Tension Pneumothorax — Tracheal and Mediastinal Shift MCQ — NEET PG Practice Question | NEETPGAI
Tension Pneumothorax — Tracheal and Mediastinal Shift
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stethoscope Medicine
A 22-year-old man presents to the emergency department with severe respiratory distress following a stab wound to the right chest. On examination, he is hypotensive (BP 78/44 mmHg), tachycardic (HR 140), tachypneic (RR 38), cyanotic, and has absent breath sounds on the right with hyperresonance to percussion. The structure marked **D** in the diagram is noted on clinical examination. Which of the following best explains the hemodynamic compromise in this patient?
A. Massive blood loss into the right pleural space causing hemorrhagic shock
B. Compression of the superior vena cava and right atrium by mediastinal shift, reducing venous return and causing obstructive shock
C. Direct myocardial contusion from penetrating trauma causing cardiogenic shock
D. Tension on the pulmonary hilum causing acute pulmonary embolism
Explanation
Why "Compression of the superior vena cava and right atrium by mediastinal shift, reducing venous return and causing obstructive shock" is right
The structure marked D — tracheal and mediastinal shift to the left — is the pathognomonic radiographic sign of tension pneumothorax that distinguishes it from simple pneumothorax. This contralateral shift of the mediastinum compresses the great vessels (particularly the superior vena cava and right atrium), reducing venous return and causing obstructive shock. This is the mechanism of hemodynamic compromise in tension pneumothorax and explains the dramatic improvement in blood pressure (78/44 → 118/76 mmHg) immediately after needle decompression and tube thoracostomy. Per ATLS 10th Edition, Chapter 4, the mediastinal shift is the critical feature that converts a simple pneumothorax into a life-threatening tension pneumothorax requiring immediate bedside decompression without waiting for imaging confirmation.
Why each distractor is wrong
Direct myocardial contusion from penetrating trauma causing cardiogenic shock: While myocardial contusion can occur with thoracic trauma, it is not the primary mechanism of shock in tension pneumothorax. The shock in this case is obstructive (due to reduced venous return), not cardiogenic. Contusion would present with arrhythmias or reduced contractility, not the dramatic hemodynamic reversal seen after decompression.
Massive blood loss into the right pleural space causing hemorrhagic shock: The clinical findings (hyperresonance to percussion, absent breath sounds) indicate pneumothorax, not hemothorax. A hemothorax would present with dullness to percussion and would not resolve with needle decompression alone. The dramatic improvement in blood pressure after air evacuation confirms the mechanism is not hemorrhage.
Tension on the pulmonary hilum causing acute pulmonary embolism: Pulmonary embolism does not explain the clinical findings of hyperresonance, absent breath sounds, or the immediate response to decompression. PE would present with hypoxia and right heart strain but not with the physical examination findings of pneumothorax or the dramatic hemodynamic improvement after needle thoracostomy.
High-YieldNEET PG
Tension pneumothorax causes obstructive shock via mediastinal shift compressing the great vessels — it is a clinical diagnosis requiring immediate bedside needle decompression (4th–5th ICS, anterior-mid axillary line in adults per ATLS 10th Edition) WITHOUT waiting for imaging.
ATLS — Advanced Trauma Life Support Student Course Manual, 10th Edition, Chapter 4: Thoracic Trauma
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