Lecture Notes on Shock

Definition of Shock

• Shock is inadequate perfusion to tissues.
  • Leads to tissue failure, organ failure, and potentially multi-system organ failure.
  • Four main types: hypovolemic, cardiogenic, obstructive, distributive.

Types of Shock and Causes

Hypovolemic Shock

• Cause: Loss of blood volume
• Pathophysiology:
  • Reduction in preload → Decreased stroke volume → Decreased cardiac output → Reduced blood pressure (perfusion pressure).
• Causes of Blood Volume Loss:
  • Hemorrhagic: Postpartum hemorrhage, GI bleeds (upper/lower), retroperitoneal bleed, ruptured aneurysms.
  • Non-hemorrhagic: Massive burns, constant sweating from fevers, vomiting, diarrhea, diuretics, third spacing (e.g., pancreatitis).

Cardiogenic Shock

• Cause: Heart's inability to pump blood effectively.
• Pathophysiology:
  • Decreases in contractility, heart rate issues, or mechanical issues can reduce cardiac output.
• Causes:
  • Myocardial dysfunction: MI, myocarditis, heart failure, cardiomyopathies.
  • Arrhythmias: Slow heart rate (heart block), Fast heart rate (AFib, VTAC, VFib).
  • Valvular dysfunction: Aortic or mitral regurgitation, stenosis.

Obstructive Shock

• Cause: Blockage impeding blood flow.
• Pathophysiology:
  • Decreased cardiac output due to obstruction affecting heart structures or vessels.
• Causes:
  • High afterload: PE, aortic stenosis.
  • Reduced venous return/preload: Tension pneumothorax, cardiac tamponade.

Distributive Shock

• Cause: Vasodilation lowering systemic vascular resistance.
• Pathophysiology:
  • Decreased systemic vascular resistance leads to drop in blood pressure.
• Types:
  • Septic shock: Infection leading to cytokine release and vasodilation.
  • Anaphylactic shock: Allergic reaction causing mast cell degranulation and vasodilation.
  • Neurogenic shock: Spinal injury leading to sympathetic flow loss, vasodilation.

Features, Complications, and Diagnostics

Vital Signs

• Hypotension: Key indicator often measured by MAP.
• Heart Rate:
  • Usually increased due to compensatory response (except neurogenic shock).
• Respiratory Rate: Can vary, often increased due to acidosis.
• Temperature: Fever in septic shock.

End-Organ Dysfunction

• Brain: Confusion, delirium, syncope, stroke.
• Liver: Elevated enzymes, jaundice.
• Kidneys: Oliguria, anuria, increased BUN/creatinine.
• Metabolic State: Lactic acidosis.

Diagnostic Tests

• CBC for infection signs.
• BuN/creatinine for kidney function.
• EKG for cardiac issues.
• Chest X-ray for pulmonary issues.
• Cultures to identify infections.
• Lactate levels for tissue perfusion.

Hemodynamic Monitoring

Hypovolemic Shock

• Low CVP, low PCWP, low cardiac index, high systemic vascular resistance.

Cardiogenic Shock

• High CVP, high PCWP, low cardiac index, high systemic vascular resistance.

Obstructive Shock

• High CVP, low to high PCWP depending on specific case (e.g., cardiac tamponade).

Distributive Shock

• Low CVP, low PCWP, high cardiac index in septic/anaphylactic shock, low index in neurogenic shock.

Treatment Approaches

Hypovolemic Shock

• Restore volume with IV fluids or blood.

Cardiogenic Shock

• Address underlying cause (e.g., MI, arrhythmia).
• Support cardiac function with inotropes.

Obstructive Shock

• Remove obstruction (e.g., thoracostomy for pneumothorax, embolectomy for PE).

Distributive Shock

• Address underlying infection or allergic reaction.
• Use vasopressors to support blood pressure.

Clinical Cases

• Case studies highlight different shock types, symptoms, and appropriate responses.

Conclusion

• Understanding the types, features, and treatments of shock is essential for effective medical intervention. Proper diagnosis and response can significantly improve patient outcomes.