Many patients require a blood transfusion after cardiac surgery. Dilution of the patient's blood with the pump prime may contribute to this need. Retrograde autologous priming (RAP) of the cardiopulmonary bypass (CPB) circuit reduces CPB prime volume, and hence haemodilution [1]. The purpose of the present study was to compare RAP of the CPB circuit with normal priming in reducing both the percentage of patients requiring homologous blood and the volume of blood transfused. The incidence of complications was noted.

After ethics approval and informed consent, 84 patients undergoing primary coronary artery surgery were recruited. Patients were randomized into control and RAP groups. Acute normovolaemic haemodilution (ANH) was performed as appropriate, aiming for a minimum haematocrit during CPB of 20%. The incidence of perioperative myocardial infarction was monitored by troponin T concentrations and new electrocardiographic changes. Haematocrit below 18% while on CPB and below 24% during the postoperative period were used as triggers for blood transfusion. All data were analyzed using the appropriate statistical tests; P < 0.05 was considered statistically significant.

The groups were matched for age, weight, New York Heart Association classification and preoperative haematological data. There was a significant difference in homologous blood transfusion between the two groups. The percentage of patients receiving homologous blood was 47.5% in the control group versus 20.0% in the RAP group (P = 0.009). The mean volume of homologous blood transfused was 296.7 ml in the control group versus 81.9 ml in the RAP group. Table 1 shows various parameters and their significance between these two groups.

The present results indicate that reducing the CPB prime and haemodilution by means of RAP of the CPB circuit is a safe and effective means of reducing homologous blood transfusion. We found no significant adverse effects.