Anatomy of Circulatory Shock: Understanding the Pathophysiology and Clinical Effects

1. What is Circulatory Shock?

• Shock is a life-threatening condition where tissue perfusion is inadequate, leading to oxygen and nutrient deficiency at the cellular level.
• Result: Organ failure if not treated.

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2. Classification of Circulatory Shock

Type	Cause (Basic Idea)
Hypovolemic	↓ Blood volume (e.g. bleeding, dehydration)
Cardiogenic	Pump failure (e.g. MI, heart failure)
Distributive	Vasodilation & pooling (e.g. septic shock)
Obstructive	Blocked blood flow (e.g. embolism, tamponade)

Mnemonic: "H-COD"

(Hypovolemic, Cardiogenic, Obstructive, Distributive)

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3. Anatomy of Shock – Organs & Responses

A. Heart

• ↓ preload (blood entering heart)
• ↓ cardiac output
• Compensatory ↑ heart rate (tachycardia)

B. Blood Vessels

• Vasoconstriction (except in distributive shock)
• Blood shunted to vital organs (brain, heart)

C. Kidneys

• Detect low BP → activate RAAS
• Renin → Angiotensin II → Vasoconstriction
• Aldosterone → Na⁺ & water retention

D. Lungs

• May show rapid breathing (compensation)
• In cardiogenic shock → pulmonary edema

E. Brain

• Reduced perfusion → confusion, fainting, coma

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4. Stages of Shock

Stage	Features
Initial	↓ perfusion, no symptoms yet
Compensated	BP maintained via reflexes (↑ HR, vasoconstriction)
Progressive	BP drops, organ hypoxia starts
Irreversible	Severe damage, multi-organ failure

5. Body's Compensatory Mechanisms

1. Baroreceptor reflex → ↑ HR, vasoconstriction
2. RAAS activation → water & Na⁺ retention
3. ADH release → water retention
4. Sympathetic activation → ↑ CO & vasoconstriction

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6. Clinical Features of Shock

Sign/Symptom	Explanation
Cold, clammy skin	Vasoconstriction
Rapid, weak pulse	↓ Cardiac output
Low BP (hypotension)	↓ Circulating volume
Altered mental status	↓ Brain perfusion
Oliguria (low urine)	↓ Kidney perfusion
Tachypnea	Compensation for acidosis

7. Clinical Conditions

Shock Type	Example Conditions
Hypovolemic	Hemorrhage, vomiting, diarrhea
Cardiogenic	Myocardial infarction, heart failure
Distributive	Septic shock, anaphylaxis, neurogenic shock
Obstructive	Pulmonary embolism, cardiac tamponade

8. Key Differences (Table)

Feature	Hypovolemic	Cardiogenic	Distributive	Obstructive
BP	↓	↓	↓	↓
HR	↑	↑	↑	↑
Skin	Cold	Cold	Warm (initially)	Cold
Neck veins	Flat	Distended	Normal	Distended