111. Shock - classification, etiology, pathogenesis, compensatory mechanisms, clinical manifestations.

Shock

Definition

Shock is a clinical syndrome characterized by acute circulatory failure, leading to inadequate tissue perfusion and cellular oxygen delivery, resulting in cellular and organ dysfunction.

Classification and etiology

1. 1 Hypovolemic shock

Etiology:

• Hemorrhage (trauma, GI bleed, ruptured aneurysm).
• Severe dehydration (vomiting, diarrhea, burns).

1. 2 Cardiogenic shock

Etiology:

• Acute myocardial infarction (most common).
• Severe heart failure.
• Arrhythmias.
• Mechanical causes (valve rupture, tamponade).

1. 3 Obstructive shock

Etiology:

• Pulmonary embolism.
• Cardiac tamponade.
• Tension pneumothorax.
• Constrictive pericarditis.

1. 4 Distributive shock (vasodilatory)

Etiology:

• Septic shock (bacterial endotoxins → vasodilation).
• Anaphylactic shock ( IgE- mediated hypersensitivity).
• Neurogenic shock (spinal cord injury → loss of sympathetic tone).

Pathogenesis

1. Impaired perfusion → cellular hypoxia.
2. Switch from aerobic to anaerobic metabolism → lactate accumulation → metabolic acidosis.
3. ATP depletion → ion pump failure → cell swelling and death.
4. Release of inflammatory mediators (especially in septic shock) → further vascular dysfunction.
5. Progression to organ dysfunction and failure if uncorrected.

Compensatory mechanisms

• Sympathetic activation → increased heart rate and contractility, peripheral vasoconstriction.
• RAAS activation → vasoconstriction, sodium and water retention.
• ADH release → water reabsorption to maintain volume.

These mechanisms aim to preserve perfusion of vital organs (brain, heart).

Clinical manifestations

General signs

• Hypotension.
• Tachycardia.
• Cold, clammy skin (except distributive shock → warm skin early).
• Oliguria (reduced urine output).
• Altered mental status (restlessness, confusion, coma).

Specific features by type

Stages of shock

1. 1 Initial (non-progressive stage)

Compensatory mechanisms maintain perfusion.

1. 2 Progressive stage

Worsening hypoperfusion, metabolic acidosis.

1. 3 Irreversible stage

Severe cellular and organ damage → death despite correction of hemodynamics.