Septic emboli are infected masses that travel through the bloodstream and obstruct blood vessels in distant parts of the body. The term “septic” refers to a systemic illness caused by infection, and “emboli” are masses that circulate until they become lodged in a vessel. A septic embolus is an infected blood clot that detaches from its source and blocks blood flow. This process creates a dual threat, combining the physical blockage of blood supply with the introduction of infectious agents to a new site.
Sources of Septic Emboli
Septic emboli originate from a primary site of infection containing a large concentration of bacteria or other microorganisms. The most common starting point is infective endocarditis, an infection of the inner lining or valves of the heart. Bacteria, often Staphylococcus aureus, colonize the heart valves, forming a clump of infectious material and blood components known as a vegetation.
These vegetations can become unstable, causing fragments to break off and travel through the circulation as emboli. Other sources include infected intravenous (IV) catheters and implanted medical devices like pacemakers. Deep-seated infections, such as an infected deep vein thrombosis or large abscesses, can also release infected material into the bloodstream.
How Emboli Affect Major Organs
The damage caused by septic emboli results from vascular occlusion (physical blockage of a blood vessel) and the infectious material within the clot. The ultimate destination of the embolus depends on which side of the heart the infection originates.
Infections on the right side of the heart, often involving the tricuspid valve, release emboli into the pulmonary circulation. These infected clots lodge in the small arteries of the lungs, causing septic pulmonary emboli. This can result in lung infection, pulmonary abscesses, or acute hypoxemic respiratory failure in severe cases.
Infections on the left side of the heart, such as those involving the mitral or aortic valves, send emboli into the systemic circulation. These clots can travel to virtually any organ in the body. In the brain, they may cause an ischemic stroke or lead to the formation of brain abscesses, resulting in neurological deficits.
Emboli frequently affect the skin, extremities, spleen, and kidneys.
- Skin and extremities may manifest painful, red or purple spots (Osler nodes).
- The spleen and kidneys are frequently involved, potentially resulting in tissue death (infarction) or the development of abscesses.
- The spleen is particularly susceptible to abscess formation, which can cause severe abdominal pain.
Diagnosis and Treatment
Diagnosing septic emboli is challenging due to varied and non-specific symptoms, typically including fever, chills, and fatigue. Providers often look for clinical signs, such as a new heart murmur, suggesting infective endocarditis as the source.
Diagnostic tools identify the pathogen and locate the emboli and their source. Blood cultures confirm the presence of bacteria in the bloodstream and determine the specific microorganism causing the infection. Imaging techniques like CT scans and MRI locate emboli and resulting abscesses in organs such as the brain, lungs, or spleen.
An echocardiogram (ultrasound of the heart) is performed to visualize the heart valves and look for vegetations, indicating the source of the infected material. Treatment requires the immediate administration of high-dose intravenous antibiotics, often started empirically before the specific bacteria is identified. This antimicrobial therapy typically lasts for four to six weeks to ensure the infection is fully eradicated.
Source control is a fundamental part of treatment and often requires surgical intervention. This may involve removing infected catheters or medical devices, draining large abscesses, or surgically replacing a severely damaged heart valve. The goal is to eliminate the original site of infection to prevent the formation of further emboli.