Shock and Circulatory Failure
Definition
Circulatory shock (or simply, shock) = acute failure of the circulatory system to supply peripheral tissues and organs with adequate blood → leads to cellular hypoxia due to tissue hypoperfusion.
Types of Shock
Hypovolemic shock
- Most common type
- Cause: Insufficient circulating (intravascular) volume.
- Non-haemorrhagic: Due to fluid loss (e.g., severe dehydration from vomiting, diarrhea, burns).
- Haemorrhagic: Due to blood loss (e.g., trauma, GI bleed). Losing >20% blood (~1L) may induce shock.
- Pathophysiology: ↓ End-diastolic volume → ↓ Stroke volume → ↓ Cardiac output (CO) → ↓ BP → activation of compensatory mechanisms (SNS → ↑ HR, vasoconstriction).
- Symptoms:
- Thirst (due to hypovolemia)
- Tachycardia (compensatory for ↓ CO)
- Cool, clammy skin (from vasoconstriction)
- Hypotension
- Oliguria (reduced renal perfusion)
Cardiogenic Shock
- Cause: Failure of heart to pump effectively due to ventricular dysfunction.
- Definition: ↓ CO, hypotension, tissue hypoxia despite adequate volume.
- Common Causes:
- Myocardial infarction (MI) – most common
- Myocardial contusion
- Sustained arrhythmias
- End-stage CAD/cardiomyopathy
- Pathophysiology:
- MI → myocardial damage → ↓ contractility → ↓ SV and CO
- SNS activation → vasoconstriction to maintain BP → ↑ afterload → worsens CO
- Symptoms:
- Hypotension (↓ CO)
- Cool, clammy skin (VC)
- Distended neck veins (↑ right atrial pressure)
- Pulmonary oedema (from left heart failure)
- Oliguria, cyanosis, fatigue (hypoperfusion and hypoxia)