In Reply: What Are We Transfusing? Evaluating the Quality and Clinical Utility of Intraoperatively Salvaged Red Blood Cells in Spinal Deformity Surgery: A Nonrandomized Controlled Trial

To the Editor: We appreciate the thoughtful commentary on our work1,2 and agree that autologous salvaged red blood cells (sRBCs) are an important tool within patient blood management across various subspecialties. However, several points raised in their critique merit closer examination. Specifically, their critique hinges on 2 key assumptions: (1) that RBCs are healthy before salvage in modern spine surgery and (2) that the high levels of hemolysis and poor sRBC quality observed result from procedural deficiencies in our institution's salvage process. Our study aimed to assess sRBC quality under real-world conditions, not to evaluate all possible salvage or procedural variables. Our institution's protocols for RBC salvage are standardized and followed by trained perfusionists. The consistency of our findings across surgeons, departments, and operating locations shows that the observed issues with sRBC quality are unlikely attributable to operator error or equipment malfunction but rather due to the harsh conditions inherent to modern spine surgery. This study focused on sRBC quality in complex spine surgery, and our findings are not generalizable to other surgical settings. Past studies on the utility and effectiveness of RBC salvage involve subspecialities with greater potential for high-flow blood loss and rapid accumulation for salvage (eg, vascular surgery, transplant, cardiac). By contrast, blood loss in spine surgery is characterized by a low-flow venous ooze, with RBCs unavoidably exposed to high-heat electrocautery, hemostatic agents, stasis, and other environmental factors. Posterior spinal dissections are performed exclusively with electrocautery throughout surgery, exposing RBCs to temperatures between 850°F and 2200°F. Bleeding from muscle, small veins, and bony surfaces is coagulated immediately or controlled using hemostatic agents. Surviving RBCs are sublethally injured, resulting in membrane fragility and hemolysis after purification. These challenges cannot be completely mitigated by refining procedural variables such as suction pressure or washing techniques, unlike other surgeries where brisk bleeding and large-volume collection maintain RBC viability. The assumption that intraoperative RBC salvage is inherently beneficial across all surgical contexts is rooted in literature primarily from nonspinal surgeries. This literature drove the adoption of RBC salvage in spine surgery. However, recent studies have questioned the clinical efficacy and cost-effectiveness of RBC salvage in spine surgery, concluding that sRBC transfusion offers little, if any, reduction in packed red blood cells (pRBC) transfusion requirements.3-5 In addition, recent efforts have challenged the assumption that sRBC transfusion is risk-free, particularly in spinal deformity surgery.6 We agree that careful interpretation of our supplemental data is warranted as the analyses were exploratory. Our mixed-effects model was designed to isolate the independent effects of sRBC transfusion on postoperative laboratory values, while controlling for key confounding variables such as operative time and blood loss. By accounting for repeated measures within individuals, we minimized biases inherent in the nonrandomized design. To clarify, of 174 patients, 22.4% did not receive blood products, 17.2% received only sRBCs, 19.5% received only pRBCs, and 40.8% received both. Our approach allowed us to identify clear trends: patients receiving sRBCs showed larger drops in postoperative hemoglobin and increases in potassium and free hemoglobin, both markers of hemolysis. In addition, platelet depletion was more pronounced in patients receiving both sRBCs and pRBCs, suggesting the combined effects of dilutional coagulopathy and consumptive coagulopathies in more complex cases. The possible role of hemolysis in platelet depletion warrants mention.7 To build on these findings, we used advanced modeling to provide a nuanced evaluation of sRBC effectiveness compared with pRBCs. Given our hypothesis and data suggesting poor sRBC quality, we moved beyond simply examining the absolute effect on pRBC requirements, which does not account for the volume of sRBC transfusion and assumes some equivalency between sRBC and pRBC. Our findings revealed that the risk reduction achieved by sRBC transfusion was minimal—comparable to that of a crystalloid bolus for reducing intraoperative pRBC needs—and significantly lower than pRBC transfusion regarding stabilizing hemoglobin and reducing postoperative transfusion requirements. These findings complement other studies evaluating the efficacy of RBC salvage in spine surgery. We acknowledge that our use of “intravascular hemolysis” could have been clearer. Our intent was to refer specifically to the continued hemolysis of the reinfused sRBCs not native RBCs. Finally, the critique misinterpreted our findings regarding the delay in resuscitation for patients receiving sRBCs. The delay we observed was not in general resuscitation but specifically in the time to the first noncrystalloid resuscitative measure, including sRBC transfusion. This delay is clinically significant, as it suggests a potential false sense of security contributing to the difference in resuscitation timing, warranting further investigation. In complex spinal deformity surgery, delayed resuscitation with resultant hemodynamic compromise is a known concern. While procedural factors like suction techniques or operator training can always be optimized, our study suggests that the fundamental challenges lie within the nature of complex spine surgery itself. The harsh surgical environment likely causes irreversible damage to sRBCs, which procedural tweaks cannot fully mitigate. Efforts to improve RBC salvage techniques in complex spine surgery may yield minimal benefits, given the fundamental limitations we have observed in sRBC quality. We encourage further research to explore more selective application of RBC salvage where it can offer clear benefits.