Surgical Splenectomy Alters Red Cell Rheology in Patients with Sickle Cell Disease
Authors: Kanne Celeste K , Sheehan Vivien A 
Published: October 2019

Abstract
Background: Many patients with sickle cell disease (SCD) require a surgical splenectomy for repeat splenic sequestration or hypersplenism, resulting in worsening anemia and/or thrombocytopenia, or abdominal discomfort. Higher rates of thrombosis, pain crises and acute chest syndrome (ACS) have been reported following surgical splenectomy, although the reasons for this are not known. We hypothesize that this clinical worsening post-splenectomy is due to hemorheological changes; studies of the effects of surgical splenectomy on hemorheology in non-SCD animal models found significant reductions in red cell deformability and increase in whole blood viscosity, or blood thickness, following splenectomy. Understanding the impact of surgical splenectomy on blood rheology is especially relevant for patients with SCD, who have many clinical complications as a result of their high whole blood viscosity for their given hemoglobin levels, and low hematocrit-to-viscosity ratio (HVR), a measure of oxygen carrying capacity. Another important measure of SCD rheology is percent dense red blood cells (%DRBC), red cells with a density>1.11 mg/mL; they are typically the result of cellular dehydration, and are less deformable and more likely to sickle. We therefore sought to use our existing longitudinal rheology data, including measures of viscosity and %DRBC, to evaluate the impact of surgical splenectomy on our pediatric patients with SCD.
Methods: We identified seven pediatric patients with multiple measurements of whole blood viscosity and %DRBC, collected before and after surgical splenectomy between November 2013 and April 2018 from SCD patients at Texas Children's Hospital on an IRB approved protocol. The cohort included 4 female and 3 male patients, ages 3-12 years old. Whole blood viscosity was measured using a cone and plate viscometer (DV3T Rheometer, AMETEK Brookfield, Middleboro, MA, USA) at 37 degrees Celsius within 4 hours of sample collection in an EDTA vacutainer tube. CBC data including %DRBC was measured on an ADVIA 120 Hematology System (Siemens Medical Solutions USA, Inc., Malvern, PA, USA). Samples collected 1 month before or after an emergency department visit or within 3 months of a packed red blood cell transfusion were omitted from analysis.
Results: We found a significant rise in %DRBC following splenectomy (p=0.01). There was a significant increase in whole blood viscosity at 45 s-1 and 225 s-1 (p=0.006 and p=0.004, respectively) and a decline in hematocrit-to-viscosity ratio (HVR) at 45 s-1 and 225 s-1 (p=0.03 and p=0.03, respectively) (Table 1). Hemoglobin and hematocrit did not significantly change after splenectomy (p=0.6 and p=0.5, respectively), suggesting that the rise in viscosity was due to intrinsic changes in red cell rheology. Platelets increased markedly (p<0.00002), a side effect commonly seen following splenectomy, known to contribute to thrombophilia.
Conclusion: Overall, the changes in %DRBC, viscosity, and HVR show a worsening of blood rheology following surgical splenectomy with no evidence of a return to baseline 800 days after splenectomy. The increase in viscosity and reduction in HVR in the setting of a rise in %DRBC suggests that the spleen may have played a role in removing these dense or irreversibly sickled cells. Further studies with a larger cohort and long term observation are needed to further elucidate the relationship between worsening rheology and SCD-related complications reported in the literature post-splenectomy. These rheological changes should be considered as part of the decision making for elective splenectomy, monitored post-splenectomy, and addressed therapeutically where possible.

Disclosures
No relevant conflicts of interest to declare.