Platelets in shed mediastinal blood used for postoperative autotransfusion

Autotransfusion of a restricted volume of shed mediastinal blood does not affect the haemostatic capacity in patients following cardiac surgery

The aim was to investigate the haemostatic capacity after autotransfusion of shed mediastinal blood in patients following cardiac surgery. Fifteen cardiac surgery patients with a chest tube drainage ≥ 300 mL blood within the first 6 hours postoperatively were included. The haemostatic capacity was evaluated using whole blood thromboelastometry (ROTEM(®)), impedance aggregometry (Multiplate(®)) and conventional coagulation tests. Measurements were carried out in (1) mediastinal blood, and in blood samples obtained, (2) before autotransfusion, and (3) after autotransfusion of mediastinal blood. In shed mediastinal blood, ROTEM(®) analyses showed reduced clot firmness in the EXTEM (p < 0.001), INTEM (p < 0.001), and FIBTEM assay (p = 0.002). Platelet function and conventional coagulation parameters were significantly impaired (p < 0.001). However, ROTEM(®), platelet function and conventional coagulation tests remained unchanged after autotransfusion.

CONCLUSION

Shed mediastinal blood has a substantially reduced haemostatic capacity, but autotransfusion of an average of 350 mL did not affect the overall haemostatic capacity.

Modeling Centrifugal Cell Washers Using Computational Fluid Dynamics

Reinfusion of shed blood during surgery could avoid the need for blood transfusions. Prior to reinfusion of the red blood cells, the shed blood must be washed in order to remove leukocytes, platelets, and other contaminants. Further, the hematocrit of the washed blood must be increased. The feasibility of using computational fluid dynamics (CFD) to guide the design of better centrifuges for processing shed blood is explored here. The velocity field within a centrifuge bowl and the rate of protein removal from the shed blood has been studied. The results obtained indicate that CFD could help screen preliminary centrifuge bowl designs, thus reducing the number of initial experimental tests required when developing new centrifuge bowls. Although the focus of this work is on washing shed blood, the methods developed here are applicable to the design of centrifuge bowls for other blood-processing applications.

Unwashed shed blood infusion causes deterioration in right ventricular function after coronary artery surgery

We investigated right ventricular function after infusion of unwashed shed blood collected from mediastinal and chest tube drainage. Changes in thromboxane B2 (TXB2) and 6-keto-PGF1 alpha, which are stable metabolites of thromboxane A2 (TXA2) and prostacyclin respectively, were also investigated. The amount of infused shed blood was 484 +/- 76 ml (mean +/- SD). Right ventricular ejection fraction decreased rapidly after the infusion and did not return to its original level until 120 minutes later (P < 0.05). Mean pulmonary artery pressure rose after infusion of the shed blood (P < 0.05). The TXB2 level in the unwashed shed blood was about 20,000 times higher than the preoperative plasma level. The plasma TXB2 level at 30 minutes after the infusion was significantly elevated (P < 0.05), and at 120 minutes it had returned to the original level. Unwashed shed blood may contain vasoactive substances that induce the release of TXA2 and increase right ventricular afterload.

Intraoperative and postoperative blood salvage

Surgical patients present unique opportunities for reducing allogeneic transfusions via perioperative blood salvage. Intraoperative cell saver techniques enable the collection of autologous blood from the surgical field and cardiopulmonary bypass circuit for return to the patient. Washing and hemoconcentration creates a product with an average hematocrit of 50% that carries normal erythrocyte survival, with minimal coagulation factors of platelets. Postoperative autotransfusion of shed blood from chest tubes or surgical drains enables additional blood conservation, reducing allogeneic transfusions by as much as 50%. Both intermittent and continuous autotransfusion systems using standard chest drainage equipment are available that require minimal setup and maintenance at the bedside. The hematocrit of shed blood is 20-25%, with depletion of clotting factors and platelet function. Potential advantages of perioperative blood salvage include the ready availability of large volumes of patient-compatible blood, with optimal oxygen-carrying capacity, that is virtually free from the risk of viral contamination. Specific indications, contraindications, and techniques for the salvage and administration of these vital products are presented.

Autotransfusion after open heart surgery: the oxygen delivery capacity of shed mediastinal blood is maintained

Autotransfusion of mediastinal shed blood after open heart surgery has become a common and accepted procedure in reducing the need for homologous transfusion during the last 15 years. The objectives of the present study were to investigate the oxygen delivery capacity of autotransfused shed mediastinal blood, compared to patient-blood, during cardiopulmonary bypass and in the postoperative period. Ten consecutive patients undergoing elective cardiac surgery were studied. Mediastinal shed blood was collected in the cardiotomy reservoir and retransfused during the first 18 postoperative hours. The oxygen delivery capacity of the blood to the tissues was calculated by use of the oxygen status algorithm (OSA 2.0) programme and measurement of the 2,3-diphosphoglycerate (2,3-DPG) concentration. Autotransfusion volume ranged from 450-1530 ml per patient (median 824 ml). Shed blood had a mean haemoglobin level of 8.8 g/dl and 7.4 g/dl at 1 h and 6 h of autotransfusion, respectively. There were no significant changes of 2,3-DPG concentration in the patient-blood during cardiopulmonary bypass or after autotransfusion compared to preoperative values. P50 for oxygen (3.6 and 3.6 kPa) and 2,3-DPG concentrations (5.3 and 5.1 mikromol/ml erythrocyte) in shed mediastinal blood (1h and 6h postoperatively) were not significantly different compared to patient-blood. The results demonstrate that the oxygen delivery capacity of shed mediastinal blood is maintained and that the oxygen affinity of patient-blood is not influenced by autotransfusion.