In-line blood warming and microfiltration devices. II. Influence of blood temperature on flow rate and hemolysis during pressure transfusion through microfilters and transfusion sets.

The influence of blood temperature on flow rate and hemolysis was studied. Homogeneous aggregate-free blood was transfused through six different microfilters and transfusion sets, combined with a large-bore venous cannula (Venflon No. 2) at a constant pressure of 20 kPa. Flow rates and plasma hemoglobin for cold (+5 degrees C) and prewarmed (+37 degrees C) blood were determined separately. Warming the blood from +5 degrees C to +37 degrees C improved the flow from 49 to 86%. The best flow rates with +37 degrees C blood were obtained with surface filters (MF10B, 275 g/l), and the poorest with depth filters (Swank, 179 g/l). However, the transfusion set and venous cannula seemed to have more influence on the total flow resistance. The Fenwal "dry-heat" warmer was found to have a great flow resistance. The pressure transfusion caused only a slight increase in free plasma hemoglobin of cold blood and no increase in prewarmed blood. It seems more practical to warm the entire blood unit before transfusion than to use so-called in-line blood warmers, because prewarming results in a flow rate approximately twice as high as that obtained with coils.