A 34-year-old man is admitted to the intensive care unit due to fever, chills, shortness of breath, and altered mental status. His symptoms began 3 days ago and have progressively worsened over the last 24 hours. His past medical history is significant for a motor vehicle accident 2 years ago in which he sustained blunt abdominal trauma and required emergency laparotomy due to internal bleeding. His blood pressure is 81/44 mm Hg and pulse is 122/min. He is started on broad-spectrum antibiotics, intravenous fluids, and vasopressors. His condition continues to deteriorate and he dies in the hospital several hours later despite extensive resuscitation efforts. Blood cultures obtained on admission grow Streptococcus pneumoniae. Impairment of which of the following mechanisms most likely contributed to the severity of this patient's infection?

Question

A 34-year-old man is admitted to the intensive care unit due to fever, chills, shortness of breath, and altered mental status.  His symptoms began 3 days ago and have progressively worsened over the last 24 hours.  His past medical history is significant for a motor vehicle accident 2 years ago in which he sustained blunt abdominal trauma and required emergency laparotomy due to internal bleeding.  His blood pressure is 81/44 mm Hg and pulse is 122/min.  He is started on broad-spectrum antibiotics, intravenous fluids, and vasopressors.  His condition continues to deteriorate and he dies in the hospital several hours later despite extensive resuscitation efforts.  Blood cultures obtained on admission grow Streptococcus pneumoniae.  Impairment of which of the following mechanisms most likely contributed to the severity of this patient's infection?

Quizplus · Accepted Answer

11ec160b_37e6_175d_9249_e5539cc0e1f8_MD0001_00 This patient likely experienced traumatic splenic rupture 2 years ago with the splenic remnants removed during laparotomy (spleen is the most commonly injured organ with blunt abdominal trauma). He subsequently experienced overwhelming asplenic sepsis, a condition that carries a 50% mortality risk. The spleen is a part of the systemic lymphoid system and receives roughly 6% of the cardiac output. Many of the splenic capillaries are open-ended and sinusoidal, permitting whole blood to flow into the red pulp cords. These cords form a reticular meshwork that acts as a fine sieve with spaces as small as 1 micron in diameter. Large numbers of macrophages line the red pulp cords and sinusoids and ingest any particulate matter that becomes trapped. The splenic red pulp is important for: Destroying aged and abnormal erythrocytes (eg, spherocytes) and serving as an emergency store of blood cells and platelets that can be delivered into the circulation when needed. Clearance of circulating bacteria that become lodged in the cords. Macrophages then present captured antigens to the B- and T-cells residing in the splenic white pulp to generate an active immune response. Nearly half of the body's total immunoglobulins are produced by splenic B-lymphocytes. Splenic opsonizing antibody is of particular importance in the clearance of encapsulated species, as the capsule allows them to resist innate phagocytosis. Vaccination against encapsulated bacteria such as Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria meningitidis is recommended for all asplenic patients. (Choice A) The liver is the primary site for complement production. C3 deficiency predisposes to recurrent infections with encapsulated organisms. Deficiencies of C5-9, the components of the membrane attack complex, can lead to recurrent infections with N meningitidis or N gonorrhoeae. (Choice B) Immediate hypersensitivity results from IgE-mediated mast cell degranulation. It is not affected by splenectomy. (Choice C) Chronic granulomatous disease (CGD) is a condition where catalase-positive organisms such as Staphylococcus aureus are phagocytosed but cannot be killed effectively. Patients experience recurrent suppurative infections (eg, abscesses). (Choice E) Interferons α and β are released from virally-infected cells and cause macrophage and cytotoxic T-lymphocyte activation, leading to destruction of infected cells. Defects in type I interferon release lead to increased susceptibility to viral infections. Educational objective: The spleen acts as both a blood filter capable of removing circulating pathogens and as a major site of opsonizing antibody synthesis. Asplenic patients are prone to infections caused by encapsulated organisms such as Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria meningitidis. __________ References: Pneumococcal and influenza immunization in asplenic persons: a retrospective population-based cohort study 1990-2002. (http://www.ncbi.nlm.nih.gov/pubmed/20649965) Infections of people with complement deficiencies and patients who have undergone splenectomy. (http://www.ncbi.nlm.nih.gov/pubmed/20930072)

A 34-Year-Old Man Is Admitted to the Intensive Care Unit