Serum oncocity and myocardial oxygen balance during haemodilution in open-heart surgery

In the first part of the present study the colloid-oncotic properties of degraded gelatin and dextran 70 were compared with each other during moderate normovolemic and extreme haemodilution. Serial serum analyses of colloid oncotic pressure and albumin concentration were performed on 39 open-heart surgery patients. The profile of albumin changes during the 24-hour period beginning with preanaesthetic measurements was identical in both colloid-groups. The data obtained strongly support the supposition that the gelatin solution easily escapes from the circulation due to gelatin's low number average molecular weight. On the other hand the oncotic and haemodynamic effects of dextran 70 may continue for many hours; dextran 70 seems therefore to be an ideal colloid for haemodilution. The second part of the study comprised an investigation of the effects on myocardial oxygen and lactate balance of moderate and extreme haemodilution with dextran 70 on 11 patients undergoing coronary bypass surgery. To compensate fully for the observed decrease in the blood O2-capacity during normovolemic haemodilution (Hct fell from 44 to 32), the coronary blood flow should have been increased by 24% in addition to the increase observed in the myocardial oxygen extraction. The compensation was considered adequate, because no myocardial ischaemia, as judged by the unchanged myocardial lactate balance, developed. The coronary sinus blood samples are, however, a poor reflection of local myocardial metabolic changes in those areas, where coronary flow is most severely restricted.