Ten per cent low molecular weight hydroxyethyl starch is a plasma substitute only recently used as priming solution in an extracorporeal circuit, in contrast to human albumin and gelatin. To evaluate the effect of priming solutions on haemodynamics and colloid osmotic pressure, we studied 36 patients elected for cardiopulmonary bypass (CPB). They were randomly assigned to 2.5% hydroxyethyl starch, 3% gelatin or 4% human albumin priming solution. Total blood loss (perioperative + intensive care unit period) was higher in the gelatin group than in the albumin and hydroxyethyl starch groups. During CPB, the colloid osmotic pressure was best preserved in the gelatin group, although no excessively low colloid osmotic pressures were measured in the other two groups. Due to the extended half-life and the additional postoperative colloid administration, the hydroxyethyl starch group had a higher colloid osmotic pressure in the postoperative phase. We conclude that, next to human albumin, 2.5% hydroxyethyl starch is a safe CPB priming solution additive and is effective as plasma substitute. Its somewhat longer half-life requires adaptation of the routine protocol for transfusion of colloids and blood products.
An overall platelet function test in whole blood, which simulates conditions under arterial pressure, is useful in measuring tbe effect of polymer materials on blood hemostatic function. We per· formed biocompatibility tests with materials or plasma substitutes by interaction of blood from healthy volunteers and then subjected these blood samples to platelet function analysis (Thrombostat). We tested also the capacity of locally applied hemostatic agents for bleeding control by direct application of these agents onto the Thrombostat measuring cell. The biocompatibility tests with materials exposed to blood appeared very discriminating between compatible and noncompatible materials. The hemostatic capacity of blood exposed to noncompatible materials (assessed by binding of active thrombin) reduced markedly after one hour incubation of the material. The plasma substitutes did not affect hemostasis significantly. However, a blood dilution of 40%, as in cardiopulmonary bypass, increased the time required for closure of tbe measuring cell by a platelet plug exponentially. Local hemostatic agents could be selected according to their capacity to enhance platelet plug formation. In addition, ADP mixed with the bemostatic agent was most effective in improving capacity. We conclude tbat platelet function analysis contributes importantly to screening of materials and plasma substitutes with regard to their interaction with primary hemostasis.Platelet function is pivotal in hemostasis, specifically at increased shear stress and under arterial pressure. The mechanism of platelet function is multifactorial; moreover, the process of platelel plug formation is complex. Therefore, one single platelet function test, such as aggregation, may be inadequate to detect wilh high sensitivity the effect of (artificial) polymers on platelets. For precise measurement of biocompatibility or for monitoring of components wilh suspected effects on platelet function, a laboratory multifactorial platelet test, that simulates the in vivo primary hemostasis may be required. We used a platelet function analyser (Throm· bostat) to measure the effect of exposure of polymeric components to whole blood on plalelet function. In this way, we were able to determine I) biocompatibility of materials, and 2) the effect of plasma substitutes on hemostasis, and we were able to rapidly screen 3) the optimal composition of new hemostasis promoting agents for surface application. These hemostatic agents are being developed to reduce local bleeding. All these assays were performed with whole blood from healthy volunteers and therefore, could be performed under standardized conditions.
Surface treatment of a cardiopulmonary bypass circuit with heparin improves its haemocompatibility. However, potential side effects of this layer of heparin are impairment of O 2 transfer and CO 2 transfer in the oxygenator and heat transfer in the heat exchanger. Therefore we studied these side effects during extracorporeal circulation with moderate hypothermia in 30 patients who underwent elective coronary artery bypass grafting surgery. All patients were heparinized systemically. In 15 patients (Duraflo II-group) we used an extracorporeal circuit (including a Bentley Bos-CM50 membrane oxygenator) which was treated with heparin. The results of this group were compared with those obtained from another group of 15 patients (control-group), who were operated upon with an identical extracorporeal circuit but without heparin surface treatment.We found no significant differences between the two groups in O 2 transfer, CO 2 transfer or heat transfer during normothermia or hypothermia.We concluded that neither O 2 transfer and CO 2 transfer of the oxygenator nor heat transfer of the heat exchanger were impaired by Duraflo II heparin surface treatment during clinical cardiopulmonary bypass with moderate hypothermia.
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