6.1 Types and causes of shock

Shock is a life-threatening condition where the body can't deliver enough oxygen to vital organs. It comes in different types, each with unique causes. Understanding these types helps first responders quickly identify and treat shock effectively.

Hypovolemic shock from blood loss, cardiogenic shock from heart problems, and distributive shock from widespread blood vessel dilation are common types. Recognizing the signs and causes of each type is crucial for proper emergency care and preventing organ damage.

Types of Shock

Categories of Shock Based on Underlying Cause

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• Hypovolemic shock occurs when there is a significant decrease in blood volume leading to reduced cardiac output and inadequate tissue perfusion (hemorrhage, severe vomiting, diarrhea)
• Cardiogenic shock happens when the heart is unable to pump effectively due to damage or dysfunction resulting in poor cardiac output and tissue hypoperfusion (myocardial infarction, arrhythmias, valvular disorders)
• Obstructive shock is caused by a physical obstruction that impedes blood flow and leads to reduced cardiac output despite normal blood volume and heart function (pulmonary embolism, tension pneumothorax, cardiac tamponade)
• Distributive shock involves abnormal distribution of blood flow due to vasodilation and increased vascular permeability causing relative hypovolemia and inadequate tissue perfusion (sepsis, anaphylaxis, spinal cord injury)

Causes of Hypovolemic Shock

Mechanisms Leading to Reduced Intravascular Volume

• Blood loss from external or internal hemorrhage can rapidly deplete intravascular volume and lead to hypovolemic shock (trauma, gastrointestinal bleeding, ruptured ectopic pregnancy)
• Dehydration from excessive fluid losses or inadequate fluid intake causes a reduction in intravascular volume and can progress to hypovolemic shock if severe (prolonged vomiting, diarrhea, heat exposure, inadequate oral intake)

Other Causes of Hypovolemia

• Severe burns cause fluid shifts from the intravascular space into the interstitial space due to increased vascular permeability leading to relative hypovolemia
• Excessive diuresis from diuretic medications or uncontrolled diabetes insipidus can lead to significant fluid losses and hypovolemia if not adequately replaced

Causes of Obstructive Shock

Pulmonary Embolism as a Cause of Obstructive Shock

• Pulmonary embolism occurs when a blood clot becomes lodged in the pulmonary arteries impeding blood flow to the lungs and reducing left ventricular preload
• The obstruction to pulmonary blood flow leads to increased right ventricular afterload, right ventricular failure, and decreased cardiac output resulting in obstructive shock

Other Causes of Obstructive Shock

• Tension pneumothorax occurs when air accumulates in the pleural space under pressure collapsing the lung and compressing the heart and great vessels leading to decreased venous return and cardiac output
• Cardiac tamponade happens when fluid accumulates in the pericardial sac compressing the heart and restricting ventricular filling resulting in reduced cardiac output and obstructive shock

Types of Distributive Shock

Anaphylactic Shock

• Anaphylactic shock is a severe allergic reaction causing massive vasodilation, increased vascular permeability, and fluid shifts leading to relative hypovolemia and distributive shock (bee stings, food allergies, medication allergies)
• The release of inflammatory mediators such as histamine and leukotrienes leads to bronchospasm, laryngeal edema, and cardiovascular collapse in addition to the distributive shock state

Septic Shock

• Septic shock occurs when an overwhelming systemic infection leads to vasodilation, increased vascular permeability, and relative hypovolemia resulting in distributive shock (pneumonia, urinary tract infections, abdominal infections)
• The release of inflammatory cytokines and other mediators leads to peripheral vasodilation, capillary leak, and myocardial depression contributing to the distributive shock state

Neurogenic Shock

• Neurogenic shock is caused by a sudden loss of sympathetic tone due to spinal cord injury leading to massive vasodilation and pooling of blood in the periphery resulting in relative hypovolemia and distributive shock
• The level of the spinal cord injury determines the extent of sympathetic dysfunction with injuries above T6 causing the most profound vasodilation and bradycardia

Causes of Cardiogenic Shock

Heart Failure as a Cause of Cardiogenic Shock

• Heart failure occurs when the heart is unable to pump effectively due to various causes leading to reduced cardiac output and cardiogenic shock (myocardial infarction, cardiomyopathy, valvular disorders)
• Systolic heart failure involves reduced contractility and ejection fraction while diastolic heart failure involves impaired ventricular filling and relaxation both leading to reduced cardiac output

Other Causes of Cardiogenic Shock

• Acute myocardial infarction causes damage to the myocardium leading to reduced contractility, arrhythmias, and mechanical complications such as ventricular septal rupture or papillary muscle rupture resulting in cardiogenic shock
• Severe arrhythmias such as ventricular tachycardia or complete heart block can significantly impair cardiac output leading to cardiogenic shock if not promptly corrected