4.1 Sepsis, Severe Sepsis & Septic Shock Resuscitation

4.1 Sepsis, Severe Sepsis & Septic Shock Resuscitation

Introduction & Evolving Definitions (Sepsis-2 vs Sepsis-3)

Sepsis is one of the most critical time-sensitive emergencies encountered in transport medicine. Historically, sepsis was conceptualized under the Sepsis-2 guidelines (2001) as a continuum beginning with Systemic Inflammatory Response Syndrome (SIRS), progressing to severe sepsis, and escalating to septic shock. SIRS required meeting at least two of four criteria: temperature $> 38.0^\circ\text{C}$ or $< 36.0^\circ\text{C}$, heart rate $> 90\text{ beats/min}$, respiratory rate $> 20\text{ breaths/min}$ (or $\text{PaCO}_2 < 32\text{ mmHg}$), and white blood cell count $> 12,000/\mu\text{L}$, $< 4,000/\mu\text{L}$, or $> 10%$ immature band forms.

In 2016, the Sepsis-3 Consensus Definitions fundamentally redefined sepsis as life-threatening organ dysfunction caused by a dysregulated host response to infection. Sepsis-3 eliminated the term "severe sepsis" and retired SIRS as a primary diagnostic criteria due to its poor specificity. Organ dysfunction is now objectively defined as an acute change in total Sequential Organ Failure Assessment (SOFA) score of $\ge 2$ points attributable to the infection.

Sequential Organ Failure Assessment (SOFA) & quick SOFA (qSOFA)

The SOFA score evaluates six organ systems, grading each from 0 (normal) to 4 (severely dysfunctional):

1. Respiration: $\text{PaO}_2 / \text{FiO}_2$ ratio ($\text{mmHg}$)
2. Coagulation: Platelet count ($\times 10^3 / \mu\text{L}$)
3. Liver: Total bilirubin ($\text{mg/dL}$)
4. Cardiovascular: Mean Arterial Pressure (MAP) or vasopressor requirements
5. Central Nervous System: Glasgow Coma Scale (GCS) score
6. Renal: Serum creatinine ($\text{mg/dL}$) or daily urine output ($\text{mL/day}$)

At the bedside or during pre-hospital and interfacility triage, the quick SOFA (qSOFA) serves as a rapid screening tool to identify patients outside the ICU who are at high risk of deterioration. A qSOFA score of $\ge 2$ points indicates high risk:

• Respiratory Rate: $\ge 22\text{ breaths/min}$
• Altered Mental Status: $\text{GCS} < 15$
• Systolic Blood Pressure: $\le 100\text{ mmHg}$

Septic Shock Definition

Septic shock represents a subset of sepsis in which underlying circulatory and cellular/metabolic abnormalities are profound enough to substantially increase mortality. Under Sepsis-3, septic shock is clinically identified by persistent hypotension requiring vasopressors to maintain a **$\text{MAP} \ge 65\text{ mmHg}$ AND a serum lactate level $> 2.0\text{ mmol/L}$ despite adequate volume resuscitation.

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Comparison of Sepsis Frameworks

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Surviving Sepsis Campaign (SSC) 1-Hour Bundle

The Surviving Sepsis Campaign (SSC) emphasizes immediate resuscitation. The 1-Hour Bundle outlines five actionable steps that must be initiated immediately upon recognition of sepsis or septic shock:

1. Measure Serum Lactate: Measure initial lactate level. If lactate is $> 2.0\text{ mmol/L}$, re-measure within 2-4 hours to guide lactate clearance tracking.
2. Obtain Blood Cultures Prior to Antibiotics: Draw at least two sets of blood cultures (aerobic and anaerobic)—one set peripherally and one through each vascular access device present $> 48\text{ hours}$. Do not delay antimicrobial administration by more than 45 minutes if culture procurement is difficult.
3. Administer Broad-Spectrum Antibiotics: Initiate empiric IV broad-spectrum antimicrobials covering all likely bacterial/fungal pathogens (e.g., Vancomycin combined with Cefepime, Piperacillin-Tazobactam, or Meropenem).
4. Administer $30\text{ mL/kg}$ Crystalloid Bolus: Rapidly infuse a minimum of $30\text{ mL/kg}$ of balanced crystalloid solution (e.g., Lactated Ringer's or Plasma-Lyte) within the first 3 hours for hypotension ($\text{SBP} < 90\text{ mmHg}$, $\text{MAP} < 65\text{ mmHg}$) or initial lactate $\ge 4.0\text{ mmol/L}$.
5. Apply Vasopressors: Initiate vasopressors during or immediately following fluid resuscitation if MAP remains $< 65\text{ mmHg}$ to restore organ perfusion.

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Fluid Resuscitation & Crystalloid Selection

Volume expansion restores intravascular filling pressures, increases mean systemic filling pressure, and boosts cardiac output via the Frank-Starling mechanism. Modern critical care mandates using balanced crystalloids (Lactated Ringer's or Plasma-Lyte) rather than $0.9%$ Normal Saline. High-volume $0.9%$ Normal Saline causes hyperchloremic metabolic acidosis, renal vasoconstriction, and increased risk of acute kidney injury (AKI) and renal replacement therapy.

Fluid responsiveness must be reassessed continuously using dynamic hemodynamic parameters rather than static CVP. Dynamic indicators include:

• Passive Leg Raise (PLR): Transiently increases preload by $\sim 300\text{ mL}$; an increase in stroke volume or pulse pressure $> 10%$ indicates fluid responsiveness.
• Stroke Volume Variation (SVV) / Pulse Pressure Variation (PPV): Values $> 12-15%$ in mechanically ventilated patients with fixed tidal volumes ($8\text{ mL/kg}$) indicate fluid responsiveness.

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Hemodynamic Titration & Vasoactive Management

When $30\text{ mL/kg}$ fluid boluses fail to maintain a $\text{MAP} \ge 65\text{ mmHg}$, vasoactive infusions are titrated immediately.

First-Line Vasopressor: Norepinephrine

Norepinephrine is the first-line vasopressor in septic shock. It is a potent $\alpha_1$-agonist with modest $\beta_1$-adrenergic activity. It increases MAP primarily through arterial venoconstriction and systemic vascular resistance (SVR) elevation while providing mild inotropic support without marked tachycardia.

• Dosing: $0.02 - 3.0\text{ mcg/kg/min}$ (or $2 - 30\text{ mcg/min}$ titrated to $\text{MAP} \ge 65\text{ mmHg}$).

Second-Line Vasopressor: Vasopressin

Vasopressin (Antidiuretic Hormone) acts on vascular $V_1$ receptors to induce vascular smooth muscle contraction. Sepsis leads to endogenous vasopressin depletion. Vasopressin is added to norepinephrine to either increase MAP or reduce norepinephrine dosage requirements ("norepinephrine-sparing effect").

• Dosing: Fixed non-titrated dose of $0.03\text{ units/min}$. Do not titrate vasopressin for MAP management; high doses ($> 0.03-0.04\text{ units/min}$) cause severe splanchnic and coronary vasoconstriction.

Inotropic Support: Dobutamine

If the patient exhibits persistent hypoperfusion (elevated lactate, low central venous oxygen saturation $\text{ScvO}_2 < 70%$, or low cardiac index) despite adequate volume resuscitation and MAP restoration, myocardial dysfunction ("septic cardiomyopathy") should be suspected. Dobutamine is a predominant $\beta_1$-agonist with mild $\beta_2$ vasodilator properties.

• Dosing: $2.5 - 20\text{ mcg/kg/min}$ continuous infusion. It enhances myocardial contractility and stroke volume.

Third-Line & Refractory Agents

• Epinephrine: Added to norepinephrine or used as second-line agent when additional inotropic and vasoconstrictive support is required ($0.05 - 0.5\text{ mcg/kg/min}$). Note that epinephrine causes transient increases in serum lactate via skeletal muscle $\beta_2$-glycolysis.
• Phenylephrine: Pure $\alpha_1$-agonist. Reserved only for patients where norepinephrine induces severe tachyarrhythmias or when cardiac output is known to be elevated.

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Vasoactive Infusion Reference Guide

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Transport Monitoring & Re-evaluation

During critical care transport of the septic patient, monitor:

• Arterial Catheterization: Continuous invasive BP monitoring is mandatory due to non-invasive cuff inaccuracy in severe vasoconstriction.
• Lactate Clearance Tracking: Serial lactate levels every 2-4 hours. Successful resuscitation is marked by a $\ge 10-20%$ lactate clearance every 2 hours, reflecting resolution of tissue hypoxia.
• Central Venous Oxygen Saturation ($\text{ScvO}_2$): Target $\text{ScvO}_2 \ge 70%$ (or mixed venous $\text{SvO}_2 \ge 65%$).
• Urine Output: Target $\ge 0.5\text{ mL/kg/hr}$ via indwelling Foley catheter with urometer.
• Mechanical Ventilation: Implement lung-protective ventilation ($6\text{ mL/kg}$ ideal body weight, plateau pressure $P_{\text{plat}} \le 30\text{ cmH}_2\text{O}$) for secondary ARDS. Avoid hyperventilation which reduces venous return.