What characterizes septic shock?

Characteristics of Septic Shock

Septic shock is characterized by poor perfusion of end organs, which is a key feature leading to organ dysfunction and increased mortality. 1

Definition and Pathophysiology

Septic shock is defined as a subset of sepsis in which underlying circulatory and cellular-metabolic abnormalities are profound enough to substantially increase mortality. Operationally, it is characterized by:

• Requirement for vasopressor therapy to maintain mean arterial pressure ≥65 mmHg
• Serum lactate level >2 mmol/L (>18 mg/dL) in the absence of hypovolemia 1, 2

The pathophysiology involves:

• Dysregulated host response to infection causing profound circulatory abnormalities
• Impaired tissue perfusion despite adequate fluid resuscitation
• Cellular and metabolic derangements 1, 3

Key Characteristics of Septic Shock

Poor End-Organ Perfusion

• Septic shock is fundamentally characterized by inadequate tissue perfusion, particularly affecting end organs 1
• Perfusion abnormalities include:
  • Lactic acidosis (reflecting tissue hypoxia)
  • Oliguria (<1 mL/kg/hr)
  • Altered mental status
  • Mottled skin or prolonged capillary refill 1

Hemodynamic Parameters

Septic shock presents with two distinct hemodynamic phases:

1. Hyperdynamic phase (early):

   • Increased cardiac output
   • Decreased systemic vascular resistance
   • Whole body oxygen consumption is increased (not decreased) 3

2. Hypodynamic phase (late):

   • Decreased cardiac output
   • Increased peripheral resistance
   • Progressive organ dysfunction 3

Fluid Management and Mortality

• Positive fluid balance is associated with increased mortality in septic shock 1
• While initial fluid resuscitation is crucial, excessive fluid administration leads to:
  • Tissue edema
  • Impaired oxygen diffusion
  • Organ dysfunction
  • Higher mortality rates 1

Hemoglobin Targets

• Maintaining hemoglobin levels greater than 10 g/dL is not recommended 1
• The target hemoglobin in septic shock is between 8-9 g/dL 1
• Higher transfusion thresholds have not been shown to improve outcomes and may increase complications 1

Management Principles

1. Early recognition using clinical criteria (hypotension, tachycardia, altered mental status, oliguria)
2. Prompt fluid resuscitation with crystalloids (target MAP ≥65 mmHg)
3. Vasopressor therapy if fluid-refractory hypotension occurs (norepinephrine as first-line)
4. Source control of infection through appropriate antimicrobial therapy and drainage/debridement when applicable
5. Monitoring of tissue perfusion markers (lactate clearance, urine output, mental status) 1

Common Pitfalls to Avoid

• Delaying recognition and treatment - Each hour of delay increases mortality
• Excessive fluid administration - Positive fluid balance is associated with worse outcomes
• Targeting supranormal hemoglobin levels (>10 g/dL) - Not supported by evidence
• Misunderstanding oxygen consumption - In early septic shock, whole body oxygen consumption is increased, not decreased
• Focusing only on blood pressure - Tissue perfusion markers are critical to assess adequacy of resuscitation 1, 4

The correct answer is A: Septic shock is characterized by poor perfusion of end organs.