Can Sepsis Cause a Stroke? Risks and Warning Signs

Sepsis substantially raises the risk of stroke, and the danger is greatest in the days immediately following a sepsis diagnosis. One large case-crossover study found that within 15 days of sepsis, the odds of having an ischemic stroke were roughly 28 times higher than normal, while the odds of a hemorrhagic stroke were about 12 times higher.¹ The connection runs through several biological pathways at once, making sepsis-related strokes harder to predict and harder to treat than strokes that arise from more conventional risk factors.

How Large Is the Risk, and How Long Does It Last

The spike in stroke risk during and just after sepsis is dramatic, but the risk does not simply vanish once the infection clears. That same case-crossover study showed the odds of ischemic stroke remained roughly two and a half times higher even six months to a year after the sepsis hospitalization. For hemorrhagic stroke, the lingering risk was even steeper, nearly four times higher during that same window.¹ In absolute numbers, a study of nearly 122,000 sepsis patients found that about one in 200 had a primary stroke diagnosis within a year of their sepsis hospitalization.² That might sound low, but it is far above the background stroke rate in the general population, and it comes on top of all the other threats sepsis survivors already face.

The takeaway for sepsis survivors and their families is that stroke vigilance should not end at hospital discharge. The weeks and months that follow are a vulnerable period, and new neurological symptoms during that window deserve urgent attention.

Why Sepsis Creates a Perfect Storm for Stroke

There is no single mechanism linking sepsis to stroke. Instead, sepsis throws the body’s blood-clotting system, immune response, and cardiovascular function into chaos simultaneously, and any one of those disruptions can trigger a stroke. Understanding the main pathways helps explain why stroke risk stays elevated for so long after the acute infection passes.

Runaway Blood Clotting

When the body detects a serious infection, the immune system activates clotting as a defense mechanism, trapping pathogens inside tiny blood clots. In sepsis, this process spirals out of control. Immune cells release substances like tissue factor and form extracellular traps that promote widespread clot formation in small blood vessels, a process that can progress to disseminated intravascular coagulation, where clotting and bleeding happen at the same time throughout the body.³ Those microclots can block blood flow to brain tissue directly, or larger clots can form and travel to the brain’s major arteries.

Blood Pressure Collapse and Watershed Strokes

Septic shock often involves dangerously low blood pressure that is difficult to reverse even with aggressive fluid resuscitation and medication. When blood pressure drops severely, the brain regions most vulnerable are the “watershed” zones, areas sitting at the border between the territories supplied by major arteries. These zones depend on adequate pressure from both sides and are the first to starve when perfusion falls. Case reports have documented patients in septic shock developing bilateral watershed infarctions, with brain scans showing damage in exactly those border-zone regions.⁴ Interestingly, watershed strokes during sepsis do not always require a documented episode of severe low blood pressure, suggesting that other factors like microclot formation and inflammation may compound the damage even when blood pressure appears only modestly reduced.⁵

The Brain’s Protective Barrier Breaks Down

The brain is normally shielded by a tightly regulated barrier that prevents most blood-borne substances from entering brain tissue. Sepsis damages this barrier. The flood of inflammatory molecules triggers endothelial cells lining brain blood vessels to loosen their tight junctions, allowing immune cells and cytokines to pour into the brain.⁶ This breach sets off a destructive cycle: activated endothelial cells ramp up the clotting cascade, microthrombi form inside brain vessels, and the resulting ischemia further increases barrier permeability, letting even more inflammatory material through.⁷ This feedback loop helps explain why brain injury during sepsis can be so extensive and why cognitive problems persist long after the infection resolves.

How Atrial Fibrillation During Sepsis Raises Stroke Risk Further

Many sepsis patients develop new-onset atrial fibrillation, a rapid, irregular heart rhythm that is one of the best-known independent risk factors for stroke in any context. In sepsis, the heart is under enormous stress from circulating inflammatory mediators, fluid shifts, and catecholamine surges, and the atria can begin firing chaotically. What makes this especially dangerous is that sepsis-driven atrial fibrillation appears to carry a higher stroke risk than pre-existing atrial fibrillation. One study found that in-hospital ischemic stroke occurred in about 2.6% of sepsis patients with new-onset atrial fibrillation, compared with about 0.6% of those who already had the arrhythmia before their sepsis admission, translating to roughly a threefold increase in stroke odds compared with sepsis patients who never developed the rhythm disturbance.⁸

This creates a genuine clinical puzzle, because the standard approach to atrial fibrillation-related stroke prevention (blood thinners) is not straightforward in sepsis. Patients are already at risk of bleeding from coagulation dysfunction, and the evidence on whether anticoagulation actually helps is unsettled. One observational study found that sepsis survivors discharged on oral anticoagulation after new-onset atrial fibrillation actually had a higher adjusted risk of ischemic stroke or transient ischemic attack at one year compared with those not given anticoagulation.⁹ A separate study of patients in septic shock found that anticoagulation did not reduce stroke rates in those with new-onset atrial fibrillation, though it was associated with significantly lower overall mortality.¹⁰ The mortality benefit may reflect anticoagulation’s effect on other organ damage rather than stroke prevention specifically. Clinicians are left making judgment calls without strong trial data, balancing bleeding risk against the potential for clot-related harm.

Why Stroke Is So Hard to Spot in Sepsis Patients

One of the most dangerous aspects of the sepsis-stroke overlap is that stroke symptoms can be masked by sepsis-associated encephalopathy, a common brain dysfunction caused by the sepsis itself. Encephalopathy during sepsis causes confusion, altered consciousness, and sometimes even focal neurological signs like weakness on one side of the body. That symptom list looks almost identical to stroke. Critically ill patients may be sedated, intubated, or too confused to report classic stroke symptoms like sudden speech difficulty or arm weakness, and medical teams may reasonably attribute new neurological changes to the encephalopathy rather than suspecting a new stroke on top of an already overwhelming illness.¹¹

Case reports illustrate how easily the diagnosis can be missed. In one instance, a septic patient with motor deficits and altered mental status underwent vascular imaging that turned out to be normal, confirming encephalopathy rather than stroke as the cause.¹² In other cases, the opposite occurs, and a true stroke is discovered only on imaging done for persistent unexplained neurological decline. The delirium that accompanies encephalopathy is more often the quiet, hypoactive type than the agitated, hyperactive type, meaning patients may simply appear drowsy or unresponsive rather than visibly distressed.¹³ This subtlety makes it even easier to miss a superimposed stroke.

What Brain Imaging Shows in Septic Shock

When researchers at a French center performed brain MRIs on septic shock patients who had developed neurological problems, the findings were striking. Among 71 patients imaged, about half had normal scans. But roughly three in ten showed ischemic strokes, and about one in five showed a pattern of widespread white-matter damage. Ischemic stroke on imaging was independently linked to disseminated intravascular coagulation, the presence of focal neurological signs, higher mortality, and worse functional outcomes at six months.¹⁴ These results suggest that a substantial minority of septic shock patients who develop neurological symptoms are in fact having strokes, and that imaging can identify them if clinicians think to order it.

The challenge is that not every confused or delirious sepsis patient gets a brain MRI. CT scans, which are faster and more widely available, are less sensitive for picking up early ischemic changes. So there is a real possibility that strokes during sepsis are underdiagnosed, with some cases attributed to encephalopathy and never investigated further. For clinicians, the presence of focal neurological deficits, seizures, or unexplained coma should lower the threshold for advanced neuroimaging.

Cerebral Venous Sinus Thrombosis

Most conversation about sepsis-related stroke focuses on arterial clots blocking blood flow to the brain, but sepsis can also cause strokes through the venous system. Septic cerebral venous sinus thrombosis occurs when infection-driven clots form in the veins that drain blood from the brain. Historically, this was common and often fatal, though modern antibiotics have made it relatively rare. The cavernous sinus, located behind the eyes, is the most frequently affected site, and the preceding infection usually involves the face or sinuses. Without prompt treatment, the clot can spread to the opposite side and cause severe complications or death.¹⁵ The symptoms differ from arterial stroke and include severe headache, swelling around the eyes, fever, and sometimes seizures. Awareness of this distinct subtype matters because the treatment approach differs from that for standard ischemic stroke.

Treating Stroke When It Happens During Sepsis

Acute stroke treatment in the general population relies heavily on time-sensitive interventions like clot-dissolving drugs or mechanical clot retrieval. In sepsis patients, both options carry extra layers of complexity. The bleeding risk from anticoagulation dysfunction can make clot-dissolving drugs dangerous. Mechanical thrombectomy, where a catheter is threaded into the brain’s arteries to physically remove the clot, remains an option but may be significantly more difficult when the stroke is related to infection. One analysis of clots retrieved during thrombectomy found that roughly 6% harbored bacteria, and the cases with infected clots required dramatically longer procedures, more retrieval attempts, and more often needed a permanent stent placed inside the brain artery to restore blood flow.¹⁶ Two of the four infected-clot cases in that series turned out to have infective endocarditis, a heart valve infection that seeds clots to the brain.

These findings underscore that when a stroke occurs during an active infection, the clot itself may be fundamentally different from a “typical” stroke clot, stickier, more adherent, and harder to remove. That does not mean thrombectomy should not be attempted, but treatment teams need to be prepared for a more complex and prolonged procedure.

Survival and Recovery When Sepsis and Stroke Overlap

Having a stroke after surviving sepsis significantly worsens the prognosis. A population-based study found that sepsis survivors who went on to have a heart attack or stroke within a year had roughly double the mortality risk at six months compared with sepsis survivors who did not develop cardiovascular complications.¹⁷ That increased risk persisted out to a full year after the cardiovascular event.

Beyond mortality, the functional burden is heavy. Patients who experience both stroke and sepsis have substantially longer hospital stays and worse disability at discharge compared with patients who have stroke alone. One study found the combined group spent roughly three times as long in the hospital, had worse consciousness levels, and were at higher risk of complications like pressure injuries.¹⁸ The rehabilitation path for these patients is steeper, because they are recovering from the physical toll of sepsis at the same time they are trying to regain neurological function after a stroke. Deconditioning, prolonged ICU stays, and sepsis-related organ injury all slow the rehabilitation process.

Why Standard Stroke Risk Scores Do Not Work After Sepsis

In the general population, doctors use scoring tools to estimate how likely a patient with atrial fibrillation is to have a stroke, and those scores guide decisions about blood-thinning medication. The most widely used score assigns points for factors like age, high blood pressure, diabetes, and prior stroke. Intuitively, you might expect these same tools to help identify which sepsis patients with new-onset atrial fibrillation need the most aggressive stroke prevention. They don’t. A study of more than 82,000 adults hospitalized with sepsis found that the standard risk score performed no better than a coin flip at predicting which patients with new-onset atrial fibrillation would go on to have a stroke or transient ischemic attack.¹⁹

The likely explanation is that sepsis-driven strokes arise from a fundamentally different set of mechanisms than strokes in chronically ill outpatients. The standard risk score captures slow-burning cardiovascular risk factors that accumulate over years, while sepsis strokes are driven by acute inflammation, coagulation chaos, and hemodynamic instability. The same study found that about 2% of the new-onset atrial fibrillation group had a stroke or TIA within a year, while over 40% died, underscoring that mortality from all causes dominates the post-sepsis landscape more than stroke alone. Developing better tools to predict which sepsis survivors face the highest stroke risk remains an open research problem, and until those tools exist, clinical decisions about anticoagulation after sepsis will continue to rely heavily on individual judgment rather than algorithm-based guidance.

Warning Signs Worth Knowing

If you or someone you know is recovering from sepsis, it helps to be aware of stroke symptoms even though they overlap with general post-sepsis malaise. The classic signs are sudden-onset and include facial drooping on one side, arm weakness or numbness, slurred or confused speech, sudden severe headache, and loss of coordination or balance. The key word is “sudden.” Post-sepsis fatigue and brain fog develop gradually and fluctuate. A stroke announces itself abruptly.

During an active sepsis hospitalization, family members should know that any new neurological change, even something as subtle as the patient becoming noticeably less responsive or suddenly unable to move one side, warrants immediate medical evaluation. The instinct to assume “they’re just sicker from the infection” can cost critical treatment time. Focal signs like one-sided weakness, a new facial droop, or sudden difficulty speaking are not typical features of sepsis-associated encephalopathy and should prompt imaging.¹¹ In the post-discharge period, the elevated stroke risk that persists for months means these warning signs deserve the same urgency they would in any other setting. Calling emergency services at the first sign of sudden neurological change remains the single most important action a bystander can take.