What are the characteristics of septic shock?

Characteristics of Septic Shock

Septic shock is defined as a subset of sepsis in which profound circulatory, cellular, and metabolic abnormalities substantially increase mortality risk, characterized by hypotension requiring vasopressors to maintain mean arterial pressure ≥65 mmHg and serum lactate >2 mmol/L despite adequate fluid resuscitation. 1, 2

Definition and Diagnostic Criteria

• Septic shock is a life-threatening condition representing the most severe form of sepsis with significantly higher mortality rates (>40%) compared to sepsis alone 2, 3
• Requires the presence of both:
  • Persistent hypotension requiring vasopressor therapy to maintain MAP ≥65 mmHg 1
  • Serum lactate >2 mmol/L (>18 mg/dL) despite adequate fluid resuscitation 1, 2
• Represents a state where underlying circulatory and cellular-metabolic abnormalities are profound enough to substantially increase mortality 1, 2

Hemodynamic Characteristics

• Hypotension (systolic BP <90 mmHg, MAP <70 mmHg, or decrease in systolic BP >40 mmHg from baseline) that persists despite adequate fluid resuscitation 1, 4, 5
• Requires vasopressor support (typically norepinephrine as first-line agent) to maintain adequate perfusion 1, 6
• May present with either:
  • Cold shock: prolonged capillary refill >2 seconds, diminished pulses, mottled cool extremities 1, 4
  • Warm shock: flash capillary refill, bounding peripheral pulses, wide pulse pressure 1, 4

Metabolic Abnormalities

• Elevated serum lactate (>2 mmol/L) indicating tissue hypoperfusion and cellular metabolic dysfunction 1, 2, 3
• Metabolic acidosis often present due to lactic acidosis and other metabolic derangements 1
• Hyperglycemia (plasma glucose >140 mg/dL) in the absence of diabetes 4
• Hyperlactatemia may persist despite restoration of blood pressure, indicating ongoing cellular dysfunction 1

Organ Dysfunction

• Acute alteration in mental status (confusion, lethargy, decreased consciousness) 1
• Oliguria (urine output <0.5 mL/kg/h for >2 hours) despite adequate fluid resuscitation 1, 4
• Respiratory dysfunction (tachypnea >20 breaths/min, PaO₂/FiO₂ <300) 1, 4
• Coagulation abnormalities (INR >1.5, aPTT >60s, thrombocytopenia <100,000/μL) 1, 4
• Liver dysfunction (hyperbilirubinemia >2 mg/dL) 1, 4
• Kidney dysfunction (creatinine increase ≥0.5 mg/dL) 1, 4

Inflammatory Response

• Dysregulated host response to infection with activation of inflammatory signaling pathways 1
• Recognition of pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) triggering immune response 1
• May present with either:
  • Fever (core temperature >38.3°C) 1, 4
  • Hypothermia (core temperature <36°C) 1, 4
• Leukocytosis (WBC >12,000/μL), leukopenia (WBC <4,000/μL), or >10% immature forms 1, 4
• Elevated inflammatory markers (C-reactive protein, procalcitonin) 4

Clinical Progression and Recognition

• Typically begins with signs of infection and systemic inflammatory response 1
• Progresses to organ dysfunction (sepsis) and then to refractory hypotension with metabolic abnormalities (septic shock) 1
• Early recognition is critical using bedside clinical criteria such as qSOFA (respiratory rate ≥22/min, altered mentation, systolic BP ≤100 mmHg) 4, 2
• Rapid deterioration can occur, requiring prompt intervention 1, 7

Management Considerations

• Requires immediate fluid resuscitation with crystalloids (at least 30 mL/kg) 1, 4
• Vasopressors (typically norepinephrine) should be initiated if hypotension persists after fluid challenge 1, 6
• Target MAP ≥65 mmHg as the initial goal during hemodynamic support 1
• Avoid fluid overload which may worsen tissue edema and increase intra-abdominal pressure 1
• Early identification of source of infection and prompt antimicrobial therapy are essential 4, 7

Pitfalls and Caveats

• Relying solely on blood pressure for diagnosis can delay recognition; tissue perfusion abnormalities may be present despite normal blood pressure 1
• Lactate elevation may result from causes other than tissue hypoperfusion (e.g., liver dysfunction, medications) 8, 3
• Fluid overload can worsen outcomes; careful monitoring during resuscitation is essential 1
• White blood cell count may not be reliable in neutropenic patients 4
• The term "severe sepsis" is now considered redundant under current definitions 1, 2