Overview
This lecture reviews the main types of shock in clinical medicine, their underlying mechanisms, clinical features, diagnostics, complications, and treatment approaches.
Types of Shock
- Four types: hypovolemic, obstructive, distributive, and cardiogenic shock.
- Hypovolemic shock: caused by loss of blood or fluids (e.g., GI losses, burns, trauma).
- Obstructive shock: caused by physical obstruction to blood flow (e.g., tension pneumothorax, cardiac tamponade, pulmonary embolism).
- Distributive shock: caused by massive vasodilation (e.g., septic shock, anaphylaxis, neurogenic shock).
- Cardiogenic shock: due to failure of the heart’s pumping function (e.g., MI, acute heart failure, severe arrhythmia).
Pathophysiology & Clinical Features
- Hypovolemic, obstructive, and cardiogenic shock: all cause reduced cardiac output and poor tissue perfusion.
- Distributive shock: marked by low systemic vascular resistance and warm, flushed extremities (except neurogenic, which has bradycardia).
- Organ malperfusion leads to multi-organ dysfunction: lactic acidosis, AKI, encephalopathy, hepatic injury, mesenteric ischemia.
- Classic findings:
- Cold, pale, mottled extremities in low-output shocks.
- Warm, red extremities in distributive shocks.
Diagnostic Approach
- Shock index = heart rate / systolic BP; >1 suggests shock.
- Elevated lactate indicates tissue hypoperfusion.
- Look for decreased organ perfusion: altered mental status, AKI (↑creatinine, ↓urine), liver injury (↑LFTs), EKG changes.
- Swan-Ganz catheter measurements help differentiate shock type (cardiac index, SVO2, SVR, CVP, PCWP).
Hemodynamic Patterns by Shock Type
- Hypovolemic: low CO, low CVP/PCWP, high SVR.
- Obstructive: low CO, high CVP, variable PCWP, high SVR.
- Cardiogenic: low CO, high CVP/PCWP, high SVR.
- Distributive: high CO, low SVR, low CVP/PCWP.
Treatment Strategies
- Hypovolemic: replace fluids or blood, treat cause.
- Obstructive: relieve obstruction (pericardiocentesis, chest tube, thrombolysis/embolectomy).
- Cardiogenic: treat underlying cause (revascularization, valve repair, antiarrhythmics, inotropes, mechanical support).
- Distributive:
- Anaphylaxis—immediate epinephrine.
- Sepsis—antibiotics, fluids, source control, vasopressors (norepinephrine, vasopressin).
Key Terms & Definitions
- Cardiac Output (CO) — volume of blood the heart pumps per minute.
- Mean Arterial Pressure (MAP) — average blood pressure in the arteries.
- Systemic Vascular Resistance (SVR) — resistance blood faces in systemic circulation.
- Central Venous Pressure (CVP) — pressure in the thoracic vena cava near the right atrium.
- Pulmonary Capillary Wedge Pressure (PCWP) — reflects left atrial pressure.
- Reflex Tachycardia — compensatory increase in heart rate in response to hypotension.
- Multiorgan Dysfunction — failure of multiple organs due to poor perfusion.
Action Items / Next Steps
- Review the clinical features and hemodynamics of each shock type.
- Practice differentiating shock based on physical findings and swan-ganz data.
- Complete recommended readings on shock management and complications.