Discussion
blood loss, hemolysis, postoperative bleeding
HYPOTONIC, BLOOD LOSS, POSTOPERATIVE BLEEDING, FRAGILITY, BLOOD, HEMOLYSIS, INFLAMMATORY RESPONSE
In this trial comparing the effects of differing anticoagulant regimens (citrate or heparin) on cell salvage in adult patients undergoing elective pump CABG, small but relevant differences were observed between the two groups. WRBC had a significantly lower hematocrit and higher MCV and a larger residual thrombocyte count in the citrate group. There were also differences in WBC differentiation between groups. In the collecting bowl (before the cell salvage washing procedure but after treatment with anti-coagulant) IL-10 was significantly higher in the citrate group. After WRBC transfusion in the patients, there were no differences in interleukin blood levels between the groups, but MPO was significantly higher in patients in the heparin group. Both intra-operatively and post-operatively, this did not result in differences in transfusion of allogenic blood products or blood loss. Washed red blood cell concentrates in both groups met the quality guidelines published by the American Association of Blood Banks [We believe the differences in MCV and MCHC can be attributed to a number of factors. ACD-A is hypotonic (400–440 mOsm/kg, sodium content 214–234 mEq/l) and acidic (pH 4.5–5.5). Both have been implicated in increased MCV, the latter especially when ACD-A concentrations are relatively high [Since ACD-A is a hypotonic solution, the osmotic effect on red blood cells would increase with increasing ATBR. However, the ATBR and incubation time of blood in the BCR was comparable in both groups. Consecutive washing cycles could possibly have an impact on WRBC quality but the volume of red blood cells washed twice and the proportion of patients per study group whose red blood cells were washed twice, were again comparable between groups.During the washing cycle, the centrifuged volume of red blood cells at which the cell saver sensor detects the buffy coat will have been comparable between the groups. In the citrate group because of the larger MCV, there are therefore fewer red blood cells. This can explain the lower Hb, but not the lower Ht, in the citrate group (since the MCH was comparable between the groups). The same cell saver device was used in all patients but can be expected to deliver a comparable Ht of WRBC in both groups, only when MCV is similar. A larger MCV, with a comparable MCH, may have caused a less efficient centrifugal movement of RBC in the citrate groups during washing. This may have led to a more dilute WRBC, which would also explain why the volume of WRBC in the citrate group was higher (though not significantly), although the total volume of fluid in the BCR was comparable between the groups. Since the product of Hb and the volume of WRBC was comparable between the study groups, the total amount of autologous Hb transfused in both groups was comparable, which argues against significant differences in hemolysis between groups. Fortunately, the quality guidelines for perioperatively salvaged RBCs, published by the American Association of Blood Banks (AABB), were met in both groups (Hct > 50%, Hb > 15 g/dl, fHb < 1.0 g/dl) [There was a significantly lower residual thrombocyte count in the WRBC in the heparin group. This could be an effect of more pronounced thrombocyte activation in the heparin group. Both in vitro [The inflammatory response elicited by cardiac surgery is characterized by a significant release of both pro- and anti-inflammatory cytokines [Interpretation of the differences found in WBC differentiation in the washed RBC concentrate is difficult because of minimal baseline differences in WBC differentiation, though the effects of citrate versus heparin as described above, especially the differing effects on polymorphonuclear degranulation, could play a role.Undoubtedly this pilot study has a number of limitations; primarily it is a small, single center study, despite which findings are statistically robust. The larger anticoagulant priming volume could cause early hemolysis when ATBR was highest, but this was masked by the washing process. A blood smear and quantification of osmotic fragility might have added reinforcing data. Heparin was given systemically in both study groups. Despite equivalent doses in both groups, a supra-additive effect of systemic heparin with heparinized saline in the heparin group cannot be excluded totally. Differences in blood loss during the first 24 h, may have been nullified by the standard algorithm for the treatment of postoperative bleeding and the effect of differing techniques and outcomes between surgeons could be a possible confounding factor. Furthermore, blinding was not complete until the patient left the operating room.