SHOCK SYNDROMES
Definition of Shock
Shock is a life-threatening state of acute circulatory failure resulting in inadequate cellular oxygen utilization, leading to cellular hypoxia, organ dysfunction, and death if untreated.
Key modern concept:
Shock is not merely hypotension – tissue hypoperfusion can exist despite normal BP.
Classification of Shock Syndromes
|
Type of Shock |
Primary Problem |
|
Hypovolemic |
↓ Preload |
|
Cardiogenic |
↓ Cardiac pump function |
|
Distributive |
↓ SVR (maldistribution of flow) |
|
Obstructive |
Mechanical obstruction to circulation |
|
Dissociative (Hypoxic) |
Impaired oxygen utilization |
Pathophysiology of Shock (Common Final Pathway)
- ↓ Oxygen delivery (DO₂)
- Cellular hypoxia
- Switch to anaerobic metabolism
- ↑ Lactate, metabolic acidosis
- Mitochondrial dysfunction
- Microcirculatory failure
- Multiple organ dysfunction syndrome (MODS)
|
Shock Type |
CO |
SVR |
CVP |
PAOP (PCWP) |
Pulse Pressure |
Skin |
ScvO₂ / SvO₂ |
|
Hypovolemic |
↓ |
↑ |
↓↓↓ |
↓↓↓ |
Narrow |
Cold, clammy |
↓ |
|
Cardiogenic |
↓↓↓ |
↑ |
↑↑ |
↑↑↑ |
Narrow |
Cold, clammy |
↓ |
|
Septic (Early / Hyperdynamic) |
↑ |
↓↓↓ |
↓ / N |
↓ / N |
Wide |
Warm, flushed |
↑ / N |
|
Septic (Late / Hypodynamic) |
↓ |
↓ |
↓ / N |
↓ |
Narrow |
Cold |
↓ |
|
Obstructive |
↓ |
↑ |
↑ |
↑ / N |
Narrow |
Cold |
↓ |
I. HYPOVOLEMIC SHOCK
Definition
Shock due to absolute or relative loss of intravascular volume, leading to ↓ preload and ↓ cardiac output.
Causes
A. Hemorrhagic
- Trauma
- GI bleed
- Ruptured aneurysm
- Post-operative bleeding
- Obstetric hemorrhage
B. Non-hemorrhagic
- Severe dehydration (diarrhea, vomiting)
- Burns (third spacing)
- Diabetic ketoacidosis
- Pancreatitis
- Excessive diuresis
Clinical Features
- Tachycardia
- Narrow pulse pressure (early)
- Hypotension (late)
- Cold, clammy skin
- Oliguria
- Altered mental status
Management
Principle: Restore volume + stop loss
- Airway & Breathing
- Rapid volume resuscitation
- Crystalloids (balanced solutions preferred)
- Blood products (1:1:1 in hemorrhagic shock)
- Control source
- Surgery / endoscopy / interventional radiology
- Vasopressors
- Only after adequate volume
- Monitor
- Lactate clearance
- Dynamic fluid responsiveness
II. CARDIOGENIC SHOCK
Definition
Shock due to primary failure of the heart to pump blood effectively, despite adequate volume.
Common Causes
- Acute MI (most common)
- Severe LV dysfunction
- Papillary muscle rupture
- Acute severe MR or VSD
- Malignant arrhythmias
- Myocarditis
- Stress cardiomyopathy (Takotsubo)
Clinical Features
- Hypotension with pulmonary edema
- Elevated JVP
- Cold extremities
- S3 gallop
- Oliguria
Management
Principle: Improve contractility, reduce afterload, revascularize
- Oxygen / NIV / Intubation
- Inotropes
- Dobutamine (first line)
- Milrinone (if on beta-blockers)
- Vasopressors
- Norepinephrine (preferred)
- Diuretics (if congested)
- Mechanical circulatory support
- IABP (limited role)
- Impella
- VA-ECMO
- Definitive therapy
- PCI / CABG / valve surgery
III. DISTRIBUTIVE SHOCK
Definition
Shock characterized by pathological vasodilation and maldistribution of blood flow, with relative hypovolemia.
Types
|
Subtype |
Cause |
|
Septic shock |
Infection-induced vasodilation |
|
Anaphylactic shock |
IgE-mediated vasodilation |
|
Neurogenic shock |
Loss of sympathetic tone |
|
Endocrine shock |
Adrenal crisis, myxedema |
A. SEPTIC SHOCK (Most Common in ICU)
Definition (Sepsis-3)
Septic shock = Sepsis + persistent hypotension requiring vasopressors to maintain MAP ≥65 mmHg AND lactate >2 mmol/L despite adequate fluids
Management (Surviving Sepsis Campaign)
- Early antibiotics (within 1 hour)
- Fluids
- 30 mL/kg crystalloid
- Vasopressor
- Norepinephrine (first line)
- Source control
- Organ support
- Reassess fluid responsiveness
B. ANAPHYLACTIC SHOCK
- Massive vasodilation
- Capillary leak
- Bronchospasm
Treatment
- IM Epinephrine (first and most important)
- Airway protection
- Fluids
- Antihistamines
- Steroids
C. NEUROGENIC SHOCK
- Seen in spinal cord injury above T6
- Hypotension + bradycardia
Management
- Fluids
- Vasopressors (norepinephrine)
- Atropine for bradycardia
IV. OBSTRUCTIVE SHOCK
Definition
Shock caused by mechanical obstruction to cardiac filling or outflow.
Causes
|
Cause |
Mechanism |
|
Tension pneumothorax |
↓ Venous return |
|
Cardiac tamponade |
↓ Ventricular filling |
|
Massive PE |
RV outflow obstruction |
|
Severe aortic stenosis |
LV outflow obstruction |
Management
Relieve obstruction urgently
- Needle decompression
- Pericardiocentesis
- Thrombolysis / embolectomy
- Surgical correction
V. DISSOCIATIVE / HYPOXIC SHOCK
Definition
Shock due to impaired oxygen utilization at tissue level, despite adequate blood flow.
Causes
- Carbon monoxide poisoning
- Methemoglobinemia
- Cyanide poisoning
- Severe mitochondrial dysfunction (late sepsis)
Key Feature
- Normal or high PaO₂
- High ScvO₂
- Persistent lactic acidosis
Management
- Treat underlying cause
- High-flow oxygen / hyperbaric oxygen
- Specific antidotes
Key Exam Points
- Shock ≠ hypotension
- Septic shock may have normal BP initially
- High ScvO₂ does NOT rule out shock
- Lactate clearance is a resuscitation target
- Norepinephrine is first-line vasopressor in most shock states
- Dynamic indices outperform CVP
Suggested Further Reading
- Harrison’s Principles of Internal Medicine – Shock & Sepsis chapters
- Irwin & Rippe’s Intensive Care Medicine
- Washington Manual of Critical Care
- Surviving Sepsis Campaign Guidelines
- Vincent JL – Circulatory Shock Review