Blood volume and haemodilution in extracorporeal circulation: changes during perfusion.

An adequate circulating blood volume is recognized to be important after open-heart surgery (Carr, Sloan, and Tovar, 1960). A number of post-operative studies have attempted to correlate clinical determinations of blood loss with volumes estimated by tracer techniques. Discrepancies noted have been attributed to extensive haemorrhage into traumatized tissue redistribution of functional extracellular fluid by plasma exudation occurring after any form of major surgery (Berger, Boyd, and Marcus, 1964), or to the homologous blood syndrome, in which there is a shift of blood from the extracorporeal circuit into the patient during perfusion and a measurable blood deficit post-operatively (Gad-showed no discrepancy in the volumes estimated by clinical and isotope methods (Theye and Kirklin, 1963). The use of haemodilution and plasma expanders during and after cardio-pulmonary bypass introduces new factors in blood volume change (Ankeney, Renner, Leverett, and Beheler, 1965) which call for measurement. The advent of a rapid, semi-automatic system (Williams and Fine, 1961) has permitted more accurate control of replacement therapy (Berger et al., 1964; Flanagan et al., 1964); whether the method is reliable in the presence of dextran or could be used during perfusion has not been previously determined. An attempt has been made to evaluate these issues. It has proved possible to provide during perfusion sufficiently stable conditions of flow rate, blood loss, and distribution of blood between the patient and the extracorporeal circuit to carry out studies of red cell and plasma volumes during bypass, particularly with low molecular weight dextran (LMWD) haemodilution. The post-operative blood volume studies on some of these patients will be reported separately. PROTOCOL The effect of LMWD on standard radioactive methods of red cell and plasma determinations was established in a group of patients who were recovering from thoracic surgery not involving bypass. These also served as a comparative control series for post-operative observations. All patients who underwent isotope investigations gave personal consent during the experimental period. Changes of blood volumes during standard per-fusion were studied using haemodilution with LMWD, and these were compared with the effects of perfusion using 5% dextrose solution in part, or whole blood for perfusion. METHODS GROUP I Six patients who were undergoing thoracic surgery without perfusion had initial red cell and plasma volume determinations made over 30 to 65 minutes immediately following the induction of anaesthesia. Blood loss and replacement during surgery and recovery was on a volume-for-volume basis with additional transfusion based on the …