What is the definition of septic shock?

Definition of Septic Shock

Septic shock is defined as a subset of sepsis with profound circulatory, cellular, and metabolic abnormalities characterized by vasopressor requirement to maintain mean arterial pressure ≥65 mmHg and serum lactate level >2 mmol/L (>18 mg/dL) in the absence of hypovolemia. 1, 2, 3

Current Definition Framework (Sepsis-3)

The current definition of septic shock is based on the Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3) published in 2016:

• Septic shock represents the most severe form on the sepsis spectrum, with particularly profound circulatory, cellular, and metabolic abnormalities 1, 2
• These abnormalities are associated with a greater risk of mortality than sepsis alone, with hospital mortality rates exceeding 40% 3
• The definition requires both:
  • Vasopressor therapy to maintain mean arterial pressure ≥65 mmHg 1, 2
  • Serum lactate level >2 mmol/L (>18 mg/dL) despite adequate fluid resuscitation 1, 3

Evolution of the Definition

The definition of septic shock has evolved significantly over time:

• Previous definitions (pre-2016) focused on sepsis-induced hypotension persisting despite adequate fluid resuscitation 4
• The Sepsis-3 Task Force eliminated the previous concept of a continuum from sepsis through severe sepsis to septic shock 3, 5
• The current definition emphasizes both circulatory failure (requiring vasopressors) and cellular/metabolic abnormalities (elevated lactate) 1, 3

Clinical Identification

Septic shock can be clinically identified by:

• Persistent hypotension requiring vasopressors to maintain mean arterial pressure ≥65 mmHg 1, 2
• Elevated serum lactate >2 mmol/L (>18 mg/dL) despite adequate volume resuscitation 1, 3
• These criteria help identify patients at substantially higher risk of mortality 3

Pathophysiology

Septic shock involves:

• Profound circulatory dysfunction characterized by vasodilation and increased vascular permeability 2
• Microcirculatory dysfunction leading to tissue hypoperfusion 2
• Cellular and metabolic abnormalities including altered cellular metabolism leading to lactate accumulation 2

Common Pitfalls in Identifying Septic Shock

• Failing to recognize that patients receiving vasopressors may still have perfusion abnormalities despite normal blood pressure 2
• Delaying vasopressor initiation while continuing excessive fluid administration 2
• Not measuring lactate levels, which are essential for the diagnosis according to current definitions 1, 3
• Confusing septic shock with other forms of distributive shock 6

Clinical Implications

• Early recognition of septic shock is crucial for improving outcomes 2, 7
• Management priorities include early initiation of vasopressors (norepinephrine as first-line) 2
• Targeting a mean arterial pressure of 65-70 mmHg is recommended 2
• Avoiding fluid overload is important as it may worsen outcomes 2
• The mortality rate associated with septic shock remains high (>40%) despite advances in care 3, 7