Shock Syndromes and Management

Shock: Definition & Classification - Perfusion Plunge

• Shock: Critical state of ↓ tissue perfusion & O₂ delivery → cellular hypoxia & organ dysfunction.
• Classification & Primary Defect:
  • Hypovolemic: ↓ Intravascular volume (e.g., hemorrhage, dehydration).
  • Cardiogenic: Pump failure (e.g., MI, severe arrhythmia).
  • Distributive: Vasodilation, ↓SVR (e.g., Sepsis, Anaphylaxis). 📌 SANe (Septic, Anaphylactic, Neurogenic).
  • Obstructive: Extracardiac flow obstruction (e.g., PE, Tamponade, tension pneumothorax).
• Key Markers:
  • MAP < 65 mmHg (resuscitation target).
  • Lactate > 2 mmol/L (tissue hypoxia).
  • Oliguria (< 0.5 mL/kg/hr).

⭐ In early septic shock (hyperdynamic phase), cardiac output may be normal or ↑, but tissue oxygen extraction is impaired, often reflected by a normal or ↑ ScvO₂/SvO₂.

Shock: Pathophysiology - Cellular Mayhem

• Initiating Event: Systemic hypoperfusion → ↓$O_2$ delivery → cellular hypoxia.
• Energy Depletion: ↓ATP production → shift to anaerobic glycolysis → ↑lactic acid (Lactate >2 mmol/L, pH <7.35).
• Membrane Dysfunction: $Na^+$ / $K^+$ pump failure → $Na^+$ & $H_2O$ influx → cellular swelling, organelle damage.
• Calcium Overload: ↑Intracellular $Ca^{2+}$ → activates proteases, phospholipases → further cell injury.
• Mitochondrial Breakdown: Critical point of no return → triggers apoptosis/necrosis.
• Inflammatory Response: Release of damaging mediators (cytokines, ROS, NO).

⭐ Mitochondrial dysfunction is a key irreversible step in shock-induced cellular injury, leading to ATP depletion and cell death.

Shock: Diagnosis - Code Red Clues

• Core Vital Signs & Mental Status:
  • Hypotension: SBP < 90 mmHg or MAP < 65 mmHg.
  • Tachycardia: HR > 100 bpm (Shock Index: $HR/SBP > \textbf{0.9}$ indicates stress).
  • Tachypnea: RR > 22/min.
  • Altered Mental Status: New confusion, lethargy (GCS < 15).
• Peripheral Hypoperfusion Markers:
  • Skin: Cool, clammy, pale/mottled (warm in early distributive shock).
  • Capillary Refill Time (CRT): > 3 sec.
  • Oliguria: Urine Output < 0.5 mL/kg/hr.
• Key Lab Indicators:
  • Serum Lactate: > 2 mmol/L.
  • Base Deficit: < -4 mEq/L (or worsening).

⭐ > Elevated serum lactate (> 2 mmol/L) is a critical marker of tissue hypoperfusion and strongly correlates with increased mortality in shock.

Shock: Management - Lifeline Tactics

Immediate Goals: Restore tissue perfusion, prevent organ damage. Optimize oxygen delivery ($DO_2$) and reduce oxygen consumption ($VO_2$). 📌 Mnemonic (VIP): Ventilate, Infuse, Pump.

• Airway & Breathing:
  • Oxygen: High flow, target SpO₂ > 94%.
  • Intubate if GCS < 8 or respiratory failure.
• Circulation:
  • Access: Two large-bore (16-18G) IV lines.
  • Fluids: Crystalloids (NS/RL) 20-30 mL/kg bolus. Reassess.
    • Caution: Cardiogenic shock.
  • Vasopressors (if MAP < 65 mmHg post-fluids):
    • Norepinephrine: 0.01-3 mcg/kg/min (1st line septic/undifferentiated).
  • Inotropes (e.g., Dobutamine 2-20 mcg/kg/min) if myocardial dysfunction.
• Monitoring:
  • Vitals, Urine Output (> 0.5 mL/kg/hr), Lactate clearance.
  • Target MAP ≥ 65 mmHg.

⭐ For septic shock, Surviving Sepsis Campaign guidelines recommend initiating vasopressors if MAP remains < 65 mmHg during or after fluid resuscitation to maintain perfusion.

High‑Yield Points - ⚡ Biggest Takeaways

• Septic shock: Norepinephrine first-line; target MAP ≥65 mmHg.
• Distributive shock (septic, anaphylactic): Key feature is ↓SVR, often warm peripheries.
• Cardiogenic shock: Presents with ↓CO, ↑PCWP, ↑SVR; treat cardiac cause.
• Hypovolemic shock: Priority is rapid crystalloid infusion & controlling loss.
• Obstructive shock (tamponade, tension pneumothorax, PE): Requires urgent specific intervention.
• Lactate elevation indicates tissue hypoperfusion; guides resuscitation.
• Recognize compensated shock (normal BP, ↑HR, cool skin) early for better outcomes.