Predicting venous thrombosis in patients undergoing elective splenectomy

Platelets mediate the clearance of senescent red blood cells by forming prophagocytic platelet-cell complexes

ABSTRACT

In humans, ∼0.1% to 0.3% of circulating red blood cells (RBCs) are present as platelet-RBC (P-RBC) complexes, and it is 1% to 2% in mice. Excessive P-RBC complexes are found in diseases that compromise RBC health (eg, sickle cell disease and malaria) and contribute to pathogenesis. However, the physiological role of P-RBC complexes in healthy blood is unknown. As a result of damage accumulated over their lifetime, RBCs nearing senescence exhibit physiological and molecular changes akin to those in platelet-binding RBCs in sickle cell disease and malaria. Therefore, we hypothesized that RBCs nearing senescence are targets for platelet binding and P-RBC formation. Confirming this hypothesis, pulse-chase labeling studies in mice revealed an approximately tenfold increase in P-RBC complexes in the most chronologically aged RBC population compared with younger cells. When reintroduced into mice, these complexes were selectively cleared from the bloodstream (in preference to platelet-free RBC) through the reticuloendothelial system and erythrophagocytes in the spleen. As a corollary, patients without a spleen had higher levels of complexes in their bloodstream. When the platelet supply was artificially reduced in mice, fewer RBC complexes were formed, fewer erythrophagocytes were generated, and more senescent RBCs remained in circulation. Similar imbalances in complex levels and senescent RBC burden were observed in humans with immune thrombocytopenia (ITP). These findings indicate that platelets are important for binding and clearing senescent RBCs, and disruptions in platelet count or complex formation and clearance may negatively affect RBC homeostasis and may contribute to the known risk of thrombosis in ITP and after splenectomy.

Two Cases of Gastric Varices with Left-sided Portal Hypertension Due to Essential Thrombocythemia Treated with Gastric Devascularization or Partial Splenic Embolization

Left-sided portal hypertension (LSPH) is a condition of extrahepatic portal hypertension that often results in bleeding from isolated gastric varices (GVs). LSPH is sometimes caused by myeloproliferative diseases, such as essential thrombocythemia (ET). We herein report two cases of GVs with LSPH due to ET that were successfully controlled by gastric devascularization (GDS) or partial splenic embolization (PSE). Since each patient with LSPH due to ET has a different pathology, optimal treatment should be performed depending on the patient's condition, such as platelet counts, hemodynamics, or the prognosis. We believe that these cases will serve as a reference for future cases.

High Rates of Pediatric Venous Thromboembolism After Elective Laparoscopic Splenectomy Suggest Need for Perioperative Prophylaxis

INTRODUCTION

In adult populations, postoperative venous thromboembolism (VTE) is a reported complication of up to 8% of elective laparoscopic splenectomy (LS) cases. VTE is a rare event in the pediatric population, affecting less than 1% of all pediatric surgical patients. We hypothesized that pediatric patients are at a higher risk of postoperative VTE after undergoing elective LS relative to other laparoscopic procedures and may warrant prophylactic treatment.

MATERIALS AND METHODS

We queried the American College of Surgeons National Surgical Quality Improvement Program-Pediatric (NSQIP-P) database from 2012 to 2020. Patients were identified using the Current Procedural Terminology code 38120 and only elective cases were analyzed.

RESULTS

The incidence of VTE in all pediatric patients undergoing surgery in the American College of Surgeons NSQIP-P database was 0.13%. The incidence of VTE in pediatric patients undergoing elective laparoscopic abdominopelvic procedures was 0.17%. There were seven total cases of VTE (0.41%) in pediatric patients undergoing elective LS, more than twice the rate of the general population (P = 0.001). Eighty percent of pediatric patients undergoing elective LS had an underlying hematological disorder.

CONCLUSIONS

By analyzing the NSQIP-P database, we evaluated the largest cohort of pediatric patients undergoing elective LS to date. We identified a higher incidence of VTE following this procedure relative to the rate of VTE in the overall population in the NSQIP-P database, as well as those undergoing elective laparoscopic abdominopelvic operations. The relatively higher incidence of VTE after elective LS is likely due to the presence of underlying hematological conditions. Given the low incidence of complications associated with pharmacologic VTE prophylaxis, the results of this study suggest that further research is warranted to establish the efficacy of perioperative pharmacological VTE prophylaxis in pediatric patients undergoing elective LS.

Aspirin Administration Mitigates Platelet Hyperaggregability After Splenectomy in a Murine Model

INTRODUCTION

Patients who undergo splenectomy (SPLN) have an estimated 10%-35% risk of venous thromboembolic events; however, the underlying mechanism and strategy for prevention have yet to be identified. The goals of this study were to 1) investigate platelet aggregation after SPLN, 2) examine if aspirin administration could mitigate this effect, and 3) determine if concomitant hemorrhage would affect post-SPLN platelet function and response to aspirin.

METHODS

Murine models of operative SPLN and submandibular bleed (SMB) were utilized. Mice were randomized to eight groups as follows: untouched, SPLN, sham (laparotomy only), SMB, SPLN + SMB, SPLN + aspirin (ASA), SMB + ASA, and SPLN + SMB + ASA. Aspirin (50 mg/kg) was administered on postoperative days (PODs) one and two via oral gavage. Mice were euthanized on POD 3, platelet counts were obtained, and blood samples were analyzed via rotational thromboelastometry and impedance aggregometry with adenosine diphosphate (ADP) and arachidonic acid (AA) as agonists.

RESULTS

By POD 3, SPLN mice displayed a significant thrombocytosis compared to untouched, SMB, and sham SPLN mice. Clotting time and clot formation time were significantly decreased in SPLN and SPLN + SMB cohorts compared to untouched and sham controls with elevated mean clot firmness. SPLN mice also displayed a significant increase in ADP- and AA-mediated platelet aggregability compared to untouched controls, SMB, and SPLN + SMB. ASA significantly decreased platelet aggregation via both ADP and AA signaling in SPLN and SPLN + SMB cohorts without affecting viscoelastic coagulation testing.

CONCLUSIONS

Platelet hyperaggregability after SPLN is mediated by both ADP and AA signaling. Early aspirin administration may prevent increased platelet aggregation exacerbated after polytrauma.

Portal vein thrombosis following elective laparoscopic splenectomy: incidence and analysis of risk factors

BACKGROUND

Minimally invasive splenectomy is now well established for a wide range of pathologies. Portal vein thrombosis (PVT) is increasingly being recognised as a complication of splenectomy. The aim was to determine the incidence and risk factors for PVT after laparoscopic splenectomy.

METHODS

All cases of elective laparoscopic splenectomy performed from 1993 to 2020 were reviewed. Parameters recorded included demographics, diagnostic criterion and post-operative outcomes. Data were analysed using Minitab V18 with a p < 0.05 considered significant.

RESULTS

210 patients (103 female, 107 male) underwent laparoscopic splenectomy (14 to 85 years). A major proportion of cases were performed for ITP (n = 77, p = 0.012) followed by lymphoma (n = 28), indeterminate lesions (n = 21) and myelofibrosis (n = 19). Ten patients developed symptomatic portal vein thrombosis (4.8%). Patients presented most commonly with pain and fever and diagnosis was confirmed by computed tomography (CT) or ultrasonography (USS). There were 10 conversions (4.8%) to open and two postoperative deaths, one from PVT and one from pneumonia. The remaining nine patients were successfully treated with anticoagulation. Of 19 patients with myelofibrosis, six patients developed PVT (p = 0.0002). Patients who developed PVT had significantly greater specimen weights (1773 g vs 348 g, p < 0.001). Forty-three patients had a specimen weight of 1 kg or greater, and of these 9 developed portal vein thrombosis (21%), versus one with PVT of 155 with a specimen weight of less than 1 kg (p < 0.0001). Myelofibrosis (p = 0.0039), specimen weight (p < 0.001) and mean platelet count (p = 0.0049) were predictive of PVT.

CONCLUSION

A high index of suspicion for this complication should be maintained and prompt treatment with anticoagulation. High-risk patients should be considered for prophylactic anticoagulation and routine imaging of the portal vein.

Assessment of thrombotic risk during long-term treatment of immune thrombocytopenia with fostamatinib

Background:

Patients with immune thrombocytopenia (ITP) are at risk of bleeding and, paradoxically, thromboembolic events (TEEs), irrespective of thrombocytopenia. The risk of thrombosis is increased by advanced age, obesity, and prothrombotic comorbidities: cancer, hyperlipidemia, diabetes, hypertension, coronary artery disease, and chronic kidney disease, among others. Certain ITP treatments further increase the risk of TEE, especially splenectomy and thrombopoietin receptor agonists. Spleen tyrosine kinase (SYK) is a key signaling molecule common to thromboembolic and hemostatic (in addition to inflammatory) pathways. Fostamatinib is an orally administered SYK inhibitor approved in the USA and Europe for treatment of chronic ITP in adults.

Methods:

The phase III and extension studies included heavily pretreated patients with long-standing ITP, many of whom had risk factors for thrombosis prior to initiating fostamatinib. This report describes long-term safety and efficacy of fostamatinib in 146 patients with up to 5 years of treatment, a total of 229 patient-years, and assesses the incidence of thromboembolic events (by standardized MedDRA query).

Results:

Platelet counts ⩾50,000/µL were achieved in 54% of patients and the safety profile was as described in the phase III clinical studies with no new toxicities observed over the 5 years of follow-up. The only TEE occurred in one patient (0.7%, or 0.44/100 patient-years), who experienced a mild transient ischemic attack. This is a much lower rate than might be expected in ITP patients.

Conclusion:

This report demonstrates durable efficacy and a very low incidence of TEE in patients receiving long-term treatment of ITP with the SYK inhibitor fostamatinib.

ClinicalTrials.gov identifiers:

NCT02076399, NCT02076412, and NCT02077192.