Which injury is MOST likely to cause obstructive shock?

• A. Cardiac tamponade
• B. Tension pneumothorax
• C. Massive pulmonary embolism
• D. Myocardial contusion

Answer: (A)

Obstructive shock occurs when a physical barrier prevents blood from flowing effectively through the heart or to the systemic circulation, so the heart can’t fill or eject adequately and tissue perfusion drops.

Cardiac tamponade from chest injury causes blood to accumulate in the pericardial sac, which increases pressure around the heart. That external pressure prevents the heart from filling properly during diastole, leading to a drop in preload, a fall in cardiac output, and shock. This direct, mechanical obstruction to filling is the classic cause of obstructive shock in trauma, making it the best answer.

Tension pneumothorax can also cause obstructive physiology by compressing the heart and great vessels, but it is typically identified by severe respiratory distress and unilateral chest findings. Massive pulmonary embolism blocks blood flow through the lungs and reduces left-sided preload, but it’s not an injury pattern like tamponade. Myocardial contusion mainly impairs the heart’s pumping ability rather than creating a true obstruction to circulation.