may help maintain central blood volume and cardiac output.