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Summary Table

Category	Details
Risk Factors	Blunt or penetrating chest trauma, rib fractures (especially lower ribs), anticoagulant therapy, coagulopathy, thoracic surgery, aortic aneurysm, pleural malignancy
Etiology	Disruption of intercostal vessels, internal mammary artery, pulmonary parenchyma, or great vessels, resulting in blood accumulation within the pleural space
Patient Presentation	Acute chest pain and dyspnea following trauma; may present with signs of hypovolemic shock if blood loss is significant
Classic Physical Exam	Decreased or absent breath sounds on the affected side, dullness to percussion, tracheal deviation to the contralateral side (in large collections), signs of hemorrhagic shock (tachycardia, hypotension, pallor)
Key Diagnostic Results	CXR: costophrenic angle blunting (upright) or diffuse haziness (supine); eFAST: fluid in the thorax; pleural fluid hematocrit >50% of peripheral blood hematocrit; CT chest for precise volume estimation
Management	Large-bore tube thoracostomy (28 to 36 Fr), IV crystalloid and blood product resuscitation, emergent thoracotomy if initial output >1500 mL or ongoing output >200 mL/hr for 2 to 4 hours
Keywords	"Dullness to percussion," "decreased breath sounds after trauma," "blood on chest tube insertion," "opacification on CXR," "trauma with hypotension and unilateral decreased breath sounds"

1. Pathophysiology

Hemothorax occurs when blood accumulates in the pleural space, the potential space between the visceral and parietal pleura. In the overwhelming majority of cases, the cause is trauma, whether blunt (such as motor vehicle collisions and falls) or penetrating (such as stab wounds and gunshot wounds). Non-traumatic causes include ruptured thoracic aortic aneurysm, malignancy eroding into pleural vessels, pulmonary embolism with infarction, and iatrogenic injury from central line placement or thoracic procedures.

The source of bleeding is most commonly the intercostal arteries or veins, which run along the inferior border of each rib. These vessels are under systemic arterial pressure and, once lacerated (often by displaced rib fractures), can bleed briskly and continuously. Injury to the internal mammary artery similarly produces high-pressure arterial hemorrhage. In contrast, injury to the low-pressure pulmonary parenchyma tends to produce self-limited bleeding due to the lower pulmonary vascular pressures and the high concentration of thromboplastin in lung tissue, which promotes local hemostasis.

As blood accumulates in the pleural space, it causes compressive atelectasis of the underlying lung. This reduces the functional surface area for gas exchange, leading to ventilation-perfusion mismatch and hypoxemia. The patient develops dyspnea and tachypnea as compensatory mechanisms. Simultaneously, ongoing hemorrhage leads to intravascular volume depletion, producing tachycardia, hypotension, and eventual hemorrhagic shock. This is why the clinical picture combines both respiratory distress (from lung compression) and cardiovascular instability (from blood loss).

An important concept is that each hemithorax can hold 2.5 to 3 liters of blood. A patient can therefore exsanguinate into their chest without any external evidence of hemorrhage. This makes hemothorax a life-threatening injury that must be identified early, particularly in the trauma setting where the focus may be on more visible injuries.

If hemothorax is not adequately evacuated, the retained blood undergoes fibrin deposition and organization, forming a clotted collection that cannot be drained by a chest tube alone. Over time, this progresses to fibrothorax, where a thick peel encases the lung and prevents re-expansion, a condition known as trapped lung. This is why timely and complete drainage is essential.

2. Classification and Clinical Manifestation

Hemothorax is classified by the estimated volume of blood in the pleural space, which correlates directly with the severity of clinical findings and dictates management.

Classification	Estimated Volume	CXR Findings	Clinical Manifestation	Management Implications
Small	< 300 to 500 mL	May be occult on upright CXR; visible only on CT or ultrasound	Mild or no symptoms; slight chest discomfort; exam may be normal or show minimal dullness at the base	Observation with serial imaging; may not require tube thoracostomy
Moderate	500 to 1500 mL	Blunting of costophrenic angle; partial opacification of the hemithorax	Dyspnea, tachycardia, decreased breath sounds, dullness to percussion on the affected side	Tube thoracostomy (large-bore); monitor output closely
Large-volume	> 1500 mL	Complete or near-complete opacification of the hemithorax	Severe dyspnea, tachycardia, hypotension, signs of hemorrhagic shock (Class III or IV), absent breath sounds, possible tracheal deviation	Immediate tube thoracostomy followed by emergent thoracotomy; aggressive resuscitation with blood products

A supine chest X-ray, which is the standard initial film in trauma resuscitation, is notoriously insensitive for hemothorax. Blood layers posteriorly and produces only a diffuse haze over the affected hemithorax, which can easily be missed. An upright CXR requires approximately 200 to 300 mL to produce visible blunting of the costophrenic angle. This is why the eFAST exam (Extended Focused Assessment with Sonography for Trauma) has become a critical adjunct, as it can detect as little as 100 mL of pleural fluid at the bedside.

3. Diagnostic Workup

Test	Role	Key Findings
eFAST (Extended FAST)	Best initial test in trauma	Anechoic stripe above the diaphragm indicating fluid in the pleural space
Upright Chest X-ray	Best initial test in non-trauma / confirmatory in trauma	Blunting of costophrenic angle (>200 to 300 mL); layering opacity; complete opacification in large collections
Supine Chest X-ray	Often obtained first in trauma (but lower sensitivity)	Diffuse haziness or "ground-glass" appearance over the affected hemithorax; easily missed
CT Chest	Most accurate test for volume estimation and source identification	Precise quantification of pleural fluid; identification of active extravasation (with IV contrast); detection of associated injuries (rib fractures, pulmonary contusion, vascular injury)
Thoracentesis / Chest Tube Output	Confirmatory (diagnostic and therapeutic)	Pleural fluid hematocrit >50% of peripheral blood hematocrit confirms hemothorax and distinguishes it from a bloody pleural effusion
CBC, Type and Crossmatch, Coagulation Studies	Baseline labs in all trauma	Falling hemoglobin/hematocrit; coagulopathy identification; preparation for transfusion

In the trauma setting, the diagnostic sequence begins at the bedside during the primary survey. The eFAST exam is the best initial test, performed within minutes of arrival. It is rapid, portable, and highly sensitive for detecting pleural fluid. The probe is placed in the right and left upper quadrants, and an anechoic (dark) stripe seen above the diaphragm indicates fluid in the pleural space. The eFAST cannot distinguish between hemothorax and pleural effusion, but in the context of trauma, any pleural fluid is treated as blood until proven otherwise.

A chest X-ray is obtained as part of the trauma workup (typically during or immediately after the primary survey). On an upright film, hemothorax appears as a meniscus sign with blunting of the costophrenic angle. On a supine film, the blood layers dependently and produces a diffuse haze, which can be subtle. Students must remember that a normal supine CXR does not exclude hemothorax.

CT chest with IV contrast is the most accurate test and is obtained in hemodynamically stable patients to quantify the volume of blood, identify the bleeding source (look for active contrast extravasation), and evaluate for associated injuries such as rib fractures, aortic injury, or pulmonary contusion. CT is not obtained in unstable patients who need immediate intervention.

In non-traumatic hemothorax, thoracentesis is both diagnostic and guides management. The key lab value is the pleural fluid hematocrit: a value greater than 50% of the peripheral blood hematocrit defines hemothorax and distinguishes it from a hemorrhagic pleural effusion (which has a lower hematocrit ratio). This distinction matters because a hemorrhagic effusion from malignancy or infection does not require the same surgical urgency.

4. Management and Treatment

Clinical Scenario	Intervention	Details
Initial stabilization (all patients)	ABCs, IV access, resuscitation	Two large-bore IV lines (16G or larger); begin crystalloid (lactated Ringer's or normal saline); type and crossmatch; activate transfusion protocol if hemodynamically unstable
Moderate hemothorax	Tube thoracostomy	Large-bore chest tube (28 to 36 Fr in adults); insert at the 4th or 5th intercostal space, anterior to the mid-axillary line; connect to an underwater seal drainage system
Large-volume hemothorax (>1500 mL initial output)	Tube thoracostomy + emergent thoracotomy	Chest tube placed first to quantify output; if >1500 mL drains immediately, proceed to emergent surgical exploration
Ongoing hemorrhage (>200 mL/hr for 2 to 4 hours)	Surgical thoracotomy	Continued bleeding indicates an arterial source (intercostal or internal mammary) that will not self-tamponade
Retained hemothorax	VATS (Video-Assisted Thoracoscopic Surgery)	If clotted blood persists after chest tube placement despite repositioning or a second tube; ideally performed within 3 to 7 days to prevent fibrothorax
Small hemothorax (stable, minimal symptoms)	Observation	Serial CXR and clinical monitoring; may resolve spontaneously without drainage

Step 1: Stabilize. As with all trauma patients, begin with the ABCs. Establish two large-bore peripheral IV lines and initiate volume resuscitation. In patients with signs of hemorrhagic shock (tachycardia, hypotension, altered mental status), activate a balanced transfusion protocol (1:1:1 ratio of packed red blood cells, fresh frozen plasma, and platelets). Do not delay resuscitation while waiting for imaging.

Step 2: Decompress the pleural space. The next best step for a symptomatic hemothorax is tube thoracostomy. A large-bore chest tube (28 to 36 Fr, though some guidelines recommend up to 40 Fr) is placed in the "safe triangle," bounded by the anterior border of the latissimus dorsi, the lateral border of the pectoralis major, and a horizontal line at the level of the nipple (approximately the 5th intercostal space). The tube is directed posteriorly and inferiorly to drain dependent blood. A small-bore pigtail catheter is inadequate for hemothorax because blood clots will occlude it.

Step 3: Quantify the output. Record the initial volume drained and monitor the hourly output. This is the decision point for surgical intervention.

Indications for emergent thoracotomy (memorize these numbers):

Initial chest tube output >1500 mL
Ongoing output >200 mL/hr for 2 to 4 consecutive hours
Hemodynamic instability despite adequate resuscitation
Need for continued blood transfusion to maintain hemodynamic stability

These thresholds indicate a source of bleeding under systemic arterial pressure that will not stop with drainage alone. The patient requires direct surgical exploration, ligation, or repair of the bleeding vessel.

Step 4: Address retained hemothorax. If follow-up imaging shows persistent opacification despite a functioning chest tube, the blood has likely clotted and cannot be evacuated by tube drainage. VATS is the preferred intervention and should ideally be performed within 3 to 7 days of injury. Delay beyond this window allows fibrin organization and cortical peel formation, which may necessitate open thoracotomy with decortication.

Step 5: Prophylaxis. All patients with hemothorax who undergo tube thoracostomy should receive prophylactic antibiotics (typically a first-generation cephalosporin such as cefazolin) to reduce the risk of empyema. Administer within the first 24 hours and continue for no longer than 24 hours after tube insertion (per current trauma guidelines, though practice varies).

5. Differential Diagnosis and Distractors

Differential	Why It Is Similar	Key Discriminator
Tension pneumothorax	Both present with unilateral decreased breath sounds, dyspnea, and hemodynamic instability after trauma	Tension pneumothorax produces hyperresonance to percussion and tracheal deviation; hemothorax produces dullness to percussion. CXR shows hyperlucency vs. opacification.
Simple pleural effusion	Both show blunting on CXR, decreased breath sounds, and dullness to percussion	Pleural effusion lacks a history of trauma and develops subacutely. Pleural fluid hematocrit is <50% of peripheral hematocrit (hemorrhagic effusion, not true hemothorax).
Pulmonary contusion	Both occur after blunt trauma and show opacification on CXR	Pulmonary contusion appears as a patchy, non-dependent alveolar opacity that does not layer; it is intraparenchymal, not pleural. No fluid is obtained on thoracentesis. Contusion worsens over 24 to 48 hours.
Cardiac tamponade	Both present with hypotension, tachycardia, and dyspnea after penetrating chest trauma	Tamponade produces Beck's triad (hypotension, muffled heart sounds, JVD), whereas hemothorax does not cause JVD (volume is lost, not obstructed). Breath sounds are typically equal bilaterally in tamponade. FAST shows pericardial fluid, not pleural fluid.
Diaphragmatic rupture	Can show opacification of the lower hemithorax on CXR after blunt trauma	Look for bowel gas pattern in the chest, a nasogastric tube tip above the diaphragm, or visible herniation of abdominal contents on CT. The opacification is from herniated organs, not blood.
Chylothorax	Both produce pleural fluid collections with dullness to percussion	Chylothorax produces milky-white (chylous) fluid with elevated triglycerides (>110 mg/dL). It typically follows thoracic duct injury from surgery or lymphoma, not acute trauma with hemorrhagic shock.

6. Traps and High-Yield Pearls

The most common way students miss hemothorax questions is by confusing the percussion findings with tension pneumothorax. Both conditions present after chest trauma with unilateral decreased breath sounds and respiratory distress. The critical discriminator is percussion: dullness indicates fluid (hemothorax), while hyperresonance indicates air (pneumothorax). If you see "dullness to percussion" in a trauma vignette, think hemothorax. If you see "hyperresonance" or "tympany," think pneumothorax.

A second common trap involves the supine chest X-ray. Students are taught to look for costophrenic angle blunting, but this is an upright film finding. In a supine trauma patient, hemothorax produces a subtle diffuse haze that can be overlooked. When a vignette describes a trauma patient with a "normal" supine CXR but persistent hypotension and decreased breath sounds, the next best step is an eFAST exam or upright CXR, not reassurance.

The surgical threshold numbers are a high-yield memorization target: initial output greater than 1500 mL or ongoing output greater than 200 mL/hr for 2 to 4 hours. These numbers appear frequently and are the basis for management questions that ask for the "next best step." Students who do not know these cutoffs will incorrectly choose continued observation when the correct answer is emergent thoracotomy.

Finally, beware of the retained hemothorax scenario. A vignette may describe a patient who initially improved after chest tube placement but then develops fever, persistent opacity on follow-up CXR, and worsening respiratory status several days later. The wrong answer is a second chest tube or antibiotics alone. The correct answer is VATS for evacuation of retained hemothorax, ideally within 3 to 7 days before fibrothorax develops. The core competency tested here is recognizing that clotted blood cannot be drained by a tube and requires surgical evacuation.

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