Injury to Great Vessels and Bronchus

PART A: INJURY TO GREAT VESSELS

Definition and Incidence

• Prevalence ranges from 0.3% to 10% in thoracic trauma.
• Over 90% of patients with great vessel injury die at the scene (exsanguination).
• Of those reaching the emergency room in a stable condition, 70-95% can survive with prompt management.
• Historically, aortic injury is the second most common cause of death in blunt trauma, after closed head injury.
• More than 90% of thoracic great vessel injuries are caused by penetrating trauma.

Aetiology / Mechanisms of Injury

1. Blunt Trauma

• High-speed deceleration: motor vehicle crashes (MVCs) - >80% of blunt aortic injuries (BAIs).
• Falls from height >4-5 meters, blast injuries, crush injuries, pedestrian versus automobile collisions.
• The chest strikes the steering wheel, transmitting force across the mediastinum. Vascular compression between the sternum and vertebral bodies causes marked increases in intraluminal pressure.
• Consider blunt aortic injury when mechanism involves sudden deceleration (fall >10 ft/3 m or MVC at speeds >30 mph/50 km/h).

2. Penetrating Trauma

• Stab wounds and gunshot wounds are the leading cause.
• In military and civilian studies, single projectile firearms cause 69% of penetrating great vessel injuries, stab wounds cause 18%, and shotguns cause 12%.
• Iatrogenic injuries from central line placement, cardiac catheterization, and other invasive thoracic procedures can also cause great vessel injury.
• 95% of persons with penetrating arch and great vessel injuries are male.

Pathophysiology

Blunt Injury - Aortic Mechanism

• Other injured vessels (in order of frequency): innominate artery (second most common), subclavian artery, pulmonic veins, venae cavae.
• The aorta is involved in ~85% of cases; branch vessels in 15%.
• Venous thoracic great vessel injuries are extremely rare and mostly fatal.

Penetrating Injury

• Pseudoaneurysm formation with delayed rupture
• Arteriovenous malformation leading to congestive heart failure

Clinical Features

• Hypotension (hemodynamic instability)
• Chest, back, or interscapular pain
• Paraplegia (distal aortic injury compressing spinal arteries)
• Mesenteric ischemia, anuria, lower extremity ischemia (distal injuries)

• Hypertension in upper extremities with hypotension in lower extremities ("pseudocoarctation" syndrome)
• Unequal blood pressures in the extremities
• External evidence of major chest trauma - seatbelt or steering wheel contusion
• Thoracic outlet expanding hematoma
• Interscapular murmurs or bruits
• Palpable sternal or rib fractures, flail chest
• Diminution of right radial/brachial pulse (innominate artery injury)

Diagnosis

1. Electrocardiogram (ECG)

• All patients with chest trauma require ECG and cardiac monitoring.
• Findings: sinus tachycardia (most common), atrial fibrillation, new Q waves, ST-T segment changes, right bundle branch block, AV blocks.
• Negative predictive value of a normal ECG approaches 90% for cardiac injury.

2. Chest Radiograph

• Widened mediastinum (>8 cm or mediastinum:chest width ratio >0.38) - most sensitive sign
• Apical capping (blood tracking over the apex of the lung)
• Depression of left main stem bronchus >40 degrees below horizontal
• Deviation of esophagus >1 cm to the right of spinous process at T4
• Obliteration of aortic knuckle
• Left-sided hemothorax
• Fractures of first/second rib, scapula, sternum

A normal mediastinum on chest radiograph does NOT rule out aortic injury.

3. CT Angiography (Gold Standard)

• Multidetector CT (MDCT) is currently the most commonly used tool.
• Identifies aortic injury with high sensitivity and specificity.
• Evaluates trajectory of missile relative to brachiocephalic vessels.

4. Transesophageal Echocardiography (TEE)

• Can be performed at the bedside or in the operating room.
• Sensitivity similar to helical CT scan in skilled hands.
• Especially useful for hemodynamically unstable patients unsuitable for CT.

5. Aortography

• Historically was the definitive diagnostic method; now largely replaced by MDCT.

6. FAST (Focused Assessment with Sonography in Trauma)

• Detects pericardial effusion/tamponade (sensitivity 100%, specificity 99%).
• Point-of-care ultrasound is invaluable for unexplained persistent shock.

Management

Resuscitation (Primary Survey - ABCDE)

• Large-bore IV access, blood transfusion, oxygen.
• Consult trauma/vascular surgeon immediately upon suspicion of great vessel injury.
• Transport hemodynamically unstable patients to operating room immediately.

Pharmacologic Blood Pressure Control

• Maintain systolic BP at 100-120 mmHg with HR ~60 beats/min.
• Goal: Decrease dP/dT (slope of pressure rise) to reduce wall tension and shearing forces on the aortic lumen.
• First-line: Short-acting IV beta-blocker (esmolol) to control heart rate.
• Second-line: Add arterial vasodilator - nicardipine or clevidipine (preferred over sodium nitroprusside due to reactive tachycardia with the latter).
• Avoid sodium nitroprusside alone.
• Avoid Valsalva maneuver and any increase in intrathoracic pressure.

Surgical Management

• Patients with hemodynamic instability, profound hemorrhage from chest tubes, or rapidly expanding mediastinal hematoma require immediate surgical repair.
• Penetrating injuries: Emergency left thoracotomy with direct aortic repair; short cross-clamp times; interposition graft rarely required.
• Blunt injuries: Delayed repair is appropriate in multiply injured patients requiring resuscitation.
• Cardiopulmonary bypass, bypass shunts, and active aortic shunts used for blunt injury repair.
• Innominate and branch vessel injuries: Surgical approach depends on location.

Thoracic Endovascular Aortic Repair (TEVAR)

• In the last decade, TEVAR has transformed management of Grade III and IV BAI.
• Results significantly better than traditional open repair.
• Lower paraplegia rates and reduced mortality.
• Has become the procedure of choice at major trauma centers.

Delayed/Non-Operative Management

• For Grade I-II injuries or in patients with life-threatening coexisting injuries (intra-abdominal injuries, severe closed head injuries).
• Risk: ~4% rupture rate within one week in delayed repair candidates.
• Strict pharmacologic BP control is mandatory.
• Use autotransfusion devices in cases of large bleeding vessels if available.

PART B: INJURY TO BRONCHUS (TRACHEOBRONCHIAL INJURY)

Definition and Incidence

Anatomy of Vulnerability

• More than 80% of tracheobronchial injuries occur within 2 cm of the carina or at the origin of lobar bronchi.
• Blunt injuries predominantly affect the intrathoracic tracheobronchial tree.
• Penetrating injuries from knife wounds almost exclusively damage the cervical trachea.
• Gunshot wounds may damage the tracheobronchial tree at any point.

Pathophysiology

Blunt Injury Mechanisms

1. Direct blow to the neck - crushes cervical trachea against vertebral bodies, transecting tracheal rings or cricoid cartilage.
2. Shear forces - produce injury at the carina and cricoid cartilage (fixed points). Sudden deceleration of the thoracic cage pulls the lungs away from the mediastinum, producing traction on the trachea at the carina; when elasticity is exceeded, rupture occurs.
3. Burst injury (barotrauma) - if the glottis is closed at the time of impact, sudden increase in intrabronchial pressure ruptures the tracheobronchial tree.

Penetrating Injury Mechanism

• Direct laceration or blast effect from missiles along any part of the airway.

Clinical Features

• Dyspnea
• Hemoptysis
• Hoarseness/aphonia (cervical tracheal injury)

• Subcutaneous emphysema - most common physical exam finding; typically dramatic and increasing
• Massive air leak through chest tube - continuous bubbling in the underwater seal device, failure to re-expand the lung
• Pneumomediastinum on CXR
• Extensive subcutaneous emphysema on CXR
• Pneumothorax (large, often not responding to chest tube)
• Hamman's crunch (crunching/rasping sound synchronous with the pulse, heard over precordium - indicates air in mediastinum)
• Sternal tenderness, fractures of upper ribs (1st-5th)

Two Distinct Clinical Presentations:

1. Wound opens into pleural space - large pneumothorax, chest tube fails to evacuate it, continuous air leak (bronchopleural fistula).
2. Complete transection without pleural communication - little or no immediate pneumothorax; peribronchial tissues support the airway. Patient is relatively symptom-free initially but develops unexplained atelectasis or repeated pneumonia within 3 weeks as granulation tissue occludes the lumen. This delayed presentation is easily missed.

Diagnosis

1. Chest X-Ray

• Pneumomediastinum
• Extensive subcutaneous emphysema
• Pneumothorax (large, unresponsive to drainage)
• Fractures of upper ribs (1st-5th)
• Air surrounding the bronchus ("fallen lung" sign - lung falls away from hilum due to bronchial disruption)
• Obstruction in the course of an air-filled bronchus
• Spherical appearance of endotracheal tube balloon (oval is normal)

2. CT Scan

• High sensitivity for detecting tracheobronchial injury.
• Distal injuries with pneumatocele formation can be seen on CT scan.
• Evaluates mediastinal hematoma or mediastinitis.

3. Bronchoscopy (Gold Standard)

• Flexible bronchoscopy is the most preferred and reliable method.
• Establishes the diagnosis and determines the site and extent of injury.
• Guides endotracheal intubation over the bronchoscope (blind intubation must never be attempted in suspected TBI).
• Directs the surgical approach.

Management

Airway Management (Priority)

• Endotracheal intubation must be performed under bronchoscopic guidance to ensure the tube passes safely beyond the site of injury.
• Avoid blind intubation (risk of false passage, converting partial tear to complete tear).
• Large air leaks may make conventional ventilation difficult.
• High-frequency oscillation ventilation is the ventilator modality of choice in the presence of massive air leak (maintains gas exchange and expands alveoli).
• Selective lung ventilation using double-lumen endotracheal tube or bronchoscopically placed bronchial blocker for severe cases.
• ECMO (extracorporeal membrane oxygenation) as a bridge to surgical repair in the most refractory cases.

Intrabronchial Bleeding Management

• Identify the involved lung and keep the other lung free of blood.
• Bronchoscopy to identify injury and control bleeding.
• Double-lumen tube to confine bleeding to one lung.
• Position the patient with the affected lung dependent.

Surgical Management

• Indications: All lacerations involving >1/3 of the bronchial circumference require operative repair.
• Right mainstem bronchus injuries (most common intrathoracic injury): right posterolateral thoracotomy (also grants access to the carina).
• Left bronchus injuries: left thoracotomy.
• Median sternotomy is NOT preferred (limited visualization posterior to the heart).
• Technique: Primary repair using 3-0 absorbable suture; buttress with intercostal muscle or pleural flaps. Avoid excessive circumferential dissection (risk of devascularization).
• Chest tubes placed; extubation as soon as possible (off positive pressure ventilation post-operatively).

Conservative Management

• Can be considered for tracheal tears <2 cm and without esophageal prolapse, mediastinitis, or massive air leakage.

Complications of Untreated TBI

• Severe mediastinitis (from untreated tracheal tears)
• Severe bronchial stenosis with atelectasis and recurrent pulmonary infections
• Concurrent esophageal injuries occur in ~25% of penetrating TBI (must perform esophagoscopy or contrast studies to exclude this)

Summary Table: Comparison

• Tintinalli's Emergency Medicine: A Comprehensive Study Guide (Chapter 262)
• Fuster & Hurst's The Heart, 15th Edition (Chapter 79)
• Rosen's Emergency Medicine: Concepts and Clinical Practice
• Mulholland & Greenfield's Surgery: Scientific Principles and Practice, 7th Ed.
• Fishman's Pulmonary Diseases and Disorders