Definition
The Japanese Clinical Practice Guidelines for Management of Sepsis and Septic Shock 2020 mention the pathology and differential diagnosis of SABD, but no standardized definition has been established to date. Even when the source of infection is not the central nervous system, sepsis symptoms may include impaired consciousness. The main pathologies include destruction of the blood-brain barrier and activation of microglia by mediators such as cytokines. It can also be caused by secondary conditions resulting from sepsis, such as electrolyte abnormalities, hypoglycemia, hypoxia, hypotension, dehydration, and hepatic and renal dysfunction. SABD is an acute diffuse brain dysfunction caused by sepsis.

Diagnostic criteria
The diagnosis is made when the criteria for sepsis are met and the patient has a GCS of 14 or less, or a GCS of 15 accompanied by delirium within 24 hours of ICU admission. However, exclude cases where sepsis is complicated by a new-onset neurological disorder, or neurological disorders complicating sepsis such as meningitis associated with infective endocarditis, subarachnoid hemorrhage due to rupture of an infective cerebral aneurysm, or cerebral infarction due to reduced cerebral perfusion. Also exclude direct infections of the central nervous system such as meningitis or brain abscess.

Diagnostic Approach
Concurrently with sepsis diagnosis, assess level of consciousness to screen for delirium. Perform head CT or MRI, and cerebrospinal fluid analysis if necessary, to rule out exclusion criteria.

Outcomes
Studies of SABD show that 30-day mortality increases with worsening GCS. A GCS of 3–8 points correlates with 30-day mortality, and even mild cases with a GCS of 13 or 14 points are associated with an increased risk of death. An association with cognitive impairment has also been reported. In patients with SABD, head MRI imaging reveals reduced volume and atrophy in structures such as the hippocampus and amygdala.