Shock classification and management

Shock Pathophysiology - Cellular Crisis Mode

• Inadequate tissue perfusion (↓ DO₂) forces cells into anaerobic glycolysis.
  • ATP production plummets: $C_6H_{12}O_6 \to 2 \text{ ATP} + \text{Lactate}$.
  • Lactic acidosis (↑ serum lactate > 2 mmol/L) develops.
• Failure of Na⁺/K⁺-ATPase pump → cellular edema, lysosomal rupture, and cell death (necrosis/apoptosis).
• Mitochondrial dysfunction becomes irreversible, sealing cell fate.

⭐ The transition to irreversible shock is marked by widespread mitochondrial failure, rendering cells unable to use oxygen even if perfusion is restored.

Shock Types - The Four Horsemen

• Hypovolemic: Loss of intravascular volume (e.g., hemorrhage, dehydration).
• Cardiogenic: Primary myocardial pump failure (e.g., MI, heart failure).
• Distributive: Severe peripheral vasodilation (e.g., sepsis, anaphylaxis, neurogenic).
• Obstructive: Extracardiac obstruction to blood flow (e.g., PE, tamponade, tension pneumothorax).

Patient Presentation - Reading The Signs

• General Signs of Hypoperfusion:

  • Hypotension (MAP < 65 mmHg), tachycardia, tachypnea.
  • Altered mental status.
  • Cool, clammy skin; oliguria (< 0.5 mL/kg/hr).

• Key Differentiators:

  • Cardiogenic: JVD, pulmonary edema (crackles).
  • Hypovolemic: Flat neck veins, dry mucosa.
  • Distributive (Septic): Fever, warm/flushed skin (early).
  • Obstructive (Tamponade): Beck's Triad (JVD, hypotension, muffled heart sounds).

⭐ Neurogenic shock is unique: presents with hypotension and bradycardia following spinal injury.

Initial Response - Stabilize & Scramble

• ABCs: Airway, Breathing, Circulation. Prioritize immediate life threats.
• Access: Two large-bore (≥16G) peripheral IVs. Administer O₂.
• Action: Start IV fluid resuscitation, typically 30 mL/kg crystalloid bolus for hypotension.

⭐ Serum lactate > 2 mmol/L is a key indicator of tissue hypoperfusion and is associated with increased mortality in shock.

Targeted Treatment - Pick Your Poison

• Cardiogenic: ↓ Contractility → Inotropes (Dobutamine), Diuretics. If hypotensive, use Norepinephrine.
• Hypovolemic: ↓ Preload → Aggressive fluid resuscitation (crystalloids, blood). Vasopressors if refractory.
• Distributive: Massive vasodilation.
  • Septic: Norepinephrine is the first-line vasopressor. Add broad-spectrum antibiotics.
  • Anaphylactic: Epinephrine (IM first!), antihistamines, corticosteroids.
  • Neurogenic: Norepinephrine or Phenylephrine to restore vascular tone.
• Obstructive: Relieve the physical obstruction.
  • Tamponade → Pericardiocentesis.
  • Tension Pneumothorax → Needle decompression.
  • Pulmonary Embolism → Thrombolysis/Thrombectomy.

⭐ In septic shock, if Mean Arterial Pressure (MAP) remains < 65 mmHg despite adequate fluid resuscitation, initiate Norepinephrine within the first hour to improve perfusion.

High‑Yield Points - ⚡ Biggest Takeaways

• Distributive shock (septic, anaphylactic) is marked by ↓ Systemic Vascular Resistance (SVR). Septic shock requires IV fluids, broad-spectrum antibiotics, and vasopressors (norepinephrine).
• Cardiogenic shock presents with ↓ Cardiac Output (CO) and ↑ Pulmonary Capillary Wedge Pressure (PCWP). Use inotropes (dobutamine), not aggressive fluids.
• Hypovolemic shock shows ↓ preload (CVP, PCWP) and ↓ CO. Treat with aggressive volume resuscitation.
• Obstructive shock (e.g., PE, tamponade) has ↓ CO from obstruction; treat the underlying cause urgently.