Types of Shock in Emergency Medicine Based on Underlying Causes
Shock in emergency medicine is classified into four major categories based on underlying pathophysiology: hypovolemic, distributive, cardiogenic, and obstructive shock. 1, 2 Each type has distinct etiologies, clinical presentations, and management approaches that directly impact patient morbidity and mortality.
1. Hypovolemic Shock
Hypovolemic shock results from inadequate intravascular volume due to:
- Blood loss (hemorrhagic shock) - most common type in trauma 1
- Fluid loss - severe dehydration, burns, excessive diuresis
- Third-spacing - pancreatitis, bowel obstruction, ascites
Clinical Presentation:
- Tachycardia
- Hypotension
- Weak pulses
- Cold, clammy extremities
- Decreased urine output
- Altered mental status
Management:
- Immediate fluid resuscitation with balanced crystalloids is the cornerstone of treatment 1
- Blood product administration for hemorrhagic shock
- Definitive control of bleeding source in trauma 1
2. Distributive Shock
Distributive shock occurs due to pathological vasodilation and redistribution of blood volume:
- Septic shock - most common form of distributive shock
- Anaphylactic shock
- Neurogenic shock
- Adrenal crisis
Clinical Presentation:
- Hypotension
- Warm, flushed skin (early sepsis)
- Tachycardia
- Normal or increased cardiac output
- Widened pulse pressure
- Decreased systemic vascular resistance
Management:
- Norepinephrine is the initial vasopressor of choice after fluid resuscitation 1
- Source control for septic shock
- Consider vasopressin (up to 0.03 UI/min) for persistent hypotension 1
- Early antimicrobial therapy for septic shock 3
3. Cardiogenic Shock
Cardiogenic shock results from primary cardiac dysfunction leading to inadequate cardiac output:
- Acute myocardial infarction - most common cause 1
- Acute decompensated heart failure
- Valvular dysfunction
- Myocarditis
- Arrhythmias
Clinical Presentation:
- Hypotension
- Pulmonary congestion
- Decreased cardiac output
- Increased systemic vascular resistance
- Cold extremities
- Altered mental status
- Oliguria
Management:
- Inotropes (dobutamine, milrinone) are first-line agents for acute heart failure 1, 3
- Norepinephrine for persistent hypotension with tachycardia 1
- Dopamine may be considered in patients with bradycardia 1
- Coronary revascularization for ischemic cardiogenic shock 1
- Consider mechanical circulatory support in refractory cases 3
4. Obstructive Shock
Obstructive shock occurs due to mechanical obstruction of blood flow:
- Pulmonary embolism
- Tension pneumothorax
- Cardiac tamponade
- Constrictive pericarditis
- Aortic dissection
Clinical Presentation:
- Hypotension
- Elevated central venous pressure
- Pulsus paradoxus (tamponade)
- Tracheal deviation (tension pneumothorax)
- Distended neck veins
- Muffled heart sounds (tamponade)
Management:
- Immediate life-saving intervention to relieve the obstruction 2
- Needle decompression for tension pneumothorax
- Pericardiocentesis for cardiac tamponade
- Thrombolytics or embolectomy for massive pulmonary embolism
Special Considerations
Mixed Shock States
Patients often present with elements of multiple shock types. For example:
- Septic shock may include both distributive and cardiogenic components due to sepsis-induced myocardial depression 1
- Trauma patients may have both hemorrhagic and neurogenic shock components
Shock Classification Systems
The Society for Cardiovascular Angiography and Interventions (SCAI) classifies cardiogenic shock into five stages:
- Stage A: At risk
- Stage B: Beginning shock
- Stage C: Classic shock
- Stage D: Deteriorating shock
- Stage E: Extremis 1
Monitoring Parameters
Effective shock management requires monitoring:
- Mean arterial pressure (target ≥65 mmHg)
- Lactate clearance
- Urine output (>30 mL/h)
- Mental status
- Skin perfusion
- Mixed or central venous oxygen saturation 1, 3
Diagnostic Approach
- Rapid assessment of airway, breathing, circulation
- Hemodynamic evaluation with ultrasound when possible 1
- Laboratory tests including lactate, blood gases, and organ function markers
- Specific diagnostic tests based on suspected etiology:
- ECG and echocardiography for cardiogenic shock 3
- Chest imaging for obstructive causes
- Cultures for septic shock
Common Pitfalls
- Delayed recognition of shock - early intervention is critical for survival
- Misclassification of shock type leading to inappropriate treatment
- Excessive fluid administration in cardiogenic or distributive shock
- Failure to identify and treat the underlying cause
- Inadequate monitoring of response to interventions
Shock management requires continuous reassessment as patients may transition between different shock states or develop multiple simultaneous shock mechanisms during their clinical course 4.