Our main objective has been to analyze the characteristics of the blood processed by the cell saver in pediatric scoliosis surgery. It is a blood saving technique which is increasingly used in major orthopedic surgery to avoid risks of allogeneic transfusions, such as transmission of viral diseases, risks associated with the storage of blood bags, blood group identification errors and potential decrease of immunomodulation5,6. It constitutes one aspect of the multidisciplinary approach to "patient blood management" 7,8, together with preoperative optimization, administration of tranexamic acid, ensuring a careful surgical technique with hemostasis, posterior surgical approach and lower transfusion triggers9.
Our results reveal that the percentage of hematocrit obtained, which is 70.38%, is similar to that described by the technical data provided by OrthoPat® for adult patients, namely, 75%. In agreement with previous studies 10-12, the blood from the cell saver presents much higher levels of hematocrit than patient blood (30-45%) and also higher than that present in red blood cell concentrates from donors (50-65%), which is quite variable. However, leukocytes are not completely eliminated from our sample, in fact their quantity is similar to the levels found in patient postoperative analysis. Several studies13,14 have further analyzed the presence of different types of white cells and inflammatory molecules in the collected blood and their relationship with postoperative infection or days of admission. Nevertheless, no relationship or differences have been established. What seems to be clearer is the lower immunomodulatory response of autologous blood with respect to allogeneic blood transfusion15.
Immunomodulation seems to be especially important in cancer patients. The use of cell saver in these cases is still controversial because of the risk of cancer cell spreading. On the other hand, the transfusion of autologous blood would reduce the risk of immunosuppression caused by allogeneic blood transfusion16,17.
There is no agreement on potential effects of the presence of leukocytes in the processed blood. Special filters for their elimination increase the cost and affect the flow conditions during retransfusion, resulting in the activation of the complement system. In the case of immunosuppressed or cancer patients, leucodepletion of these concentrates could be considered for safety reasons during major orthopedic surgery18,19.
The amount of platelets in autologous blood is, despite its great variability, consistently smaller than that found in pre and postoperative blood samples of the patient. These platelets levels are consistent with previous studies20,21. They suggest that the processing of platelets by the cell saver is more efficient than in the case of leukocytes. According to M. Muñoz et al.3, the processing of platelets in a postoperative recovery model with OrthoPAT® would in fact reach 88%. The importance of reinfusion of processed platelets is not clear, but it may not be functional due to the discontinuous centrifugation of this device.
The hemolysis index is close to the maximum, which indicates that in the blood from the cell saver there is a high level of red blood cell breakdown. In experimental models of processed blood3 the concentration of free hemoglobin in plasma was reduced by 96% with the OrthoPAT® cell saver. As for the ions, potassium deserves special attention since a rapid reinfusion of high levels can have serious consequences. Its elimination in experimental models is around 97%3. None of our patients showed ECG abnormalities or significantly increased concentrations of this ion in the subsequent gasometric controls, despite the fact that some cases presented high concentrations of around 8 mEq x l-1. Nevertheless, the total amount of potassium in the autologous blood transfused to the patient is unlikely to be harmful. The levels of sodium and chlorine that ensure homeostasis for cell preservation are found to be similar to those in the patient blood.
The volume of red blood cells from the cell saver is directly related to the hematocrit thereof. The minimum volume obtained is 50ml, which corresponds to a 17 kg patient undergoing neuromuscular scoliosis. For this type of patients, with weights less than 25 kg, it might be advisable to process blood with continuous processing devices, in order to obtain the largest possible reinfusible volumes and increased hematocrit concentrations22,23.
According to the microbiological analysis of the samples of autologous blood, despite surgical asepsis and antibiotic prophylaxis, it is inevitable that bacterial contamination will appear in almost half of the cases (42.86%). These data are consistent with previous publications24-29 in which the contamination exceeds 40%. However, the reinfusion of this contaminated blood did not cause a higher incidence of fever or SSI, in agreement with the findings of the previously mentioned studies. As the isolated bacteria come from skin and environmental flora, no pathogenic germ has been found, which indicates good asepsis procedures and correct antibiotic prophylaxis of our patients. Many factors may be responsible for contamination of the blood processed, including a prolonged exposure of a wide surgical field, which is characteristic of scoliosis surgery, complex and multiple instrumentation, many professionals working in the surgical field, including the replacement of team members, as well as multiple manipulations of vascular access and fluid administration among others.
Concerning immunocompromised patients, the use of a cell saver could contribute to the development of infections. To prevent this risk, adding antibiotics to the samples of processed blood in addition to applying leucodeplection should be considered as additional measures30,31. Another very different case is the immunocompetent patient, as are the majority of patients undergoing pediatric scoliosis. With careful aseptic techniques, adequate antibiotic prophylaxis and not exceeding the storage time of the blood concentrates (6 hours at room temperature or refrigerated at 4 °C for 24 hours), it continues to be a safe technique. The ranges of SSI in pediatric scoliosis can vary from 0.5% to more than 25% depending mainly on whether or not of the scoliosis is of neuromuscular origin32,33. The latter consitutes a risk factor, together with the length fo the stay, surgical instrumentation, the surgical intervention of the sacrum, the incorrect administration of antibiotic prophylaxis or the persistence of postoperative spine curvature34.
Pediatric scoliosis surgery remains one of the surgeries with the highest bleeding rates35. In the present study, analytical differences between the preoperative and the immediate postoperative period have been observed. The implication is that one should continue applying and introducing new blood-saving measures. The analysis of preoperative hemoglobin revealed that 25% of the patients had a value of less than 13 g / dl, with a minimum of 10.4 g / According to this results, there are patients (<25%) with preoperative hemoglobin around or below the limit to be considered anemic. Following the multidisciplinary approach of “Patient Blood Management”, preoperative anemia should be optimized to reduce days of stay and perioperative transfusions 36-38. One of the goals of our center in this regard is that no anemic patient without prior optimization should undergo such surgery. As the associated blood loss is considerable, and it is a programmed surgery, its date could be delayed until the patient's condition improves. In addition, we observe how the preoperative hematocrit is directly related to the volume of autologus blood obtained. Our results show that scoliosis surgery continues to cause coagulopathy and a decrease in hemoglobin level (pre-surgery 13.68 g / dl, post-surgery 10.90 g / dl). To prevent such undesired effects, it is necessary to reduce bleeding by means of pharmacological agents (tranexamic acid), maintenance of low arterial pressure, hemodilution with fluid therapy, intraoperative techniques applied by surgeons to improve hemostasis, the use of cell saver and restrictive transfusion triggers to contribute to the reduction of transfusion ratios. These measures are reviewed and carried out according to the latest guidelines on blood management in pediatric scoliosis surgery39,40.
The main limitation of our study is the small sample size. To obtain stronger results, it would be necessary to expand it. Moreover, it is a heterogeneous group of patients in terms of weight and origin of their scoliosis, among other factors. For instance, neuromuscular scoliosis is associated in most cases with increased morbidity and a higher risk of bleeding. In addition, other influential factors in bleeding such as the number of fusion levels or Cobb angle are not considered. We should also stress that this is a prospective study conducted in a single center.
From our results we conclude that, in the pediatric patient, the cell saver used in this study obtains red blood cell concentrates with a percentage of hematocrit which is in agreement with commercial information. The reinfusion of this product seems safe from an infectious and biochemical point of view. Its implications at the immunological level are not fully clarified either in the previous literature or in our study. Broader studies that are specifically focused on this last aspect would be helpful in this regard.