Pathophysiology
P-II-24. Circulatory shock, Case 3
循環性ショック 症例3
Case Presentation
An 85-year-old man, cared for in a nursing home, is brought to the intensive care unit by the ambulance with a sudden onset of pain in the lower right chest region, aggravated by difficulty breathing.
History (seven days previously): The patient had developed difficulty breathing seven days previously, when he had also experienced swelling / oedema in both legs and feet. He had a slightly enlarged liver and prominent jugular veins. He had been given diuretics. Due to feeling considerably weak, he had been mostly bedridden.
Physical examination:
- Swelling in his right leg was significantly larger, with a tensing pain there
- Chest X-ray showed a faint shadow in the peripheral region of the right lower lobe of the lung
Acute deterioration: After the examination, his breathing suddenly became uneven, then stopped, his pulse was not palpable, and he needed resuscitation.
Key Quotes & What They Tell Us
| Quote / Value | Interpretation |
|---|---|
| “mostly bedridden” for several days | Immobility → venous stasis (Virchow’s triad) → risk of deep vein thrombosis |
| “Swelling in his right leg was significantly larger, with a tensing pain” | Unilateral leg swelling and pain → deep vein thrombosis (embolic source) |
| “sudden onset of pain in the lower right chest … difficulty breathing” | Acute pleuritic chest pain + dyspnoea → pulmonary embolism |
| CXR: “faint shadow in the peripheral region of the right lower lobe” | Possible pulmonary infarction (peripheral wedge-shaped opacity) |
| “prominent jugular veins” / slightly enlarged liver / leg oedema | Elevated central venous pressure and right-heart strain — congestion hallmark of obstructive shock |
| “breathing … stopped, his pulse was not palpable” | Cardiac arrest from a massive embolism obstructing pulmonary outflow |
Key Points
- Type of shock: Obstructive shock caused by a massive pulmonary embolism.
- Source: Deep vein thrombosis of the right leg, promoted by prolonged immobility (venous stasis).
- Pathophysiology: Embolus obstructs the pulmonary arterial outflow → ↑right-ventricular afterload → ↓left-ventricular preload → ↓cardiac output → circulatory collapse.
- Distinguishing sign: Elevated central venous pressure (distended jugular veins) with a mechanical obstruction to flow — characteristic of obstructive shock.
- Course: Rapid progression to cardiopulmonary arrest requiring resuscitation.
一問一答
▶What type of shock is caused by a massive pulmonary embolism?
Obstructive shock.
▶What is the embolic source in this bedridden patient?
Deep vein thrombosis of the right leg.
▶What are the three components of Virchow's triad?
Venous stasis, endothelial injury, and hypercoagulability.
▶How does prolonged immobility predispose to DVT?
It causes venous stasis, a key element of Virchow's triad.
▶What is the pathophysiology of obstructive shock in pulmonary embolism?
The embolus obstructs pulmonary outflow, raising right-ventricular afterload, reducing left-ventricular preload, and dropping cardiac output.
▶Why are the jugular veins distended in obstructive shock?
Obstruction to right-heart outflow raises central venous pressure, distending the neck veins.
▶How does raised central venous pressure distinguish obstructive (and cardiogenic) shock from hypovolaemic shock?
Obstructive/cardiogenic shock have high CVP/distended neck veins, whereas hypovolaemic shock has low CVP/collapsed veins.
▶Why does this patient have pleuritic chest pain and dyspnoea?
Pulmonary embolism causes acute pleuritic pain and breathlessness, sometimes with pulmonary infarction.
▶What does the peripheral wedge-shaped opacity on chest X-ray suggest?
Pulmonary infarction from the embolism (a Hampton's hump-type peripheral opacity).
▶Why can a massive pulmonary embolism cause sudden cardiac arrest?
Acute right-ventricular failure and collapse of cardiac output abruptly stop effective circulation.
▶What is the first-line investigation to confirm pulmonary embolism?
CT pulmonary angiography (CTPA).
▶What is the treatment of a massive pulmonary embolism causing shock?
Thrombolysis (or embolectomy) plus anticoagulation and supportive care.
▶What other conditions cause obstructive shock besides pulmonary embolism?
Cardiac tamponade and tension pneumothorax.
▶Why does pulmonary embolism cause hypoxaemia?
Obstructed pulmonary perfusion creates ventilation-perfusion mismatch and dead space, impairing oxygenation.
▶What earlier signs in this patient suggested right-heart strain before the arrest?
Leg/foot oedema, enlarged liver, and prominent jugular veins (raised central venous pressure).
▶How can DVT be prevented in immobile/bedridden patients?
Pharmacological prophylaxis (e.g. low-molecular-weight heparin), mechanical compression, and early mobilization.
▶Why does unilateral leg swelling and pain point to DVT?
Thrombotic obstruction of deep leg veins causes localized swelling, tenderness, and increased venous pressure on one side.
▶What ECG/echocardiographic signs suggest right-heart strain in PE?
Sinus tachycardia, the S1Q3T3 pattern, right axis deviation, and right-ventricular dilatation/hypokinesis on echo.
▶Why does obstructive shock reduce left-ventricular preload?
Obstruction of pulmonary blood flow decreases the volume returning to the left heart, lowering preload and output.
▶What is the role of D-dimer in suspected pulmonary embolism?
A normal D-dimer helps exclude PE in low-probability patients; it is non-specific and elevated in many conditions.