Cerebral oxygenation and hemodynamics during blood donation studied by near-infrared spectroscopy

BACKGROUND: Blood donation is a safe human model for acute blood loss. This study investigated associated changes in regional cerebral oxygenation and cerebral blood volume (CBV) by near-infrared spectroscopy (NIRS). STUDY DESIGN AND METHODS: Fifty healthy blood donors donated 450 mL of whole blood within 4 to 9 minutes. Changes in regional cerebral oxygen saturation (rSO(2)) and cerebral tissue Hb concentration (HbT) were semiquantitatively measured by NIRS. Venous Hb concentration was measured before and after blood donation. The predonation and postdonation CBV was estimated from HbT and venous Hb concentration. Differences between pre- and postdonation study parameters were analyzed by paired t tests (p < 0.05). RESULTS: Within the study group, rSO(2) decreased by 0.44 sat percent (p < 0.01) on average during blood donation, which is still within the range of individual physiologic baseline variation. The average venous Hb concentration decreased significantly by 4.6 percent, whereas HbT increased significantly by 2.5 percent and CBV increased even by 7.5 percent on average. CONCLUSION: The increase in CBV indicates cerebral vasodilation, which seems to be the major compensation mechanism during acute blood loss. The decrease in rSO(2) was relatively small, indicating that cerebral oxygenation was maintained within the physiologic range.