Understanding the Neurological Complications of Sepsis

Sepsis describes systemic infection (i.e. infection spreading throughout the body via bacteria in the bloodstream). Lower respiratory tract sepsis describes the situation where the original source of infection is in the lungs, and infection then spreads into the bloodstream and triggers the systemic sepsis response.

Sepsis is identified by a range of clinical markers. In general, the following steps are taken to diagnose sepsis:

  • Patient looks unwell OR has a NEWS (National Early Warning Score) of 5 or above

  • Patient has evidence of a source of infection (which could be respiratory, intra-abdominal, urinary, superficial or neurological as examples)

  • Patient has clinical red flags present:
    • Objective evidence of new or altered mental state
    • Systolic BP ≤ 90 mmHg (or drop of >40 from normal)
    • Heart rate ≥ 130 per minute
    • Respiratory rate ≥ 25 per minute
    • Needs O2 to keep SpO2 ≥ 92% (88% in COPD)
    • Non-blanching rash / mottled / ashen / cyanotic
    • Lactate ≥ 2 mmol/l
    • Recent chemotherapy
    • Not passed urine in 18 hours (<0.5ml/kg/hr if catheterised)

Sepsis can lead to a range of complications. Most critically it is commonly fatal, particularly if the diagnosis is delayed, or in patients with other significant health problems. Critical illness polyneuropathy can develop in the ICU, the result of sepsis-related damage to the peripheral nerves and muscles.

Neuropathy is a disorder of central or peripheral nerves leading to impaired nerve function: this may manifest by causing problems in key nerve functions such as motor (leading to weakness) or sensory (leading to numbness and altered sensation). These issues can lead to problems with mobility and independence. The causes of neuropathy are legion, but a classification of causes would include diabetes, other systemic diseases, inherited diseases, autoimmune disorders, environmental causes and toxins. A cause cannot be identified for a significant proportion of neuropathies which are termed ‘idiopathic’. Charcot Marie Tooth disease is a hereditary neuropathy.

Neuropathy is not a result of immobility. The precise aetiology of critical illness neuropathy is unknown, but it is believed to be a consequence of the systemic inflammatory response, possibly related to impaired blood flow to the peripheral nerves. While patients with severe inflammatory responses are more likely to develop neuropathy, it is a common consequence of sepsis of any severity.