What is septic shock?

Definition of Septic Shock

Septic shock is defined as a subset of sepsis with profound circulatory, cellular, and metabolic abnormalities associated with a higher risk of mortality than sepsis alone, clinically identified 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

Current Definition Framework (Sepsis-3)

• Septic shock represents the most severe form on the sepsis spectrum, characterized by particularly profound circulatory, cellular, and metabolic abnormalities 3
• The operational criteria for identifying septic shock include:
  • Requirement for vasopressor therapy to maintain mean arterial pressure ≥65 mmHg 1
  • Serum lactate level >2 mmol/L (>18 mg/dL) 2
  • Persistence of these abnormalities despite adequate fluid resuscitation 3
• This combination of hypotension requiring vasopressors and hyperlactatemia is associated with hospital mortality rates exceeding 40% 2

Evolution of the Definition

• Previous definitions (pre-2016) described septic shock as "sepsis-induced hypotension persisting despite adequate fluid (volume) resuscitation" 3, 4
• The older definition included perfusion abnormalities such as lactic acidosis, oliguria, or acute alteration in mental status 3
• The 2016 Sepsis-3 consensus refined the definition to focus on the underlying circulatory and metabolic/cellular abnormalities that substantially increase mortality 3, 2
• The current definition eliminated the systemic inflammatory response syndrome (SIRS) criteria that were previously central to sepsis definitions 1, 5

Pathophysiology of Septic Shock

• Septic shock involves profound circulatory dysfunction characterized by:
  • Vasodilation and increased vascular permeability 3
  • Myocardial depression 6
  • Microcirculatory dysfunction leading to tissue hypoperfusion 1
• Cellular and metabolic abnormalities include:
  • Impaired cellular oxygen utilization 2
  • Mitochondrial dysfunction 6
  • Altered cellular metabolism leading to lactate accumulation 1
• These abnormalities result from a dysregulated host response to infection that damages multiple organ systems 3, 2

Clinical Identification and Management Implications

• Early identification of septic shock is crucial for improving outcomes 1, 7
• Management priorities include:
  • Immediate administration of appropriate antimicrobials 7
  • Fluid resuscitation in those who are fluid responsive 7
  • Early initiation of vasopressors (norepinephrine as first-line) 3, 7
  • Targeting a mean arterial pressure of 65-70 mmHg 3
  • Avoiding fluid overload which may worsen outcomes 3
• Patients with septic shock should be monitored for:
  • Mean arterial pressure 3
  • Mental status changes 7
  • Capillary refill time 7
  • Lactate levels 1, 7
  • Urine output 7

Special Considerations

• Elderly patients may present with attenuated inflammatory responses despite severe septic shock 1
• Immunocompromised patients have increased susceptibility to septic shock due to pre-existing immune system dysfunction 1
• The clinical presentation and response to treatment may vary based on the causative pathogen and host factors 1
• Consider adjunctive therapies such as hydrocortisone and fludrocortisone in refractory septic shock 7

Common Pitfalls in Identifying Septic Shock

• Relying solely on hypotension without assessing lactate levels may miss cases of septic shock 2
• Failing to recognize that patients receiving vasopressors may still have perfusion abnormalities despite normal blood pressure 3
• Attributing hypotension to other causes without considering underlying sepsis 4
• Delaying vasopressor initiation while continuing excessive fluid administration 3, 7