[Modified hemoglobin as a blood substitute in a rat model]

The use of modified haemoglobin solutions as blood substitutes has been investigated extensively during the past decades. Ultrapurified, polymerised bovine haemoglobin (upbHb) is a promising new substance in this respect. It was the aim of the present investigation to study the cardiovascular and respiratory effects of massive blood replacement with upbHb in a new model of conscious rats with continuous haemodynamic monitoring. METHODS. The right femoral artery and vein of 13 male Sprague-Dawley rats were catheterised during halothane-N2O-O2 anaesthesia. A thermistor catheter was placed in the descending aorta via the left femoral artery for measuring cardiac output by the thermodilution method. After recovery from anaesthesia blood replacement was achieved by arterial blood withdrawal and simultaneous venous infusion of upbHb in equal amounts. The haematocrit was lowered to < 3% and the animals were then left undisturbed in a rat restrainer while breathing room air. RESULTS. The animals showed no signs of disturbed behaviour patterns, distress, or adverse reactions. There were no significant changes in cardiac index and oxygen delivery during the investigation period of 4 h. A marked increase in mean arterial pressure (MABP) and systemic vascular resistance (SVR) of 30% was observed while stroke volume remained unchanged. Blood gases, acid-base status, and plasma glucose showed no major changes. Plasma oncotic pressure increased during the investigation period. CONCLUSIONS. The results indicate that there is adequate oxygenation and sufficient systemic oxygen delivery in conscious and drug-free rats after isovolaemic haemodilution with upbHb to a final haematocrit of < 3%. In contrast to previous haemodilution studies, which have tested non-oxygen-carrying solutions, no changes in cardiac index were observed. The cause of the increase in MAP and SVR remains to be established.