Acute responses during blood substitution in the conscious rat

Changes in the cellular components of blood in response to exchange transfusion with the fluorocarbon emulsion blood substitute Fluosol-DA 20% have been examined in conscious chronically catheterized rats. Continuous isovolemic exchange transfusion at 1 ml X min-1 for 40 min reduced the mean haematocrit from 36% to less than 2%. The animals behaved normally during blood replacement and no significant changes in mean arterial blood pressure, heart rate or respiration rate were observed. An exponential decline in circulating red and total white cell count was observed during exchange transfusion. However, the rates of decline were significantly different for red and white cells as was reflected in the half-times (t1/2) for the decrease in cell numbers (red blood cells: 7.5 min; white blood cells: 27.5 min) and the fractional turnover rates (k). An exponential decline in total plasma protein and plasma albumin concentrations occurred in response to blood substitution with highly significant inverse log-linear relationships with time and with closely similar half-times (t1/2) for the decrease in concentration (total protein: 10.5 min; albumin: 11.3 min) and the fractional turnover rates (k). If a single well-mixed compartment is assumed for each type of blood cell and plasma proteins, the differences in turnover rates can be attributed to the volumes of these compartments (red blood cells: 10.9 ml.; white blood cells: 40.0 ml.; total protein: 15.2 ml.; albumin: 16.4 ml.). Possible anatomical boundaries for these compartments are considered. Plasma sodium concentration showed a significant decrease in response to blood substitution; no corresponding changes in either plasma potassium or total plasma calcium concentrations were observed. A progressive rise in plasma glucose concentration occurred during blood substitution, with levels at the end of the experiment approximately 2-fold higher than the mean initial value. There was also a small but not statistically significant decrease in plasma urea concentration during the procedure.