Shock Types, Pathophysiology, Clinical Presentation & Management

Core Definition & Pathophysiology of Shock

• Universal Definition: Inadequate tissue perfusion → cellular hypoxia → cellular death → system failure → cardiovascular (CV) collapse → death.

• Key Chain

  • ↓ Blood flow → ↓ O₂ delivery + ↓ waste removal.

  • Primary lethal event in all shocks = CV collapse, regardless of initiating cause.

• Pump / Power / Pathway Analogy

  • Pump = Heart.

  • Power (Volume) = Blood/Fluid.

  • Pathway = Vasculature (arteries/veins).

  • Shock results when ANY of the three components fails.

• Shared Early VS Pattern (except neurogenic)

  • $\downarrow BP \; (hypotension)$

  • $\uparrow HR \; (tachycardia)$ – compensatory to restore CO.

  • $\uparrow RR$ – compensatory to ↑ O₂ uptake.

• Late Outcome: Multi-organ failure → irreversible CV collapse.

Classification Overview (6 Types)

• Hypovolemic – volume loss.

• Cardiogenic – intrinsic pump failure.

• Obstructive – mechanical barrier to forward flow.

• Distributive (massive vasodilation)

  1. Anaphylactic – histamine-mediated.

  2. Septic – inflammatory/ endotoxin-mediated.

  3. Neurogenic – loss of sympathetic tone.

1. Hypovolemic Shock

• Pathology: ↓ Intravascular volume → inadequate preload → ↓ SV → ↓ CO.

• Major Etiologies

  • Hemorrhage/trauma.

  • Severe GI loss: profuse vomiting/diarrhea.

  • Major burns → plasma exudation.

• Key Clinical Findings

  • VS: $\downarrow BP,\; \uparrow HR,\; \uparrow RR$.

  • Cool, pale, clammy skin.

  • ↓ Skin turgor.

  • Oliguria / urine output ↓.

  • Altered mentation.

• Management

  • Rapid large-bore IV access (≥2 lines); begin fluid resuscitation immediately.

  • Priority order: 1) Fill the tank (crystalloids, blood) 2) Control source (e.g., pressure, surgery, cautery).

  • Monitor VS, urine output, mental status.

2. Cardiogenic Shock

• Pathology: Primary pump failure → ↓ SV despite adequate volume/pathway.

• Common Causes

  • Extensive MI / ischemia.

  • Cardiomyopathy.

  • Severe valvular disease (regurgitation, stenosis).

  • Dysrhythmias (VTach, VFib, brady-arrhythmias).

  • Advanced heart failure (L or R sided).

• Cardiac Example: VTach (“tombstones”) may present with pulse but poor CO.

• Clinical Clues

  • Typical VS pattern.

  • Chest pain/pressure.

  • Possible pulmonary edema (left HF overlay).

• Therapeutic Focus

  • Inotropes: Digoxin (watch for toxicity – visual halos, N/V), dopamine, dobutamine to ↑ contractility.

  • Treat underlying rhythm (defibrillate, cardiovert, antiarrhythmics).

  • Revascularize coronary arteries (PCI, CABG) if ischemia.

  • Surgical valve repair/replacement if valvular.

3. Obstructive Shock

• Core Concept: Heart is structurally/ functionally normal but externally impeded OR pathway blocked.

• Pump-External Compression

  • Pericarditis → inflammation & swelling → squeezing.

  • Pericardial effusion → progresses to Cardiac Tamponade.

  • Tension pneumothorax / hemothorax → intrathoracic pressure ↑, compresses heart.

• Pathway Blockage

  • Aortic aneurysm rupture.

  • Aortic dissection.

  • Massive pulmonary embolism (PE).

• Signs & Symptoms

  • Classic VS pattern.

  • JVD (↑ intrathoracic / pericardial pressure).

  • Chest pain, dyspnea if thoracic cause.

• Treatment

  • Remove/compress obstruction: pericardiocentesis, chest tube for pneumo/hemo, surgical repair for aneurysm/dissection, thrombolysis/embolectomy for PE.

  • Concurrent fluid/blood resuscitation if secondary hemorrhage.

4. Distributive Shock – Shared Features

• Massive vasodilation → ↓ SVR → “big straw” analogy: heart cannot generate enough force to move blood through widened vessels.

• Shared S/S

  • Warm, flushed skin (↑ peripheral flow from vasodilation).

  • ↓ BP; tachycardia (except neurogenic); ↑ RR.

4a. Anaphylactic Shock

• Trigger: Severe Type I hypersensitivity → massive histamine release.

• Pathophysiology: Histamine → systemic vasodilation + ↑ capillary permeability & bronchospasm.

• Key S/S

  • Warm, flushed.

  • Marked airway compromise: stridor, wheeze, dyspnea, edema.

• Management Priorities

  • Secure airway (may need intubation).

  • Remove offending antigen.

  • Epinephrine IM/IV (first-line).

  • Antihistamines (H1 & H2 blockers), IV corticosteroids.

  • High-flow O₂, possible bronchodilators.

4b. Septic Shock

• Trigger: Disseminated infection (bacterial, fungal, viral) → systemic inflammatory response.

• Dual Vasodilation Drivers

  • Inflammatory mediator release.

  • Pathogen cell-wall/endotoxin products.

• Distinct S/S

  • Warm, flushed skin.

  • Fever (often > $38.3^{\circ}C$) or hypothermia.

  • Possible chills, rigors.

• Management

  • Broad-spectrum IV antibiotics within 1 h (“golden hour”).

  • Aggressive fluid resuscitation (30 mL/kg crystalloid recommended early).

  • Vasopressors (norepinephrine) if hypotension persists.

  • Source control (drain abscess, remove line, etc.).

  • Monitor lactate, organ function (kidney, liver, CNS).

4c. Neurogenic Shock

• Rarest form; injury to sympathetic pathways (spinal cord, brainstem, spinal anesthesia, tumor).

• Mechanism: Loss of sympathetic tone → unopposed parasympathetic vascular relaxation.

• Unique VS Pattern

  • $\downarrow BP$ (vasodilation).

  • $\downarrow HR$ (no sympathetic compensation – bradycardia!).

  • $\uparrow RR$ (hypoxia compensation still intact).

• Other S/S

  • Warm, flushed skin below level of injury.

  • Possible motor/sensory deficits indicating cord involvement.

• Management

  • Maintain airway/oxygen.

  • Cautious fluid resuscitation.

  • Vasopressors (e.g., phenylephrine, norepinephrine) to restore SVR.

  • Atropine or pacing if severe bradycardia.

  • Stabilize spine, treat edema (high-dose steroids debate), remove tumor if indicated.

Cross-Comparison Cheat Sheet

Ethical & Practical Considerations

• Time-critical interventions (fluids, epi, antibiotics) are life-saving; delays correlate with mortality – reinforces ethical duty for rapid recognition.

• In polytrauma, differentiating obstructive (tamponade, pneumothorax) from hypovolemic is vital; inappropriate fluid overload before chest decompression may worsen tamponade.

• Monitor for transition: e.g., ruptured AAA causes initial obstructive → quickly evolves to hypovolemic as hemorrhage ensues.

Numerical Pearls & Formulas

• Blood ≈ $90\%$ water – supports aggressive crystalloid replacement in burns/GI loss.

• Standard sepsis bundle: $30\,\text{mL/kg}$ crystalloid in first hour.

• Shock Index (SI) = $\dfrac{HR}{SBP}$ – values > $0.9$ indicate impending decompensation.

Quick Treatment Algorithm

1. ABC + O₂ (secure airway, breathing, circulation).

2. Identify category via Hx/assessment (pump, power, pathway).

3. Initiate category-specific treatment while continuing supportive care.

4. Reassess VS, mental status, urine output q5-15 min.

5. Prevent progression to irreversible CV collapse.

Memory Aids

• “3 Ps”: Pump (cardiogenic), Power (hypovolemic), Pathway (obstructive).

• “WARM shocks” = Distributive (Anaphylactic, Septic, Neurogenic).

• Only Bradycardic Shock = Neurogenic.

• Straw Analogy: Normal straw (normal SVR); straw-as-big-as-head (massive vasodilation) – heart can’t propel fluid.