Page 2612 - Hematology_ Basic Principles and Practice ( PDFDrive )

Chapter 160 The Spleen and Its Disorders 2325

enter the bloodstream and would ordinarily be removed by splenic may be related to subsequent thrombocytosis that leads to enhance-
macrophages are able to evade recognition by macrophages whose Fc ment of plaque formation. Statistically, the increased risk for athero-
and C3b receptors appear to be less avid than those of splenic mac- sclerosis is not particularly high, but for individuals with other risk
rophages. Circulation of the blood through the liver and lung is more factors such as hypertension, diabetes, high levels of cholesterol or
rapid than through the spleen, and there is little opportunity for homocysteine, heterozygous protein C or S deficiency, or factor V
macrophages to recognize organisms with surfaces containing little Leiden, splenectomy may pose a more significant risk. Although no
IgG and only small amounts of C3bi. The important filtration func- human data are currently available in this area, some studies have
tion of the venous sinus endothelial cells is absent following splenec- suggested that the spleen might be involved in lipid metabolism in
tomy. The generation of cytokines, including TNF-α and bacterial both rats and rabbits.
endotoxins, leads to cardiovascular collapse and shock. It is difficult
to rescue an asplenic patient once shock develops, even with effective
antibiotic therapy. The risk that this will happen varies with the Prevention of Complications
indication for splenectomy (Table 160.4) and the patient’s medical
condition. Factors that impair host defenses significantly increase the Postsplenectomy Septicemia
risk for infection. These include deficient opsonins (hypogamma-
globulinemia and specific antibody-production deficiency), reticulo- The major risk for postsplenectomy sepsis is infection with encapsu-
endothelial blockade related to increased phagocytic activity of lated organisms such as Staphylococcus pneumoniae, H. influenzae type
macrophages in other organs, impaired antigen processing or recogni- b, and N. meningitidis, which require opsonization for effective
tion (AIDS, lymphoma, other malignancies, and some collagen vas- phagocytosis. Polysaccharide vaccines are available for all three bacte-
cular diseases), neutropenia, and high iron load (thalassemia). The ria. 26,27 The highest risk period for children is in the first 2 years of life,
tetrapeptide tuftsin, primarily produced in the spleen, enhances the when their ability to mount an antibody response to purified polysac-
phagocytic activity of monocytes and neutrophils; its absence in charides has not developed completely, so protein-conjugated vaccines
asplenic patients appears to contribute to depressed neutrophil func- are now in widespread use. This has significant potential benefit for
tion and the subsequent increased risk for infection. patients when asplenia is not recognized, because they might then be
Patients at the lowest risk for overwhelming postsplenectomy immunized as part of their routine care. The antibody responses to
sepsis are those in whom splenectomy cures the underlying problem, vaccines, especially the conjugated vaccines, differ in IgG subclasses
such as isolated ITP, hereditary spherocytosis, and trauma. Patients from those produced following natural infection. Overwhelming
undergoing splenectomy for trauma have a 50-fold greater risk for postsplenectomy sepsis and death from sepsis in functionally
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subsequent septic death than trauma patients with intact spleens, hyposplenic patients should be preventable. It is recommended that
whereas the risk in patients with sickle cell disease is increased 350- immunization be done at least 14 days prior to the anticipated sple-
fold over that of the general population, and other authors report the nectomy in order to optimize antigen recognition and processing, and
risk to be 600 times greater. Similar to use of hemodialysis to attempt induce more effective immunity. If emergency splenectomy is per-
to replace the function of the kidney, work is ongoing to devise an formed, it is recommended that vaccination be postponed until at least
artificial spleen as a mechanical way to filter pathogens from the 14 days postsplenectomy to avoid the transient immune suppression
blood. often seen with general anesthesia and surgery (see box on Vaccination
An increased risk for vascular complications may result from of a Patient Scheduled for Elective Versus Emergency Splenectomy).
splenectomy. Acute portal vein thrombosis occurs within 2 months Adults are generally presumed to be immune to H. influenzae type b
of splenectomy in 5%–37% of patients, which is probably the result and may receive the 23-valent pneumococcal polysaccharide vaccine
of local surgical factors. The surgical approach seems to affect the rate (PPSV23) and meningococcal vaccines alone. Reimmunization for
of postsplenectomy portal and splenic vein thrombosis, with a lapa- children is recommended 2–5 years after initial immunization. Sple-
roscopic approach and morcellation associated with a higher rate of nectomized adults should be revaccinated with the PPSV23 once after
thrombosis compared with open splenectomy (55% vs. 19%, respec- 5 years, whereas meningococcal revaccination should occur every 5
tively). Patients with thalassemia and prior splenectomy appear to years. Recently, the Advisory Committee on Immunization Practices
also have an increased incidence of venous thromboembolism beyond clarified recommendations that adult patients who are vaccine naive
the portal venous system. In addition, splenectomy appears to be a receive the pneumococcal conjugate vaccine (PCV13) followed 8
risk factor for the development of pulmonary hypertension. Vascular weeks later by the pneumococcal polysaccharide vaccine (PPSV23).
events after splenectomy are likely multifactorial in origin, being Because these recommendations change with experience and vaccine
attributed to a combination of hypercoagulability, platelet activation, use, it is wise to consult current guidelines for individual patients. The
activation of endothelium due to the persistence of particulate matter, US Centers for Disease Control website should be consulted for the
and damaged cells in the bloodstream. most up-to-date recommendations. Additional organisms to consider
Atherosclerosis that develops many years after splenectomy in in postsplenectomy sepsis include Escherichia coli, Pseudomonas aeru-
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patients with hereditary spherocytosis or hereditary stomatocytosis ginosa, and Capnocytophaga canimorsus. There are fewer data on the
efficacy of prophylactic antibiotics for asplenic patients, except for
TABLE Incidence of Postsplenectomy Sepsis
160.4 Vaccination of a Patient Scheduled for Elective Versus Emergent
Cumulative Incidence of Bacterial Splenectomy
Indication for Splenectomy Sepsis (%)
A 50-year-old man with refractory ITP is scheduled for splenectomy.
Trauma 1.5 Having heard there is a risk for different types of infection after sple-
Hematologic disorders 3.4 nectomy, he asks about what he can do to reduce his risk.
• Patients scheduled for elective splenectomy should receive the
Portal hypertension 8.2 following at least 14 days prior to the procedure:
Hodgkin disease 10 • Streptococcus pneumoniae vaccine
• Haemophilus influenzae vaccine
Sickle cell disease 15 • Neisseria meningitis vaccine
Thalassemia 25 • Consider administration of the influenza vaccine as influenza
is a risk factor for secondary bacterial infection.
Data from Gorse GJ: The relationship of the spleen to infection. In Bowlder AJ, • If the procedure is done emergently, wait at least until the 14th
editor: The spleen: Structure, Function, and Clinical Significance, New York,
1990, Van Nostrand Reinhold, p 269, with permission. postoperative day.