Shock: Types and Mechanisms

Study Notes

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.

Description

This quiz covers the different types of shock, including hypovolemic and cardiogenic shock, and their underlying mechanisms. Understand the causes, clinical presentations, and how impaired tissue perfusion affects cellular metabolism. Test your knowledge on this critical aspect of physiology.