Shock in Medical Emergency

Definition and Objectives

• Shock is a medical emergency that affects all body systems, making it life-threatening.
• At the end of the presentation, students should be able to effectively manage shock and hemorrhage in emergency and trauma situations.

Definition of Shock

• Shock is a clinical syndrome characterized by inadequate tissue perfusion, resulting in cellular, metabolic, and hemodynamic derangements.
• Shock can be defined as a condition in which systemic blood pressure is inadequate to deliver oxygen and nutrients to support vital organs and cellular function, leading to cellular and tissue injury.

Review of Circulatory System

• Tissue perfusion requires a balance of:
  • Adequate cardiac pump (myocardial contractility)
  • Effective vasculature (adequate vascular tone)
  • Sufficient blood volume
  • Blood flow (dependent on Mean Arterial Pressure, MAP)

Classification of Shock

Hypovolemic Shock

• Occurs after a loss of intravascular fluid volume (whole blood, plasma, or water and electrolytes)
• Can be either absolute or relative volume loss
• Relative hypovolemia: fluid shift from vascular space to extravascular space (e.g., intracavitary space, third spacing)

Cardiogenic Shock

• Occurs when the heart's ability to contract and pump blood is impaired
• Causes: coronary (myocardial infarction) or non-coronary (cardiac tamponade, dysrhythmias)
• Leading cause of death from acute myocardial infarction

Obstructive Shock

• Occurs when there is a physical impairment to adequate circulatory blood flow
• Causes: impaired diastolic filling, increased right ventricular afterload, increased left ventricular afterload
• Obstruction of the heart or great vessels impedes venous return to the right side of the heart or prevents effective pumping action

Distributive Shock

• Caused by:
  • Anaphylactic shock (acute, life-threatening hypersensitivity reaction)
  • Neurogenic shock (loss of sympathetic tone, e.g., spinal cord injury, spinal anesthesia)
  • Sepsis (systemic inflammatory response to a documented or suspected infection)
• Characterized by vasodilation, leading to inadequate tissue perfusion

Pathophysiology of Shock at Cellular Level

• Normal cellular metabolism: Fuel + Oxygen → Carbon dioxide + water + ATP
• Reduced oxygen supply leads to anaerobic metabolism, producing less ATP and lactic acid
• Lactic acid accumulation creates an acidotic intracellular environment, leading to cell damage and death

Stages of Shock

Initiation Stage

• Shift from aerobic to anaerobic metabolism, causing lactic acid buildup
• No obvious clinical indications of hypoperfusion
• Decrease in cardiac output can be detected on invasive hemodynamic monitors

Compensatory Stage

• Body activates compensatory mechanisms to maintain blood flow to vital organs and restore homeostasis
• Appropriate interventions can reverse shock with minimal morbidity

Progressive Stage

• Compensatory mechanisms can no longer maintain tissue perfusion
• Deterioration of the cardiovascular system perpetuates symptoms of shock
• Aggressive interventions are necessary to prevent MODS (Multiple Organ Dysfunction Syndrome)

Irreversible/Refractory Stage

• Point at which organ damage is so severe that the patient does not respond to treatment
• Multiple organ dysfunction progressing to complete organ failure, with impending death