Shock: Types and Mechanisms

Shock: Types and Mechanisms

• Shock is defined as decreased tissue perfusion and impaired cellular metabolism.
• Shock types are classified by functional impairment or site of origin.

Hypovolemic Shock

• Characterized by a loss of intravascular fluid volume.
• Vessel size is unaffected.
• Decreased blood/plasma volume reduces venous return to the heart, leading to decreased cardiac output.

Absolute Hypovolemia

• Fluid loss from the body.
  • Hemorrhage
  • Gastrointestinal loss (vomiting, diarrhea)
  • Diabetes insipidus
  • Diuresis
  • Fistula drainage

Relative Hypovolemia

• Fluid shifts from the vascular space to the extravascular space ("third spacing").

  • Burns increase capillary permeability.

• Clinical presentation: tachycardia, hypotension, tachypnea, oliguria, pallor, cold

Cardiogenic Shock

• The heart's inability to pump enough blood for the body's metabolic needs.
• This represents direct pump failure despite adequate blood volume.
• Causes include myocardial ischemia (impaired blood flow to the heart muscle) and dysrhythmias (irregular heartbeats).

Obstructive Shock

• A physical blockage of blood flow.
• Causes include pulmonary embolism, cardiac tamponade (fluid buildup around the heart), tension pneumothorax (air trapped in the chest cavity), and superior vena cava syndrome.
• Obstruction reduces ventricle filling, diminishing cardiac output and reducing oxygen delivery. This is an indirect pump failure.
• Blood flow blockage prevents diastolic filling of the ventricles, increasing afterload and reducing filling pressures.

Distributive Shock

• Abnormal blood flow distribution in the vessels.
• Heart output generally remains normal

Septic Shock

• Sepsis with hypotension despite fluid resuscitation.
• Originates from an infection triggering a systemic inflammatory response.
• This response leads to peripheral vasodilation, increased capillary permeability, excessive cellular activation, and increased coagulation.

Neurogenic Shock

• Loss of vascular tone due to interruption of the sympathetic nervous system.
• Causes include severe pain, anesthesia, stress, spinal cord injury, and head trauma.

Anaphylactic Shock

• An allergic reaction to a substance (food, drug, or chemical).
• Results in massive vasodilation and increased capillary permeability.
• Fluid shifts from the vasculature to the interstitial space.