Hemotoraks

01Pathophysiology

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.

02Classification 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.

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.

03Diagnostic Workup

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.

04Management and Treatment

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).

05Differential Diagnosis and Distractors

06Traps 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.