Colloid oncotic pressure (COP) is an important factor in cardiac surgery, owing to its role in haemodilution. The effect of cardiopulmonary bypass prime fluids on the COP is unknown. In this study, the effect of crystalloid and colloid prime fluids, with or without retrograde autologous priming (RAP), on the COP during elective cardiac surgery was evaluated.

Randomized controlled trials and prospective clinical trials comparing crystalloid and colloid priming fluids or with RAP were selected. The primary outcome was the COP; secondary outcomes were fluid balance, fluid requirements, weight gain, blood loss, platelet count and transfusion requirements.

From 1582 records, 29 eligible studies were identified. COPs were comparable between gelofusine and hydroxyethyl starch (HES) during bypass [mean difference (MD): 0.69; 95% confidence interval (CI): −2.05, 3.43; P = 0.621], after bypass (MD: −0.11; 95% CI: −2.54, 2.32; P = 0.930) and postoperative (MD: −0.61; 95% CI: −1.60, 0.38; P = 0.228). Fluid balance was lower with HES than with crystalloids. RAP reduced transfusion requirements compared with crystalloids. Blood loss was comparable between groups.

COPs did not differ between crystalloids and colloids. As a result of increased transcapillary fluid movement, fluid balance was lower with HES than with crystalloids. Haematocrit and transfusion requirements were comparable between groups. However, the latter was lower when RAP was applied to crystalloid priming compared with crystalloids alone. Finally, no differences in blood loss were observed between the groups.