Obstructive Shock

 Obstructive Shock  

Etiology (Causes)

1. ↓ Diastolic Filling (Impaired ventricular filling)

• Cardiac tamponade

• Constrictive pericarditis

• Restrictive cardiomyopathy

2. ↓ Venous Return (Impaired preload)

• Tension pneumothorax

• Intrathoracic tumors

• Abdominal compartment syndrome

3. ↑ Ventricular Afterload (Obstruction to outflow)

• Massive pulmonary embolism (PE)

• Aortic dissection

• Aortic stenosis

• Large systemic emboli

• Severe pulmonary hypertension

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Pathophysiology

• Common Mechanism: Obstruction of heart or great vessels → ↓ cardiac output (CO) → compensatory ↑ systemic vascular resistance (SVR).

Specific Mechanisms:

1. Pulmonary embolism / severe pulmonary hypertension

   • Obstruction → ↓ PCWP → ↑ RV pressure → right heart failure

   • RV pressure compresses LV → ↓ LV diastolic filling → ↓ CO

2. Tension pneumothorax

   • ↑ Intrathoracic pressure → ↓ venous return → ↓ preload → ↓ PCWP

   • ↓ LV filling → ↓ CO

3. Cardiac tamponade

   • ↑ Pericardial pressure → ↑ RV pressure → ↓ RV diastolic filling → right heart failure

   • ↑ LV pressure → ↓ LV diastolic filling → ↓ CO

   • Elevation & equalization of all cardiac chamber pressures is classic

Key Point:

• Many causes of obstructive shock are preload-dependent, even if PCWP appears high (e.g., tamponade, severe pulmonary hypertension).

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Treatment

Immediate Goals:

• Hemodynamic support (fluids if preload-dependent)

• Vasopressors or inotropes if needed

Definitive Treatment by Cause:

Cause	Intervention
Cardiac tamponade	Pericardiocentesis
Pulmonary embolism	Thrombolysis or embolectomy
Tension pneumothorax	Needle thoracostomy → chest tube
Other obstructions (tumor, abdominal compartment)	Surgical or decompressive intervention

Notes:

• Assess fluid responsiveness before giving fluids

• Correct the underlying obstruction as rapidly as possible

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