20.2 Sepsis-3 Definitions, Septic Shock, and Hemodynamic Resuscitation

20.2 Sepsis-3 Definitions, Septic Shock, and Hemodynamic Resuscitation

Sepsis is a complex, time-critical medical emergency. Understanding the consensus definitions, the hemodynamic categorization of undifferentiated shock, and the evidence-based resuscitation algorithms is central to intensive care and perioperative medicine.

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The Sepsis-3 Consensus Definitions (2016)

The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3) eliminated the Systemic Inflammatory Response Syndrome (SIRS) criteria from the formal definition of sepsis, recognizing that SIRS represents an appropriate physiological host response that lacks discriminatory diagnostic validity.

1. Sepsis

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection.

• Operational Clinical Definition: Organ dysfunction is identified clinically as an acute change in total Sequential Organ Failure Assessment (SOFA) score $\ge 2$ points consequent to an infection.
• Baseline Score: The baseline SOFA score is assumed to be zero unless the patient is known to have pre-existing chronic organ dysfunction prior to the acute infection.
• Clinical Impact: An acute SOFA increase $\ge 2$ points correlates with an in-hospital mortality rate exceeding $10\%$ in the general ICU population.

2. The Sequential Organ Failure Assessment (SOFA) Score

The SOFA score grades dysfunction across six physiological systems from 0 (normal) to 4 (most severe):

3. Quick SOFA (qSOFA)

qSOFA is a simplified bedside screening tool developed to prompt clinicians to further investigate for organ dysfunction, initiate therapy, or escalate to intensive care.

• Criteria (1 point each; score range 0–3):
  1. Respiratory Rate: $\ge 22\text{ breaths/min}$
  2. Altered Mentation: Glasgow Coma Scale score $<15$
  3. Systolic Blood Pressure: $\le 100\text{ mmHg}$
• Interpretation: A qSOFA score of $\ge 2$ identifies non-ICU patients at substantially higher risk of prolonged ICU stay or in-hospital death. Note: Current Surviving Sepsis Campaign (SSC) guidelines recommend against using qSOFA as a single screening tool for sepsis compared to SIRS, NEWS (National Early Warning Score), or MEWS due to its lower sensitivity.

4. Septic Shock

Septic shock is defined as a subset of sepsis in which particularly profound circulatory, cellular, and metabolic abnormalities are associated with a greater risk of mortality than with sepsis alone.

• Clinical Criteria (Both Required):
  1. Persistent hypotension requiring vasopressors to maintain a $\text{MAP} \ge 65\text{ mmHg}$;
  2. Serum lactate level $>2\text{ mmol/L}$ ($>18\text{ mg/dL}$) despite adequate volume resuscitation.
• Mortality: In-hospital mortality for patients meeting both criteria exceeds $40\%$ (compared to approximately $20-25\%$ for hypotension alone without hyperlactatemia or hyperlactatemia alone without hypotension).

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Differential Diagnosis of Shock: Hemodynamic Profiles

Shock is characterized by widespread cellular dysoxia resulting from an imbalance between systemic oxygen delivery ($D\text{O}_2$) and cellular oxygen consumption ($V\text{O}_2$).

Note on Distributive Hemodynamics: The classic hemodynamic profile of early resuscitated septic shock is "warm shock": high cardiac output, bounding arterial pulses, low diastolic pressure, and paradoxically elevated $S_{cv}\text{O}_2$. Elevated $S_{cv}\text{O}_2$ occurs because inflammatory microvascular endothelial dysfunction leads to microcirculatory shunt, capillary uncoupling, and mitochondrial dysfunction ("cytopathic dysoxia"), preventing peripheral tissues from extracting delivered oxygen.

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Surviving Sepsis Campaign: The 1-Hour Bundle

The Surviving Sepsis Campaign bundle represents a set of evidence-based interventions that should be initiated immediately, ideally within 1 hour of sepsis or septic shock recognition.

Sepsis or Septic Shock Recognized
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  ├── 1. Measure Blood Lactate Level (Remeasure within 2-4 hours if initial > 2 mmol/L)
  ├── 2. Obtain Blood Cultures PRIOR to Starting Antibiotics (Aerobic + Anaerobic sets)
  ├── 3. Administer Broad-Spectrum IV Antimicrobials within 1 Hour
  ├── 4. Rapidly Infuse 30 mL/kg Balanced Crystalloid for MAP < 65 or Lactate >= 4 mmol/L
  └── 5. Initiate Vasopressors (Norepinephrine First-Line) to Maintain MAP >= 65 mmHg

1. Measure Blood Lactate Level: Remeasure lactate within $2-4\text{ hours}$ if the initial lactate is $>2\text{ mmol/L}$. Resuscitation guided by serial lactate clearance (targeting a reduction of $\ge 10-20\%$ every 2 hours) is associated with reduced mortality.
2. Obtain Blood Cultures Prior to Antimicrobial Administration: Collect at least two sets of blood cultures (both aerobic and anaerobic bottles)—one percutaneous set and one from each vascular access device in place $>48\text{ hours}$. Antimicrobial therapy must never be delayed for difficult venous access if blood cultures cannot be rapidly obtained.
3. Administer Broad-Spectrum Antimicrobials: The Surviving Sepsis Campaign 2021 guideline recommends empirical antimicrobials within 1 hour for possible septic shock or a high likelihood of sepsis; for possible sepsis without shock, a rapid assessment is followed by antimicrobials within 3 hours if concern persists. Every hour of delay in antibiotic administration correlates with an incremental increase in mortality.
4. Administer Intravenous Fluid: The guideline suggests about $30\text{ mL/kg}$ of intravenous balanced crystalloid within the first $3\text{ hours}$ for sepsis-induced hypoperfusion (manifested by $\text{MAP} < 65\text{ mmHg}$ or serum lactate $\ge 4\text{ mmol/L}$).
   • Crystalloid Selection: Balanced crystalloids (e.g., Plasma-Lyte, Hartmann's solution / lactated Ringer's) are suggested over $0.9\%$ normal saline (a weak recommendation). Large-volume $0.9\%$ saline causes hyperchloremic metabolic acidosis, and the SMART and SALT-ED trials found modestly more major adverse kidney events with saline, although BaSICS and PLUS found no mortality difference.
   • Fluid Responsiveness: Once initial fluid is delivered, further fluids should be guided by dynamic measures of fluid responsiveness (e.g., passive leg raise [PLR] coupled with continuous cardiac output measurement, stroke volume variation [SVV], or pulse pressure variation [PPV] in mechanically ventilated patients with closed chests and no arrhythmias), rather than static pressures (CVP).
5. Apply Vasopressors: Initiate vasopressors during or immediately following fluid resuscitation if the patient remains hypotensive, titrating to a target $\text{MAP} \ge 65\text{ mmHg}$.

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Vasoactive Drug Algorithm in Septic Shock

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Corticosteroid Therapy in Septic Shock

• Mechanism: Sepsis often induces critical illness-related corticosteroid insufficiency (CIRCI), characterized by hypothalamic-pituitary-adrenal (HPA) axis dysfunction, suppression of ACTH release, and peripheral glucocorticoid receptor down-regulation. Exogenous corticosteroids restore vascular $\alpha_1$-adrenergic receptor responsiveness to catecholamines and suppress pro-inflammatory cytokine transcription via nuclear factor-kappa B ($NF\text{-}\kappa B$) inhibition.
• Clinical Indication: Intravenous hydrocortisone is recommended only in patients with septic shock who have an ongoing requirement for vasopressor therapy (e.g., norepinephrine or epinephrine dose $\ge 0.25\text{ mcg/kg/min}$ for at least $4\text{ hours}$) despite adequate fluid resuscitation.
• Dosing Regimen: $200\text{ mg/day}$ of intravenous hydrocortisone, administered either as a continuous infusion ($8.3\text{ mg/hour}$) or as $50\text{ mg}$ intravenous boluses every 6 hours.
• Trial Evidence:
  • APROCCHSS Trial (2018): In severe septic shock, hydrocortisone plus fludrocortisone significantly lowered 90-day all-cause mortality ($43.0\%$ vs $49.1\%$, $p = 0.03$) and shortened the duration of shock.
  • ADRENAL Trial (2018): Hydrocortisone infusion in septic shock accelerated shock resolution and reduced the duration of mechanical ventilation and ICU stay, though 90-day all-cause mortality was not significantly changed.

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Clinical Pearls and Exam Traps

• The Sepsis-3 SIRS Trap: SIRS criteria (fever, tachycardia, tachypnea, leukocytosis) are no longer used to define sepsis. SIRS can be triggered by non-infectious insults (e.g., trauma, burns, acute pancreatitis, bypass surgery). Sepsis strictly requires an infection plus an acute increase in SOFA score $\ge 2$ points.
• Understanding Hyperlactatemia: Serum lactate elevation in septic shock is not simply a marker of anaerobic metabolism secondary to macrovascular hypoperfusion. A major contributor is stress-induced $\beta_2$-adrenoceptor stimulation (endogenous epinephrine surge), which up-regulates skeletal muscle sodium-potassium pumps ($Na^+/K^+$-ATPase), accelerates glycolysis, and produces pyruvate exceeding the handling capacity of pyruvate dehydrogenase. Concurrently, hepatic lactate clearance is impaired.
• Blood Culture Timing: Never postpone antimicrobial administration beyond 1 hour if blood cultures cannot be obtained due to difficult vascular access.