Air rushes in, the one-way valve holds it there, and the pressure climbs until the mediastinum shifts and the vena cava collapses. Learn the mechanism chain, the clinical triad, and why you needle before you image.
The Mechanism
Air In, No Way Out
Everything deadly about tension pneumothorax flows from one structural defect. Walk the chain once and the whole disease makes sense.
A 32-year-old construction worker falls from scaffolding onto his left side. He arrives by EMS in severe respiratory distress: blood pressure 68/40 mmHg, heart rate 148. His left chest is silent to auscultation and hyperresonant to percussion. The trachea has shifted to the right. His neck veins are visibly distended.
Which single mechanism explains the cardiovascular collapse?
Start with the valve. A tear in the pleuraThe pleura is the two-layered membrane lining the inside of the chest wall and the outside of each lung. The potential space between the layers is the pleural space. acts like a one-way door: air enters the pleural space on inspiration (when the chest expands and creates negative pressure) but cannot escape on expiration. With every single breath, more air is trapped and there is nowhere for it to go.
Now the pressure chain. Air accumulates → intrapleural pressure climbs above atmospheric pressure → the affected lung is compressed and collapses → the entire mediastinum (the central chest compartment holding the heart, great vessels, and trachea) is pushed toward the opposite side → the vena cava (the main vein returning blood to the heart) kinks under the shifted structures → venous blood cannot return to the right atrium → preload falls to zero → cardiac output crashes. This is obstructive shock: the heart muscle is working fine, but nothing is reaching it to pump.
What creates the one-way valve? Any pleural injury that leaves a flap that opens on inspiration but seals on expiration. Flip each card.
TraumaTap to flip
Blunt or penetrating chest injuryA rib puncturing the visceral pleura, a stab wound, or a blast injury can create the one-way tear. Blunt trauma is the most common traumatic cause. Penetrating chest wall wounds can also behave as an open pneumothorax that converts to tension if improperly sealed.
Mechanical VentilationTap to flip
Positive pressure barotraumaPatients with fragile emphysematous lungs on mechanical ventilation are at high risk. Positive pressure ruptures blebs or alveoli, creating the pleural tear. High peak airway pressures plus sudden hemodynamic collapse in a ventilated patient is tension pneumothorax until proven otherwise.
Spontaneous PTX That ValvesTap to flip
Primary or secondary spontaneousA spontaneous pneumothorax (ruptured apical bleb in tall thin young men, or secondary to COPD or Marfan syndrome) can progress to tension if the defect develops one-way valve physiology. It starts stable and then deteriorates as pressure climbs.
From the Attending
Name what type of shock this is before you touch the patient. Tension pneumothorax is obstructive shock: the myocardium is healthy, the filling failed. That distinction matters because treatments for other shock types (fluids, vasopressors, inotropes) do not fix a kinked vena cava. Only releasing the pressure fixes it. Know your mechanism and you will always know your treatment.
At the Bedside
The Clinical Triad
The exam gives you the diagnosis. The triad is distinctive. Two other emergencies share pieces of it, and the exam separates them in seconds.
The patient looks like they are dying, because they are. Severe respiratory distress and a sense of impending doom open the picture. The specific exam findings separate this from every other cause of shock. Tap each sign.
Absent Breath Sounds
Tap to reveal
On the affected side. The collapsed, airless lung transmits no breath sounds. This is the most specific finding for the pleural space and rules out cardiac tamponade, which has normal bilateral breath sounds because both lungs are intact.
Hyperresonance to Percussion
Tap to reveal
On the affected side. The pleural space is full of air, not tissue. Tapping the chest produces a hollow drum note rather than a dull thud. Hyperresonance means air. Dullness would mean blood (hemothorax) or fluid.
Tracheal Deviation
Tap to reveal
Away from the affected side. The mediastinum is pushed toward the opposite side by the trapped air. Tension on the right pushes the trachea left. This is anatomic proof of mediastinal shift. Do not confuse the direction: the trachea runs from the affected side, pointing away.
Distended Neck Veins (JVD)
Tap to reveal
Jugular venous distension. Blood is backed up in the venous system because it cannot enter the kinked vena cava. The elevated venous pressure is visible in the jugular veins. JVD is the marker of obstructive physiology and distinguishes tension pneumothorax (and cardiac tamponade) from simple pneumothorax, where neck veins are flat.
Hypotension and Tachycardia
Tap to reveal
Obstructive shock. Preload is gone because the vena cava is kinked. Cardiac output falls. The body compensates with tachycardia and peripheral vasoconstriction. Hypotension combined with unilateral absent breath sounds and JVD demands immediate treatment without imaging.
Board Trap
Cardiac tamponade also causes hypotension and distended neck veins. The separating exam findings: tension pneumothorax has absent breath sounds and hyperresonance on one side, plus tracheal deviation away. Tamponade has equal and normal breath sounds bilaterally, muffled heart sounds, and no tracheal deviation. Tamponade is pericardial fluid squeezing the heart. Tension is pleural air pushing the mediastinum. Different anatomy, different exam.
From the Attending
In a hypovolemic trauma patient who is also hemorrhaging, the JVD may be absent even with tension pneumothorax because low blood volume flattens the neck veins. Do not rule out tension because the neck veins are flat in a bleeding patient. Absent unilateral breath sounds plus tracheal deviation in a trauma patient means tension. Treat it.
Confirming It
Clinical, Not Radiographic
This is one of the few diagnoses where imaging in an unstable patient is a wrong answer. Work the decision logic, then see the three-type comparison.
The rule. Tension pneumothorax is a clinical diagnosis. In an unstable patient with the triad, you diagnose and treat simultaneously. A portable chest radiograph takes minutes you do not have. The patient arrests in the scanner while you wait for a picture. The wrong answer on every board question involving an unstable patient with the classic triad is any option that involves imaging before treatment.
If imaging is available in a temporarily stable patient, a chest x-ray shows: complete collapse of the lung on the affected side, mediastinum (heart shadow and trachea) shifted to the contralateral side, and flattening or inversion of the ipsilateral diaphragm. Practice the three decision points.
An unstable patient has absent breath sounds on the right, JVD, tracheal deviation to the left, and a blood pressure of 70/42 mmHg. A nurse asks if you want a portable chest radiograph. What is your response?
The clinical triad is present. Tension pneumothorax is a clinical diagnosis. Ordering imaging before treatment in an unstable patient is the classic board trap. Triad present, patient unstable: needle decompression immediately. Imaging comes after, if at all.
Imaging before treatment in an unstable tension pneumothorax patient is the board trap. This patient can arrest before the film is read. Treat first. Imaging is not needed to act.
A more stable patient has a chest radiograph available. The right lung is completely collapsed. The heart shadow and trachea are shifted to the LEFT. Where is the tension, and where do you decompress?
The mediastinum is pushed away from the affected side. Trapped air on the right pushes everything left. Always decompress the side with absent breath sounds and hyperresonance, not the side toward which the trachea deviates. The trachea points away from the problem. Treat the collapsed lung side. Decompress where the problem is.
The mediastinum is pushed AWAY from the trapped air. The collapsed lung marks the affected side. Decompress the side with absent breath sounds, not where the trachea is pointing.
Both tension pneumothorax and cardiac tamponade cause JVD and hypotension. What single bedside finding most reliably separates them?
The pleural exam is the separator. Tension collapses one lung: that side is silent and hyperresonant, and the trachea deviates away. Tamponade leaves both lungs ventilating normally, gives muffled heart sounds, and has no tracheal deviation. Auscultation separates them in seconds. Silent side plus tracheal deviation equals tension. Normal bilateral breath sounds equals tamponade.
The pleural exam separates them fastest. Listen and percuss: absent breath sounds plus hyperresonance on one side is tension. Normal bilateral sounds is tamponade.
The three-type comparison. Pneumothorax is tested in three forms, often against each other. Fix this table in your mind before you move to management.
Feature
Simple / Spontaneous PTX
Open PTX
Tension PTX
Mechanism
Air enters pleural space, no ongoing valve; equilibrates with atmosphere
Chest wall defect allows bidirectional airflow through the wound
One-way pleural valve: air enters each breath and cannot escape
Mediastinal shift
None to minimal
None (unless converting to tension)
Yes, pushed contralateral to affected side
Neck veins (JVD)
Flat
Flat (unless converting to tension)
Distended: backed-up venous blood
Breath sounds
Decreased affected side
Decreased affected side; air movement audible at wound
Absent affected side
Percussion
Hyperresonant affected side
Hyperresonant affected side
Hyperresonant affected side
Hemodynamics
Stable
Variable; may be compromised by associated injuries
Unstable: obstructive shock (hypotension and tachycardia)
Tracheal deviation
None
None
Away from affected side
Initial treatment
Small: observe plus supplemental oxygen. Larger or symptomatic: aspiration or chest tube
Three-sided occlusive dressing (flutter valve), then chest tube
Immediate needle decompression, then chest tube
Time pressure
Hours
Minutes
Seconds. Cardiac arrest without treatment.
The Treatment
Needle First, Questions Later
Two steps for tension. One decision for the open chest wound. Three board traps in management that cost the patient their life if you get them wrong.
Step one: needle decompression. Insert a large-bore needle or angiocatheter on the affected side to release the trapped air. The classic location is the 2nd intercostal space at the midclavicular line, going just above the 3rd rib to avoid the neurovascular bundle that runs along the inferior edge of each rib. Updated trauma protocols also accept the 4th or 5th intercostal space at the anterior axillary line, where chest wall thickness is more predictable in most patients. A rush of air confirms proper placement. Blood pressure typically recovers within seconds as venous return is restored. You have converted a life-threatening tension pneumothorax into a manageable simple pneumothorax.
Step two: tube thoracostomy. The needle is temporary. It can kink, clot, or be too short to reliably reach the pleural space in a large patient. Definitive treatment is a chest tube at the 4th or 5th intercostal space at the anterior axillary line, providing continuous drainage and allowing the lung to re-expand. The needle bought you the time. The chest tube closes the problem.
You confirm tension pneumothorax on the right side. You are performing needle decompression. Where exactly does the needle go?
Always decompress the affected side (the side with absent breath sounds and hyperresonance). Go just above the rib because the intercostal neurovascular bundle (artery, vein, nerve) runs along the inferior edge of each rib. The classic location is 2nd ICS at the MCL; the 4th/5th ICS at the AAL is now preferred in trauma protocols for more reliable chest wall depth. Affected side. Above the rib. 2nd ICS MCL or 4th/5th ICS AAL.
Decompress the AFFECTED side (the side with absent breath sounds). Going through the rib damages the intercostal neurovascular bundle running below each rib. Affected side, above the rib.
Needle decompression is performed. An audible rush of air is heard and blood pressure improves from 68/40 to 110/72 mmHg. What is the definitive next step?
Needle decompression is a bridge, not a destination. The underlying pleural defect is still there and the angiocatheter is not sufficient for sustained drainage. A chest tube at the 4th or 5th intercostal space anterior axillary line provides continuous air drainage and allows the lung to fully re-expand. Needle decompression buys time. Chest tube closes the deal.
The needle bought time but the pleural defect is still active. The angiocatheter is not definitive treatment. Place a chest tube for continuous drainage.
A paramedic finds a 3 cm stab wound in the right chest wall. Air is audibly moving in and out of the wound with each breath. Blood pressure is 104/70 mmHg, trachea midline, neck veins flat. What do you apply to the wound?
The three-sided dressing acts as a flutter valve. On inspiration, negative intrathoracic pressure holds the dressing against the wound, blocking air from entering through the defect. On expiration, positive pressure lifts the open edge and releases trapped air. A fully sealed dressing would block that escape route and convert this open pneumothorax into a tension pneumothorax. A chest tube follows for definitive management. Three sides sealed, one open. Flutter valve prevents conversion to tension. Chest tube follows.
A fully sealed dressing converts the open pneumothorax to tension. The open edge is not optional. Three-sided dressing, then chest tube.
From the Attending
The three-sided dressing is not a trick to memorize. The physics is straightforward: you are preserving one-way outflow. Think of it as building a flutter valve out of a piece of plastic. Air must be able to escape on expiration, or the first breath after sealing the wound builds pressure inside the chest. Know it from mechanism, not memorization, and you will never confuse it.
Board Trap
Positive pressure ventilation worsens a tension pneumothorax. In a patient with unrecognized tension, intubating and bagging them forces additional air through the pleural tear with each ventilator breath, rapidly escalating the pressure and accelerating cardiovascular collapse. Ventilated patient with sudden high peak airway pressures plus asymmetric breath sounds: tension pneumothorax until proven otherwise. Decompress before adjusting ventilator settings.
Prove It
Board Walkthrough
Six original clinical vignettes, 5 dealt per round, answer choices shuffled, never repeating within a round. Tap a wrong answer first to see why it almost works, then read the glowing clues.
Medically reviewed by Kaitlyn Cocuzzo, MD and Fatima Ali, DO · Last reviewed June 2026
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