Fibrinogen-I¹³¹, T-1824, and red cell-Cr⁵¹ spaces following hemorrhage

¹ Department of Physiology, Medical College of Georgia, Augusta, Georgia

Altered hemodynamics following hemorrhage causing extended mixing time of indicators, fluid shifts, and changes in indicator disappearance slopes were studied in 17 anesthetized splenectomized dogs. Fibrinogen-I¹³¹, T-1824, and red cell-Cr⁵¹ spaces were determined simultaneously and the animals were bled 11.3 ml/kg. There was a significant decline in concentration of the three indicators that could not be accounted for on the basis of hematocrit or plasma protein concentration changes. After 20 min stabilization, the spaces were again measured, and the animals were bled an average of 17.7 ml/kg (to an arterial pressure of 60 mm Hg). The decline in indicator concentration was again observed. After allowing the animals to stabilize for 20 min, the spaces were again measured. There was a mobilization of red cells following the first hemorrhage and a trapping of red cells following the second hemorrhage. Fibrinogen-I¹³¹ and T-1824 spaces agreed closely with the expected spaces calculated from changes in hematocrit or plasma protein concentration. The fibrinogen space was consistently less than the T-1824 space. The ratio BV_cells/BV_fibrinogen significantly increased from 0.92 to 0.99 following the hemorrhages. This suggested a possible redistribution of "extra plasma" or a smaller involvement of extravascular space in the plasma volume determination. BV_cells/BV_T-1824 did not change following the hemorrhages. Possible causes for the decline in indicator concentration following hemorrhage are discussed.